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THE ROLE OF ESTUARIES IN SOUTH AFRICANFISHERIES: ECONOMIC IMPORTANCE AND
MANAGEMENT IMPLICATIONS
Steve Lamberth • Jane Turpie
WRC Report No. 756/2/03
Water Research Commission
THE ROLE OF ESTUARIES IN SOUTH AFRICANFISHERIES: ECONOMIC IMPORTANCE AND
MANAGEMENT IMPLICATIONS
Report to the Water Research Commission
Edited by
Steve Lamberth and Jane Turpie
WRC Report No. 756/2/03ISBN No. 1-86845-981-0ISBN Set No. 1-86845-978-0
February 2003
Disclaimer
This recort emanates from a project Guanoed by the Water Research Commission (WKQ andis approved for publication. Approval does not sigmiy that the contents necessarily reflect theviews and policies of the V/RC or the members of the project steering commmee. nor doesmention of trade names or commercial products constitute endorsement or recomoencation rot
kise.
THE ROLE OF ESTUARIES IN SOUTH AFRICAN FISHERIES:ECONOMIC IMPORTANCE AND MANAGEMENT IMPLICATIONS
SECTION 2
Steve Lamberth & Jane Turpie
Submitted to:Institute of Natural Resources
February 2001
Dr Jane K. TurpieEcological and Resource EconomicsConsulting3 Ocean View, Gatesville Road, Kalk Bay 7975or c/o Percy FitzPatrick Institue, University ofCape Town, Rondebosch 7701, South [email protected]
1. INTRODUCTION
South Africa has roughly 255 functioning estuariesalong its approximately 3100 km coastline. Theseestuaries are subject to increasing pressures, bothindirectly from the effects of catchment utilisation,which affect their water supply, and directly from theincreasingly large numbers of people who reside inor visit the coastal zone. Estuaries are productivesystems which provide a valuable supply of goodsand services, ranging from fisheries to recreationalopportunities, but there have been no previousattempts to estimate the economic value of theseecosystem services, with the result that theircontribution to the national economy has beenunder-appreciated.
Many human activities which are carried out inestuaries and their catchment areas impact directlyon estuarine biodiversity and resource stocks, anddifferent activities often conflict with one anotherthrough such impacts. If estuaries and theircatchments are to be managed in an optimalsustainable way, it is necessary to understand thefull economic value of the goods and services thatthey provide.
One of the most important values of estuarinesystems is their contribution to fisheries. Residentfish populations are exploited directly in estuarinerecreational and subsistence fisheries. But moreimportantly, estuaries provide nursery areas fornumerous species of fishes which are exploited byrecreational and commercial harvesting in theinshore marine environment. These species aredependent on estuaries for the early stages of theirgrowth.
The management of estuaries in South Africa hasnot been well organised in the past. Now, with theincreasing realisation of their value, as well as ofthe pressures that threaten these systems, effortsare being made to redress the situation and to setin place sound decision-making processesregarding the management and conservation of
estuaries. This is both in terms of the managementof catchments and determination of freshwaterinflows into estuaries, and in terms of the directmanagement of estuaries and activities within them.
One such effort is the current development of adecision support system for the management andconservation of estuarine systems being developedby the Institute of Natural Resources (INR). Thelatter study recognises that effective managementstrategies that lead to sustainable and optimal useof resources need to be built on a sound economicrationale as well as an ecological understanding.This study was commissioned by the INR to providean overview of the economic value of estuarinefishery resources in South Africa, and to commenton the implications of the findings for estuarymanagement.
The main aims of this study were as follows:
• To list the estuarine fish species exploitedin South African fisheries, giving theirdegree of dependence on estuaries;
• To describe the types of estuarine andmarine fisheries exploiting estuarinefishes, and their total participation andeffort;
• To estimate the total catches of estuarinespecies in estuaries and the marineenvironment;
• To explain the contribution to fisheriesmade by different types of estuaries;
• To estimate the contribution that estuarineand estuary-dependent fishes make to theeconomic value of estuarine and marinecatches.
• To give rough estimates of the status ofstocks of important estuarine fish species;and
• To comment on the implications of theabove findings for estuary management.
2. STUDY APPROACH AND METHODS
Subdivision of the study area
The South African coast can be considered in terms
of three biogeographical regions:1. the Cool Temperate region on the West Coast;2. Warm Temperate region from Cape Point to
approximately the Bashee River in the formerTranskei; and
3. the Subtropical region to the north-east of theBashee.
The second boundary, is rather poorly defined,largely because the presence or absence of fish isso strongly influenced by a major tropicalsubtraction effect from Kosi to Cape Point (Turpie etai. 1999), rather than any natural geographicalbreak.
The South African coast has usually been dividedinto five regions for the collection of fisheries data,corresponding with the Cape Point biogeographicaldivision, but not the second division:1. West coast Orange R. to Cape Point2. South coast Cape Point to Port Elizabeth3. East coast Swartkops to Kei River4. Transkei: between Kei R. and Port Shepstone5. KwaZulu-Natat, Port Shepstone to Kosi Bay
Thus the warm temperate zone is mostly dividedinto two sections, and the former Transkei (hithertoreferred to simply as the Transkei) constitutes avery broad transition area between biogeographicalzones.
Estuarine fish and their dependence onestuaries
General information on biology and distribution ofestuarine fish species was obtained from Whitfield(1998) and Mann (2000). Information on which ofthese species are utilised was derived from avariety of sources, including the National MarineLinefish System (NMLS) database, the NetfishSystem database, and various published papersand reports.
Types of fisheries, participation and effort
For estuarine fisheries, we included legal and illegalseine and gillnet fisheries, recreational shore,castnet and recreational boat fisheries, as well astraditional fisheries. For marine fisheries, therecreational boat, recreational shore, recreationalspear and commercial boat and beach seine and
gill net fisheries were considered. Pelagic fisherieswere excluded as none involve estuary-associatedspecies.
There are no comprehensive nationwide studies ofestuarine fishing participation or effort. However,these were obtained from published andunpublished literature on a number of individualestuaries (Beckley et ai. 2000, Hutchings &Lamberth 1999, in press a,b,c, Kyle 1995, 1999,Mann 1994, 1995, 1996, Sowman et al. 1997,Guastella 1994, Lamberth 2000a,b, Baird &Pradervand 1999, Baird ef at. 1996, Pradervand &Baird in prep., Marais & Baird 1980), as well asextrapolation from coastal fisheries. For marinefisheries, participation and effort in recreationalshore angling, boat fishing and spear fishing wasestimated from the regional reports of the NationalLinefish Survey (Brouwer 1996, Brouwer et al.1997, Lamberth 1996, Sauer & Erasmus 1996,Sauer et at. 1997, Mann et al. 1996, 1997, 1998,McDonald ef al. 1998), and attributed to particularspecies on the basis of the proportion of successfulfishers that had caught that species, extrapolated tothe total estimated number of fishers. For thecommercial boat fishery, participation was gaugedas the sum of the mean number of crew carried bythe boats that reported catches of particular speciesto the NMLS over a five-year period. Similarly,participation for the beach seine and gill-netfisheries was estimated as the sum of the numberof permit holders that had reported catching aparticular species to the NMLS multiplied by themean crew size (Lamberth et al, 1997, Hutchings &Lamberth 1999).
Estuarine catch estimates
Esiimaibs uf estuarine catches and their speciescomposition were obtained from the literature{Hutchings & Lamberth 1999, Kyle 1995, 1996,1999 2000a,b, Mann 1994, 1995, Beckley et al.2000, Sowman ef al. 1997, Guastella 1994,Lamberth 1996, 2000a,b, Baird & Pradervand 1999,Pradervand & Baird in prep., Baird et al. 1996,Marais & Baird 1980} and from unpublished dataand estimates supplied by Bruce Mann(Oceanographic Research Institute), Paul Cowley{JLB Smith Institute of Ichthyology) and SteveLamberth (Marine & Coastal Management).Estimates were based on sampling, counts offishers, surveys, and confiscated catches.Estimates of annual catches were obtained for all
estuaries on the west coast, all south coastestuaries between Cape Point and Mossel Bay, allestuaries on the south-east coast from Swartkopsto Keiskamma, and all estuaries in Kwazulu-Natal.No data were available for estuaries betweenMossel Bay and Port Elizabeth or for estuaries inthe former Transkei. Existing data were analysedto explore relationships between catch and variousparameters. General linear modelling was used tocreate predictive models to estimate catches for theremaining estuaries. Dependent variables usedwere estuary size (Brian Colloty, UPE, unpublisheddata), biogeographical region and estuary type(Whitfieid 1992).
Marine catch estimates
For marine fisheries, total catches for each specieswere estimated from the regional reports of theNational Linefish Survey (recreational shore anglingand spear fishing catches, 1994-1996; Brouwer1996, Brouwer et a/. 1997, Lamberth 1996, Sauer &Erasmus 1996, Sauer et al. 1997, Mann etal. 1996,1998, Lechanteur 2000, McDonald et al. 1998), theNMLS (commercial boat catches, recreational boatcatches, 1992-1996) and catch reports from theMarine & Coastal Management Netfish System(commercial beach-seine and gill net catches,excluding KwaZulu-Natai, 1992-1996). The latterwere corrected using validated catches fromLamberth ef al. (1997) and Hutchings & Lamberth(1999, in press a,b). KwaZulu-Natal net fishcatches were estimated from Beckley & Fennessy(1996).
It is difficult to attribute the actual contribution ofindividual estuaries to the marine catch, but datawere disaggregated as far as possible, to coastalsections.
Inshore marine fishery catches were analysed interms of the amount made up of estuary-associatedfish, and the percentage dependency of the totalcatch on estuaries. The latter was estimated on thebasis of the dependence categories (Whitfieid1994) of different estuarine species in catches,assigning a percentage to each category reflectingthe degree to which that species would be lost frommarine catches if all estuaries were to disappear.
Economic value
Estimates of the economic value of fisheries inSouth Africa have mainly been confined to marinecommercial and recreational fisheries. Estimates of
the economic contribution of each of the marine linefisheries were obtained from McGrath ef al. (1997),based on NMLS data, and of the marine andestuarine net fisheries were obtained fromHutchings & Lamberth (1999) and Hutchings &Lamberth (in press b).
For marine fisheries, the relative contribution ofeach species was determined according to themethodology used by Lamberth & Joubert (1999).Fish prices were obtained in telephonic interviewwith dealers countrywide. The mean price per kg ofeach species was multiplied by the total mass ofthat species caught, and summed to obtain the totallanded catch value for each sector, The proportionthat each species contributed to this landed valuewas multiplied by the total economic contribution ofthat sector (including subsidiary industries) asdetermined by McGrath ef al. (1997) and Hutchings& Lamberth (1999, in press b). Overall valuesobtained for each species were reduced accordingto the percentage dependence on estuaries for thatspecies to estimate the estuarine contribution to themarine fishery values.
No comparable estimate of the overall economicvalue of estuaries has been made. Consequently,the economic value of estuarine fisheries wasestimated on the basis of catch estimates. Forrecreational fisheries and commercial fisheries, weassume that the value per landed kg of fish is thesame as for marine fisheries. Traditional estuarinefisheries were assigned the same value per landedkg as commercial marine gillnet fisheries, which isclose to market values.
Stock status and vulnerability of utilisedestuarine fish species
The conservation status of exploited estuarine fishspecies was gauged according to abundance (stockstatus), level of knowledge, endemicity, level ofexploitation throughout a species' range andvulnerable life history traits, following the methodsof Lamberth & Joubert (1999), all attributes beingscored on a scale of 1-100:(a) Abundance. Depending on availability of datathis score was based on the percentage of pristinespawner biomass remaining, ratios of present tohistorical catch per unit effort (CPUE), or ratios ofpresent to historical contribution to total catches.Species for which data were available were used asa baseline against which species which lacked datacould be assessed by expert opinion. Data wereobtained from various sources, e.g. the NMLS,
Mann (2000), CMS (2000). Each species wasscored on a scale of 1-100, with score rangesindicating the stock as underexploited, optimallyexploited, over exploited or collapsed (Griffiths et at.1999).(b) Level of knowledge. 14 factors (described inVan der Elst & Adkin (1999), Mann 2000), wereused for scoring the current level of knowledge foreach species on a scale of 1 to 100.(c) Endemicity. Each species was scoredaccording to how many regions it occurred in, asfollows: one region = 100, two regions - 60, threeregions = 40, four regions = 20, southern Africa =10, cosmopolitan = 0. Range data was mostlyobtained from Smith & Heemstra (1986).(d) Level of exploitation. This was scoredqualitatively on the basis of Mann (2000), CMS
(1999) and expert opinion. For example, a speciesheavily exploited throughout its range scored 100,medium = 50, and low = 0.(e) Vulnerability. This was gauged using 8 lifehistory traits, nameiy estuarine dependence, sexchanges, spawning migrations, predictableaggregations, high age at maturity, longevity,residency and high catchability. Species displayingnone of these characteristics scored 0, those withone, two or three characteristics scored 70, 80 or90, and those displaying four or more of thesecharacteristics scored 100 (see Lamberth & Joubert1999 for rationale).
3. ESTUARINE FISH AND THEiR DEPENDENCE ON ESTUARIES
Categories of estuarine fish species
About 160 species occur in South African estuaries,of which about 80 species are utilised in fisheries.This report is only concerned with the latter species.Of these, different species have different degrees ofassociation with estuaries, and estuarine fish havebeen classified into five broad categories of
association, which may be further subdivided into 9types (Whitfield 1994, Table 1). Category I and Haspecies are entirely dependent on estuaries, as arecategory IV and V species. Category lib speciesare largely dependent on estuaries, while numbersof category lie species are augmented by estuaries.Category ill species are found in estuaries, but arenot dependent on them.
Table 1. The five major categories and subcategories of fishes which utilise southern African estuaries (Whitfield 1994).Categories Description
Estuanne species which breed in southern African estuanes.la. Resident species which have not been recorded spawning in marine or freshwater environments.Ib. Resident species which also have marine or freshwater breeding populations.Euryhaline manne species which usually breed at sea with the juveniles showing varying degrees ofdependence on southern African estuaries.Ha. Juveniles dependent on estuanes as nursery areas.lib. Juveniles occur mainly in estuaries, but are also found at sea.lie. Juveniles occur in estuaries but are usually more abundant at sea.Manne species which occur in estuaries in small numbers but are not dependent on these systems.
IV Freshwater species, whose penetration into estuaries isdetermined primarily by salinity tolerance. This category includes some species which may breed in bothfreshwater and estuarine systems. ___ _ _ ^ _ _ _ _ _ _ _ _ _
V Catadromous species which use estuaries as transit routes between the marine and freshwaterenvironments but may also occupy estuanes in certain regions.Va. Obligate catadromous species which require a freshwater phase in their development.Vb. Facultative catadromous species which do not require a freshwater phase in their development
Utilised estuarine fish species and theirdistribution
Of the 80 utilized species, 3, 47, 21, 3 and 6species fall into categories I to V, respectively(Table 2). Of particular importance are the categoryI and I! species, for which management of estuariesplays a crucial role in fisheries. Catches ofestuarine-associated fish species differ from west tceast around the coast, following biogeographicalchanges from the Cool Temperate region on thewest coast through to the Subtropical region northof the Bashee River in the Transkei. The Cool
Temperate region is relatively species poor butproductive, and the fisheries include only about 19estuarine-associated species (Table 2). Numbersof estuarine species in catches almost doubleimmediately east of Cape Point, and increasetowards the east, with up to 71 species in KwaZuluNatal (Table 2). Some 28 estuarine-associatedspecies are caught only or predominantly inJC\»IO7II I I i . Wifhin rminn.9composition of catches within estuaries also differsbetween estuaries of different types and sizes, withgreater species richness associated with larger andpermanently open estuaries.
Tabie 1 Estuarine-associated species caught in South African fisheries, given in order of estuanne dependence category(Table 1), and giving distribution of catches around the coast. Distribution is divided into West coast (Orange River to CapePoint), South Coast (Cape Point to Port Elizabeth), East Coast (Swartkops to Kei River), Transkei and Kwazulu Natal (PortEdward to Kosi Bay). The three biogeographical provinces are separated by Cape Point and roughly at the Bashee River inthe Transkei (Emanuel etal. 1992, Turpie era/. 1999, Maree etat. 2000a,b).
Species
Ambassis productus
Ambassis gymnocephalus
Ambassis natalensis
Common name
Longspine glassy
Bald glassy
Slender glassy
Dependence
category
laIbIb
CoolTWest
Distribution
Warm Temp
South East
X X
Tkei
X
Subtrop
KZnXXX
Rhabdosargus holubi
Argyrosomus japonicus
Mug;/ cephalus
Elops machnata
Lichia amia
Acanthropagrus berda
Pomadasys commersonni
Lithognathus lithognathus
Monodactylus falciformis
Uza macrolepis
Vaiamugii cunnesius
Valamugii robustus
Terapcn jarbua
Gaieichthyes feliceps
Sphyraena barracuda
Caranx sexfasciatus
Caranx ignobilis
Rhabdosargus sarba
Scomberoides lysan
Uza tricuspidens
Thryssa vitrirostris
Genes acinaces
Gerres methueni/rappi
Leiognathus equuia
Monodactyius argenteus
Uza alata
Uza dumerilii
Uza luciae
Platycephaius indicus
Diplodus sargus
Pomatomus saltatrix
Uza nchardsonii
Pomadasys hasta/kakaan
Johmus dussumieri
Sphyraena jeilo
Lutjanus argentimactulus
Sillago sihama
Sarpa salpa
Rhabdosargus giobtceps
Carcharhinus leucas
Strongyiura leiura
Caranx meiampygus
Cape stumpnose
Dusky kob
Flathead/spnnger muilet
Ladyf i s h/te npo u nder
Leervis/gamck
Perch/riverbream
Spotted grunter
White steenbras
Cape/Oval moony
Largescale muilet
Longarm mullet
Robust mullet
Thomfish
Barbel
Barracuda
Bigeye kingfish
Giant kingfish
Natal stumpnose
Doublespotted queenfish
Stnped mullet
Orangemouth glassnose
Smallscale pursemouth
Evenfin pursemouth
Slimy
Natal/Round moony
Diamond mullet
Groovy mullet
St Lucia mullet
Bartailed flathead
Dassie/blacktail
ElfHarder
Javelin grunter
Mini kob
Pickhandle barracuda
River snapper
Silver sillagio
Strepie
White stumpnose
Zambezi shark
Yellowfin needlefish
Bluefin kingfish
llaHallalla
llallallaHaHallallallalla
liblibliblibliblibliblibilbliblibIlbIlbIlbIlblielielielielielieHelielielielielielielie
X
X
X
X
X
XX
X
XXXXX
XX
X
X
X
XXX
XX
XXXXX
XXX
XX
X
X
XXXX
X
XX
XXXXXXXXX
XXXX
XX
X
XXX
XXX
X
X
X
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXX
XXX
continued.
Table 2 continued.
Species
Caranx papuensis
Chanos chanos
Lutjanus fulviflamma
Valamugil buchanani
Vaiamugil seheli
Dasyatis chrysonota
Himantura uamak
Gymnura nataiensis
Myiiobatus aquiia
Mustelus mustelus
Rhinobatos annulatus
Epinephelus andersoni
Epinephelus maiabancus
Pomadasys muitlmaculatum
Pomadasys oiivaceum
Chelidonichthyes capensis
Trachurus trachurus
Uthognathus mormyrus
Otoiithes ruber
Trachinotus africanus
SpondyliGSoma emarginatum
Sparodon durbanensis
Diplodus cen/inus
Kuhlia mugil
Muraenesox bagio
Thrysoidea macmra
Oreochromis mossambicus
Ciarius gariepinus
Glossogobius giuris
Anguilla bengalensis
Anguilla bicolor
Anguilla marmorata
Anguilla mossambica
Megalops cyphnoides
Myxus capensis
TOTAL
Common name
Brassy kingfish
Milkfish
Dory snapper
Bluetail mullet
Bluespot mullet
Blue stingray
Honeycomb stingray
Butterfly/diamond ray
Eagieray
Smooth houndshark
Lesser guitarfish/sandshark
Catface rockcod
Malabar rockcod
Cock gmnter
PiggyGurnard
Maasbanker
Sand steenbras
Snapper kob
Southern pompano
Steentjie
White musselcracker
Zebra/wildeperd
Barred flagtail
Pike conger
Slender giant moray
Mozambique tiiapia
Sharptooth catfish
Tank goby
African mottled eel
Shortfin eel
Giant mottled eel
Longfin eel
Oxeye tarpon
Freshwater mullet
Dependence
category
HelielielielieINIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII111IIIIIIIIIIIIIIIIIIIIIIIIIVIVIV
VaVaVaVaVbVb
CoolT
West
X
XXX
XXXX
X
XX
19
Distribution
Warm TempSouth i
X
XXXX
XXX
XXX
XX
XXXX
X34
East
X
XXXX
XXX
XXXXXX
XX
XXXX
X41
Tkei
X
XXX
XXXXXX
XX
XXXX
X43
Subtrop
KZnX
XXXX
XX
X
XXX
XXXXXXXXXXXXXXXXX71
3. ESTUARINE FISHERIES
Types of fisheries, participation and effort
a. Linefishinq
Linefishing may take place from the shore or fromboats ranging from canoes or small dinghies tolarge skiboats, and using handlines or rods.Linefishing is popular in estuaries throughout SouthAfrica, primarily as a recreational pursuit, althougha small number of subsistence fishers are active,mainly from Port Elizabeth to KwaZulu-Natal. Nocommercial linefishing is permitted in estuaries.Angling in estuaries requires a marine recreationalangling permit, and subsistence permits are in theprocess of being introduced.
No large scale studies of angling participation oreffort in estuaries have been made in South Africa,and existing studies are confined to a few specificestuaries. On the west coast, the fishery is limited,primarily due to lack of suitable angling fish, butassuming densities similar to adjacent shorelines,there may be up to 0.12 anglers per km of estuaryat any one time, or a maximum of 4400 angler daysper year on west coast estuaries. This representsthe effort of approximately 147 fishers (Lamberth2000a). Ail the effort is currently recreational,although about 14% of these anglers admit toselling part of their catch (Lamberth 1996).
On the south coast, between Cape Point andMossel Bay, based on angler densities on adjacentshorelines and angler and boat counts on theBreede, Klein, Bot and Heuningnes estuaries, thereare an estimated 66 200 angler days per year inestuaries aiong this coast. This represents theeffort of approximately 2209 fishers. These effortestimates are probably extremely conservative, asthe Overberg district council issues 1200 boatpermits per year, mostly for the Breede River. Inaddition, current confusion over estuarineregulations and commercial linefish permits has ledto commercial linefishers moving illegally intoestuaries to an unknown extent. Extrapolating tothe entire south coast, we estimate a total effort of133 000 angler days and a total of 7400 anglers.
Little is known about angling effort on the eastcoast, but it is estimated that there are at least130 000 angler days of effort expended per year inestuaries from the Swartkops to the Keiskamma,representing about 8000 anglers (extrapolated fromPradervand & Baird, in prep). Extrapolating to the
entire east coast region, we estimate that there areapproximateiy 168 000 angler days and 9300anglers in total.
There is no information on estuarine angling for theentire Transkei coastline. However, a shore-angling survey in the Transkei found about 400 000angier-days per year, representing the effort ofabout 19 000 anglers (McDonald eta!. 1998, Mannet al. 1998). Using similar assumptions as for otherparts of the South African coastline, it is estimatedthat there are approximately 112 000 angler daysspent in estuaries, representing the effort of 5-6000anglers.
In KwaZulu-Natal, some preliminary estimates havebeen made of angling effort in Kosi Bay (10 000boat angling outings per year), St Lucia (30 000boat angler outings and 18 000 shore-angleroutings per year), Durban Bay (21 000 boat angleroutings and 100 000 shore angler outings per year)and Umgeni estuary (11 000 shore-angler outingsper year) (Beckley et al. 2000). The number ofanglers using estuaries in KwaZulu-Natai isestimated to be over 50 000 (Beckley etal. 2000).
The total number of anglers using estuaries inSouth Africa is estimated to be in the region of67 000 {Table 3). This is not too dissimilar to vander Eisr/s (1989) estimate of 50 000 anglersoperating from light tackle boats in estuaries.
b. Castnettinq
Castnetting is mainly used by recreational andsubsistence anglers to catch bait fish such asmullet, is practised throughout South Africa, andrequires a castnet permit. There is one commercialcastnet permit in KwaZuiu-Natai, for Durban Bay.The gear used is restricted to a weightedmonofilament or braided nylon net of 1.5-4mdiameter, with a mesh size of 15-2Gmm. On theeast and KwaZulu-Natal coasts, the larger nets areused for catching linefish species, but amendmentsto the regulations are intended to curtail thispractice. The regulations will restrict castnets to 2mdiameter, with mesh sizes of 13-20mm.
On the west coast, castnets are used regularly byabout 95 recreational shore anglers, almostexclusively targeting harders, with a total effort ofabout 2837 angler days per year. This accounts forapproximately 1.2% of angler effort (Lamberth
2000a,b). On the south coast, approximately 300shore-anglers use castnets regularly, with a totaleffort of approximately 8972 angler days per year{Lamberth 1996). The amount of castnetting alongthe east coast is unknown, but is estimated to beabout 10 800 days per year by 600 fishers (basedon Brouwer 1996). Castnetting is less common inthe Transkei, where there are probably about 75castnet users, with an estimated effort of 1300 daysper year. In KwaZulu-Natal, 4511 recreationalcastnet licences were issued in 1997 (Mann 2000).Effort is unknown, but probably amounts to at least10 800 days per year. Also important is that aquota system has been developed for estuaries inKwaZulu-Natal, with a set number of castnetpermits for each estuary (Beckley et at. 2000).
The total number of castnetters using estuaries inSouth Africa is estimated to be about 5 700 (Table3).
c. Gillnettinq
Gillnetting is a passive form of fishing usingmonofiiament or woven nylon nets, deployed eitherfrom a boat or walking out from the shore, in thehope that a shoal of fish will swim into them andbecome entangled. These nets may either drift, bestaked or be anchored, but in terms of legislationthey may not be left unattended except in KwaZulu-Natal where they are set overnight and retrieved inthe morning. Permits for estuaries are only issuedon the west coast and KwaZulu-Natal, wherepermit-holders are restricted to the use of one net,ranging from 35-75m in length, depending on theestuary in which they operate. Minimum meshsizes vary from 44-48mm. . In addition to legalnetting, substantial illegal gillnetting occurs inestuaries throughout South Africa. Overall, catchrates dictate that the fishery changes from a largelycommercial venture on the west coast to moresubsistence in nature as one moves eastwards toKwaZulu-Natal.
On the west coast, gillnetting takes place in theOlifants, Berg and Rietvlei/Diep estuaries. Thereare 85 gillnet permit holders in the Olifants estuary,and an additional 20-30 people operating withoutpermits. Annual effort is about 15 300 net days/year(Lamberth 2000a). On the Berg River estuary,there are 120 gillnet permit holders, plus about 100illegal operators, and annual effort is about 13 230net days of legal effort plus at least 4000 net daysof illegal effort (Hutchings & Lamberth 1999). The
Rietvlei/Diep system is fished by about 10-12poachers (Lamberth 2000a).
Aiong the south coast, at least 3 teams of illegalnetters operate in the Bot/Kleinmond and Kleinestuaries (2-6 people per team), and according toCape Nature Conservation, up to 5 nets have beenfound in either estuary at any one time. There arealso up to 10 illegal nets used in the Breede andDuiwenhoks estuaries, mostly by landowners andholiday home owners, but sometimes also by west-coast gillnetters targeting spotted grunter andflathead mullet. Similar effort probably takes placein the Goukou, Gouritz, Klein Brak, and Groot Brakestuaries.
Little is known about illegal gillnetting in the eastcoast estuaries, but it occurs sporadically in severalof these systems, where poachers often make useof cheap fine-meshed nets such as the netting usedin fruit packing. It is also reported that illegaloperators in this region sometimes make use oflocal people in rural areas to masquerade assubsistence collectors (Cowley 2000). There isevidence that giilnetting has been increasing alongthe east coast over the last few years. Almostnothing is known about gillnetting activities in theTranskei.
In KwaZulu-Natal, available information suggeststhat there is currently gillnetting in about 12estuaries, most of which is illegal (Beckley et at.2000). In Kosi, 45 permits are rotated amongstapproximately 90 people, and there are roughly 90regular illegal gillnetters, excluding transient peoplefrom Mozambique and the Pongola floodplain. In StLucia, there are 37 gillnet permits, but an estimated270 people operating illegally in the system. Thereis a small experimental gillnet fishery in theMsundusi/Mfolozi system, involving about 28fishers. Illegal netting also occurs in Richards Bay,Nhlabane, Umlalazi, Amatikuiu/Nyoni, Tugela,Zinkwazi, Nonoti, Durban Bay, Kosi.
We estimate that there are approximately 1200gillnetters operating in estuaries in South Africa(Table 3).
d. Seine netting
Seine netting is an active form of fishing in whichwoven nylon nets are either rowed or walked out toencircle a shoal of fish. The net is then hauled toshore by a crew of 6 to 30 persons, depending onthe size of the net and the length of the haul
10
(Lamberth et a/. 1997}. There are currently no seinenet permits estuaries on the west, south, east andTranskei coasts, and only one permit issued inRichards Bay, KwaZulu-Natal, for mullet for bait(Beckley et al. 2000). Nevertheless, a smallamount of seine netting also occurs illegally inestuaries throughout South Africa, often using fine-meshed shade cloth for nets. Illegal seine nettingoccurs in the Heuningnes and Breede estuaries. InKwaZulu-Natal illegal seine netting is known tooccur in Lake St Lucia, Richard's Bay, Mhlatuze,Amatikulu/Nyoni, Zinkwasi, Tugeia, Miaiazi,Nhlabane and Mfolozi estuaries. Some of thisillegal effort is targeted at prawns. Thus the totalnumber of seine netters using South Africanestuaries probably does not exceed 150 (Table 3).
e. Traditional fisheries
Traditional fishing methods, which are common intropical countries to the north, are mostly, if notexclusively, confined to the Kosi system in SouthAfrica. These fisheries use fish traps, spears andbaskets. Traditional fish traps are parallel guidefences made of poles, sticks and brushwoodcollected from the surrounding coastal forest, whichchannel fish into a terminal collecting pen on thefalling tide. There are about 120 bonefide trappersoperating about 150 traps in Kosi (Kyle 2000b).Traditional spear fishing is carried out using a tongstraight branch with a sharpened piece ironreinforcing rod inserted in the end (Kyle 1995). Fishare stalked in the shallows and the spear is thrownat them. Fishing baskets are oblong baskets whichare baited to catch fish. In addition, children alsofish in the Kosi system with sticks and lines,providing a vital supply of protein to theirhouseholds. An average of 50 children are foundfishing in these lakes daily (Kyle 2000b).
Table 3. Estimated numbers of fishers participating in different types of fisheries around the South African coast (legally andillegally).Estuarine fisheries
LJnefishingCastnettingGillnettingSeine nettingTraditional methodsTOTAL*
West
14795
55000
697
South
7 40030050<50
7455
East
9 300600
?50+00
9350
Transkei
5 50075
?few?0
5500
KwaZulu-Natal
50 0004 500
550140
120+50 810
TOTAL
72 3475 570
-1200-150120+
73 812* excludes castnet figures as most are anglers.
Total catches within estuaries
Of the 255 functional estuaries considered in thisstudy, catches have been estimated for about halfthe estuaries (n - 129): all 9 estuaries on the westcoast, 24 out of 52 estuaries on the south coast, 23out of 54 on the east coast, none of the 67 Transkeiestuaries, and all 73 estuaries in KwaZulu-Natal. Interms of biogeographical regions, data exist for all 9estuaries in the Cool Temperate region, 47 out of125 in the Warm Temperate region, and 73 out of121 in the Subtropical region.
In order to extrapolate the existing catch estimatesto the remaining estuaries, the relationshipsbetween estuarine catches and estuary size, typeand biogeographical region were analysed usingsimple and multivariate models. The best predictivemodels were obtained by analysing data separatelyfor each biogeographical region. The St Lucia
estuary in KwaZulu-Natal, and the Bot and Kleinestuaries on the south coast, were excluded fromanalyses: these are large estuaries in whichcatches are disproportionately low (in the case of StLucia this is partly due to exclusion zones).
With the exclusion of the abovementionedestuaries, estuary size alone explains over 80% ofthe variation in catch in the Warm Temperate regionand over 90% of variation in catch in the ColdTemperate and Subtropical regions (Fig. 1). Thesteeper slope in the Cold Temperate region reflectsgreater productivity in that region as compared withthe other two, which have similar slopes.
Data for the Warm Temperate and Subtropicalregions were further analysed to examine the effectof estuary type (specifically permanently open andtemporarily closed estuaries which are the twopredominant types) on catches. The slope of the
11
regression between estuary area and catch issteeper for permanently open estuaries (Fig. 2),indicating higher productivity. Note also, that
temporarily closed estuaries are generally smallerthan 150 ha, whereas permanently open estuariesinclude large estuaries of up to 500 ha.
co
o• 4 — '
600
500
400
300
200
100
0
120
100
80
60
40
20
0
600
500
400
300
200
100
0
Cold Temperate
y = 0.1388x - 19.532
FT= 0.9159
1000
Warm Temperate
y = 0.0789x- 1.0558
R*= 0.8058
200
Subtropical
y = 0.0503x +0.1956
^=0.9438
2000 3000 4000
400 600 800
0 1000 2000 3000 4000
Estuary size (ha)
Figure 1. Relationships between estuary size and catch in each of the three biogeographical regions of the
South African coast
12
15 4
10
:ons
aO
ID"DCCCD
"CDO1—
5
0
60
50
40
Temporarily closed estuaries y = 0.0366x +0.0499
R2 = 0.627
Z. 0 50 100 150 200
Permanently open estuaries
y = 0.075x+ 1.2894
R2 = 0.7354
100 500 600200 300 400
Estuary s ize (ha)
Figure 2. Difference in the reiationship between estuary size and catch for permanently open and temporarilyclosed estuaries in the Warm Temperate and Subtropical regions.
Finally, both estuarine size (ha) and type (all 5types) were used to explain catches within theWarm Temperate and Subtropical biogeographicalregions using general linear models. Again, thesemodels exclude the three outlying estuaries
Warm Temperate region:Catch (tons) = 0.904 +0.068*Size
mentioned above. The models were able to explain82% and 98% of the variance in catches for the tworegions, respectively. Both models were highlysignificant (p < 0.001):
• 2.510 (if Permanently open)
Subtropical region:Catch (tons) = -3,461 +0.055*Size +8.213 (if Lake) -27.23 (if Bay)
+ 5.605 (if Permanently open) + 10.140 (if River mouth)
These models were applied to the area and typedata for the remaining estuaries to estimate totalestuarine catches. Existing estimates of catches for129 estuaries amount to 1700 tons per annum, andthe new estimates for the remaining 126 estuariesbrings the total to 2482 tons (Table 4, details forindividual estuaries in Appendix 1).
Anglers (including castnet activities) and gillnettersaccount for 93% of the total catch, with totalcatches being roughly equal for the two groups offishers. Seine-net and traditional fisheries accountfor the remainder (Table 4).
13
Table 4. Estimated total catches (tons) per fishery for all estuaries in each of five coastal regions in South Africa.
Estuaries Ha Angling Castnet Gill-net Seine-net Traps Spear Total kg/ha
WestSouthEastTranskeiKZN
952546773
5 884.012 865.93 763.92611.846 810.6
14.0409.6223.5
141.1245.4
2.231.119.912.552.4
625.0151.651.532.5296.5
12.0
72 73 16
641.2604.3294.3186.1755.3
109.047.078.371.216.1*
TOTAL 155 71 936.2 1Q33.6 118.1 1157.0 84.0 73.0 16.0 2481.7 34.5* excluding St Lucia, the average yield for KwaZulu-Natal is 58.1 kg/ha
West coast estuaries have the highest yields per ha{Table 4), reflecting the generally high fisheryproductivity of this region. Indeed, the high overallcatch comes from a small number of largeestuaries, mainly the Berg and Olifants estuaries. InKwaZulu-Natal, most of the catch is from Kosi andSt, Lucia estuaries. On the south coast, Knysna isestimated by the model to have a catch of over 250tons, but this is likely to be an overestimate.
Catch composition
Catches within estuaries in South Africa aredominated by harders, most of which are caught onthe west coast (Table 5). Spotted grunter anddusky kob are the next most important species
caught in estuaries, being the main catch of the restof the country (Table 5). These three species makeup 69% of the total biomass of fish caught inestuaries. On the west coast, harders make up86% of catches, and elf make up most of Iheremaining catch (10%). On the south coast,spotted grunter makes up 45% of catches, harder18% and white steenbras 10%, and dusky kobmakes up 6% of catch weight. On the east coast,catches are dominated by dusky cob (48%) andsported grunter (31%). Catch composition inTranskei is unknown. In KwaZulu-Natal, catchesare dominated by dusky kob (35%), flathead mullet(11%) and spotted grunter (11%), and evenfinpursemouth, Mozambique tilapia, groovy mullet,largescale mullet make up >5% of catch weight
Table 5. Catch composition by weight and percentage,Natal.
excluding Transkei catches and traditional fisheries in KwaZuiu-
Species
Liza richardsoniiPomadasys commersonniArgyrosomus japonicusMugil cephaiusPomatomus saltatrixUthognathus lithognathusGenes methueni/rappiUza dumenliiOreochromis mossambicusUza macrolepisClanus ganepinusUza tncuspidensUchia amiaRhinobatos annulatusAcanthropagrvs berdaElops machnataRhabdosargus hoiubiLeiognathus equulaRhabdosargus sarbaTrachums trachurus
Common name
HarderSpotted grunterDusky kobFlathead mulletElfWhite steenbrasEvenfin pursemouthGroovy mulletMozambique tilapiaLargescale mulletSharp tooth catfishStriped mulletLeervis/garrickLesser guitarfishPerch/riverbreamLadyfishAenpounderCape stumpnoseSlimyNatal stumpnoseMaasbunker
liellallallaliellaliblibIVllaIVlibllaIIIllallallaliblibIII
WestTons539.7.9
--
10.6462.580.22
--
0.20---
0.790.200.63
----
12.14
SouthTons110.89270.62
36.3513.560.87
60.22-
13.02---
26.3421.1322.94
--
14.26---
EastTons
17.9173.51
113.312.161.634.47
-0.50
---
1.464.09
-0.677.381.63
---
KZNTons
-71.88
227.5172.14
1.47-
50.5235.0744.1135.2028.34
---
19.339.36
-14.2514.17
-
TOTALTons
668.5416.0377.198.566.564.950.548.544.335.228.327.826.023.120.616.715.814.214.112.1
%31.5219.6117.784.643.143.062.382.292.091.661.341.311.231.090.970.790.750.670.670.57
Continued.
14
Table 5 continued.
Species Common name West SouthTons Tons
EastTons
KZNTons
TOTALTons
Pomadasys basta/kakaanGaleichthyes felicepsDiptcdus sargus
Lutjanus argentjmactulusMyxus capensisRhabdosargus globicepsSparodon durbanensisJohnius dussumien
Cbeiidontchthyes capensisCarcharhtnus leucas
Platycepnalus indicusMuraenesox bagioChanos chanosMonodactyius faiciformisCaranx ignobilisCaranx sexfasciatusCaranx melampygusCaranx papuensisDiplodus cervinusUza atata
Scomberoides iysanLithognathus mormyrvsThryssa vtirirostnsGerres aanacasMegalops cyprinoidesDasyatis chrysonotaSarpa salpaMustelus mustelusMonodactylus argenteusPomadasys muttimacuiatumMyiiobatus aquilaSphyraena barracudaSphyraena jelloTerapon jarbuaGlossogobius giunsAnguilla bengaiensisAnguilla bicoiourAnguilla marmorataAnguilia mossambicaSpondyiicscma emarginatumLutjanus fuiviflammaAmbassis productusAmbassis gymnocephalusAmbassis nataiensis
Javelin grunterBarbelDassie/blacktailRiver snapperFreshwater mulletWhite stumpnoseWhite musselcracker
Mini kobGurnardZambezi sharkBartaiied flathead
Pike congerMiikfishCape/Oval mconyGiant kingfishBigeye kingfishBluefin kingfishBrassy kingfishZebra/wildeperd
Diamond mulletDblespatted queenfish
Sand steenbrasOmgemouth giassnoseSmailscale pursemouth
Oxeye tarpon
Blue stingrayStrepieSmooth houndsharkNatal/Round moonyCock grunterEaglerayBarracudaPickhandle barracuda
Thorn fishTank gobyAfrican mottled ee!
Shortfin eelGiant mottled ee!Longfin eelSteentjieDory snapperLongspine glassyBald glassySlender glassv
Total catch (tons)
DC
liblielieVblie111lieIIIHeHeIIIlieHalibliblielieIIIliblibIIIliblibVb111lieIIIlib
III111libliellaIVVaVaVaVa111lielaIbIb
•
1.55
---
0.13
--
0.28
----
0.06
-----•
•
-
-
-
-
0.26
-0.10
--
0.07
--------
0.01
----
629.64
-1.623.18
-0.462.602.60
------
0.61
-
--
0.56
-0.410.41
----
0.15
-----------------
602.79
-3.58
0.27
--
0.110.16
-2.01
----
0.07
---•
0.07
-------
0.070.11
----------------
235.15
10.06
--
3.382.39
--
2.70
-2.172.17
1.361.09
-0.700.700.700.70
-0.58
--
0.410.280.27
---
0.15
0.08•
0.050.050.020.020.020.020.020.02
-0.010.010.010.01
653.49
10.0
6.73.43.32.82.82.72.72.22.12.11.31.00.70.70.70.70.70.60.50.40.40.40.20.20.20.20.20.10.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
2121.0
U.4/
0.32
0.16
0.160.130.130.130.130.11
0.100.10
0.060.050.03
0.030.030.03
0.030.030.030.02
0.020.020.010.01
0.010.010.010.01
---------------
15
4. ESTUARJNE CONTRIBUTION TO INSHORE MARINE FISHERIES
Types of fisheries, participation and effort
Recreational shore angling
Most recreational shore angling is by rod and reel,but this sector also includes those fishing from theshore, piers and jetties with handlines. A proportionof these anglers use off-road vehicles to get to lessaccessible fishing areas. There are an estimated412 000 regular shore anglers in South Africa(McGrath et ai. 1997). The majority of recreationalanglers come from the upper two quintiles ofincome earners in South Africa (McGrath et ai.1997). Total shore angling effort amounts toapproximately 2 778 000 angler days per year, ofwhich 53% is in KwaZulu-Natal (Brouwer et ai1997, McDonald etat. 1998, Mann etai 1998).
Recreational boat angling
Recreational boat fishing gear includes both rodand reels and handlines. Boats used range fromsmall dinghies to skiboats of 6-8 m in extent, to thelarge tuna or striker craft. There are an estimated12 054 recreational boat anglers, operating from3 444 boats (McGrath ef ai 1997), on 92 988 boat-days per year. However, in many cases, thedistinction between commercial and recreationalboat fishermen is blurred, ranging from purelyrecreational fishers to those selling some catches tofinance boating expenses or to supplement anexisting income, to those who fish on a permanentcommercial basis.
Recreational spearfishing
Recreational spearfishers operate from boats orswim out from the shore, with spearguns. There isconsiderable investment in fishing equipment,including wetsuits, fins and other paraphernalia inaddition to spearguns. There are an estimated7000 participants in the recreational spearfishery(Mann et al 1997), responsible for about 126 000spearfishing days per year.
Commercial boat-based linefishing
Boats used in the commercial linefishery range fromsmall dinghies and skiboats to large decked freezerboats which operate to the edge of the continentalshelf (Griffiths 2000). There are approximately 18533 commercial line fishers operating from 2 581
registered boats (Griffiths & Lamberth in prep.), for380 800 boat-days per year.
Commercial gillnet and beach seine netting
The gear and fishing methods used in thesecommercial fisheries are similar to those describedfor the estuarine fisheries. Depending on the areain which they operate, gillnetters are restricted tothe use of either two or four 75 m nets of 44-178mmmesh size, but separate permit -holders may jointheir nets. Gillnet permits are issued exclusively forcatching harders and St Joseph sharksCaiorhynchus capensis, and a maximum of 10 by-catch linefish are allowed per day. All gillnetpermits issued for the marine environment are onthe west coast, from Yzerfontein northwards(approximately 321 permits), apart from a limitednumber of permits issued at Hawston on the southcoast (currently 3 permits), and occasionalexperimental fisheries elsewhere. In addition,illegal gillnetting occurs throughout the SouthAfrican coastline, though mostly on the west andsouth coasts. There are an estimated 268 illegalgillnets on the west coast, 60 on the south coast,and 120 on the KwaZulu-Natal coast.
Beach-seine permit holders to the west of WalkerBay on the south coast are restricted to nets of275m long, while on the rest of the south and eastcoasts they are restricted to 137m, and in KwaZulu-Natal, 100m. Minimum mesh sizes are 14mm inKwazuiu-Nata! and 44mm everywhere else. Thereare 84 beach-seine permits on the west coast, 76on the south coast, 8 on the east coast and 27 inKwaZulu-Natal. Except for three, the KwaZulu-Natal permits are issued exclusively for pilchardsSardinops sagax during the annual sardine run. Inaddition, there are at least 10 illegal beach-seinenets in use on the south coast, but no estimateshave been made for the rest of the country.
There are approximately 2 700 people who derivesome sort of income in the legal insnore netfisheries along the west and south coasts, with atotal effort of approximately 32 000 net-days peryear. About half of the crew numbers are employedin the beach seine fishery. There is evidence thatillegal gillnetting and beach-seining activities haveboth increased dramatically over the last threeyears, since the introduction of the Marine LivingResources Act.
16
Overall, it is estimated that there are about 431 000recreational fishers and well over 21 000commercial fishers active in the inshore marineenvironment in South Africa.
Inshore Marine Catches
The total inshore marine catch is estimated to be27 519 tons per year {Tabie 6). Of this 60% is
made up by the commercial linefish sector and23.5% by the commercial netfishery, the remainderbeing made up of recreational fisheries. Inshorefishery catches on the west coast, which make up53% of the total catch, are predominantlycommercial, whereas recreational catches arecomparable to commercial catches in the rest of thecountry, becoming relatively more importanttowards KwaZulu-Natal (Table 6).
Table 6. Inshore marine catches for different fisheries along different sections of the South African coast. All values are intons per year.
West South East Transkei KwaZulu-Natal TotalRecreational shore anglingRecreational boat anglingRecreational SpearfishingCommercial linefishingCommercial net fishing
115407
1910 1914 303
1021171
79 (S28481827
1 039236
& E coast)2615
159
336No dataNo data
39No data
66247025
765192
31731283
12316 4596 481
TOTAL 14 675 5 907 4 088 345 2114 27 519
Estuary-associated species in marine catches
Numerous estuary-associated species have beenrecorded in all types of inshore marine fisheries(Table 7). Recreational shore angler catches andcommercial gill- and seine-net catches aredominated by estuary-associated species (83% ofnumbers and 83% of mass, respectively). On theother hand, recreational boat and spearfishers, andcommercial boat fishers catch a relatively smallproportion of estuary-associated species, whichmake up about 7% of catches (Table 7}.
The main estuary-associated species caught byrecreational shore anglers are elf and strepie, whichtogether make up over 50% of the catch. Both ofthese species are estuary-dependent (category He).Numbers of dassie (lie) and piggy are alsosignificant, making up more than 5% of the catch.Commercial net catches are dominated by harders(75%).
The most important estuary-associated speciesfeatured in recreational boat catches is catfacerockcod (3%), although this is not an estuary-dependent species (category ill). In commercialboat catches, the highly estuary-dependent duskykob (category lla) features most importantly, butonly makes up 1% of total catch. This lowproportion is partly due to the collapsed status ofthe stock.
Zebra and white mussel cracker are the mostcommon estuary-associated species in recreationalspearfishing catches, but these each only make upless than 3% of catches. However, these arecategory III species, and the most commonestuarine-dependent species is leervis (1%), whichis completely dependent on estuaries for thejuvenile phase of its life-cycle.
The contribution of different categories of estuary-associated species to inshore marine fisheries issummarised for each part of the coast in Table 8.Category I species, which are largely resident inestuaries, hardly feature at alt in inshore marinecatches. Category lla species, which are entirelydependent on estuaries, generally make up arelatively small percentage of catches, ranging from1.3% of recreational boat and spear catches to3.7% of commercial gillnet catches, 5.9% ofcommercial boat catches and 7.1% of recreationalshore catches. However, they do make up highproportions of certain catches in certain regions(Table 8). Historically, dusky kob and whitesteenbras comprised a large proportion of shoreangler catches, but overexploitation of thesespecies has led to stock collapses to present levelsof 4% and 6% of pristine spawner biomass,respectively (Griffiths 1997, Bennett 1993). Theproportion of category lib species in catches isgenerally lower than of category lla species (Table8).
17
Table 7. Percentage contribution of estuarine associated species to the overall catches in different inshore marine fisheries,and total percentage of estuarine species in catches. Figures are percentage of total biomass in all cases exceptRecreational Shore Angling, in which data are in numbers of fish.
SpeciesAcanthropagrus herdaArgyrosomus japonicusArgyrosomus spp.Eiops machnataLJchia amiaLithognathus lithognathusLiza macroiepisMugil cephalusPomadasys commersonniRhabdosargus holubiCaranx ignobilisCaranx sexfasciatusGaleichthyes feiicepsGerres methueni/rappiLeiognathus equulaUza alataUza dumeriliiUza tncuspidensRhabdosargus sarbaCaranx meiampygusCaranx papuensisCarcharhmus ieucasChanos chanosDiplodus sargusJohnius dussumieriUza richardsoniiLutjanus argentimactulusPlatycephalus IndicusPomadasys hasta/kakaanPomatomus saltatnxRhabdosargus globicepsSarpa salpaSillago sihamaCheiidonichthyes capensisDasyatls chrysonotaDipiodus cervinusEpinephelus andersoniGymnura natalensisUthognathus mormyrusMuraenesox bagioMustelus mustelusMyliobatus aquiiaOtolithes ruberPomadasys oiivaceumRhinobatos annutatusSparodon durbanensisSpondyliosoma emarginatumTrachinotus afncanusTrachums trachurusMyxus capensisTotal % of estuarine species
Common namePerchAiverbreamDusky kobSilver and dusky kobLadyfish/tenpo underLeen/is/garrickWhite steenbrasLargescale mulletRathead/springer mulletSpotted grunterCape stumpnoseGiant kingfishBigeye kingfishBarbelEvenfin pursemouthSlimyDiamond mulletGroovy mulletStriped mulletNatal stumpnoseBluefin kingfishBrassy kingfishZambezi sharkMilkfishDassie/blacktailMini kobHarderRiver snapperBartailed flatheadJavelin grunterElfWhite stumpnoseStrepieSilver sillagioGurnardBlue stingrayZebra/wildeperdCatface rockcodButterfly/diamond raySand steenbrasPike congerSmooth houndsharkEagleraySnapper kob
PiggyLesser guitarfish/sandsharkWhite musselcrackerSteentjieSouthern pompanoMaasbunkerFreshwater mulletin catch
llalla
-/llallallallallallallallaliblibliblibliblibliblibliblielielielielielieHelielieiiclielielielieIII111IIIIIIIIIIIIIIIillHIIIIIII111IIIIIIIIIIIIVb
Shore0.16173
-0.060.461.40
-0.121.092.10
--
0.52----
1.030.76
---
7.64-
2.67-
0.020.02
27.181.40
24.300.080.200.040.460.070.020.93
-0.260.060.046.100.540.470.430.260.54
-83.14
RecreationalBoat
-0.210.98
-0.06
---
0.040.020.08
-0.05
-----
0.08----
0.02---
0.010.200.700.570.01
-0.04
-0.102.93
---
0.16-
0.240.04
--
0.10-
0.15-
6.79
Spear----
1.300.01
---
-------
0.09----
0.63---------
-2.47
----
0.01----
2.41-
0.01-
6.93
CommercialBoat
-1.184.75
---------
0.01---------------
0.020.270.890.01
-0.02
--
0.03-----
0.01---
0.13-
0.06-
7.40
Net0.080.651.020.040.020.820.180.560.300.01
-0.010.060.510.140.010.180.070.080.010.010.020.010.070.05
74.970.030.02
-0.910.880.13
-0.04
---
0.010.010.010.600.03
--
0.03-
0.07-
0.340.02
83.03
18
The majority of estuary-associated fish biomass inrecreational shore-angling and in commercial gillnetcatches is made up of category lie species, whichare species whose juveniles are found mainly inmarine environments but also occur in estuaries.Category II! species occur in estuaries but are notdependent on them. These make up over 10% ofshore-angling catches, 3.8% of recreational boatand 4.9% of recreational spearfishing catches, but
are not particularly important in commercial catches[Table 8). Category IV species are freshwaterspecies, and thus do not feature in marine catches.Category V species have only been recorded invery small quantities in KwaZulu-Natal, thoughsmall quantities are also known to be caughtelsewhere. These species are entirely dependenton estuaries, but they are normally caught in rivers,beyond the scope of this study.
Table 8. Percentage contribution of different categories of estuarine associated fish to the inshore marine fisheries in eachof the coastal sections. All percentages :n terms of biomass except recreational shore angling, in terms of numbers.
Dependence categoryla Ib lla lib He III IV Va Vb Total
Recreational shore WestSouthEastTranskeiKZN
Total
0.515.319.00
11.525.22
0.171.271.641.973.98
41.2658.8159.6445.9778.40
13.89.1
18.63.63.9
7.12 2.30 63.31 10.4
55.7574.5288.9863.1291.52
83.14
Recreational boat WestSouthEastTranskei
_KZNTotal
0.02 <0.01 0.80 0.17.31 <0.01 3.72 0.70.33 0.24 0.47 1.7
0.74 0.42 1.84 9.0
1.31 0.20 1.51 3.7
0.9211.796
2.80
12.056.79
Recreational spear West
South & eastKZNTotal
0.050.584.67 0.441.31 0.09
0.090.96
0.06.72.7
0.63 4.8
0.238.297.88
6.93
Commercial boat WestSouthEastTranskeiKZN
0.09 <0.01 0.80 0.17.31 <0.01 3.72 0.7
27.45 0.03 0.24 0.18.08 0.91 0.01 0.26.13 0.11 0.44 0.8
0.9111.8027.869.267.49
Total 5.94 0.02 1.20 0.2 7.40
Seine & gillnet WestSouthEastTranskeiKZN <0.01 <0.01
TotalSpecies total
<0.01 <0.01
i
1.054.462.16
14
0.040.050.97
80.8676.0396.59
3.67 1.08 77.10
15 19
1.11.40.0
45.46 27.51 4.94 0.71.1
0.02
0.010.70.0
83.0681.9899.73
79.37
83.03
19
5. ECONOMIIC VALUE OF ESTUAR1NE FISH
Values considered
All values are considered in terms of value added tothe economy (contribution to Gross DomesticProduct). Subsistence outputs are not actuallyrecorded as part of GDP, but would be in an idealworld. The value of subsistence fisheries wastaken as the gross vaiue of landed catches, basedon the market value of fish caught. The values ofcommercial and recreational fisheries werecalculated mainly on the basis of data in McGrath etal. (1997). Commercial fishery values include thevalue added by subsidiary industries. Recreationalvalues comprise the expenditure by anglers onequipment and travel to fishing sites. Note that thelatter may be an overestimate of value since fishare one part of a recreational package which mayinclude enjoyment of coastal areas, etc.Furthermore, in the absence of fish, some anglersmay turn to alternative recreational activities whichstill incur some expenditure in the economy.Nevertheless, we feel that most angling expenditureis currently attributable to the fishery resource andshould be reflected as such.
The total value of estuaries to South Africanfisheries comprises the value of fisheries withinestuaries plus the value that estuarine inputscontribute to inshore marine fisheries. These twocomponents are discussed separately below.
Value of estuarine fisheries
Applying the average per-kg vaiues of the differentfisheries to the total catches in each coastal region,the total vaiue of fisheries within South Africanestuaries is estimated to be about R433 million peryear (1997 Rands; Table 9). This is based on anestimated total annual catch of 2 482 tons (Table4).
Ninety-nine percent of this value (nearly R429million) is the value of recreational angling, whilenet and traditional fisheries together make up theremaining 1% of value (Table 9). This distributionof values among estuarine fishery sectors is verydifferent from the distribution of catches (Table 4),which are equally dominated by recreational andgillnet fishing. Furthermore, the estimated value ofcommercial fisheries (about R3.8 million), derivedfrom marine fishery values, may be slightly
overestimated. This is because fish caught inestuaries are generally smaller than in marinecatches, which means that catch masses are madeup of proportionally more individuals. Smaller fishare of 'lower quality' and do not fetch the sameprices per kg as those in the larger size classes.
With over 72 000 anglers in the recreational fishery,compared with some 1350 in the commercialfisheries, these aggregate values (Table 9)translate to average values of about R6000 perrecreational angler per year (expenditure), versusabout R2800 per commercial fisher (income). Therecreational value is realised as income to anunknown number of participants in subsidiaryindustries.
Thus substantial amounts are spent annually bylarge numbers of anglers in estuaries, most ofwhom belong to middle-upper income groups,whereas a relatively few fishers from lower-middleincome groups are apparently earning an averageannual income well below the poverty line. Indeed,it is increasingly being realised that commercialestuarine fisheries are generally non-viable assustainable long-term ventures. Prices forestuarine fish are often low, and operating costs arestill relatively high, even though they are slightlylower than in the marine environment. The onlyway these fisheries can be profitable, at least in theshort term, is through targeting the more vulnerablelinefish species, as fishing solely for mullet andsimilar species in estuaries is non-profitable(Hutchings & Lamberth 1999, Beckley et a!. 2000,Kyle 2000a). However, targeting linefish is usuallyonly profitable for a short period until stocksbecome locally depleted.
Exacerbating this problem is the fact thatcommercial estuanne fisheries in South Africa aredrastically oversubscribed, the large amount oflatent effort making the fisheries economicallyinefficient. The investments in inputs intocommercial fisheries in estuaries are often muchhigher than gross income. For example, giilnetpermit holders on the Berg River estuary onaverage operate at a loss of about R5 600 perannum. It has been estimated that an effortreduction in the region of 60% is required in order toobtain maximum economic yield from this estuarinegillnet fishery (Hutchings & Lamberth in press b).
20
Table 9. Estimated annual value (1997 rands) of estuarine fisheries along different stretches of the South African coast.West South East Transkei KZN TOTAL " %
AnglingCastnetGill-netSeine-netFish traps
5 803 9806 776
1 925 000
169 813 301
95 821
466 82136 854
92 657 453
61 140
158 510
58 484 198
38 591100 050
101 735 478161 392913 220221 760224 840
428 499 410363 719
3 563 601258 614224 840
990.10.80.10.1
SpearTotal
%7
-735 756
1.8170
-417 798
39.492
-877 103
21.558
-622 838
13.5103
49 280305 970
23.9
49432 959
280 <0.1465
Comparatively few people are involved in thetraditional fisheries, which are worth just a fractionof the other fisheries, amounting to about R2300per fisher per year in terms of subsistence income.Viewing the traditional fisheries in the sameeconomic terms as other fisheries may besomewhat misleading in terms of their importance.It should be noted that these fisheries form anintegral part of the survival of communities whichrely on them for their protein source. Indeed, suchfisheries in tropical Africa commonly contribute ahigh percentage of household income (Turpie et at.1999b, Turpie 2000b).
A similar type of argument might by made for thecommercial fishenes, especially when compared tothe recreational fishery. However, on the westcoast, where much of the commercial effort takesplace, it is evident that the people involved in thefishery are not heavily reliant on the fisherycontributing to their income (Hutchings & Lamberthin press b). On the Berg estuary, none of thefishers interviewed regarded netfishing as theirmain occupation, 80% of them being employed inother sectors, and the remainder being retired.Indeed, the net fishery contributed over 50% ofincome for only 10% of the fishers (Hutchings &Lamberth in press b).
Estuarine contribution to inshore marine fisheryvalues
The total value of inshore marine fisheries is aboutR2.44 billion per year (1997 rands; Table 10).Approximately 83% of this value is the value of therecreational fishenes (almost all from shoreangiing), the remaining 17% being commercialvalue. Similar arguments apply to thedisproportionately high value of recreationalfisheries in comparison to catch ratios as for theestuarine fisheries. The recreational value, spreadamong about 431 000 fishers, amounts to an
average value (expenditure) of about R4300 perfisher per year, whereas the approximately 21 000people involved in commercial fisheries gain anaverage of R19 000 per year (income).
Roughly half of the total inshore marine fisheryvalue (52%) is made up of estuary-associatedspecies (Table 10). However, not all of these fishare equally dependent on estuaries. Category la,Ib, lla, Va and Vb species are 100% dependent onestuaries to complete their life cycles. Because thejuveniles of Category lib species are largelyconfined to estuaries, their level of dependence onestuaries was considered to be very high, and wasestimated as 90%. The overall numbers ofCategory lie species, whose juveniles mainly occurin marine environments, are augmented by thepresence of estuarine habitat areas. Estuarine areacomprises about 30% of the juvenile habitatavailable to these species, and those juvenilesusing estuaries are frequently in better conditionthan those in marine habitats (De Decker & Bennett1985). We thus estimate that 30% of the marinecatches of Category He species can be attributed toestuarine export. Thus adjusting values accordingto the level of contribution that estuaries make tothe catches of species of different categories, theestimated contribution from estuaries to inshoremarine fisheries is 2 1 % of the total value, or R519million per year (Table 10). In other words, thisvalue would be lost if estuaries were 'removed' fromthe coastline.
The relative contribution of estuaries to fisheriesvaries between types of fisheries and around thecoast. The contribution of estuary-dependentspecies to recreational shore angling valuesincreases from 6% on the west coast to 36% on theKwaZulu-Natal coast. Estuaries contribute 25% ofthe total value of the recreational shore fishery,whereas they contribute only 0.3% and 0.7% to thevalue of the recreational boat and spear-fisheries
21
{Table 10). Overall, the estuarine contribution tomarine recreational fishery values is about R469.74million per year. This is 90.5% of the totalestimated estuarine contribution to marine fisheries.
The estuarine contribution to commercial boatfisheries ranges from 0.3% of value on the westcoast to a peak of 37% on the east coast, andaverages 11% for the whole coastline (Table 10).
Estuaries contribute a substantial portion of thevalue of the gillnet and seine-net fisheries,increasing from about 25% on the west and southcoasts, to 68% on the KwaZulu-Natal coast.However, as most of the fishery is concentrated onthe west coast, the overall contribution is about26% (Table 10).
The overall contribution of estuaries to inshorefishery values is summarised in Table 11.
Table 10. Percentage contribution of estuarine associated fishes to the total value of the inshore marine fishing sectors inthe different coastal regions, the total annual values of the fishenes, the amount and percentage of total which is comprisedof estuary-associated species, and the contribution of estuaries to total fishery values. The latter is calculated on the basisof 100% of the value of Categoiy la, Ib, lla, Va and Vb species. 90% of the value of Category lib species, and 30% of thevalue of Category lie species. Category III species are not included in this value.
Estuary-associatedla Ib
Recreational shore
West
SouthEast
Transkei
KZNTotal
Recreational boatWest
South
East
KZNTotal
Recreational spearWest
S & E
KZN
Total
Commercial boatWest
SouthEast
KZNTotal
Seine & gillnetW. coast
S. coast
E. coast
KZN 0.01 0.01
Total 0.01 0.01
TOTAL
lla
0.60
7.2916.25
23.22
11.47
11.42
0.00
0.37
0.04
0.12
0.19
4.79
0.53
0.04
11.09
36.52
7.09
11.05
3.89
10.99
9.12
57.48
7.30
lib
0.03
0.29
1.130.89
4.46
1.09
0.00
0.00
0.02
0.00
0.44
0.03
0.00
0.000.01
0.04
0.00
0.02
0.01
0.50
2.70
0.06
species categoriesHe
18.05
38.3246.15
36.65
69.15
43.05
0.39
3.771.66
1.08
0.79
0.06
0.41
0.34
0.78
2.50
0.16
0.21
0.97
72.90
46.25
90.04
25.15
62.72
III Va
2.24
5.75
21.48
4.32
5.51
9.74
0.01
0.22
2.16
0.05
0.12
8.28 '
13.15
7.57
0.05
0.200.03
0.99
0.15
1.86
2.11
0.03
6.31 0.01
1.97 0.01
Totalvalue
Vb R million
105.70
825.70
513.00
174.49
233.29
1852.18
112.06
14.48
0.88
0.58
128.00
7.2443.23
4.24
54.70
188.89
82.0986.00
29.02
386.00
11.927.49
0.41
0.01 0.25
0.01 20.07
2440.94
Estuary fishcontribution
R million
22.12
426.45
436.12113.56
211.32
1209.66
0.45
0.63
0.03
0.01
1.13
0.023.84
0.78
4.64
1.66
11.33
31.58
2.42
46.98
9.37
4.45
0.41
0.23
14.46
1276.77
%
20.92
51.65
85.01
65.08
90.58
65.31
0.41
4.36
3.84
1.08
0.88
0.30
0.13
18.38
8.48
0.88
13.80
36.72
8.33
12.17
78.67
59.36
99.70
91.64
72.05
52.3
Value dueto estuaries
R million aj
6.39
157.29
159.63
61.10
84.50
469.02
0.13
0.22
0.00
0.00
0.36
0.01
8.88
0.22
0.36
0.53
9.7231.45
2.09
43.79
3.07
1.86
0.15
0.17
5.26
518.79
'o
6.0
19.0
31.135.0
36.2
25.3
0.1
1.50.5
0.30.3
0.1
0.3%
5.20.7
0.3
11.836.6
7.211.3
25.8
24.9
36.6
67.5
26.2
21.3
22
Table 11. Summary of the estimated total contribution of estuanes to the annual value (1997 Rands) of inshore marinefishenes along different stretches of the South Afncan coast, by fishery.
Estuarine contribution tomarine inshore fishery values
West South East Transkei KZN Total
Recreational shore
Recreational boat
Recreational spear
Commercial boat
Seine & gillnet
6.39
0.13
0.01
0.53
3.07
1570091
.29
.22
.15
.72
.86
159.63
00.15
31.45
0.15
61.1 84.5 469.02 90.40 0.36 0.1
0.22 0.36 0.1
2.09 43.79 8.40.17 5.26 1.0
Total 10.13 169.24 191.38 61.1 86.98 518.79
2.0 32.6 36.9 11.8 16.8
Total value of estuarine fish
The total value of estuarine and estuary-dependentfishenes is estimated to be R951.75 million in 1997Rands (Table 12). This is equivalent to R1.162billion in 2000 rands.
Furthermore, this total estuarine fish value is ratherunevenly distributed around the coast, with westcoast estuaries contributing less than 2% of thetotal value. Estuaries along the warm temperate
coast have the highest aggregate value, andaverage per estuary values (Table 12). East coastestuaries, in particular are worth over R75 000 perha per year (1997 rands) in terms of fish production(Table 12).
However, average values may not be very reliablepredictors of individual estuary values, which arerelated to several factors such as size and mouthstatus, as well as geographical location.
Table 12. Summary of the value of estuarine fisheries and estuary contribution to marine fisheries around different parts ofthe coast. Values given in 1997 Rands.
Estuanne fisheries (R million)
Inshore marine (R million)
TOTNo estuanes
Ha
Average value/estuary (R million)
Average value/ha (R)
West
7.7
10.1
17.9
9
5,884
2.03,036
South East
170.4
169.2
339.7
52
12,866
6.526,400
92.9
191.4
284.3
54
3,764
5.375,520
Transkei KZN
58.6
61.1
119.7
67
2,612
1.845,836
Total
103.3
87.0
190.3
7346,811 •
2.64,065
433.0
518.8
951.7
255
71,937
3.713,230
23
6. STOCK STATUS OF ESTUARINE FISH SPECIES
Fishing in South Africa is a rapidly-growing activity.It is already evident that the high national fishingeffort has taken its toll on fish stocks. This hasbeen quantified in coastal fisheries, where shore-angling catches per unit effort have declinedmarkedly over the past two decades (Bennett &Attwood 1993, Griffiths 2000), as well as in someestuaries.
In the Swartkops and Sundays estuaries, spottedgrunter and dusky kob make up 87% and 90% ofangler catches, respectively (Baird et a/. 1996),indicating a tendency for anglers to concentratetheir efforts on particular species, rendering themhighly vulnerable to overexploitation. These fearshave been confirmed by gillnettling studies in thetwo estuaries which have indicated a decline inspotted grunter over the past 20 years (Baird et ai.1996). Similarly, catch rates of sported grunterwere also found to have declined in Durban Bayestuary over a period of 16 years (Guastella 1994).Moreover, elf was once as abundant as spottedgrunter in angler catches in the Swartkops estuary,but has now almost disappeared. White steenbras,a highly sought-after species, has been depletedboth in estuaries and in the marine environment(Bennett 1993, Lamberth 2000c). In the Swartkopsestuary, this species formed an importantcomponent of catches in 1918, by the 1970s, wasreduced to only 3% of anglers catches, and werealmost totally absent from catches in the 1990s(Whitfield & Marais 1999).
•The status of stocks is judged as overexploited,maximally exploited or underexploited on the basisof its current size as a percentage of pristine stocksize (or spawner biomass). An maximally exploitedstock (one which is exploited close to the maximumsustainable yield) is considered to be at a level of40-50% of pristine biomass. It should be noted thatthese judgements assume that current biomass isonly a function of harvesting, and that carryingcapacity {or maximum stock) has remainedconstant. In reality, the latter may also be affectedby changes in habitat quality, thus also affectingcurrent biomass.
Under the above assumptions, fourteen of the 80utilised estuary-associated species are consideredoverexploited (Table 13). Of these, elf, dassie, kob,white steenbras, white stumpnose and natalstumpnose are ranked in the top 30 fish across all
inshore sectors in terms of catch, targeting, and thenumber of people reliant on them (Lamberth &Joubert 1999). The stocks of six of these fourteenspecies are in a collapsed state, including whitesteenbras and kob, which are Category Ita species(Table 13). A further 27 species, including spottedgrunter and leervis, are regarded as maximally oroptimally exploited, and are likely to be subject toadditional fishing pressure in future. The remaining40 species are considered underexploited, as theirstocks are at levels greater than 50% of pristinespawner biomass. However, with few exceptions,these are small species such as strepie, flatheadmullet and striped mullet, which on a national scale,have limited value to commercial or recreationalfishers. Some of them are species which are eitherat the edge of their range, or have a limited range,with South Africa, but they may be locally importantin certain areas, e.g. pursemouths in Kosi Bay.
It is difficult to assess what contributes more to thedecline of an estuarine species: estuarine habitatdegradation or overexpioitation. Estuarinedependence immediately creates a life-historybottleneck for many species, especially when itcomes to entering temporarily closed estuaries. Inaddition to estuarine dependency, sex changes,spawning migrations, predictable aggregations,high age at maturity, longevity, residency and highcatchability all contribute to a species vulnerabilityto overexploitation. For example, white steenbrasexhibits seven of these life-history traits, excludingsex change, and is currently at 6% of its pristinespawner biomass, and on the critical list. Half of allspecies considered have vulnerable life-historycharacteristics in addition to estuarine dependency,and a quarter of them fall into the most vulnerablecategory (Table 13).
Very few of the species considered are rangerestricted (Table 13). A quarter of species arehighly exploited throughout their range (Table 13),23 species are under medium exploitation, and therest are subject to medium to low exploitation.
On the whole, knowledge of exploited estuarine fishspecies is poor, with three quarters of specieshaving low knowledge scores up to half theoptimum. For most of these species, nocomprehensive stock assessments have beendone.
24
Table 13. The slock status (abundance trend) (A), vulnerability (V), range (R), exploitation level (E) and knowledge (K) of
utilized estuanne-associated species in South Africa.
Family
Carcharhinidae
Dasyatidae
Mustelidae
Myliobatidae
Rhlnobatidae
Ambassidae
Anguillidae
Ariidae
Belonidae
Carangidae
Chanidae
Charangidae
Cichlidae
Clanidae
Elopidae
Engraulidae
Gerreidae
Gobiidae
Haemulidae
Kuhliidae
Leiognathidae
Lutjanidae
Megalopidae
Monodactylidae
Mugilidae
Species
Carcharhinus leucas
Dasyatis chrysonota
Gymnura natalensis
Himantura uamak
Mustelus musteius
Myliobatus aquila
Rhinobatos annulatus
Ambassis gymnocephalus
Ambassis productus
Ambassis natalensis
Anguilla bengaiensis
Anguilla marmorata
Anguilla mossambica
Anguilla bicolor
Galeichthyes feliceps
Strongylura leiura
Caranx sexfasciatus
Caranx melampygus
Caranx papuensis
Scomberoides lysan
Caranx ignobilis
Trachurus trachurus
Trachinotus africanus
Chanos chanos
Uchia amia
Oreochromis mossambicus
Clarius ganepinus
Elops machnata
Thryssa vitrirostris
Genes methueni/rappi
Genes acinaces
Glossogobius giuris
Pomadasys multimacuiatum
Pomadasys hasta/kakaan
Pomadasys olivaceum
Pomadasys commersonni
Kuhlia mug/7
Leiognathus equula
Lutjanus fuMflamma
Lutjanus argentimadutus
Megalops cyprinoides
Monodactylus faicsformis
Monodactylus argenteus
Valamugil seheli
Valamugil buchanani
Uza alata
Mugil cephalus
Myxus capensis
Common name
Zambezi shark
Blue stingray
Butterfly/diamond ray
Honeycomb stingray
Smooth houndshark
Eagleray
Lesser guitarfish
Bald glassy
Longspine glassy
Slender glassy
African mottled eel
Giant mottled eel
Longfin eel
Shortfin eel
Barbel
Yellowfin needlefish
Bigeye kingfish
Bluefin kingfish
Brassy kingfish
Doublespctted queenfish
Giant kingfish
Maasbunker
Southern pompano
Milkfish
Leervis/gamck
Mozambique tilapia
Sharptooth catfish
Ladyfish/tenpounder
Orangemouth glassnose
Evenfm pursemouth
Smaliscale pursemouth
Tank goby
Cock grunter
Javelin grunter
PiggySpotted grunter
Barred flagtail
Slimy
Dory snapper
River snapper
Oxeye tarpon
Cape/Oval moony
Natal/Round moony
Bluespot mullet
Bluetail mullet
Diamond mullet
Fiathead/spnnger mullet
Freshwater mullet
Cate-
gory
HeIIIIIIIIIIIIIIIIIIIblaIbVaVaVaValiblieliblielieliblibIIIHIliellaIVIVllalibliblibIV111lieIIIllaIIIliblielieVbllaliblielielibilaVb
CONSERVATION
A456060605560655555555050505055555555555545505055505055655555554045455040555550306055555050556540
V1000
90909070707070701001001001001007070707070807070809000
1007070707090907010007070909070707070709070
R01040000100101010101010100000000100010000
1000000000000000000040
IMPORTANCE
E752550501002525000505050507502525025501005025755050250
50500
505075100000755000025505050
K57715029864350292929505050507121432121750792143648686363643293629295757293629291436211429295036
continued.
25
Table 13 continued.
Family Species
Liza dumenlii
Liza nchardsonii
bza macrolepis
Vaiamugil cunnesius
Valamugil robustus
Uza luciae
Liza tncuspidens
MuraenesocidaeMuraenesox bagio
Platycephate
Pomatomidae
Sciaenidae
Serramdae
Siilaginidae
Spandae
Sphyraenidae
Teraponidae
Tnglidae
i Piatycephaius indicus
Pomatomus saltatrix
Argyrosomus japonicus
Johnius dussumieri
Otolithes ruber
Epmephelus andersoni
Epinephelus malabancus
Sillago sihama
Rhabdosargus hoiubi
Diplodus sargus
Rhabdosargus sarba
Acanthropagrvs berda
Uthognathus mormyrus
Spondyliosoma emarginatum
Sarpa saipa
Sparodon durbanensis
Uthognathus Uthognathus
Rhabdosargus giobiceps
Diplodus cervinus
Sphyraena barracuda
Sphyraena jello
Terapon jarbua
Chelidomchthyes capensis
Common name
Groovy mullet
Harder
Largescate mullet
Longarm mullet
Robust mullet
Si Lucia mullet
Striped mullet
Pike conger
Bartailed flathead
EifDusky kob
Mini kob
Snapper kob
Cattace rockcod
Malabar rockcod
Silver sillagio
Cape stumpnose
Dassie/blacktail
Natal stumpnose
Perch/riverbream
Sand steenbras
Steentjie
Strepie
White musselcracker
White steenbras
White stumpnose
Zebra/wildeperd
Barracuda
Pickhandle barracuda
Thomfish
Gurnard
Cate-
gory
libliellaHallaliblibIIIlieHellalie111HIIIIliellalielibllaIIIIIIlieIIIllaHeIIIlibliellaIII
CONSERVATION
A504550505050655555344
556013206540353535207067306
203550605560
V709070707070800
701001009080100100801001001001000
809010010010010080707080
R010001010040000
4000
6000401000040204040204000010
IMPORTANCE
E501007500
255000
1001002550100750
7510075
75251001001001001001005050025
K362629293614036368686295729147
5057506414217171505736500
2950
26
7. IMPLICATIONS FOR MANAGEMENT
This study has shown that estuaries contribute asignificant value to the economy in terms of bothestuarine fisheries and their contribution to inshoremarine fisheries, with the latter contribution slightlyexceeding the value realised within estuaries.Although commercial catches are substantial bothwithin estuanes and in the marine environment, it isrecreational fishing activities that add most value tothe economy, with 22 times as many participants(about half a million vs under 23 000) and realisinga value more than 100 times greater per kg of fishcaught. Subsistence fisheries are very localised,and involve very small numbers of fishers and lowvalues, but important in the context of theirlivelihoods.
However, an assessment of the status of estuarinefish stocks suggests that the currently high value ofestuarine fish production is probably notsustainable- Dwindling fish stocks will affectcatches per unit effort and overall catches, and thevalue realised from these fisheries may well dropsubstantially if current trends are maintained. Thiswould have much greater impact on commercialfisheries, upon which many people rely for theirlivelihoods, particularly in marine fisheries, than onrecreational fisheries, which are less sensitive tocatch returns. It is clear that sound managementpractices will need to be put in place in order tosustain these values in future, as well as to ensurethe conservation of estuanne biodiversity.
Management strategies chosen for estuarinespecies may differ depending on socio-economicgoals, e.g. whether to secure livelihoods of small-scale commercial fishers, or whether to increaseoverall contribution to the economy. No doubt, anequitable balance of these goals is required.Nevertheless, any management strategy ultimatelyhas to concentrate on maintaining maximalproductivity of resources if benefits are to besustained in the long term.
Linefish and netfish management is currentlyundergoing complete revision in order to addressthese challenges. A linefish management protocolhas been developed (Griffiths et al. 1999) whichrequires species-specific management plans.Under the Marine Living Resources Act, estuariesfall within the marine environment, and thesemanagement plans include estuarine populations.Apart from the reduction of overall commercialeffort, including in estuaries, there has been a
substantial revision of bag and size limits forrecreational, subsistence and commercial fisheries.With compliance, the effort directed at many ofthese species is likely to decrease.
Reduced catches in estuanes are needed to secureestuanne contributions to marine inshore fisheries.If current regulations were complied with, this wouldbe achieved, providing the estuarine environments(e.g. freshwater inflows) were also sufficientlyprotected. In the recreational fishery, a largeproportion of landed catches comprise undersizedfish, ranging from 90% on the west coast to 50%and 60% on the south and east coasts, respectively(Lamberth 1996, 2000a, Cowley 2000). In otherwords, catches would be much lower if there wascompliance. A reduction in angler pressure wouldalmost certainly serve to increase presentabundance of certain species. For example, alongthe east coast of the Eastern Cape and in KwaZulu-Natal, elf has increased in numbers followingincreased protection (van der Elst & De Freitas1987, Garrett & van der Eist 1990). Technically,catches could be reduced without reducing thevalue of the fishery, as most recreational anglerswould still go fishing if they were more strictlypoliced. It also makes good economic sense toremove ail commercial fisheries from estuaries,thereby halving the catch, but only reducingeconomic contribution by 1%. Commercial fishingin estuaries is predominantly gillnetting, which isunselective, usually with a high by-catch ofundersized and immature linefish and otherspecies. These species are already overexploitedand this fishing pressure occurs during aparticularly vulnerable stage of their life while theyare in estuaries. It has already been stressed thatthese fisheries are seldom viable in the short termand almost never in the long term. By removingcommercial fisheries, much greater recruitment willbe allowed into the sea.
Furthermore, subsistence and commercial effortshould be excluded from temporarily closedsystems, whether large or small, as these stocksare easily overexploited (Pease 1999). Theprotection of small and closed systems should notbe done at the expense of the larger, permanentlyopen systems, however. Protection should belevelled at all estuarine types at a rational scale, asthey all support different and valuable fishcommunities.
27
Ideally, different fisheries should target differentspecies within the same estuaries. Muiti-userfisheries are seldom sustainable. However this isdifficult to control, especially those sectors assignedless lucrative species, this is thus a furtherargument against including commercial fisheries inestuaries. Estuarine exploitation in South Africashould be limited to subsistence and recreationaluse. However the South African experience is thatdesignated subsistence fishers soon realise thevalue of their non-target species, and it is hard toprevent them from shifting to these species. Thisoften leads to chaos and user conflict, as hashappened in Kosi and St. Lucia. Subsistencefisheries should be confined to traditional fisheries,and preferably assigned to homogenouscommunities. In other areas, the ad hoc allocationof subsistence rights should rather be addressed byfinding alternative livelihoods for the fishersinvolved.
In general, the protection of estuarine fishresources will also depend on the soundmanagement of activities which affect estuarineenvironments. Apart from the direct effect on fishstocks, recreational angling involves boat traffic andbait digging, leading to disturbance, trampling anddepletion of prey for fish. More importantly,perturbations that occur in the marine environmentor catchment may negatively impact on fishpopulations in estuaries (Whitfield & Marais 1999).In particular, if freshwater requirements of estuariesare not adequately met, the resultant chemical andbiophysical changes in the estuarine headwatersand in mouth condition can severely hamper fishrecruitment. Indeed, freshwater inputs probablyhave the most important impact on speciesdistribution, composition and abundance inestuaries. For these reasons it is stronglyadvocated that a philosophy of ecosystem
preservation be used in management policy(Whitfield & Marais 1999) in addition to individualspecies conservation efforts. Such policies will leadto more rational decisions in terms of alldevelopments which affect estuarine ecology,including development of marinas (which tend tofavour ichthyoplankton but not large fish - Cloete1993).
Thus, in summary, the most sensible overall policywould be to conserve estuarine stocks as nurseryand source areas for marine fisheries. This is themost efficient option in terms of maximisingresource productivity, economic benefits andbiodiversity conservation. Resource productivity inboth estuaries and the inshore marine environmentcan be enhanced by concentrating conservationefforts on estuarine stocks. Stock status can onlybe improved by reduction of catches. In order tominimise the cost of this, it should be targeted atfisheries which are either low value per unit catch(e.g. estuarine commercial net fisheries), orfisheries whose value is not strongly affected bycatch rates (i.e. the recreational fishery, which ismuch smaller in estuaries than on the open coast).Conserving estuary stocks requires the soundholistic management of estuaries, a spin-off beingthe improved conservation of all estuarinebiodiversity.
ACKNOWLEDGEMENTS
This study was funded by the Water ResearchCommission. We gratefully acknowledge the datacontributions made by Bruce Mann and PaulCowley.
28
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31
Appendix 1. Estimated total catches by fishery for each estuary. Totals in italics estimated in this study.
BiogReg
CC
cccccccwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww
CoastSection
WestWestWestWestWestWestWestWestWestSouthSouth
SouthSouthSouthSouthSouthSouthSouthSouthSouthSouthSouthSouthSouthSouthSouthSouthSouthSouthSouth
SouthSouthSouthSouthSouthSouthSouthSouthSouthSouthSouthSouthSouthSouthSouthSouthSouthSouthSouthSouth
ESTUARY
Orange (Gariep)OlifantsBerg (Groot)Rietvlei/DiepHoutbaaiWildevoelvlei
BokramspruitSchusterKromSilvermineSandEersteLourens
Sir Lowry's PassSteenbrasRooielsBuffels (Oos)PalmietBot/KIeinmondOnrusKleinUilskraalsRatelHeuningnesKlipdrifsfonteinBreeDuiwenhoksGoukou (Kaffirkuils)GouritsBlinde
HartenbosKlein BrakGroot BrakMaalgateGwaingKaaimansWildernessSwartvlei
GoukammaKnysnaNoetsiePiesangKeurboomsMatjies/BitouSout (Oos)Groot (Wes)
BloukransLottering
ElandsbosStorms
Size(ha) Type974.5 River mouth701.7 Perm open
36i5.0Permopen
515.0Temp closedRiver mouth
75.8Temp closedTemp closedTemp closedTemp closed
6.5Temp closed155.5Temp closed
10.2Temp closed7.1 Temp closed3.0 Temp closed1.9 Perm open
10.8Temp closed17.3Temp closed33.0 Perm open
1698.4Lake41.1 Temp dosed
2958.9 Lake104.7Temp closed10. OTemp closed
172.5Perm openTemp closed
455.3 Perm open203.1 Perni open154.8Permopen112.6Permopen
Temp closed40.6Temp closed96.OTemp closed
113.9Temp closed13.5Temp closed
Temp closed8.0 Perm open
Lake1076.6Lake270.0Temp closed
3594.0 Bay8.0 Temp closed
92.2Temp closed295.2 Perm open
Temp closed52.2 Perm open
39.3Temp closedRiver mouth
17.QRiver mouth6.0 River mouth
River mouth
EstimatedAngling Castnet (
1.0
1.010.02.00.00.00.00.00.00.0
10.00.00.00.00.00.00.00.15.00.0
10.01.00.05.60.0
40.05.0
10.010.00.02.02.02.0
0.10.11.01.00.00.00.00.00.00.01.00.00.00.01.00.10.00.11.00.01.00.10.00.10.01.00.11.01.00.00.10.10.1
annual3illnet
0.0120.0500.0
5.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
10.00.05.01.00.00.00.03.0
10.02.05.00.00.01.01.0
catchSeine
0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.01.00.02.00.00.00.00.00.00.00.0
(tons)Traps
0.00.00.00.00.00.0
0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Spear0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Total
1.1121.1511.0
8.00.00.00.00.00.00.0
11.00.00.00.01.00.10.00.2
16.00.0
16.02.10.06.70.0
46.015.113.016.00.02.13.13.11.8
4.0
73.919.2
244.61.47.2
23.40.00.00.00.00.00.0
32
AppendjxJ continued.BiogRegWWWW
wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww
CoastSection
SouthSouthSouthSouthSouthSouthSouthSouthSouthSouthSouthEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEastEast
ESTUARYElandsGroot (Oos)TsitsikammaKlipdnfSlangKrom Oos (Kromme)SeekoeiKabeljousGamtoosVan StadensMaitland
SwartkopsCoega (Ngcura)SundaysBoknesBushmansKariegaKasukaKowieRufaneRietKleinemond WesKleinemond OosKlein PalmietGreat FishOld woman'sMpekweniMtatiMgwalanaBira
GqutywaBlue KransMtanaKeiskammaNgqinisaKiwaneTyolomnqaShelberisstroomLilyvaleRoss' CreekNceraMleleMcantsiGxuluGodaHloziHickman'sBuffaloBlindHlazeNahoon
Size(ha) Type
River mouthRiver mouthTemp closedTemp closedTemp closed
240.3Perm open132.2Temp closed117.9Temp closed467.0Perm open28.0 Temp closed0\2Temp closed
499.0Permopen10.1 Temp closed
173.4 Perm open27. OTemp closed
213.0Perm open. 198.0Permopen
38.0Temp closed118.6Perm open
Temp closed73.1 Temp closed80.OTemp closed35.OTemp closed
Temp closed365.7 Perm open
25.1 Temp closed141.4Temp closed124.2 Temp closed123.6 Temp closed97.5Temp closed51.6 Temp closed2.5Temp closed
15.7Temp closed493.8 Perm open
12.7Temp closed
18.8Temp closed107.4Temp closed
Temp closed2.3Temp closed
Temp closed28.4Temp closed3.6Temp closed9.OTemp closed
48.5Temp closed17.2Temp closed0.7Temp closed4.3 Temp closed
98.0 Perm open0.5Temp closed
1.5Temp closed57.7Perm open
Estimated annualAngling Castnet Gillnet 5
30.01.0
25.01.0
10.010.02.0
10.0
0.01.02.01.00.0
30.01.02.02.02.05.01.00.01.0
15.0
3.00.23.00.10.50.50.10.30.00.10.20.10.02.0
0.10.20.20.20.50.10.00.12.0
2.00.05.00.01.01.00.01.00.00.Q0.00.00.05.00.01.02.02.03.01.00.01.0
10.0
catchseine
0.00.00.00.00.00.00.00.0
0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
(tons)Traps
0.00.00.00.00.00.00.00.0
0.00,00.00.00.00.00.00.00.00.00.00.00.00.00.0
Spear
0.00.00.00.00.00.00.00.0
0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Total
19.79.98.9
35.12.80.9
35.01.2
33.01.1
11.511.52.1
11.30.01.12.21.10.0
37.01.13.24.24.28.52.10.02.1
27.01.82.28.2
1.1
2.81.11.54.22.11.01.2
10.10.91.07.3
Appendix 1 continuedBiogReg
CoastSection ESTUARY
Size(ha) Type
Estimated annual catch (tons)Angling Castnet Gillnet Seine Traps Spear Total
Wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwsssssssssssssssss
East QjniraEast GqunubeEast KweleraEast BuluraEast CungeEast CintsaEast CefaneEast KwenxuraEast NyaraEast Haga-hagaEast MtendweEast QukoEast MorganEast CwiliTranskei Great KeiTranskei GxaraTranskei NgogwaneTranskei QoloraTranskei NcizeleTranskei Kobonqaba
Transkei Nxaxo/NgqusiTranskei CebeTranskei GqunqeTranskei ZaluTranskei NgqwaraTranskei Sihlontlweni/GciniTranskei QoraTranskei JujuraTranskei NgadlaTranskei ShiximTranskei NqabaraTranskei Ngoma/KobuleTranskei MenduTranskei MbasheTranskei Ku-MpenzuTranskei Ku-Bhula/MbhanyanaTranskei NtlonyaneTranskei NkanyaTranskei XoraTranskei BulungulaTranskei Ku-amanzimuzamaTranskei MncwasaTranskei MpakoTranskei NengaTranskei MapuziTranskei MtataTranskei MdumbiTranskei LwandilanaTranskei LwandileTranskei Mtakatye
Transkei Hluleka/Majusini
72.1 Temp dosed53.4Permopen50.1 Perm open35.5 Temp closed0.5Temp closed
29.3Temp closed82.7Temp closed29.1 Temp closed17.1Temp closed3.4Temp closed
11.2Temp closed36.2Temp closed24.OTemp closed
1.2 Temp closed222.4Perm open23.9Temp closed9.1 Temp closed
22.9Temp closed6.6 Temp closed
26.4Perm open159.5Perm open
16.5Temp closed17.9Temp closed12.4Temp closed19.4Temp closed11.OTemp closed
89.6 Perm open4.8Temp closed
13.9Temp closed22.1 Perm open
109.7Perm open10.1Temp closed23.8Temp closed
132.0Permopen13.4Temp closed7.6Temp closed
41.3Temp closed15.5Temp closed
150.6 Perm open18.4Temp closed3.7Temp closed
19.2Temp closed13.5Temp closed10.OTemp closed15.9Temp closed
168.8 Perm open76.1 Perm open9.7Temp closed
22.2 Temp closed116.8Perm open
14.9Temp closed
5.87.06.83.30.92.96.519111.11.73.42.51.0
18.52.51.52.51.45.2
14.22.02.11.7121.79.512184.9
10.81.6159.40.00.00.00.0
10.40.00.00.00.00.00,0
11.46.30.00.08.60.0
34
Appendix 1 continued
BJog Coast
Reg Section ESTUARYSize(ha)
Estimated annual catch (tons)
Angling Castnet Gillnet Seine Traps Spear Total
ssssssssssssssss3
ssssssssssssssssss3
sssssssssssssss
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
Transkei
K2NKZNKZNKZNKZN
KZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZN
Mnenu
M tonga
Mpande
Sinangwana
Mngazana
Mngazi
Bululo
Mtambane
Mzimvubu
Ntlupeni
Nkodusweni
Mntafufu
Mzintlava
Mzimpunzi
Mbotyi
Mkozi
Myekane
Lupatana
Mkweni
Msikaba
Mgwegwe
Mgwetyana
Mtentu
Sikombe
Kwanyana
Mnyameni
Mpahlanyana
Mpahlane
Mzamba
Mtentwana
Mtamvuna
Zolwane
Sandlundlu
Ku-boboyi
Tongazi
Kandandhlovu
Mpenjati
Umhlangankulu
Kaba
Mbizana
Mvutshini
Bilanhlolo
Uvuzana
Kongweni
Vungu
Mhlangeni
Zotsha
Boboyi
Mbango
Mzimkulu
Mtentweni
90.5Temp closed
32.2Temp closed
15.OTemp closed
13.2Temp closed
224.9Permopen
17.1 Temp closed
12.6Temp closed
10.9Temp closed
151.0 River mouth
4.4Temp closed
32.6Temp closed
24.1 Perm open
23.1 Perm open
5.1 Temp closed
50.4Temp closed
4.0 Temp closed
1.9Temp closed
3.6Temp closed
7.OTemp closed
15.1 Perm open
8.8Temp closed
3.3Temp dosed
52.9Perm open
11.5Temp closed
7.1 Temp closed
27.9Temp closed
3.9Temp closed
3.9 Temp closed
70.9 Perm open
11,4Temp closed
63.5Temp closed
0.5Temp closed
4.0Temp closed
1.1 Temp closed
0.8Temp closed
1.8 Temp closed
11.6Temp closed
9.7Temp closed
2.4Temp closed
12.4Temp closed
0.9Temp closed
2.6Temp closed
0.6Temp closed
1.4Temp closed
1.1 Temp closed
3.6 Temp closed
7.3Temp closed
1.3 Temp closed
0.9Temp closed
74.0 Perm open
8.0 Temp closed
2.00.10.10.10.1
0.10.30.20.10.40.10.10.10.10.00.10.50.10.13.00.1
0.50.10.10.10.10.10.00.10.10.20.10.10.10.10.00.10.20.10.1
1.00.1
0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
0.00.00.00.00.0
0.00.00.00.00.00.00.00.00.00.00.00.00.0
0.00.00.0
0.00.00.00.00.0
0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
0.00.00.00.00.00.00.00.00.0
o.o0.00.00.0
0.00.00.00.00.00.00.00.0
1.50.00.00.0
14.5
0.00.00.0
15.0
0.00.03.53.40.00.00.00.00.00.03.00.00.05.10.00.00.00.00.06.00.02.50.20.20.20.20.20.30.30.20.60.20.20.20.20.0
0.20.70.20.24.00.2
35
Appendix 1 continuedBiog CoastReg Section ESTUARY
Size(ha)
Estimated annual catch (tons)Angling Castnet Gillnet Seine Traps Spear Total
ssssssssssssssssssssssssssssssssssssssssssssssssssss
KZNK2NKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZNKZN
MhlangamkuluDambaKoshwanaIntshambiliMzumbeMhlabatshaneMhlungwaMfazazanaKwa-MakosiMnamfuMtwalumeMvuziFafaMdesinganeSezelaMkumbaneMzintoMzimayiMpambanyoniMahlongwaMahlongwanaMkomaziNganeUmgababaMsimbaziLovuLittle ManzimtotiManzimtotiMbokodweniSipingoDurban BayMgeniMhlangaMdlotiTongatiMhlaJiSeteniMvotiMdlotaneNonotiZinkwasiTugeia/ThukelaMatigulu/NyoniSiyayaMlalaziMhlathuzeRichard's BayNhlabaneMfoloziSt LuciaMgobezeleniKosi
3.9 Temp closedUTemp closed1.2Temp closed1.7 Temp closed
15-8Temp closed2.3Temp closed3.1 Temp closed2.1 Temp closed2.5Temp closed1.3Temp closed
24.8Temp closed0.8Temp closed
29.0Temp closed0.4Temp closed
12.OTemp closed0.3Temp closed7.OTemp closed1.OTemp closed2.3Temp closed5.9Temp closed6.8Temp closed
77-9 Perm open1.4Temp closed
17.6Temp closed13.2Temp closed10.5Temp closed1.5Temp closed6.7Temp closed7.2Temp closed6.8Perm open
Bay48-0 Temp closed
100. Hemp closed58.1 Temp closed37.3Temp closed21.OTemp closed
1-1 Temp closed18.4 River mouth25.4Temp closed18.OTemp closed71.2Temp closed55-0 River mouth
192.0Permopen7.7Temp closed
202.4Permopen1691.OBay1800.0 Bay
14.4 Lake180.0River mouth
38290.0 Lake1.3 Lake
3500.0 Lake
0.10.10.10.10.10.10.50.30.20.10.10.10.50.10.00.10.30.10.00.40.25.00.11.00.50.50.10.10.10.1
46.02.20.10.50.10.10.10.50.10.30.52.03.00.05.05.0
68.01.03.0
70.01.0
18.0
0.10.10.10.10.20.10.30.20.20.10.10.10.30.10.00.10.30.10.10.30.22.00.10.50.30.50.10.10.10.15.01.00.00.50.50.50.10.50.10.30.53.02.00.03.03.0
10.01.01.0
10.00.00.0
0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.02.00.50.00.00.00.00.00.00.00.01.0
10.05.00.05.0
15.02.05.0
10.0150.0
1.090.0
0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.01.02.05.00.02.0
20.08.02.02.0
30.00.00.0
0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
73.0
0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
16.0
0.20.20.20.20.30.20.80.50.40.20.20.20.80.20.00.20.60.20.10.70.47.00.21.50.81.00.20.20.20.2
53.03.70.11.00.60.60.21.00.20.63.0
17.015.00.0
15.043.088.0
9.016.0
260.02.0
197.0
36
I II pi I l l j l .
Other related WRC reports available
Water quality modelling of estuaries
JH Slinger, S Taljaard, M Rossouw and P Huizinga
The development of estuarine water quality monitoring expertise was identified as apriority research requirement by the Co-ordinated Programme on Decision Supportfor the Conservation and Management of Estuaries. This project investigated thesuitability of the one-dimensional Mike 11 Water Quality Model to predict water qualityin South African estuaries. The two estuaries selected were the Berg and the Swartkops,both of which are relatively long and narrow with permanently open mouths which suitone-dimensional modelling. In addition, both are data-rich by South African standards.The model showed good correlation between measured and simulated temperature anddissolved oxygen (DO), even predicting the low DO levels in the upper reaches of theBerg Estuary in the summer, although the high variability near the mouth wasunderestimated. This is possibly due to insufficient data on the inshore marine environment.One area of difference between these estuaries and those of the Northern Hemisphereis the sediment oxygen demand. It was postulated that this could be the result of arelatively small freshwater input. The effect of the 'black tide1 on the Berg Estuary wasmodelled successfully. This indicates that Mike 11 can also be used for linking waterquality to biological processes.
Nutrients such as soluble reactive phosphate and silicate were strongly correlated tosalinity, but total dissolved nitrogen showed no correlation to any parameter eithermeasured or modelled. Another current limitation is that the model cannot, in its presentform, simulate bacterial water quality.
Report Number: 664/1/98 ISBN: 1 86845 438 X
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