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A project supported by the European Union's INTERREG IVA Programme managed by the Special EU Programmes Body
The Impact of
Catch-and-Release Management Practices
on Fish
John B. Hume +44 (0)7745 550 116
http://lampreydoctor.wix.com/jbhumebio
Twitter @thatlampreyguy
A report commissioned for the
IBIS Knowledge Transfer Programme
2013
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The impact of catch-and-release management practices on fish
INTRODUCTION……………………………………………………………………………..1
METHODS…………………………………………………………………………………….4
LETHAL EFFECTS OF CATCH-AND-RELEASE MANAGEMENT PRACTICES……….5
Total mortality…………………………………………………………………………………5
Does body size matter?..............................................................................................................7
Anatomical hook location……………………………………………………………………...7
The impact of hook type……………………………………………………………………….9
Treble vs. single hooks………………………………………………………………………...9
Small vs. large hook sizes……………………………………………………………………10
Circle vs. J-hooks…………………………………………………………………………….11
Barbed vs. barbless hooks……………………………………………………………………12
The influence of bait type…………………………………………………………………….13
Can line-cutting reduce mortality rates of deeply hooked fish?..............................................14
The effect of air exposure & handling times…………………………………………………16
The influence of capture depth……………………………………………………………….18
The impact of barotrauma……………………………………………………………………20
Can venting mitigate the effects of barotrauma?.....................................................................21
SUB-LETHAL EFFECTS OF CATCH-AND-RELEASE MANAGEMENT
PRACTICES…………………………………………………………………………………23
The impact of C&R management practices on physiology……………………………..……23
The influence of water temperature………………………………………………………….25
The impact on post-release growth…………………………………………………………..26
Retention vs. immediate release following capture…………………………….…………….28
The impact of capture on post-release behaviour……………………………………………29
The effects of capture in nets…………………………………………………………………31
Other impacts of C&R management practices……………………………………………….32
THE EFFECTS OF CATCH-AND-RELEASE MANAGEMENT PRACTICES ON IBIS
PRIORITY-MANAGEMENT SPECIES…………………………………………………….33
CASE STUDY - BROWN TROUT Salmo trutta……………………………………………33
CASE STUDY – ATLANTIC SALMON Salmo salar……………………………………...34
CASE STUDY – NORTHERN PIKE Esox lucius…………………………………………..37
CASE STUDY – SHARKS (Selachimorpha spp.)…………………………………………..39
CASE STUDY – SKATES (Rajidae spp.)…………………………………………………...42
REFERENCES……………………………………………………………………………….43
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INTRODUCTION
Wild populations of both freshwater and marine fishes are heavily exploited by recreational
fisheries, usually considered to be those where fishing is conducted by individuals for sport
or leisure, and sometimes also for personal consumption (Cooke & Cowx, 2006; Cowx et al.,
2010). Globally, 220 to 700 million people are believed to participate in these fisheries
(Arlinghaus et al., 2013) and global trends of both fisheries catches and participation are
generally increasing (Cooke & Cowx, 2004; 2006). This pressure on fish stocks can be just as
intense as commercial exploitation (Post et al., 2002), thus affecting populations in a similar
manner and requiring dedicated research, policy and management initiatives (Cowx et al.,
2010; Arlinghaus et al., 2013). To ensure these fisheries resources are sustainable, concerted
actions must be adopted by both individuals and stakeholders (Arlinghaus et al., 2002), one
example being the Code of Conduct for Sustainable Fisheries (CCRF) by the United Nation’s
Food and Agricultural Organisation (FAO, 1995). Recently, the European Inland Fisheries
Advisory Commission (EIFAC) and European Angling Alliance (EAA) highlighted the need
for an international Code of Practice (CoP) for recreational fisheries (Arlinghaus et al., 2012),
and this provides a general collection of best practice guidelines for the sustainable
development and maintenance of those fisheries (EIFAC, 2008; Arlinghaus et al., 2010).
In its simplest form, the capture and subsequent release (catch-and-release, hereafter
C&R) of an individual fish is the most basic of applied outcomes from such CoP guidelines,
and is now widespread in global recreational fisheries (Arlinghaus, 2007; Ferter et al., 2013)
having been discussed in at least three symposia since 1977 (Cooke & Schramm, 2007).
Although harvest regulations for both recreational and commercial fisheries require some
form of C&R, a low post-release survival rate could render any regulations ineffective
(Pollock & Pine, 2007; Ferter et al., 2013) and conflict can arise between those groups who
practice voluntary C&R and those mandated by regulation (Arlinghaus, 2007; Goodyear,
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2007). Conflict can also arise between recreational fisheries and non-fishery related aquatic
biodiversity conservation objectives (Cowx et al., 2010), including practices detrimental to
the health of non-target fish species (Hewlett et al., 2009).
The sub-lethal effects of C&R could be equally important when considering the long-
term resilience of fish populations (Arlinghaus et al., 2007) particularly in the context of a
heightened awareness of fish welfare issues in contemporary society (Huntingford et al.,
2006; Arlinghaus et al., 2012). The definition adopted by the EIFAC CoP was “good welfare
means that an individual fish is in good health, with its biological systems functioning
properly and with no impairment of fitness”, thus it is relevant when, for example, a fish has
been captured but released with an injury to the mouth. If recovery of the fish following the
C&R event is rapid and objectively measurable states of fitness have not declined (e.g.,
fecundity, quality of gametes, growth) (Cooke & Suski, 2005), then the impact of C&R on
the individual’s welfare is negligible (Arlinghaus et al., 2010). The welfare of fish in a
recreational fishery context is, however, a complex and frequently contentious issue and is
reviewed elsewhere (Cooke & Sneddon, 2007; Arlinghaus et al., 2009; Diggles et al., 2011).
To provide guidance to recreational fisheries the EIFAC CoP outlined
recommendations for appropriate behaviour and techniques that would act to minimise
negative impacts on fish welfare during C&R events and maximise post-release survival. For
example, the duration of landing should be minimised (Meka & McCormick, 2005); air
exposure should be minimised (Ferguson & Tufts, 1992); as should injury (Arlinghaus et al.,
2008), all of which can be achieved through alterations to tackle and gear as well as angler
behaviour. Angling should also be avoided during warm weather or the reproductive period
(Cooke & Suski, 2005). If fish are being held for a period of time as opposed to immediate
release, then any devices, such as keep-nets or live-wells, should provide sufficient space and
high water quality throughout (Arlinghaus et al., 2010). Although these generalities have
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their limitations, they do, however, provide some level of protection to all species (Cooke &
Suski, 2005).
Ultimately, the success of any fisheries regulations, and in particular C&R
management practices, depends on ensuring a high rate of post-release survival is achieved
through reductions to both sub-lethal effects and mortality rates (Pelletier et al., 2007;
Pollock & Pine, 2007). Mortality impacts the demographic characteristics of fish populations
and, by extension, fisheries managers impact the population by altering those rates of
mortality. Therefore, estimates of mortality as a result of C&R management practices can and
should be integrated with existing fisheries management strategy (Cooke & Schramm, 2007;
Pollock & Pine, 2007; Ferter et al., 2013). The effects of implementing C&R practices are
not, however, immediately observable, as was the case with European grayling Thymallus
thymallus in northern Sweden for example, which required a decade of no-take angling to see
positive effects on population demographics (Näslund et al., 2005). Managers must,
therefore, remain patient. Additionally, although the sub-lethal effects of C&R practices are
generally of lesser concern to fisheries managers, academics would contend that sub-lethal
effects, in particular alterations to a fish’s physiology and behaviour, are more likely to
provide mechanistic reasons underlying post-release mortality and should, therefore, draw
greater attention from managers (Cooke & Schramm, 2007; Pelletier et al., 2007).
In order to evaluate the potential effectiveness of C&R management practices to
priority-management marine and freshwater fish species in the Integrated Aquatic Resources
Management Between Ireland, Northern Ireland and Scotland (IBIS) study area, factors that
influence post-release mortality and sub-lethal effects have been reviewed from the primary
literature. This is followed by more specific accounts of the efficacy of C&R management
practices for six priority fish species or groups in the IBIS study area: Atlantic salmon Salmo
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salar, brown and sea trout Salmo trutta, northern pike Esox lucius, skate (Rajidae) spp. and
shark (Selachimorpha) spp.
METHODS
ISI Web of Knowledge (Thompson Reuters) was used to identify peer-reviewed literature
that examined the efficacy of catch-and-release (C&R) management practices and its
applicability to IBIS priority-management marine and freshwater fish species. Irrelevant
articles were removed by reading abstracts and full articles where necessary, and excluded if
it was not evident that the article contained quantitative data on the short- and long-term
conservation value and/or economic value of C&R management practices. A combination of
search terms was used to maximise the number of relevant articles. Articles must have
included in their title, abstract or keywords one of the following search terms: ‘catch and
release management AND fish’, ‘Salmo salar AND catch and release’. ‘Salmo trutta AND
catch and release’, ‘Esox lucius AND catch and release’, ‘skate AND catch and release’,
‘shark AND catch and release’. All articles resulting from this search were collated into a
database for further consideration. The literature search was supplemented by a single-pass
reading of each article in the database to find additional relevant cited literature. This
literature search resulted in a total of 340 peer-reviewed articles, 46% (n = 157) of which
were abstracts only.
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LETHAL EFFECTS OF CATCH-AND-RELEASE MANAGEMENT PRACTICES
Total mortality
Estimates of C&R-induced mortality can vary widely depending on a variety of intrinsic and
extrinsic factors, and is both highly species- and fishery-specific (Cooke & Suski, 2005),
making general conclusions undesirable and potentially misleading. However, knowledge of
the number of fish that die as a result of C&R practices is essential for basic fisheries
management (Cooke et al., 2006). A meta-analysis of 274 studies found average mortality as
a result of C&R practices to be 18% and, although highly skewed, mortality distributions
were remarkably similar for both marine and freshwater taxa (Bartholomew & Bohnsack,
2005). Within this study, and ratified elsewhere (Cooke et al., 2006), seven mortality factors
were found to be significant: anatomical hook location, bait type, removal of deep-set hooks
(i.e., from the gut, oesophagus), J-hooks, capture depth, water temperature and handling
times. In some fisheries release rates can be as high as 100% (e.g., course fisheries in western
Europe) and, globally, approximately 60% of fish captured by recreational anglers are
released (Cooke & Cowx, 2006). However, an unknown proportion of these subsequently die
post-release (Cook et al., 2002).
The following table presents the short-term (< 48 hours post-release) total mortality
rates for a range of freshwater and marine species that support active recreational fisheries,
and which were captured using standard hook-and-line methodology.
Mortality rates of fish species following a C&R event vary widely; with an average of
18% across freshwater and marine species.
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Species Common name Mortality Rate (%)
Citation
Acanthopagrus butcheri
black bream 15.5 Grixti et al. (2008)
Centropomus undecimalis
common snook 2.1 Taylor et al. (2001)
Centropristis striata black sea bass 4.7 Bugley & Shepherd (1991) Cynoscion nebulosus spotted seatrout 4.6 - 11 Murphy et al. (1995); Stunz &
McKee (2006) Cynoscion regalis weakfish 2.6 Malchoff & Heins (1997) Epinephalus morio red grouper 20 Burns et al. (2012)
Glaucosoma hebraicum
west Australian dhufish
51 St John & Syers (2005)
Lutjanus campechanus
red snapper 20 - 49.1 Render & Wilson (1994); Burns et al. (2012)
Macquaria ambigua golden perch 0 Hall et al. (2010) Macquaria
novemaculeata Australian bass 0 - 6 Hall et al. (2009); Dowling et al.
(2010) Megalops atlanticus tarpon 3.7 Edwards (1998)
Micropterus dolomieu smallmouth bass 0 – 8.9 Jackson & Willis (1991); Hartley & Moring (1995); Dunmall et al. (2001)
Micropterus punctulatus
spotted bass 8.5 Muoneke (1992)
Micropterus salmoides
largemouth bass 1.42 - 38 Meals & Miranda (1994); Hartley & Moring (1995); Kwak & Henry (1995); Weathers & Newman (1997); Neal & Lopez-Clayton (2001); DeBoom et al. (2010)
Morone saxitilis striped bass 31 Millard et al. (2003) Oncorhynchus mykiss rainbow trout 16 Schill (1996)
Platycephalus bassensis
sand flathead 1 - 6 Lyle et al. (2007)
Pomatomus saltatrix bluefish 8 - 25 Fabrizio et al. (2008); Broadhurst et al. (2012)
Pomoxis annularis white crappie 9.3 Muoneke (1992) Salmo salar Atlantic salmon 8 – 12 Brobbel et al. (1996); Dempson et
al. (2002) Salmo trutta brown trout 5 Boyd et al. (2010) Salvelinus
leucomaenis white-spotted charr 6.7 Tsuboi et al. (2002)
Salvelinus namaycush lake trout 24 Persons & Hirsch (1994) Sander vitreus walleye 0 - 54 Reeves & Bruesewitz (2007);
Schramm et al. (2010) Sciaenops ocellatus red drum 2 Vecchio & Wenner (2007)
Sparus aurata gilthead seabream 11.7 Veiga et al. (2011) Sphyraena barracuda great barracuda 0 O’Toole et al. (2010)
Spondyliosoma cantharus
black seabream 2.8 Veiga et al. (2011)
Tetrapturus albidus white marlin 12.5 Horodysky & Graves (2005) Thunnus thynnus Atlantic bluefin tuna 1.7 Stokesbury et al. (2011)
Table 1. Selection of studies in which mortality rate following a C&R event has been estimated.
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Does body size matter?
The size of an individual fish is not consistently correlated with its rate of mortality following
a C&R event, as some studies have shown larger fish to suffer greater mortality than smaller
individuals, or the opposite effect, but the majority of studies fail to find any effect of body
size on mortality rates (reviewed in Bartholomew & Bohnsack, 2005; Alos et al., 2009). The
size of an individual, however, may lend itself to greater mortality rates through certain
intrinsic factors such as alterations in foraging strategy. For example, among Trachynotus
ovatus there is a tendency for larger specimens to become deeply hooked, which may
increase post-release mortality rates as a result of injury (Alos, 2009) and a similar trend is
seen in captured black bream Acanthopagrus butcheri (Grixti et al., 2007).
The body size of a fish can affect the likelihood of mortality following a C&R event;
however, the cause of such an effect differs between species.
Anatomical hook location
In general, fishes hooked in critical body areas (e.g., gut, oesophagus, gills) suffer higher
mortality rates compared to those hooked in the mouth (Bartholomew & Bohnsack, 2005;
Butcher et al., 2006; Alos, 2008; Alos et al., 2008; Grixti et al., 2008). Bleeding, often a sign
of severe trauma is correlated with anatomical hook location (Domeier et al., 2003; Prince et
al., 2007; Mapleston et al., 2008; Grixti et al., 2010). For example, among groupers, bleeding
was more likely to occur when a specimen was hooked in the gills (66.7%) and gut (40%)
compared with the mouth (5%) (Bacheler & Buckel, 2004). However, the extent of any such
bleeding varies among species (Rudershausen et al., 2007). Capture-related injury is the
primary source of mortality in black bass Micropterus spp. for example, and has been related
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to the level of angler experience, hook type and bait type (Siepker et al., 2007). Among
derbio Trachynotus ovatus fisheries 85% of fish hooked in the oesophagus, gills or gut died
within two hours of capture (Alos et al., 2008) and suffered greater mortality compared to
those hooked in the mouth (Alos, 2009). A similar effect was seen in silver perch Bidyanus
bidyanus (van der Walt et al., 2005), striped bass Morone saxitilis (Millard et al., 2003), lake
trout Salvelinus namaycush (Persons & Hirsch, 1994), spotted seatrout Cynoscion nebulosus
(Murphy et al., 1995), yellowfin bream Acanthopagrus australis (Broadhurst et al., 2005),
red drum Sciaenops ocellatus (Flaherty et al., 2013), snapper Pagrus auratus (Grixti et al.,
2010), sand flathead Platycephalus bassensis (Lyle et al., 2007) and walleye Sander vitreus
(Reeves & Bruesewitz, 2007), with specimens hooked in the gut or oesophagus suffering
greater mortality rates compared to those hooked in the mouth or gills.
St John & Syers (2005) found that 70% of west Australian dhufish Glaucosoma
hebraicum died following hooking in the gut, as did 69% of striped bass Morone saxitilis
(Millard et al., 2003). In this latter species, a deeply-hooked fish was 12-times more likely to
die as a result of capture compared to a shallow-hooked specimen, strikingly similar to red
porgy Pagrus pagrus, which were 11-times more likely to survive if hooked in the lip
compared to deep locations (Overton et al., 2008). Contrary to these findings, however,
DeBoom et al. (2010) found that largemouth bass Micropterus salmoides exhibited similar
levels of mortality when experimentally deep-hooked or hooked in the mouth, and Pope &
Wilde (2010) also found similar results for this species in field trials. This suggests that some
species are better able to tolerate injuries related to deep hooking.
The likelihood of hooking a fish in a critical location varies depending on the species’
foraging strategy, gear type and angler experience. (Schill, 1996; Dunmall et al., 2001; Cooke
et al., 2012). For example, sparids have a tendency to be hooked more frequently in the
mouth or jaw (Veiga et al., 2011). In some species, such as the roman Chrysoblephus
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laticeps, larger individuals were found to be more susceptible to being hooked in the gut
compared to smaller specimens (Gotz et al., 2007) and the probability of deep-hooking in
black bream Acanthopagrus butcheri increased with fish length (Grixti et al., 2007).
Generally, deeply hooked fish require greater handling times and this could contribute
the greater mortality rates seen among such specimens (Diggles & Ernst, 1997; Grixti et al.,
2010). In both annular Diplodis annularis and striped seabream Lithognathus mormyrus, 54%
and 92% of deeply hooked cases were unhooked with ‘difficulty’ and was the most important
factor explaining mortality rates over a 4-5 hour observation period (Alos et al., 2009). The
rate of removal of deeply-set hooks decreased significantly in larger specimens of black
bream Acanthopagrus butcheri, with a 0.8 less chance of hook removal for every one
centimetre increase in fish length (Grixti et al., 2008).
The evidence strongly suggests that fish suffer increased mortality rates following a
C&R event when hooks are set in anatomical locations other than the mouth.
The impact of hook type
Treble vs. single hooks.
DuBois et al. (1994) found that treble hooks caused fewer mortalities in northern pike Esox
lucius than did single large hooks, and single hooks also caused significantly greater
mortality rates (5.1%) in yellow stripey Lutjanus carponotatus and the wire-netting cod
Epinephelus auoyanus compared to treble-hooked lures (0.4%) (Diggles & Ernst, 1997).
However, no differences in mortality rates were found between these hook types in cutthroat
trout Oncorhynchus clarkii or common snook Centropomus undecimalis populations
(Bartholomew & Bohnsack, 2005), as well as several trout species (DuBois & Dubielzig,
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2004). Ayvazian et al. (2002), however, found that treble hooks caused significantly higher
mortality of tailor Pomatamus saltatrix compared to four other hook types, including single
hooks, and may have caused extensive lacerations and other physical trauma (O’Toole et al.,
2010; Mandelman et al., 2012). Treble hooks could act to reduce mortality rates by being less
likely to set in critical anatomical locations compared to single hooks, but as they generally
take longer to remove compared to single hooks (O’Toole et al., 2010) this positive effect
may be offset (Gjernes et al., 1993). Only four of 49 fishery agencies in North America
recommend the use of single hooks over treble hooks (Pelletier et al., 2007) suggesting that,
at least in that region, fishery managers believe treble hooks to be less injurious to fish.
The evidence is that single and treble hooks result in different outcomes following a
C&R event; with a reduced likelihood of mortality when using treble hooks as a result of
shorter handling times.
Small vs. large hook sizes.
In a general sense, larger hooks capture larger specimens (Alos et al., 2008). However, in
some specialised fisheries, such as common carp Cyprinus carpio, small hooks tend to
capture larger specimens (Rapp et al., 2008). Hook size can be a significant predictor of
mortality rates following a C&R event. For example, small hooks (size 1/0) were found to
account for 25% mortality in captured blue cod Parapercis colias compared to zero mortality
when using large hooks (size 6/0) (Carbines, 1999), and smaller hooks (sizes 14 and 12)
caused greater mortality of derbio Trachynotus ovatus compared to larger hooks (sizes 10, 8
and 6) (Alos et al., 2008a). Large hook sizes were, however, found to result in increased
incidences of deeply hooked fish in some studies (Alos et al., 2008b; Mapleston et al., 2008;
Rapp et al., 2008) but the opposite effect was seen in a mixed grouper fishery, where small
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hooks resulted in more deeply hooked specimens (χ2 = 8.99, d.f. = 3, P = 0.03) (Bacheler &
Buckler, 2004). Black bream Acanthopagrus butcheri are 6.6-times more likely to be deeply
hooked on small hooks compared to large hooks (Grixti et al., 2007). No effect of hook size
on mortality was found in striped bass Morone saxitilis or cutthroat trout Oncorhynchus
clarkii (Bartholomew & Bohnsack, 2005), suggesting that the effect of hook size on mortality
rates is species specific.
The evidence suggests that hook sizes can affect mortality rates following a C&R
event; however, the effect varies between species.
Circle vs. J-hooks.
Circle hooks are more likely to become set in the corner of fishes mouths during capture thus
reducing handling time, while J-hooks are more likely to be swallowed and become set in the
gut or oesophagus (Domeier et al., 2003; Cooke & Suski, 2004; Meka, 2004; Bartholomew &
Bohnsack, 2005; Beckwith & Rand, 2005; Prince et al., 2007). For example, there was a
significant correlation (χ2 = 119.71, d.f. = 1, P < 0.001) between the anatomical hooking
location and unhooking time of painted comber Serranus scriba caught using J-hooks (Alos,
2008). In a mixed grouper fishery gut hooking was significantly higher when using J-hooks
compared to size 12/0 circle hooks (χ2 = 21.78, d.f. = 3, P < 0.001) (Bacheler & Buckler,
2004). However, in North America only 5 of 49 surveyed fisheries agencies recommended
the use of circle hooks, indicating a lack of adherence with current scientific opinion in this
region (Pelletier et al., 2007), perhaps as a result of the perceived reduced hooking and
landing efficiencies of circle hooks (Cooke et al., 2003), and that not all studies agree hook
type affects anatomical hooking location (Alos, 2009) or hook retention (Jones, 2005; van der
Walt et al., 2005).
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The proportion of Atlantic Istiophorus albicans and Pacific sailfish I. platypterus
hooked in the mouth using circle hooks was 85%, compared to 25% with J-hooks, and
resulted in deeply hooked fish on only 2% of occasions compared to 46% when using J-
hooks (Prince et al. 2002) leading to fewer injuries when the fishery employed circle hooks.
Circle hooks also more frequently penetrated the lip region of white seabass Atractoscion
nobilis (73%) compared to J-hooks (41%) (Aalbers et al., 2004). There were fewer
mortalities among bluefin tuna Thunnus thynnus (Skomal et al., 2002), sand flathead
Platycephalus bassensis (Lyle et al., 2007), seabream Diplodis annularis (Alos et al., 2009),
red drum Sciaenops ocellatus (Vechio & Wenner, 2007), striped bass Morone saxitilis
(Millard et al., 2005) and Chinook salmon Oncorhynchus tshawytscha (Grover et al., 2002)
when caught using circle hooks compared to J-hooks, and striped bass Morone saxitilis suffer
greater mortality when caught using J-hooks as a result of frequent deep hooking
(Bartholomew & Bohnsack, 2005). Hooking injuries as a result of deeply-set J-hooks can
cause delayed mortality in those specimens with trauma such as severed oesophagi (Burns et
al., 2012; Flaherty et al., 2013).
However, no effect of hook type on mortality was seen in white seabass Atractoscion
nobilis (Aalbers et al., 2004), red drum Sciaenops ocellatus (Flaherty et al., 2013), yellowfin
tuna Thunnus albacares or summer flounder Paralichthys dentata populations captured,
although circle hooks did generally result in fewer critical anatomical hooking locations
(reviewed in Bartholomew & Bohnsack, 2005). Large circle hooks, but not small ones, have
been found to reduce the incidence of deep-hooking relative to using J-hooks in red drum
Sciaenops ocellatus fisheries (Beckwith & Rand, 2005). Even among pelagic longline
fisheries the odds of post-release survival for many target and bycatch species were found to
be significantly higher if circle hooks were employed (Horodysky & Graves, 2005;
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Carruthers et al., 2009; Graves & Horodysky, 2010; Serafy et al., 2012) and this holds true
for a variety of circle hook models (Graves & Horodysky, 2008).
Despite variation among studies due to factors such as hook size, fishing style and
feeding mode of the target species (Cooke et al., 2012; Walter et al., 2012), the evidence is
that mortality rates appear to be consistently lower when circles hooks are used compared to
J-hooks (Cooke & Suski, 2004; Wilson & Diaz, 2012).
Barbed vs. barbless hooks.
Barbless hooks are easier to remove when compared to barbed hooks (DuBois & Dubielzig,
2004; Meka, 2004), significantly reducing air exposure for some species such as rock bass
Ambloplites rupestris (Cooke et al., 2001; Pelletier et al., 2007) and yellow stripey Lutjanus
carponotatus (Diggles & Ernst, 1999). Barbed hooks are, therefore, believed by some authors
to be the most significant determinants of injury and/or mortality following a C&R event
(reviewed in Muoneke & Childress, 1994). However, Cooke et al. (2001) found no
differences in mortality rates of rock bass Ambloplites rupestris captured on barbed vs.
barbless jigs or barbed vs. barbless worms and no delayed mortality was observed after five
days. Neither were there significant differences in the mortality rates of several trout species
captured on single barbless hooks compared with barbed singles or trebles (DuBois &
Dubielzig, 2004) or in bluegills Lepomis macrochirus experimentally hooked in the
oesophagus (Robert et al., 2012).
Barbed hooks do, however, in general cause higher rates of injury compared to
barbless hooks, for example, in rainbow trout Oncorhynchus mykiss fisheries (Meka, 2004).
This was not found to be the case though for walleye Sander vitreus, which exhibited similar
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levels of hook-related damage when captured using barbed vs. barbless live-bait hooks
(Reeves & Staples, 2011). In a meta-analysis by Schill & Scarpella (1998) it was concluded
that the use of barbless hooks played no role in reducing post-release mortality rates among
salmonids, and that barbed hook restrictions appear to be more of a social issue among
anglers and managers rather than based on scientific evidence.
There is little empirical evidence supporting the widely held belief that barbless hooks
result in a reduced likelihood of mortality following a C&R event for most fish species.
The influence of bait type
Specific studies relating to effect of bait type on anatomical hook location are not common,
despite the fact that natural baits are widely believed to lead to greater incidences of deep
hooking as fish are more likely to ingest those compared with artificial baits or lures (Schill,
1996; Diggles & Ernst, 1997; Nelson, 1998; Cooke et al., 2001; Dunmall et al., 2001; Stunz
& McKee, 2006), of which they may be more wary (Diggles & Ernst, 1997). Natural baits
have been found to lead to greater mortality rates in some fish species when compared with
artificial lures or flies, such as cutthroat trout Oncorhynchus clarkii and rainbow trout
Oncorhynchus mykiss, but not in others such as striped bass Morone saxitilis, common snook
Centropomus undecimalis (Muoneke & Childress, 1994; Bartholomew & Bohnsack, 2005) or
black bass Micropterus spp. (Siepker et al., 2007).
Using beach worms was found to result in a significant increase in the probability of
deep hooking among sand whiting Sillago cilliata, therefore resulting in greater rates of
mortality (Butcher et al., 2006). In a mixed-species marine recreational fishery bait type was
found to have a significant effect on hooking location, with 26.9% (n = 537) of fish captured
16""
using worm bait being deeply hooked, whereas 14.1% (n = 214) of fish captured using
shrimp as bait were deeply hooked (Alos et al., 2009). Rock bass Ambloplites rupestris were
also found more likely to be deeply hooked when captured using worms compared to a lure
(Cooke et al., 2001). The probability of mortality in Australian bass Macquaria
novemaculeata as a result of capture using natural bait was found to be 12-times higher than
for those captured using artificial lures (Hall et al., 2009).
The evidence suggests that, in general, natural baits have the potential to result in a
greater likelihood of mortality following a C&R event compared with artificial lures.
Can line-cutting reduce mortality rates of deeply hooked fish?
Cutting the line on a deeply-set hook is likely to significantly improve survivorship of a fish
following capture, as attempts to retrieve the hook could cause additional internal injuries
(Bartholomew & Bohnsack, 2005; Grixti et al., 2008; Grixti et al., 2010). In North America
90% (n = 44) of surveyed fishery agencies recommended cutting the line when a fish was
deeply hooked (Pelletier et al., 2007). Deeply-hooked, experimentally angled Trachynotus
ovatus that had the line cut experienced a 50% reduction in post-release mortality, although
this was not a statistically significant effect (Alos, 2009), and a similar non-significant effect
was seen among deeply-hooked silver perch Bidyanus bidyanus (van der Walt et al., 2005).
In black bream Acanthopagrus butcheri cutting the line on deeply-hooked fish resulted in a
92.7% (n = 105) delayed (1-72 hours) survival rate, compared to 69.5% (n = 51) in those
where the hook was removed, despite almost identical initial (< 1 hour) survival rates (84.7%
vs. 83.6%) (Grixti et al., 2008). In addition, there was little evidence found among 27
recreationally-caught Australian species that cutting the line negatively impacted recapture
rates (Wilde & Sawynok, 2009) and, although survival rates were not found to be
17""
significantly affected by line-cutting in deeply hooked walleye Sander vitreus (Reeves &
Bruesewitz, 2007), most studies agree line cutting has a positive effect on survival rates
following C&R events.
In deeply hooked snapper Pagrus auratus 13% of 59 specimens were able to shed the
hook in less than three days (Grixti et al., 2010), fewer than the evacuation rate seen in
deeply-hooked white-spotted charr Salvelinus leucomeinis (32.9%, n = 82 hooks in 72 fish)
(Tsuboi et al., 2006) and masu salmon Oncorhynchus masou masou (70-100% in 21 days)
(Doi et al., 2005). Yellowfin bream Acanthopagrus australis were also found to be able to
shed ingested nickel-plated J-hooks in 5-56 days and had oxidised the hook to c. 94% of the
original weight and often broken into two pieces (Broadhurst et al., 2007).
These results suggest that, for some species, line-cutting for those specimens deeply-
hooked is a viable management practice that reduces the likelihood of mortality following a
C&R event.
The effect of air exposure & handling times
Several recent studies have concluded that air exposure is a significant factor affecting
survival rates and stress condition in fish experiencing a C&R event (Bartholomew &
Bohnsack, 2005; Cooke & Suski, 2005; Arlinghaus et al., 2007; Gingerich et al., 2007;
Wedemeyer & Wydoski, 2008). Removing a fish from water following capture is stressful as
it deprives them of oxygen at a critical point when they must recover following exertion, and
this can lead to extended recovery times (Cooke et al., 2001) and, in some cases, permanent
tissue damage (Cooke & Suski et al., 2005). Most surveyed fishery agencies in North
America (84%, n = 41) strongly emphasise that fish should be brought in as quickly as
18""
practical to avoid unnecessary struggling of the fish (Pelletier et al., 2007). The
cardiovascular system of fish is heavily impacted during air exposure and the duration of a
C&R event generally correlates positively with the magnitude of physiological disturbance
and subsequent recovery times (Cooke & Suski, 2005). For example, when rock bass
Ambloplites rupestris where exposed for either 30 or 180 seconds their cardiac output, stroke
volume and heart rate required significantly longer to return to base levels following longer
durations of air exposure (Cooke et al., 2001). A strong correlation between the time taken
for cardiovascular variables to return to normal and the duration of air exposure was also
noted in smallmouth bass Micropterus dolomieu (Cooke et al., 2002).
Mortality rates tend to be increased by exposing fish to air following capture. For
example, rainbow trout Oncorhynchus mykiss exposed to air following 60 seconds of
exhaustive exercise had a mortality rate of 72%, compared to 12% mortality of individuals
exhaustively exercised but not exposed (Ferguson & Tufts, 1992). Longer air exposure, and
greater overall handling times were significant predictors of the loss of equilibrium in
bonefish Albula vulpes but were not directly related to the risk of subsequent predation
(Danylchuk et al., 2007). Bonefish exhibited significant increases in plasma glucose,
haematocrit and blood lactate when exercised experimentally for four minutes compared to
resting values, and can take up to 10-times longer to regain equilibrium than individuals
exposed to air for just one minute (Suski et al., 2007). In bluegill Lepomis macrochirus fish
exposed for 960 seconds during experimental treatments suffered higher levels of mortality,
and did so faster, than those exposed for 480 and 240 second treatments, indicating a linear
relationship between the duration of air exposure and mortality rates (Gingerich et al., 2007).
Largemouth bass Micropterus salmoides also exhibited a positive correlation between
the duration of air exposure, length of time to regain equilibrium and increased glucose
concentrations, suggesting C&R events could have had a significant impact on their post-
19""
release behaviour (White et al., 2008). Among nesting black bass Micropterus spp. exposed
to simulated tournament angling conditions, which include extended handling times when
they are weighed, there is a significant trend towards the abandonment of broods as a result
of increasing the duration of treatment times (Hanson et al., 2007). A similar effect on brood
abandonment was also seen in the congeneric species Micropterus dolomieu exposed to
simulated tournament conditions (Hanson et al., 2008). The magnitude of physiological
disturbance on tournament-caught walleye Sander vitreus was also found to be strongly
positively correlated with the duration of air exposure during the weigh-in process (Killen et
al., 2006). Brook trout Salvelinus fontinalis exposed for 120 seconds or more suffered from
severe reductions in swimming performance (equivalent to 75%) (Schreer et al., 2005).
However, handling time was not found to be a significant predictor of post-release survival in
coho salmon Oncorhynchus kisutch captured using seine nets, neither did it appear to affect
subsequent migration rates following release (Raby et al., 2012). In a perhaps extreme case
air exposure for periods up to five minutes had no significant effect on survival rates of silver
perch Bidyanus bidyanus (van der Walt et al., 2005), suggesting a species-specific tolerance
for air exposure.
There is strong evidence to suggest that a period of air exposure, and exacerbated by
periods of exercise prior to landing the fish, increases the likelihood of mortality during a
C&R event. However, there are significant differences between species.
The influence of capture depth
In conjunction with anatomical hook location Bartholomew & Bohnsack (2005) considered
capture depth to be the most important factor influencing the mortality rates of fish released
following a C&R event. In general, increased depth of capture results in a variety of injurious
20""
conditions as a result of barotrauma, which can subsequently increase the mortality rate
(Diggles & Ernst, 1997; Alos, 2008). In painted comber Serranus scriba mortality rates
increased as capture depth increased, and fish captured deeper than 16 m had a 50% chance
of experiencing some form of barotrauma (Alos, 2008). Only 2% of sauger Sander
canadensis captured at depths of less than 9 m suffered mortality, compared to 33% of those
captured at depths of 9-24 m (Meerbeek & Hoxmeier, 2011). Mortality rates among west
Australian dhufish Glaucosoma hebraicum increased from 21% at capture depths of 0-14 m
to 86% at depths greater than 45 m (St John & Syers, 2005). Similarly, more than 60% of gag
Mycteroperca microlepis captured at 36 m depth or greater, and 95% of red grouper
Epinephelus morio captured at depths greater than 41 m, exhibited distended stomachs
(Bacheler & Buckel, 2004). The survival rates of red grouper captured at depths greater than
44 m was less than 33% (Wilson & Burns, 1996). Red snapper Pagrus auratus exhibited very
little mortality when captured at depths of less than 30 m (0-2%), but this increased rapidly to
39% mortality at depths of 30-44 m and 55% between 45 and 59 m (Stewart, 2008). This
indicates a general positive relationship between capture depth and the incidence of
barotrauma and associated mortality.
However, annular seabream Diplodus annularis captured at depths of down to 42 m
exhibited no correlation between mortality and capture depth (Alos et al., 2009) and a linear
relationship between capture depth and signs of barotrauma was not noted in experimentally
captured red emperor Lutjanus sebae (Brown et al., 2010). Survival rates of yelloweye
rockfish Sebastes ruberrimus were not significantly influenced by capture depths ranging 18-
72 m (Hochhalter & Reed, 2011).
The evidence suggests that even among those groups susceptible to barotrauma from
capture at great depths there is much inter-individual variation, generating conflicting
results between studies (Rudershausen et al., 2007).
21""
The impact of barotrauma
Barotrauma, which results from a rapid ascension from depth, can include a variety of
conditions that negatively impact the mortality rates of fish following a C&R event (Rummer
& Bennett, 2005; Schreer et al., 2009), and includes the formation of gas bubbles in tissue
that can result in clotting of the blood, embolisms and haemorrhaging (Alos, 2008; Butcher et
al., 2012) as well as a range of other physiological alterations (Morrissey et al., 2005).
Various injuries can also result from the expansion of the gas bladder, including protrusion of
the intestines through the anus and the stomach through the mouth, or protrusion of eyes
(exophthalmia) (Brown et al., 2010; Butcher et al., 2012). In extreme cases of exophthalmia
mean (± S. E.) eye displacement can be as much as 60.9 ± 5.1% of total body length (Rogers
et al., 2011). Gas bladder expansion can also render fish positively buoyant, preventing them
from returning to depth and exposing them to predation (Shasteen & Sheehan, 1997;
Bartholomew & Bohnsack, 2005; St John & Syers, 2005; Alos, 2008; Campbell et al., 2010).
Additionally, ripe females experiencing expanded gas bladders may release their ova,
therefore compromising their future reproductive potential (Roach et al., 2011). The
susceptibility of species to these effects is a function of their anatomy. Some fishes have a
pneumatic duct connecting the gas bladder and digestive tract (physostomous species) and
these species can regulate the volume of their gas bladder rapidly compared to physoclistous
species, which lack this duct (Bartholomew & Bohnsack, 2005; Pelletier et al., 2007).
In snapper Pagrus auratus clinical signs of barotrauma become apparent at capture
depths of 11 m and 19% (n = 315) of specimens captured at depths of down to 60 m exhibited
a distended coelomic cavity, with none showing signs of subcutaneous gas bubbles or
exophthalmia (Butcher et al., 2012). The presence of a ruptured gas bladder (84.4%) was the
only clinical sign positively associated with capture depth in this study. Among
experimentally angled red snapper Lutjanus campechanus captured at depths of 30-50 m 53%
22""
(n = 63) of individuals exhibited external signs of barotrauma (42% stomach eversion; 12%
exophthalmia; 2.5% gut expulsion) (Diamond & Campbell, 2009). In the west Australian
dhufish Glaucosoma hebraicum injuries resulting from barotrauma (bubbles in the eyes,
exophthalmia, everted stomach and enlarged gas bladder) increased in both frequency and
severity with increasing capture depth (St John & Syers, 2005).
The effects of barotrauma are highly species-specific as evidenced by studies of mixed
fisheries capturing a range of species at the same depths under the same environmental
conditions with similar gear types (e.g., Rudershausen et al., 2007).
Can venting mitigate the effects of barotrauma?
Venting relieves internal pressure by puncturing the expanded gas bladder of a positively
buoyant fish with a hypodermic needle, preventing that fish from floating once released - a
condition that could render them susceptible to predatory attack or increasing stress (Siepker
et al., 2007). In North America the techniques to do so, and advice provided, by fishery
agencies is inconsistent and this could reflect the uncertainty of the usefulness of this
technique in the scientific literature (Pelletier et al., 2007; Brown et al., 2010). In painted
comber Serranus scriba that experienced excess gas as a result of rapid decompression
mortality rates were halved following venting, although this effect was not statistically
significant (Alos, 2008). Snapper Pagrus auratus were able to immediately regain control of
their buoyancy following venting, and were able to swim faster than untreated fish (Butcher
et al., 2012) and mortality rates among west Australian dhufish Glaucosoma hebraicum did
not appear to be negatively affected by venting (St John & Syers, 2005). Smallmouth bass
Micropterus dolomieu that experienced barotrauma and were subjected to venting did not
suffer any mortality, and their subsequent mean daily movement following treatment was not
23""
affected (Nguyen et al., 2009). There is some indication that the Lutjanus spp. coral reef
fishery could benefit from venting as the recapture rate of some species appeared to be
positively affected by the technique (Sumpton et al., 2008). Venting yellow perch Perca
flavescens was found to have a significant positive effect on survival rates for up to three
days post-release, and mark-recapture studies indicated long-term survival was not impacted
(Kinery et al., 1996).
However, in a meta-analysis of studies (n = 17) investigating the effects of venting on
fish following a C&R event Wilde (2009) concluded that the technique may in fact be
detrimental as a conservation measure for both marine and freshwater fisheries as it appears
harmful to fishes captured from deep waters. In an experimental study of the effects of
barotrauma on Australian bass Macquaria novemaculeata the only mortalities recorded (n =
4) were due to venting, most likely caused by severe internal injury (Roach et al., 2011).
Bruesewitz & Coble (1993) found no evidence that the mortality rates of burbot Lota lota that
exhibited expanded gas bladders were positively affected by venting, and a similar non-effect
was noted in largemouth bass Micropterus salmoides (Lyle, 1992) and red snapper Lutjanus
campechanus (Render & Wilson, 1994).
The evidence is that despite mitigating against the effects of barotrauma, venting may
also cause significant harm to fish and is unlikely to reduce the likelihood of mortality
following a C&R event.
24""
SUB-LETHAL EFFECTS OF CATCH-AND-RELEASE MANAGEMENT PRACTICES
The impact of C&R management practices on physiology
During a C&R event a fish will undergo a combination of aerobic and anaerobic exercise that
result in physiological changes, such as depletion of energy stores, accumulation of lactate
and cardiac and osmoregulatory disturbance (Cooke et al., 2001; Cooke & Suski, 2005;
Siepker et al., 2007; Suski et al., 2007). All of these may have sub-lethal effects on post-
release survival rates as the fish may or may not recover (Cooke et al., 2004; Arlinghaus et
al., 2007). However, as a result of the enormous variation in capture methodology,
environmental variables, angler experience, etc. the physiological consequences of C&R
practices for fish are extremely context dependent (reviewed in Cooke et al., 2013).
Laboratory based studies of the sub-lethal effects of C&R, despite their commonality
(Cooke et al., 2004), are not always directly relevant to what occurs in the wild and novel
wild-based methodologies are better able to provide more meaningful measures of stress and
the correlation of mortality rates with post-release physiology (Siepker et al., 2007; Cooke et
al., 2013). For example, using telemetry (Cooke et al., 2002; reviewed in Donaldson, 2008)
or blood sampled from fish immediately following capture in the wild is more likely to be
representative of the natural stress response of an individual than is blood sampled from a
fish artificially stressed in a laboratory (Skomal, 2007). In a study of experimentally angled
largemouth bass Micropterus salmoides heart-rate telemetry was able to show that higher
maximal heart rates were consistently seen in wild vs. laboratory-exercised fish, and that
those rates were independent of water temperature and could persist for as long as 300
minutes post-release (Cooke et al., 2004).
The duration of capture of largemouth bass Micropterus salmoides was positively
correlated with increases in plasma glucose, chloride, osmolarity and lactate levels
25""
(Gustaveson et al., 1991; White et al., 2008) and similar effects were noted in captured
Atlantic salmon Salmo salar (Thorstad et al., 2003), striped bass Morone saxitilis (Ridley et
al., 1997), tigerfish Hydrocynus vittatus (Smit et al., 2009) and red drum Sciaenops ocellatus
(Gallman et al., 1999). In smallmouth bass Micropterus dolomieu an increase in lactate and a
decrease in energy stores was more severe for individuals that were angled for two minutes
compared to those angled for 20 seconds (Kieffer et al., 1995) and was always higher in
exercised fish compared to controls (Hanson et al., 2008). In Atlantic cod Gadus morhua
capture methodology had a profound effect on an individual’s physiology, with those caught
on a longline exhibiting 13- to 14-times greater serum cortisol concentrations, and higher
serum glucose and plasma lactate levels compared to those caught on a jig (Mandelman et al.,
2012). However, some authors advise against collecting blood samples in the field due
uncontrolled variables (Diamond & Campbell, 2009) and a lack of control samples (O’Toole
et al., 2010).
Holding fish in tanks or cages for observation following a C&R event may also add
additional stresses and negatively impact on an individual’s physiology. In sea bream Pagrus
major captured using hook-and-line methodology the plasma cortisol levels (mean ± S.E.) of
resting fish (12.21 µg ml-1; n = 12) were significantly lower compared to those sampled from
captured fish, and increased as capture duration was extended from 10 minutes to three hours
(up to 104.1 ± 34.8 µg ml-1; n = 8) (Chopin et al., 1996). In common carp Cyprinus carpio
retained in so-called ‘carp sacks’ following simulated capture, plasma cortisol and plasma
glucose concentrations were significantly higher than control fish, and retention also had a
significant negative effect on plasma lactate, blood-pH and osmolality (Rapp et al., 2012). A
similar effect was also noted in walleye Sander vitreus (Killen et al., 2006) and largemouth
bass Micropterus salmoides (Suski et al., 2003) that were being weighed following
tournament angling, with large increases in white muscle and plasma lactate concentrations
26""
and significant cardiac disturbance. Wild coho salmon Oncorhynchus kisutch captured using
beach seines also experienced significant changes in their plasma physiology as a direct
function of handling time (Raby et al., 2012) as did several commercially caught pelagic
fishes retained on longlines such as sharks, tunas and billfishes (reviewed in Skomal, 2007;
Fabrizio et al., 2008).
However, in the case of sand whiting Sillago cilliata captured using hook-and-line
methodology and released into sea cages no significant differences were detected in the mean
(± S.E.) plasma glucose concentrations between six wild (3.42 ± 0.32 mmol l-1) and 22
experimental (4.13 ± 0.23 mmol l-1) fish following seven days of holding (Butcher et al.,
2006). Several salmonids were also found not to exhibit physiological disturbance as a result
of retention in net-pens following a C&R event (Wedemeyer & Wydoski, 2008), suggesting
some species can return to resting physiological rates more quickly than others.
The evidence suggests that a C&R event significantly elevates stress hormone levels,
cardiac output and disrupts osmoregulatory capacity in fish; all of which may negatively
impact mortality rates. However, some species appear physiologically more tolerant of such
disturbances.
The influence of water temperature
At higher water temperatures there is less oxygen available, yet a fish’s respiratory rate
increases resulting in physiological stress during a C&R event (Muoneke & Childress, 1994;
Cooke & Suski, 2005). This can lead to inflated mortality rates in warmer water conditions
due to limitations in the maximal cardiovascular performance as fish approach their maximal
metabolic rate and an exposure to greater oxygen debts following exercise (Cooke & Suski,
27""
2005). For example, Atlantic salmon Salmo salar exhibited low levels of mortality when
captured at temperatures between 8°C and 18°C, but mortality rates associated with C&R
events increased exponentially at temperatures higher than 18°C (Thorstad et al., 2003). In a
meta-analysis of 83 peer-reviewed articles 70% suggested that warm water conditions
(relative to a particular species thermal tolerance) contributed to both increased indices of
stress and subsequent mortality rates (Gale et al., 2013). In addition, higher water
temperatures have been found to result in an increased prevalence of secondary infection
following injury (Muoneke, 1992). However, approximately half of the studies examining
recovery rates following C&R events indicate that warmer temperatures facilitate or expedite
recovery time (Gale et al., 2013) and relative surface temperatures appear to have a negligible
effect on post-release mortality (Alos, 2009).
The evidence suggests a complex interaction between water temperatures and fish
physiology that is highly context dependent; however, in general warm water temperatures
appear to increase the likelihood of mortality following a C&R event.
The impact on post-release growth
Normal feeding behaviours can be interrupted by C&R events, impairing the growth of an
individual and potentially the reproductive capacity of that individual and its population
(Cooke & Schramm, 2007; Siepker et al., 2007). But results of bioenergetics models appear
inconsistent. A compromised feeding ability, caused by either injury, stress or a feeding delay
following C&R, can negatively affect the growth of black bass Micropterus spp. (Siepker et
al., 2006) and rainbow trout Oncorhynchus mykiss (Meka & Margraff, 2007). However, in
experimental studies of rainbow trout, where individuals were hooked in the mouth, no
change in growth was recorded (Pope et al., 2007). Neither were differences in growth rate
28""
observed in captured vs. un-caught: largemouth bass over a 40-day period (Pope & Wilde,
2004), white-spotted charr Salvelinus leucomaenis over a 50-day period (Tsuboi et al., 2001),
white seabass Atractoscion nobilis over a 90-day period (Aalbers et al., 2004), or in
largemouth bass over an 11-month period (DeBoom et al., 2010).
Despite the prevalence of deep-hooking as a result of some hook-and-line
methodologies in one particular study of yellowfin bream Acanthopagrus australis that had
experimentally ingested a hook (n = 17) no significant differences were noted in their ability
to digest and assimilate food compared to control fish (n = 20) (Broadhurst et al., 2007). No
effect of air exposure was noted in the growth of zander Sander lucioperca exposed for 0 –
240 seconds following simulated angling (Arlinghaus & Hallerman, 2007), suggesting even
the most severely injurious implications of C&R practices do not always result in
compromised growth.
In some species the number of times an individual fish has been captured, as well as
water temperature, have both been implicated in the degree to which growth rate was reduced
(Siepker et al., 2007). In a long-term (27 years) mark-recapture study of largemouth bass
Micropterus salmoides 1050 individuals were tagged and released to monitor growth
performance following C&R events (Cline et al., 2012). In this study some individuals were
captured one to six-times each season (1-98 day intervals) and exhibited a post-release
weight-loss period (up to six days post-release), but a subsequent compensatory growth
period (six to 27 days post-release), resulting in negligible impact on growth patterns overall.
The evidence suggests that multiple C&R events do not necessarily result in
compromised long-term growth.
29""
Retention vs. immediate release following capture
In recreational fisheries, catches are typically released at or close to the site of capture,
allowing the fish to return to its original position. However, in competitive angling
competitions, such as with North American black bass Micropterus spp., fish are retained in
either a keep-net or live-well and transported to a central location to be weighed (Siepker et
al., 2007). Following the weigh-in, competitor’s catches are usually released near to the
weigh-in site, as opposed to the original capture location and this can further exacerbate
fitness costs to the individual (Siepker et al., 2009). Despite recent improvements aimed at
reducing the mortality of black bass retained during tournaments (e.g., continuous water flow
in live-wells, aeration, early starts in warm weather, reduced catch limits) some events still
exhibit mortality rates exceeding 50% of captured fish (Suski et al., 2006; Siepker et al.,
2007). Mortality rates may also be increased when live-wells are employed as the result of an
increased prevalence of largemouth bass virus (LMBV) (Siepker et al., 2007), which has
been shown to transmit from infected to uninfected juvenile bass through shared water alone
(Grant et al., 2005). A variety of other pathogenic bacteria have also been identified from
tournament-caught black bass (Steeger et al., 1994).
In largemouth bass Micropterus salmoides captured and retained during tournaments
nest abandonment was far higher (90%) than those fish captured and immediately released
(33%) (Diana et al., 2012) and the same effect on nest abandonment was seen in the
congeneric Micropterus dolomieu (Hanson et al., 2008). Smallmouth bass also rapidly
disperse following tournament capture, moving an average 1,475 m away from the release
site (Kaintz & Bettoli, 2010). Among common carp Cyprinus carpio captured using hook-
and-line methodology and retained in so-called carp sacks, fish retained for less than 9 hours
moved significantly shorter distances compared to control groups released immediately
(Rapp et al., 2012).
30""
The evidence suggests that fish should be released as close to the point of capture as
possible, and retained for as short a period of time as possible, to ensure they are best able to
return to their original location.
The impact of capture on post-release behaviour
The behaviour of fish following a C&R event could have a strong effect on any subsequent
mortality or sub-lethal effects, especially if that behaviour is atypical. In a review of post-
tournament dispersal of captured black bass Micropterus spp. it was noted that smallmouth
bass Micropterus dolomieu exhibited greater dispersal distances (mean 7.3 km) and returned
more frequently to their capture location (mean 37%) than did largemouth bass Micropterus
salmoides (mean dispersal distance = 3.5 km; 14% return rate) (Wilde, 2003). Dispersal rates
for these species did not differ between fishing locations, and across all studies fish took
between four days and two years to return to their capture sites (Wilde, 2003; Wilde &
Paulson, 2003). Black bass that had been captured using hook-and-line methodology in
general exhibit a trend for greater swimming distances and take longer to return to nests than
in control experiments (Hanson et al., 2007 and references therein; Kaintz & Bettoli, 2010).
Additional impacts on population structure following C&R events are those which
affect the reproductive success of captured individuals. This is exemplified by those species
exhibiting parental care, such as black bass Micropterus spp., and which are frequently
angled for during the spawning season, leading to increased nest abandonment rates and
depressed reproductive output (Siepker et al., 2007). Largemouth bass Micropterus salmoides
captured prior to spawning also produced smaller offspring, indicating more wide ranging
effects of C&R practices on the population as a whole (Ostrand et al., 2004). In simulated
and wild angling studies there is a general trend for increased nest/brood abandonment in
31""
black bass as a result of any angling practice compared to control groups (Phillip et al., 1997;
Ridgway & Schuter, 1997; Suski et al., 2003; Hanson et al., 2008; Siepker et al., 2009;
Hanson et al., 2010; Diana et al., 2012). However, population level studies of black bass
populations exploited by tournament fishing have so far produced negligible, or even neutral,
effects (Siepker et al., 2007). This would suggest C&R practices in this fishery have a
minimal effect on the population size overall. Similarly, common snook Centropomus
undecimalis do not appear to be prevented from reproducing even if captured and released
from spawning aggregations (Lowerre-Barbieri et al., 2003).
Although predation following a C&R event is commonly reported this source of post-
release mortality has rarely been quantified (Donaldson et al., 2010). For example, a bonefish
Albula vulpes released following capture was selectively predated by lemon sharks
Negaprion brevirostris, despite aggregating with un-caught bonefish (Danylchuk et al., 2007)
and in areas where shark numbers were high 39% of bonefish were attacked within 30
minutes of release (Cooke & Phillip, 2004). Similarly, a single black marlin Makaira indica
was predated by a shark following release from capture on hook-and-line gear, although
seven other tracked individuals in this study exhibited typical behaviours (Pepperell & Davis,
1999). Red snapper Lutjanus campechanus that had been captured by hook-and-line
methodology, vented and then released infrequently (5.6%) exhibited erratic swimming
behaviour and were exposed to predation close to the release site (30 – 60 m), possibly as a
function of the C&R event or the swimming behaviour itself (Campbell et al., 2010).
The evidence suggests that although short-term behaviour may be altered following a
C&R event many species do not exhibit long-term effects. This could suggest fish populations
are not severely impacted by the disturbance of small numbers of individuals even during
sensitive periods of the life cycle, such as spawning.
32""
The effects of capture in nets
Sea bream Pagrus major captured in 10 x 2 m trammel nets exhibited elevated cortisol levels
after 10 minutes and these remained significantly higher than resting levels for up to 18 hours
of retention in the net (Chopin et al., 1996). Delayed mortality rates of 11% (n = 11) in these
fish occurred between eight and 18 days later, while 28% (n = 28) of fish died in the nets.
These nets also caused scale removal as well as deep and superficial cuts and resulted in
greater levels of stress, injury and mortality compared to hook-and-line capture (Chopin et
al., 2006). Spotted seatrout Cynoscion nebulosus mortality as a result of capture in “run-
around” gill nets in Florida was found to be 28%, significantly greater than individuals
captured using hook-and-line (4.6%) (Murphy et al., 1995). Southern flounder Paralichthys
lethostigma suffered greater short-term mortality (< 72 hours) in commercial gill nets set in
the summer (70-78%) compared to autumn fisheries (13-26%) (Smith & Scharf, 2011).
The survival rates of lake trout Salvelinus namaycush released from commercial gill
nets in Lake Superior in winter was estimated at 21% (range = 18-24%) and in spring 31%
(range = 36-36%) and, in general, trout larger than 25 cm total length had greater survival
rates compared to smaller individuals (Gallinat et al., 1997). This is much lower than the
survival rates of black bream Acanthopagrus butcheri captured using commercial gill nets in
the Gippsland Lakes, Australia. Here, total survival rate (initial survivorship plus delayed
survivorship) of black bream (c. 6,000 from 372 nets) was estimated as 90.8% (± 3.8% S. E.)
(Grixti et al., 2010).
There is some indication that C&R methodology using nets may have a greater
negative impact than that of hook-and-line methodology on some species, especially in warm
water conditions.
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Other impacts of C&R management practices
An interesting impact of C&R management practices on fish populations that has rarely been
explored is the risk of cumulative mortality as a result of multiple C&R events on a single
fish. This effect is particularly important for long-lived or heavily exploited species.
Bartholomew & Bohnsack (2005) produced a cumulative mortality model for red grouper
Epinephelus morio that indicated that at high encounter rates post-release mortality reached
near certainty for long life-spans (72% cumulative probability following 10 C&R events).
However, if individual fish learn or express avoidance behaviour following a C&R event then
their susceptibility to capture will become lower. Thus, even fisheries enforcing 100% C&R
will experience a decline in catch rates over time as a result of decoupling from fish density
and/or angler effort. For example, in an experimental study of five lakes in British Columbia,
Canada stocked with rainbow trout Oncorhynchus mykiss a sustained fishing effort (8 angler-
hours day-1 ha-1) quickly depressed catch rates after just seven to 10 days (Askey et al., 2006).
Models fitted to those data suggested that the population contained a group of readily
catchable fish that were rapidly captured and then released, but subsequently avoided
secondary capture. The same effect was also seen among common carp Cyprinus carpio in
stocked ponds, with decreased catches of individuals following experience of just a single
C&R event (Raat, 1985). These results compliment experimental work with largemouth bass
Micropterus salmoides that suggested vulnerability to capture by angling is actually a
heritable trait in this species (Phillip et al., 2009; Redpath et al., 2009).
Anglers are not, however, universally attracted to fisheries with high catch rates
(Johnston et al., 2011) and so these trends may not necessarily be detrimental to participation
numbers. In fact, some studies have suggested that anglers will adjust effort relative not only
to perceived fish quality (trophy specimens, hard fighting, etc.) but also in relation to travel
time, resulting in poor quality fisheries close to population centres (Post & Parkinson, 2012).
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Some anglers, such as those targeting trophy specimens, will be negatively impacted by C&R
management practices in some cases as post-release mortality rates can depress recruitment to
older year classes for certain species such as brook trout Salvelinus fontinalis (Risley &
Zydlewski, 2010).
Handling techniques, another potentially causative agent of post-release mortality for
captured fish, are highly species specific but injury as the result of scale or mucus removal is
often attributed to handling the fish with dry hands, or damage to the gills when held by the
operculum (Pelletier et al., 2007). Currently there are no scientific studies examining the
effect of handling or orientation on captured fish.
THE EFFECTS OF CATCH-AND-RELEASE MANAGEMENT PRACTICES ON IBIS
PRIORITY-MANAGEMENT SPECIES
CASE STUDY - BROWN TROUT Salmo trutta
Brown trout Salmo trutta (hereafter termed trout) are frequently targeted by recreational
anglers in small streams and rivers through to dedicated fishing ponds and up to large lake
systems and even estuaries and coastal waters. Such is their socio-economic importance
(Cooke & Cowyx, 2006) that hatchery-reared trout are regularly stocked in order to
supplement wild populations (e.g., Hesthagen et al., 1999), particularly in areas exposed to
high intensity fishing pressure (Arlinghaus et al., 2002). This practice often runs contrary the
desires of conservation managers who wish to protect localised populations (Araguas et al.,
2008). From a fishery perspective the impact of this management practice may be seen as
either positive or negative, depending on the response by anglers. If fishing effort remains
35""
constant then a greater density of fish (mixed wild and stocked) could reduce the chance that
any particular individual would be captured, and perhaps is more beneficial to wild fish that
may be less susceptible to capture compared to stocked fish. If, however, anglers are attracted
by higher catch rates then a greater density of fish may result in an overall increase in fishing
pressure.
For example, in a mark-recapture study Baer et al. (2007) found that recently stocked
trout accounted for 67-83% of all fish caught in a German river fishery over a two year
period, and that individual stocked trout were captured in less than 160 days. In central Spain,
angling pressure has negatively impacted trout populations by decreasing density, biomass,
fecundity and brood stock relative to unexploited rivers elsewhere (Cooke & Cowx, 2006).
However, it is unlikely hook-and-line fisheries are as capable of depleting trout stocks as
rapidly or as comprehensively as the use of gillnets, as was seen in Finland (Syrjänen &
Valkeajärvi, 2010). In Montana, United States where trout are non-native, mortality rates
related to C&R angling using single hooks were less than 5%, and were unrelated to water
temperatures (Boyd et al., 2010). Osmoregulatory and metabolic disturbances in another non-
native trout population were not found to be significantly impacted by C&R practices in the
western United States (Wedemeyer & Wydoski, 2008).
CASE STUDY – ATLANTIC SALMON Salmo salar
Many Atlantic salmon Salmo salar (hereafter termed salmon) populations undertake
extensive migrations into freshwater systems to spawn, and some subsequently leave the
system as a “kelt” following successful spawning (Haltunnen et al., 2010). Different
components of these populations exhibiting variation in migration timing can be differentially
exploited by anglers in some river systems (Thorley et al., 2007). This can be problematic as
36""
during the migratory period salmon do not feed and are exposed to a wide range of ambient
water temperatures during different seasons (Brobbel et al., 1996). Therefore, these factors
have the potential to exacerbate the sub-lethal physiological effects of C&R practices and
potentially result in inflated post-release mortality rates (Tufts et al., 1991). For example,
kelts are exhausted during a C&R event more quickly (mean ± S. E., 187 ± 11 s) than pre-
spawning salmon (320 ± 26 s) (Brobbel et al., 1996). White muscle phosphocreatine levels
were decreased to a greater extent in kelts (57%) compared to pre-spawning salmon (25%),
and lactate levels were also lower in kelts (22.1 ± 1 mmol L-1) compared to pre-spawning
salmon (40.6 ± 3.6 mmol L-1) (Brobbel et al., 1996). Despite these findings, however, no
kelts in this study died while 12% of pre-spawning salmon died within 12 hours of post-
release. Glycogen concentrations in grilse (one sea-winter fish) can be depressed by as much
as 73% during a C&R event and be as low as 44% of resting levels as long as 12 hours post-
release (Booth et al., 1995). In addition, this study also found that the lactate concentrations
of the white muscle of grilse were significantly greater than those of multi-sea-winter salmon
and, elsewhere, lactate concentrations increased in a linear fashion with the angling duration
(Thorstad et al., 2003).
The influence of water temperature could have a strong impact on C&R-related
mortality as salmon angled at 8°C were found to have a resting heart rate of 40 ± 0.28 (mean
± S. E.) beats-per-minute (BPM), at 16.5°C it was 66.9 ± 0.5 BPM and at 20°C was 72.3 ±
0.4 BPM, with heart rates remaining elevated for up to 16 hours post-release (Anderson et al.,
1998). The impact of water chemistry on physiological changes during C&R events is
unclear, but water hardness (CaCO3 mg L-1) appears to have very little effect on exhaustively
exercised salmon (Kieffer et al., 2002).
Mortality rates of salmon captured in Newfoundland using hook-and-line
methodology were 8.2% (Dempson et al., 2002) and 4% of kelts captured in Norway suffered
37""
mortality following a C&R event (Haltunnen et al., 2010). On the Kola Peninsula, Russian
Federation approximately 11% of angled salmon that were released survived to be
recaptured, with up to 10% being recaptured a second time and 0.5% three times (Whoriskey
et al., 2000) suggesting hook-and-line methodology results in low levels of post-release
mortality. However, in a trap-net fishery in the Bay of Bothnia average mortality rates as a
result of capture were 11% (4-21%) indicating this could be a more injurious technique for
populations overall (Siira et al., 2006). In spite of this Siira et al. (2006) go on to suggest
(derived from modelling data) that cumulative mortality following three capture events for
any given individual was less than 7%, and that maximum cumulative mortality for the total
population following repeated C&R events could be as low as 2% overall. Commercial
trawling appears highly injurious to salmon populations, as a Finnish lake pelagic trawl killed
significantly more salmon than either brown trout Salmo trutta or pike-perch Stizostedion
lucioperca (Jurvelius et al., 2000), despite using the same gear and in similar environmental
conditions.
In a wide-scale study of salmon anglers in Norway, Thorstad et al. (2003) found that
fish were hooked in the mouth on 93% of occasions, while 7% were deeply-hooked. Those
deeply-hooked fish were characterised as being in ‘bad’ or ‘very bad’ condition compared
with fish hooked in the mouth (χ2 = 124.5, d.f. = 1, P < 0.01). These salmon tended to move
downstream (83%, n = 25) and migrated an average of 2.2 km (range 0.13-5.1 km) in the first
week post-capture (Thorstad et al., 2006). Salmon that have recently entered freshwater (< 1
week) and subjected to a C&R event do not appear to be strongly negatively affected, as 17
of 18 captured and released fish were subsequently (1 – 3.5 months) located on spawning
grounds in a study by Thorstad et al. (2007). However, it was found that they took an average
of 34 days (range 0-94 days) to migrate just one kilometre, indicating a significant delay in
migration may be caused by C&R practices.
38""
The post-release behaviour of salmon does not appear to be altered drastically as a
result of C&R practices, as Norwegian kelts were found to migrate similar distances (> 30
km) and at similar speeds to control fish, although there was a short delay in river descent in
captured fish (Haltunnen et al., 2010). However, in a comparative study between hook-and-
line and gillnet capture methodologies of upstream migrating salmon found that fish captured
in gillnets moved up to 17.5 km day-1 back downstream, while those captured using hook-
and-line moved up to 2.1 km day-1 (Mäkinen et al., 2000). These fish did not resume their
migration for up to 28 days post-release. It appears that in salmon a short-term downstream
movement is typical following a C&R event, and that typical migration patterns resume
following a short delay (Jensen et al., 2010). In a recent study of an entire population of
salmon from a river in Québec, Canada it was found that 20% of multi-sea-winter fish were
captured and subsequently released, and that these fish were at least one of the parents for
22% of the offspring from that river that were genotyped (Richard et al., 2013). This suggests
that the captured fish played an important role in the population’s total reproductive output,
despite reducing their chances of mating (on an individual level) by 12%, confirming
previous studies that suggested the viability of gametes in salmon that have experienced a
C&R event are not negatively affected (Booth et al., 1995).
CASE STUDY – NORTHERN PIKE Esox lucius
Northern pike Esox lucius (hereafter termed pike) populations are a popular target of anglers
in both Europe and North America and C&R management practices are an important factor in
many fisheries (Arlinghaus & Mehner, 2004; Margenau et al., 2008; Arlinghaus et al., 2010;
Jansen et al., 2013), especially given the susceptibility of the species to overexploitation
(Pierce et al., 1995; Post et al., 2002; but see Kuparinen et al., 2012).
39""
Exhaustive exercise (60 seconds) results in muscle lactate concentrations increasing to
double the rate of resting fish, but these levels return to normal after one hours’ rest
(Arlinghaus et al., 2009). Both phosphocreatine and muscle ATP levels decline as a result of
exhaustive exercise (70% & 66% respectively), returning to normal after one hour (for
phosphocreatine) and six hours (for muscle ATP) (Arlinghaus et al., 2009). Exhaustive
exercise also caused significant increases in plasma glucose, potassium and sodium
concentrations. Interestingly though, additional air exposure (up to 300 seconds) was found to
cause only minimal levels of additional physiological disturbance, despite its significant
effect on post-release behaviour (Arlinghaus et al., 2009).
Following air exposure of up to 300 seconds pike spend a greater proportion of time
remaining stationary (vs. active swimming) and can take up to 15 minutes to exhibit
movement, typically moving less than 50 metres in the first hour post-release (Arlinghaus et
al., 2008; Arlinghaus et al., 2009). Despite moving rapidly away from the release site the day
following capture (typically 1.5 – 2.5 km) pike will return to capture sites in less than three
weeks (Arlinghaus et al., 2009). Pike that had been captured using hook-and-line artificial
lures and had the lines cut (vs. C&R following hook removal) moved significantly less in the
first hour post-release, spent significantly more time resting, took significantly longer to
initiate movement and then moved farther from the capture site the day after release
(Arlinghaus et al., 2008). This movement pattern would appear to be common to pike
populations in general (Klefoth et al., 2008). The foraging strategy of pike following a C&R
event appears to be significantly impacted. For example, the growth rates of pike following a
C&R event were significantly smaller than those of uncaptured pike (44%) (Stålhammar et
al., 2012). However, pike released back into groups were found to initiate feeding faster
compare to those released alone suggesting some mitigation may be achievable.
40""
Short-term mortality of pike appears generally low and not significantly influenced by
bait type. For example, initial mortality was found to average 2.4% (± 1.5 S.E) when using a
range of natural baits and artificial lures (Arlinghaus et al., 2008), and was just 1% when
angled with size 4 treble hooks baited with live fish (DuBois et al., 1994). However, the use
of so-called pike hooks (or Swedish hooks) in conjunction with live-bait was found to result
in 33% mortality, mainly associated with deeply set hooks, and would appear to be highly
injurious to pike populations (DuBois et al., 1994). In a congeneric species, the muskellunge
Esox masquinongy, the use of live baits resulted in a 22% mortality of those fish hooked in
the gut, most likely from extensive internal trauma (Margenau, 2007). In a hoop net fishery
(Ontario, Canada) more than 80% of captured pike exhibited jaw damage, scale loss and fin
damage when retained for between two and six days (Colotelo et al., 2013). In this study 25%
of pike retained in nets for six days (17°C) suffered mortality while 5.3% died if held for just
two days.
CASE STUDY – SHARKS (Selachimorpha spp.)
Sharks are typically top-level predators in both marine and freshwater environments and their
life history traits (long life span, slow maturity and low reproduction rates) make them
especially vulnerable to exploitation, leading to global concern for their management and
conservation (Martin, 2005; Lynch et al., 2010; Afonso et al., 2011; Hsu et al., 2012). Much
of this concern is related to the difficulty in assessing post-release mortality or sub-lethal
effects caused by physiological disturbance, particularly for pelagic or migratory species
(reviewed in Skomal, 2007; Marshall et al., 2012).
Longline fisheries for other target species frequently result in the unwanted bycatch of
sharks (reviewed in Molina & Cooke, 2012) and may lead to exceptionally high mortality
41""
rates usually as a factor of the gear type used (Diaz & Serafy, 2005; Gilman et al., 2008;
Afonso et al., 2012; Bromhead et al., 2012; but see Yokota et al., 2006). For example, in an
Atlantic pelagic longline fishery blue Prionace glauca, silky Carcharhinus falciformis and
oceanic whitetip Carcharhinus longimanus sharks suffered greater mortality with J-hooks
compared to circle hooks, while the night shark Carcharhinus signatus had 100% mortality
on both hook types and the nurse shark Ginglymostoma cirratum had 0% mortality on both
(Afonso et al., 2011). When captured on J-hooks these species were frequently hooked in the
oesophagus or gut, although circle hooks captured more sharks. However, in a mixed pelagic
fishery Afonso et al. (2012) found no significant differences between circle and J-hooks in
regards to the catchability or mortality rates in a variety of shark species, and Yokota et al.
(2006) drew the same conclusion when studying a single species, the blue shark Prionace
glauca.
During trawling, gummy sharks Mustelus antarcticus were found to suffer very high
rates of mortality (up to 87%) while Port Jackson sharks Heterodontus portusjacksoni were
not killed using the same gear for the same tow duration (Frick et al., 2010). Spiny dogfish,
or spurdog, Squalus acanthias are frequently targeted by northwest Atlantic fisheries and
average mortality rates among those captured in otter trawls (24% ± 6% S. D) are similar to
those captured by hook-and-line methodology (29% ± 12%), although the blood parameters
of trawled individuals appear to be more perturbed compared to those captured on hook-and-
line (Mandelman & Farrington, 2007). In a study of immediate C&R mortality among
tracked Atlantic sharpnose sharks Rhizoprionodon terraenovae mortality (10%) did not
appear to be correlated with anatomical hook location as the one individual that died (< 45
minutes post-release) was hooked in the gills, while four specimens were gut hooked and
tracked for up to 309 minutes (Gurshin & Szedlmayer, 2004). The sand tiger shark
Carcharias taurus appears particularly susceptible to being hooked in the gut (87.4%, n =
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184) as they were found to generally consume prey in a single piece (93.7%), leading to
injuries to the oesophagus, gut and pericardium (Lucifora et al., 2009).
Sharks are believed to experience prolonged recovery periods following anaerobic
exercise compared with teleosts as elasmobranchs lack several physiological mechanisms
found among the bony fishes. In gummy sharks Mustelus antarcticus experimentally gill-
netted for 60 minutes intramuscular lactate concentrations appeared to be the most useful
predictor of post-release mortality, as those individuals in poorest condition also exhibited the
highest concentrations (Frick et al., 2012). At 180 minutes, gummy sharks exhibited up to
70% mortality when captured in gillnets, while Port Jackson sharks Heterodontus
portusjacksoni appeared to be much more resilient to the same capture stress (100%
survivorship) (Frick et al., 2010). In common thresher sharks, plasma lactate and haematocrit
increased significantly during C&R events and was positively related to the duration of the
angling event (Heberer et al., 2010) and may be similar in additional species (Hyatt et al.,
2012). However, in juvenile sandbar sharks, experimental C&R angling using hook-and-line
methodology had less of an impact on blood-oxygen delivery than was expected, due to an
apparent species-specific physiological reaction (Brill et al., 2008). In this study a 21%
increase in haematocrit was seen in angled sandbar sharks, a result of c. 28% increase in
mean red blood cell volume (approximately twice the value seen in rainbow trout
Oncorhynchus mykiss) and not recorded in other shark species. It seems unlikely such a
response is confined only to a single shark species and further investigation of sub-lethal
effects of C&R on sharks is required (e.g., Manire et al., 2001; Marshal et al., 2012).
Air exposure times of 10 minutes were found to exacerbate physiological disturbance
in both gummy Mustelus antarcticus and Port Jackson sharks Heterodontus portusjacksoni,
although it was not the main factor contributing to mortality rates (Frick et al., 2010). Similar
additive effects of handling times on physiological disturbance were noted among
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bonnethead Sphyrna tiburo, lemon Negaprion brevirostris and bull sharks Carcharhinus
leucus (Hyatt et al., 2012).
The post-release behaviour of sharks appears to be minimally affected by C&R
management practices (Stevens et al., 2000; Hight et al., 2007), particularly those that are
captured using hook-and-line methodology (Mysyl et al., 2011). For example, the long-term
mortality of blue sharks Prionace glauca following longline capture was modelled using
blood samples from tracked sharks and predicted that those specimens landed in a healthy
condition (defined by blood chemistry) had a greater than 95% chance of survival post-
release (Moyes et al., 2006). Common thresher sharks Alopias vulpinus that experienced a
C&R event did not exhibit unusual movement patterns following capture (Heberer et al.,
2010) and Atlantic sharpnose sharks Rhizoprionodon terraenovae do not alter movement
patterns following C&R events, regardless of anatomical hooking location (Gurshin &
Szedlmayer, 2004).
CASE STUDY – SKATES (Rajidae spp.)
Skates (Rajidae) are, like sharks, elasmobranchs and as such they too are slow growing, late
maturing and exhibit a generally low fecundity, although this is higher than in sharks (Dulvy
et al., 2000; Ellis et al., 2011). Such life history traits make them vulnerable to exploitation,
even under low intensity effort (Cedrola et al., 2005). This group has historically, and is
currently, a commercially important group in both the U.K. and elsewhere in Europe and
North America (ICES, 2009). In the U.K. since the 1950s there has been a general decline in
the landings of skates (tonnes), a reduction in the abundance of larger species (with a
concomitant increase in smaller species), and the local extirpation of several skate species
44""
(common Dipturus batis, long-nosed Dipturus oxyrhinchus and white Rostroraja alba)
(Dulvy et al., 2000).
In the Bristol Channel, U.K. beam trawls of a short duration (< 2 hours) resulted in a
mean 13% mortality rate of three Raja spp. after two days, while a typical commercial trawl
(2.7 – 4.3 hours) resulted in 45% mortality of four species (Enever et al., 2009). In a study of
the impact of commercial trawling gear on four northwest Atlantic skate species (n = 1288)
initial mortality was found to be low (< 1%), rising to 15% (range 8 – 59%) after 72 hours
(Mandelman et al., 2013). However, in this study 44% of all specimens landed were
classified as ‘injured’, ranging from ‘minor trauma’ and ‘diminished vigour’ through to
‘deep-tissue trauma’ and ‘appearing moribund’, suggesting that delayed post-release
mortality among many skate species is likely to be higher than initial mortality.
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48""
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49""
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50""
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51""
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52""
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53""
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54""
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55""
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56""
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57""
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58""
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59""
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60""
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61""
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62""
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72""
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73""
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76""
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84""
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