Trawling for cephalopods off the Portuguese coast —Fleet dynamics and landings composition...

Trawling for cephalopods off the Portuguese coast—Fleet dynamics and landings composition

Reporter：林信宏

Fisheries Research 92 (2008) 180–188Tereza Fonseca a, Aida Camposa,∗, Manuel Afonso-Dias b, Paulo Fonseca a, Jo˜ao Pereira a

1. Introduction

crustacean

finfish(Remaining marine resources)Cephalopod

Cephalopod• 2002 14%

• 2003 10%

• 2004 13 %

1. Introductiontargeting cephalopods

• good index of abundance

Objective

related Study

Management

Fishing ground

Species composition

Distribution

• Analyses of the landings were restricted to the fish trawling fleet operating within the depth range of distribution of these cephalopods, extending up to 200m

1. Monthly landings

1. Monthly landings

HCAHCA

1. Year2. Season3. Vessel4. GT 、 HP

1. Year2. Season3. Vessel4. GT 、 HP

GLMGLM

Objective

Estimation and Management

2. Materials and methods

• 2.1. Data sources

• 2.2. Data analysis

Hierarchical clustering analyses

2.1. Data sourcesLanding matrix

15m(VMS)

1618 observations (rows)

31 s

peci

es(c

olum

ns)

1618 48 X 3 X 12 = 1728

landed at least 9 months

98.3% of the total landings

Time ： 2002-2004Region ： Portuguese coastSpecimen ： 48 vessels

Number ： 1618 monthly landingsfisheries ： fish trawl fisheries

65mm mesh size cod-ends

Select of cephalopod

• Loligo spp. • Loligo forbesi • Loligo vulgaris• Octopodidae • Octopus vulgaris • Eledone cirrhosa• Sepia officinalis • Ommastrephidae

Fleet spatial dynamics

GeoCrust

VMSGPSSpeed

-----

------

10 min

Inspeccao-Geral das Pescas (IGP)

-----------

2.2. Data analysis

• Hierarchical clustering analyses

• Generalized linear models

• GeoCrust

Hierarchical clustering analyses (HCA)

• landing profiles(LP)

• Ward’s minimum variance

• Euclidean distances

HCAspecies

(1618 X 31)

Generalized linear models (GLM)

The statistical analyses ----- S-Plus 2000

GTHP

year vessel

season

3.Results

• 3.1. Landing profiles

• 3.2. GLM

• 3.3. Spatial patterns of fishing activity

octopus cuttlefish

horse mackerel squid

horse mackerel

Fig. 1. Results from HCA undertaken in a matrix of 1618 rows (monthly landings)×31 columns (species) comprising the period 2002–2004 for the 48 vessels selected from the fish trawling fleet. The number of cases in the xx axis was grouped by landing profiles (LP) defined in Table 1. The horizontal line at linkage distance 2 allowed the identification of 12 separate clusters corresponding to different LP. Four of the identified clusters correspond to LPs (3, 8, 10 and 12) associated with cephalopods.

octopuspoutinghorse mackerel

octopusdemersal

cuttlefish solesoctopus

squid horse mackerelpouting octopus

horse mackerel

13 species

• Regarding the landings of cephalopods LP12 ： cuttlefish (about 52%)

LP3 ： squid (about 46%)

LP2 ： squid (about 27%)

• octopus landings were scattered throughout the different LPs

LP2 ： octopus ( 19.8% )

LP8 ： octopus ( 18.5% )

• Vessels related to LP4 also landed considerable amount of cephalopods

octopus ： 16.3%

squid ： 11.5%

cuttlefish ： 6.1%

• south ： octopus (LP10 )

cuttlefish (LP12)

• west ： octopus (LP3)

squid (LP8)

other species

50 nautical miles

Fig. 6. Visual display of trawling operation associated with cephalopod landings (effort distribution) from 2002 to 2004 obtained by using GeoCrust 2.0 software. (a) LP10-Octopus and (b) LP12-cuttlefish, associated with fish trawlers targeting octopus and cuttlefish off the southern coast; (c) LP3-Squid and (d) LP8-Octopus,associated with trawlers targeting octopus and squid off the west coast. Each map presents VMS data individually filtered by trawler after excluding the navigation routes. Trawling intensity (10 classes) is represented as the number of points by square (in this case 0.3 nm×0.3 nm) where the minimum corresponds to white colour and the maximum to black colour (grey scale). Maximum number of points per square (0.3 nm×0.3 nm) differs from (a) to (d).

6% 16%

production value

Fig. 2. Mean monthly landings of octopus, squid and cuttlefish associated to the selected 48 vessels of the fish trawl fleet from 2002 to 2004.

suggesting a seasonal alternation between octopus and cuttlefish

• cuttlefish ： autumn

winter

• octopus ： spring

summer

Fig. 4. Cuttlefish and octopus monthly landings made by the small group of vessels permanently targeting cephalopods, from 2002 to 2004.

LP12

LP10

• landing squid instead of octopus between July and December

Fig. 5. Monthly landings of squid and octopus from 2002 to 2004, made by the group of fish trawlers associated with LP3 (squid) and LP8 (octopus).

LP 3

LP 8

octopus seasonally

LP12

LP10

LP 3

LP 8

Fig. 3. Patterns of monthly fishing activity (landing profiles’ temporal distribution) displayed by the 48 vessels (rows) selected from the fish trawling fleet from 2002 to 2004. Light grey: LP12; Dark grey, LP10; Black, LP8; Dotted, LP3; White, non-cephalopod targeting LPs.

3.2. GLM

3.3. Spatial patterns of fishing activity

Fig. 7. Visual display of trawling operations (effort distribution) by (a) the 48 selected fish trawlers and (b) excluding the trawlers associated with the four cephalopods landings profiles, from 2002 to 2004, obtained by using GeoCrust 2.0 software. Maximum number of points per square (0.3 nm×0.3 nm) differs between (a) and (b)

LP3 、 LP8 、LP10 、 LP12

48 fish trawlers

Discussion

south

1. seasonal alternation (cuttlefish 、 octopus)

2. exclusively target these species

3. abundance cycles and matches their life-cycles

4. The landings of octopus in the Algarve increased substantially during the second quarter of the year

5. Likewise the increase in the landings of cuttlefish is also probably related to its reproductive strategy

Alternation species

1. reproductive strategy

2. available to the fishery after the spawning peak period

3. (Coelho and Martins, 1991)

1. These vessels are old and technologically less advanced

2. operating almost at all times in sheltered areas

3. limiting factor target species

patterns of vessel operation

south

vessel

west

Alternation species

1. inter-annual shifts (squid 、 octopus)

2. Seasonal shifts (cephalopods 、 fish)

3 caused by environmental change (e.g. Sobri˜no et al., 2002; Erzini,2005)

4. high levels of mortality in the life-cycle takes place at pre-recruitment life-stages

(e.g. Boyle and Rodhouse, 2005; Mangold, 1983; Roberts, 2005; Worms, 1983)

5. octopus abundance is positively correlated to temperature (Lourenc¸o and Pereira, unpublished data)

west

1. fishing strategy

2. depending on the yearly recruitment of these species

1. These vessels are larger trawlers and technologically more advanced

patterns of vessel operation

vessel

winter

(horse mackerel)

autumn

(squid)

spring/summer (octopus)

effect on landing

advanced tracking devices

lower towing speeds

observe the alternation from the market