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INCOFISH : WP7 Simple indicators for sustainable fisheries Lima, 4-7 december 2006

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Reports Activities

By

Birane SAMB and Fambaye Nâ€™GOM

Centre de Recherches OcÃ©anographiques de Dakar Thiaroye

Dakar SÃ©nÃ©gal

MAP of AFRICA

Atlantic Ocean

Map of Senegal

- 11 500 000 habitants with more than 50% of population in coastal zone
- 700 km coastline, with continental shelf area of 24 000 km2
- First sector of export

- Takes an important place in the supply of animal proteins
- 600 000 indirect employments
- 15% of the working population
- Annual consumption 26kg/year/ha where in Africa the mean consumption is 8.2 /year/ha

- The artisanal fishery consists of motorised canoes using a variety of gear. Essential catches are done by artisanal fisheries
- The industrial fishery is undertaken by trawlers or purse seiners, some of which are foreign vessels operating under commercial agreements.

- Marine resources are characterized by their diversity
- (i) Pelagic resources consisting of clupeids engraulids, carangids, scombrids, tuna and sharks. These species constitute up to 75% of the stocks. (ii) Demersal resources which have a higher economic value include crustaceans (shrimps, lobsters, and crabs), molluscs, cephalopods as well as bony fish (serranids, lutjanids, sciaenids, mullets, etc.), rays, and sharks. (iii) Coastal and estuarine resources, comprising bivalves and fish (cichlids, mullets, etc).

- Database
- List of species with biological parameter and reference
- Fish ruler
- Calcul of simple indicators for some species

Length frequency

from catches

Length frequency

Length frequency

from survey

Other biological

parameter

Lm

growth parameter

L max

- SEE FILE

Calcul of simple indicators for some important species in Senegal

- Length frequency data from catches of artisanal fisheries
- Biological parameter from database
- Indicators_spreadsheet_tool.xls

- Lm is Length at first maturity and refers to the length at which 50% of the individuals in a population have reached reproductive maturity.
- L90-100 is the length where 90-100% of individuals in a population have reached reproductive maturity and is calculated as Lm x 1.14
- Lopt is the length at which the fewest individuals of a population have to be harvested in order to reach the maximum biomass. The optimum harvest range is that from 10% lower than Lopt to 10% higher than Lopt (Lopt Â± 10%)
- Lopt = Linf * (3 / (3 + M/K))
- Mega-spawner is an individual who has reached a size at least 10% larger than Lopt for a population.

- Pagellus bellotii
- Sparus caeruleostictus
- Galeoides decadactylus
- Pseudupeneus prayensis

Read Pandora Pagellus bellotii

Most fish are captured after their first size of maturity.

But these fish were captured before the economic optimal size.

The large specimens withsize 10 % larger than the optimal size miss almost in the captures.

Figure 1. Length frequency of Pagellus bellotii landed from 1990 to 2003 in Senegal where Lm is the length of first maturity, Lopt is length with maximum yield per recruit can be obtained and Lmax is the maximum size reached during this period

- The annual percentage of mature fish in the captures is close to or approaching the target of 100%.
- The annual percentage of fish with the optimal size in the captures is relatively low compared with the target of 100 %.
- The annual percentage of mega-spawners is below 30 - 40% representative a healthy structure of age.
- It would be more interesting to capture fish with a higher size to approach the optimal weight

Figure 2. Annual percentages of fish mature, fish at size optimal and megaspawners of Pagellus bellotiiin the catches

Bluespotted seabream

Sparus caeruleostictus

Most of fish are caught before their first length of maturity.

Fish are caught before the optimal size.

Mega-spawners miss almost in the captures.

Figure 3. Length frequency of Sparus caeruleostictuslanded from 1990 to 2003 in Senegal where Lm is the length of first maturity, Lopt is length with maximum yield per recruit can be obtained and Lmax is the maximum size reached during this period

- The annual percentage of mature fishes is very low compared with the target of 100%.
- The annual percentages of fishes with the optimal size and mega-spawners in catches is very low.
- This very weak value is an indication of depletion of stock.
- These indicators suggest that the stock is in a state of overexploitation

Figure 4. Annual percentages of fish mature, fish at size optimal and megaspawners of Sparus caeruleostictusin the catches

Small captain

Galeoides decadactylus

Most of fishes are above the size for first maturity and in the range of the optimal size where the maximal yield can be obtained.

Mega-spawners are little represented in the total catches.

Figure 5. Length frequency of Galeoides decadactyluslanded from 1990 to 2003 in Senegal where Lm is the length of first maturity, Lopt is length with maximum yield per recruit can be obtained and Lmax is the maximum size reached during this period

- The annual percentage of mature fishes is below the target of 100 %.
- The annual percentage of fishes with the optimal size declined since 1993to reach 18 % in 2003.
- The annual percentage of mega-spawners is below 30 â€“ 40 % representative a healthy structure of age.
- In spite of the increase of mature fishes in catches, indicators suggest that the stock of the small captain is also threatened by an overexploitation.

Figure 6. Annual percentages of fish mature, fish at size optimal and megaspawners of Galeoides decadactylusin the catches

West african goatfish

Pseudupeneus prayensis

The catches are constituted by individuals whose size is in the range length where the maximum yield can be obtained.

The mega-spawners are also little represented in catches.

Figure 7. Length frequency of Pseudupeneus prayensislanded from 1990 to 2003 in Senegal where Lm is the length of first maturity, Lopt is length with maximum yield per recruit can be obtained and Lmax is the maximum size reached during this period

- The percentage of mature fishes is very low compared with the target of 100 %.
- However the percentage of fish with the optimal size increased since 1990 to reach 80 % in 2003.
- But he percentage of mega-spawners is below 30 â€“ 40 % representative a healthy structure of age.
- These results suggest that the stock is not in situation of overexploitation .

Figure 8. Annual percentages of fish mature, fish at size optimal and megaspawners of Pseudupeneus prayensisin the catches

Thanks for your attention