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

INCOFISH : WP7
Simple indicators for sustainable fisheries
Lima, 4-7 december 2006
Reports Activities
By
Birane SAMB and Fambaye N’GOM
Centre de Recherches Océanographiques de Dakar
Thiaroye
Dakar Sénégal
Senegal is located in North West
Africa
Atlantic Ocean
Map of Senegal
MAP of AFRICA
Importance of fisheries sector in
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
Importance of fisheries sector in
Senegal (suite)
• 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
Fisheries
– 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
• 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).
Differents step of work
• Database
• List of species with biological parameter
and reference
• Fish ruler
• Calcul of simple indicators for some
species
DATA BASE
Length frequency
from catches
Length frequency
Length frequency
from survey
Espèce1
Other biological
parameter
Lm
growth parameter
L max
List of species with biological
parameter (example of output)
Nom commun
Taxon scientifique
Taille de 1°
maturité
sexuelle :
L50 ♀ (cm)
Taille de
1°
maturité
sexuelle :
L50 ♂ cm)
Taille de 1°
maturité
sexuelle des
indéterminés
:L50 (cm)
Zone d'étude
Référence Taille de 1ère maturité
POISSONS
Sardinelles
Sardinelle ronde
Sardinella aurita
Sardinelle plate
Sardinella maderensis
18.0 LF
20.0 LF
16.0 LF
17.6 LT
16.8 LT
Sénégal
Sénégal
Sénégal
Sénégal
Camarena Lurhrs T., 1986
Conand, C., 1977
Camarena Lurhrs , T., 1986
Diouf, P.S., 1996
18.5 LF
15.5 LF
Afr.centre est
18.0 LT
18 -19 LF
13.6 LT
17.5 LT
Sénégal
Sénégal
Sénégal
Diouf, P.S.,1996
Scheffers, W.J., 1976
Diouf, P.S.,1996
40.0 LF
33 à 34 LS
27.0 LS
32 à 36 LS
Sénégal
Sénégal
Sénégal
Sénégal
Levenez, J. J., 1993
Sembène, B., 1995
Sembène, B., 1995
Sembène, B., 1995
14.5 LF
14.1-15.3 LF
Sénégal
Sénégal
Sénégal
Sénégal
Levenez, J. J., 1993
Franqueville, C., 1979
Franqueville, C., 1983
Franqueville, C., 1983
Guinée
Guinée
Guinée
Guinée
Domain, F. et al., 1999
Domain, F. et al., 1999
Sidibe, A., 2003
Domain, F. et al., 1999
Sénégal
Levenez, J. J. ,1993
Ndiaye, A.M., 1994
Sardines
Sardine commune
Sardina pilchardus
FAO, 1979
Ethmaloses
Ethmalose d’Afrique
Ethmalosa fimbriata
Alose rasoir
Mérous
Ilisha africana
Mérou gris
Epinephelus aenus
Mérou badèche
Badèche
Epinephelus alexandrinus
Mycteroperca rubra
Pageots
Pageot à taches rouges
Pagellus bellottii
16.5 LT
15.50
Machoirons
Machoiron banderille
Machoiron de Gambie
Arius heudelotii
Arius latisculatus
Arius parkii
34. 0 LF
30. 0 LF
27.0-28.0 LF
31.0 LF
Pagres
Pagre à points bleus
Sparaillon africain
Sparus caeruleostictus
Diplodus bellottii
23.0 LF
12.0 LS
Geret, M., 1974
Dentés
Denté à gros yeux
Dentex macrophtalmus
Dentex angolensis
Dentex gibbosus
18.0 LT
17.0 LT
15.4 LT
34.7 LT
38.6 LT
Cap vert
AF. ouest
Côte d'Ivoire
Iles Canaries
Magnússon, J. and J.V.V. Magnússon, 1987
Domaneski, L.N. et Stepkina, M.V., 1971
Konan, J., 1979
Pajuelo, J.G. and J.M. Lorenzo, 1995
Merlus
Merlu du Sénégal
Merluccius senegalensis
Merlu d'Afrique tropicale
Merluccius polli
38.0 LT
35.0 LT
35.2 LT
32.0 LT
Sénégal
Sénégal
Sénégal
FAO, 1980
FAO, 1986
FAO, 1986
Fish ruler
• SEE FILE
Calcul of simple indicators for
some important species in
Senegal
Material
• Length frequency data from catches of
artisanal fisheries
• Biological parameter from database
• Indicators_spreadsheet_tool.xls
Method
• 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 ± 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.
ANALYSE ON THE STATE OF SOME DEMERSAL
SPECIES CAUGHT BY SENEGALESE FISHERIES
USING SUSTAINABLE INDICATORS
• Pagellus bellotii
• Sparus caeruleostictus
• Galeoides decadactylus
• Pseudupeneus prayensis
20000
Lopt
Lm
18000
Read Pandora Pagellus bellotii
Lmax
Fréquence
16000
14000
12000
10000
8000
6000
4000
Juvéniles
Superreproducteurs
Matures
2000
Most fish are captured after their first size of maturity.
But these fish were captured before the economic optimal
size.
The large specimens with size 10 % larger than the
optimal size miss almost in the captures.
0
10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 43
Taille (cm)
Pourcentages dans les 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
100
•The annual percentage of mature fish in the captures
Matures
close to or approaching the target of 100%.
80
is
•The annual percentage of fish with the optimal size in the
60
captures is relatively low compared with the target of 100
%.
40
•The
Taille optimale
annual percentage of mega-spawners is below 30 40% representative a healthy structure of age.
20
Super-reproducteurs
0
1990
1992
1994
1996
1998
2000
2002
Années
Figure 2. Annual percentages of fish mature, fish at size optimal and
megaspawners of Pagellus bellotii in the catches
It would be more interesting to capture fish with a higher
size to approach the optimal weight
.
5000
Lm
4500
Lopt
Bluespotted seabream
Sparus caeruleostictus
Lmax
4000
Taille
optimale
Fréquence
3500
3000
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.
2500
2000
1500
1000
Superreproducteurs
500
Juvéniles
0
10
20
Matures
30
40
50
60
75
Taille (cm)
Figure 3. Length frequency of Sparus caeruleostictus 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
Pourcentages dans les captures
70.00
•The annual percentage of mature fishes is very low
60.00
50.00
compared with the target of 100%.
Matures
•The annual percentages of fishes with the optimal size and
40.00
mega-spawners in catches is very low.
30.00
20.00
This very weak value is an indication of depletion of stock.
Taille optimale
10.00
Super-reproducteurs
0.00
1990
1992
1994
1996
1998
2000
Années
Figure 4. Annual percentages of fish mature, fish at size optimal and
megaspawners of Sparus caeruleostictus in the catches
2002
These indicators suggest that the stock is in a state of
overexploitation
3500
Lmax
Lopt
Lm
Small captain
3000
Taille
optimale
Fréquence
2500
Galeoides decadactylus
2000
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.
1500
1000
Super-reproducteurs
Juvéniles
500
Matures
0
1
9
13
17
21
25
29
Taille (cm)
33
37
41
45
49
Pourcentages dans les captures
Figure 5. Length frequency of Galeoides decadactylus 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
80.00
Matures
70.00
target of 100 %.
Taille optimale
60.00
is below the
• The
annual percentage of fishes with the optimal
size declined since 1993 to reach 18 % in 2003.
50.00
40.00
•The
30.00
20.00
•The annual percentage of mature fishes
annual percentage of mega-spawners is below
30 – 40 % representative a healthy structure of age.
Super-reproducteurs
10.00
0.00
1990
1992
1994
1996
1998
2000
2002
Années
Figure 6. Annual percentages of fish mature, fish at size optimal and
megaspawners of Galeoides decadactylus in the catches
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.
Lm
Fréquence
2000
Lopt
Lopt
Lmax
Lmax
Taille
optimale
1500
Pseudupeneus prayensis
1000
Super reproducteurs
500
West african goatfish
Juvéniles
Matures
0
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 48
Taille (cm)
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 prayensis 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
Pourcentages dans les captures
•The percentage of mature fishes is very low compared
100.00
90.00
80.00
70.00
60.00
50.00
40.00
30.00
20.00
10.00
0.00
with the target of 100 %.
Taille optimale
•However the percentage of fish with the optimal size
Matures
Super reproducteurs
1990
1992
1994
1996
Années
1998
2000
2002
Figure 8. Annual percentages of fish mature, fish at size optimal and
megaspawners of Pseudupeneus prayensis in the catches
increased since 1990 to reach 80 % in 2003.
•But he percentage of mega-spawners is below 30 – 40 %
representative a healthy structure of age.
These results suggest that the stock is not in situation of
overexploitation .
Thanks for your attention