Habitat and Biology
Climatic zone: Unspecified. Bottom type: Unspecified. Depth zone: Coastal (0 m - 50 m); Shelf (50 m - 200 m); Slope (200 m - 1000 m). Horizontal distribution: Unspecified. Vertical distribution: Pelagic.
Jurisdictional distribution: Shared between nations
Considered a single stock: No
Sardinellas caught in the southern CECAF Area from Guinea to Angola are composed of two species, the round sardinella (Sardinella aurita) and the flat sardinella (Sardinella maderensis). The surveys carried out in the CECAF area show that the two species are found in a vast area stretching from the southern Moroccan stock to south of Angola. The FAO/CECAF Working Group for the moment has agreed on the existence of four stocks for these two species in the Southern CECAF area. These are the northern (Guinea and Sierra Leone), western (Côte d’Ivoire, Togo, Ghana and Benin), central (Nigeria and Cameroon) and southern (Gabon, Congo and Angola).Western stock (Côte d’Ivoire, Togo, Ghana and Benin)
As the Côte d’Ivoire scientist was not in the meeting no information is provided for this country. The catches are dominated by S. aurita off Ghana and Togo while S. maderensis is the dominant species off Benin. The two sardinellas are exploited mainly by the artisanal fleets in Ghana, Togo and Benin and to a lesser extent by the semi-industrial (inshore) fleet of Ghana. In all the three countries, the
artisanal fleet use either artisanal purse seine gear (locally called Poli/Watsa) or beach seine to exploit the two species. These gears are operated from canoes which are between 15–20 m in LOA. The purse seine canoes are powered by outboard motors of 40 hp. The Ghanaian semi-industrial vessels also exploit the species using purse seine gear. These vessels are over 20 m in LOA with engine power of 100 hp.
Catch and effort
Peak catches of the two species occur in June–September which coincides with the major upwelling period in the area.
The Schaefer logistic production model was used on an Excel worksheet.
Assessments were made for S. maderensis (north), S. aurita (west), S. maderensis (west) and Sardinella spp. (south). The model could not be fitted for the rest of the stocks.
The input data was catch and effort data on S. aurita
and S. maderensis
from the artisanal and semi-industrial fisheries for the period 1990–2004. Côte d’Ivoire data was not available. The CPUE of Ghana’s artisanal fishery was used in the assessment of S. maderensis
while that of Ghana’s semi-industrial fishery was used in the assessment of S. aurita
Overall Assessment Results
The model fitted reasonably well for all the above stocks although in the case of S. maderensis (west) the R2 values were low. A summary of the results of the assessments is presented in Table 1.
Table 1: Summary of the state of the stock
|S. aurita wes/CPUE_GhInd/
|S. maderensis west/CPUE_GhArt/
Bcur/B0.1: Ratio between the estimated biomass for the last year and the biomass corresponding to F0.1.
Fcur/FSYcur: Ratio between the observed fishing mortality coefficient during the last year of the series and the coefficient that would give a sustainable yield at current biomass levels.
Fcur/FMSY: Ratio between the observed fishing mortality coefficient during the last year of the series and the coefficient giving maximum long term sustainable yield.
Fcur/F0.1: Ratio between the observed fishing mortality coefficient during the last year of the series and F0.
The main limitation to the assessment is non-availability of data for some countries in the region. In the north, Sierra Leone has a very short data time, while data for Côte d’Ivoire was not available for the western stock. With the exception of S. maderensis (west), the current biomass of the different stocks is less than the biomass at B0.1. The current fishing effort is greater than fishing effort at MSY and if effort is not reduced the stock level will decrease further in the future.
Scientific AdviceFuture research
for Management considerations
- Biological sampling intensification.
- Continue with Nansen surveys to obtain fisheries independent data.
- Adoption of a sampling programme for the commercial fleet.
Reduction in catch is recommended and there should be no licensing of new vessels. The canoe fleet numbers should be controlled.
The stock of S. aurita
is overexploited, catches should not be increased (not exceed 80 000 tonnes); S. maderensis
should not exceed the average of the last five years (18000 tonnes).
Biological State and Trend
Exploitation state: OverexploitedExploitation rate: Fcur/F0.1: 202 %
Abundance level: Bcur/B0.1: 56%
Exploitation state: Moderately exploitedExploitation rate: Fcur/F0.1: 64 %
Abundance level: Bcur/B0.1: 143 %
Stock is not fully exploited.
Source of information
FAO Fishery Committee for the Eastern Central Atlantic/Comité des pêches pour l’Atlantique Centre-Est. “Report of the FAO/CECAF Working Group on the Assessment of Small Pelagic Fish – Subgroup South” Limbe, Cameroon, 25 September–1 October 2006
“Rapport du Groupe de travail FAO/COPACE sur l’évaluation des petits poissons pélagiques – Sous-Groupe Sud” Limbé, Cameroun, 25 septembre-1er octobre 2006
Rome, FAO . 2009
The bibliographic references are available in the report included in "Source of Information".