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West African croakers - Côte d'Ivoire, Ghana, Togo and Benin
Marine Resource  Fact Sheet
CECAF Scientific advice 2016
West African croakers - Côte d'Ivoire, Ghana, Togo and Benin
Fact Sheet Citation  
Otolithe (Pseudotolithus spp) - Côte d'Ivoire, Ghana, Togo et Bénin
Owned byFood and Agriculture Organization (FAO) – More
Related observationsLocate in inventorydisplay tree map
 
Species:
Geographic extent of West African croakers - Côte d'Ivoire, Ghana, Togo and Benin
Main Descriptors
Considered a single stock: Yes        Spatial Scale: Regional
Management unit: Yes        Reference year: 2010
 
 
Biological State and Trend
State & Trend Descriptors
PartnerFIRMS
Exploitation rateFcur/F0.1 = 85%; Fcur/FMSY = 77%Not applicable
Abundance levelBcur/B0.1 = 107% ; Bcur/BMSY = 117%Not applicable
FAO Categories
Exploitation stateFully exploited

Fcur/F0.1: Ratio between the observed fishing mortality coefficient during the last year of the series and 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 the current biomass level.
Fcur/FMSY: Ratio between the observed fishing mortality coefficient during the last year of the series and the coefficient that would give a maximum sustainable yield over the long term.
Bcur/B0.1: Ratio between the estimated biomass for the last year and the biomass corresponding to F0.1.
Bcur/BMSY: Ratio between the estimated biomass for the last year and the biomass corresponding to FMSY.
Unless otherwise indicated, the indicators were based on the Schaefer dynamic production stock assessment model.
Habitat and Biology
Climatic zone: Tropical.   Bottom type: Soft bottom clean sand; Soft bottom muddy or muddy-sand.   Depth zone: Coastal (0 m - 50 m).   Horizontal distribution: Littoral.   Vertical distribution: Demersal.  

Geographical Distribution
Jurisdictional distribution: Shared between nations

Water Area Overview
Spatial Scale: Regional

Geo References
Resource Structure
Considered a single stock: Yes


Three species of Pseudotolithus spp. are exploited in the zone. These are P. senegalensis, Pseudoplesiops typus and P. elongatus. They are not separated in the catch and are therefore considered as a single stock.
Exploitation
 
Fishery Indicators
TypeMeasureValueUnitTime period
ProductionCatch 2771tonnes1990
Catch 2608tonnes1991
Catch 3211tonnes1992
Catch 1652tonnes1993
Catch 1983tonnes1994
Catch 1738tonnes1995
Catch 2017tonnes1996
Catch 3326tonnes1997
Catch 2410tonnes1998
Catch 2346tonnes1999
Catch 1720tonnes2000
Catch 2302tonnes2001
Catch 2636tonnes2002
Catch 2178tonnes2003
Catch 2566tonnes2004
Catch 3399tonnes2005
Catch 2763tonnes2006
Catch 2472tonnes2007
Catch 2494tonnes2008
Catch 2463tonnes2009
Catch 2344tonnes2010
Assessment
 

Assessment year: 2011
The CECAF Working Groups have adopted the following Biological Reference Points (BRPs):
- Limit Reference points: BMSY and FMSY
- Target Reference Points: B0.1 and F0.1
Stock status is assigned based on current estimates of fishing mortality (Fcur) and biomass (Bcur) relative to these target and limit reference points (Bcur/BMSY, Fcur/FMSY, Bcur/B0.1, Fcur/F0.1). The results from the stock assessment of this stock are found under the “Biological state and trend section”.
Assessment Model
Type:  Biomass-aggregated
Schaefer dynamic production model

For the period 1990-2010, long time series of data on catch and effort of the industrial and artisanal fleets were made available to the Working Group. For data on catch of Pseudotolithus spp, the Working Group used the total catch series for 1990-2010. For the abundance index, the Working Group used eight abundance index series: (i) Industrial trawlers Ghana; (ii) Coastral trawlers Ghana; (iii) Artisanal Hook and line Ghana; (iv) Artisanal set-net Ghana; (v) Artisanal purse seiners Ghana; (vi) Artisanal beach seine Togo; (vii) Industrial Côte d’Ivoire; and (viii) Industrial Benin. The Working Group considered that the series of Ghanaian coastal trawlers best reflected the stock abundance trends. The initial input parameters were, r (intrinsic growth rate) = 0.50; K (initial biomass) = 6 000 tonnes and BI/K (biomass of the stock at the start of the data series, compared with the initial biomass) = 50 percent.
Assessment Model
Type:  Size-structured
Length Cohort Analysis (LCA)

To apply the LCA model, the Working Group used the length frequency data of the species/group of species of Côte d’Ivoire from 2006 to 2010. An extrapolation coefficient (total quantity of catches/total quantity of the sample) was applied to bring the length frequencies to the total catch of the zone. The FiSAT software was then used to determine the growth parameters (L∞, K, and M) for all the species. The parameters of the weight-length ratio (a and b) were obtained from FishBase. The final matrix involves individuals of between 8 and 60 cm in length.
Yield per Recruit Analysis (Y/R)
Overall Assessment Results

The model provides a satisfactory fit to the series of data on the Ghanaian coastal trawlers (Figure 3.7.4 of FAO, 2015) and the assessment results were also considered satisfactory.The assessment results are provided in Table 3.7.4 of FAO, 2015 [see also "Biological state and trend"]. They indicate that the stock is overexploited both in terms of biomass and fishing mortality. The current biomass is at the level of that corresponding to maximum balanced production (Bcur/BMSY) and is very close to the target reference point B0.1 (Bcur/B0.1). The current fishing mortality is 85 percent of that necessary to bring the stock to the level of the biomass B0.1 (Fcur/F0.1). It is 93 percent of the fishing mortality that would maintain the biomass at a sustainable level (Fcur/FSycur). After the necessary adjustment, the analysis shows that the LCA model is in keeping (consistent) with the results of the global model, that the stock is fully exploited. Nevertheless, the overexploitation resulting from the model should be treated with caution. The model provides a satisfactory fit to the data. The results indicate that the stock is fully exploited in terms of biomass and fishing mortality. Compared with the results of the assessment carried out in 2008 according to which the model did not provide a fit, it appears that there has been some improvement in the quality of the data series. However, efforts must be made to continue improving the quality of data on catch and effort and on the biological parameters of the species.
Scientific Advice

As a precautionary approach and in the hope that the data time series collected will be more complete and reliable for the next meeting, the Working Group recommends not to increase the fishing effort. The catches should not exceed the average of the last five years estimated at 2 300 tonnes.
Management
Management unit: Yes
Source of information
 
FAO. 2016. Fishery Committee for the Eastern Central Atlantic, Report of the seventh session of the Scientific Sub-Committee, Tenerife, Spain, 14–16 October 2015 / Comité des pêches pour l’Atlantique Centre-Est Rapport de la septième session du Sous-Comité scientifique. Tenerife, Espagne 14-16 octobre 2015. FAO Fisheries and Aquaculture Report / FAO Rapport sur les pêches et l’aquaculture No. 1128. Rome, Italy.  Click to openhttp://www.fao.org/3/a-i5301b.pdf
FAO. 2015. Report of the FAO/CECAF Working Group on the Assessment of Demersal Resources – Subgroup South. Accra, Ghana, 15–24 November 2011 / Rapport du Groupe de travail FAO/COPACE sur l’évaluation des ressources démersales – Sous-groupe Sud. Accra, Ghana, 15-24 novembre 2011. CECAF/ECAF Series/COPACE/PACE Séries. No. 15/76. Rome, Italy/Italie.  Click to openhttp://www.fao.org/3/a-i5138b.pdf
Bibliography
 
All references to figures, tables and bibliography in the text are found within the source of information.
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