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Dentex - Côte d'Ivoire, Ghana, Togo and Benin
Marine Resource  Fact Sheet
CECAF Scientific advice 2016
Dentex - Côte d'Ivoire, Ghana, Togo and Benin
Fact Sheet Citation  
Denté (Dentex spp) - Côte d'Ivoire, Ghana, Togo et Bénin
Owned byFood and Agriculture Organization (FAO) – More
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Species:
Geographic extent of Dentex - 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
FAO Categories
Exploitation stateUncertain/Not assessed

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); Shelf (50 m - 200 m).   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


The Dentex spp. group defined by the Working Group, includes Dentex canariensis, D. gibbosus, Dentex angolensis and Pagrus caeruleostictus and P. caeruleostictus. These species are not separated in the catch, as is the case with Dentex angolensis and Dentex congoensis. For the assessment, the Working Group therefore considered this group of species as a single stock.
Exploitation
 
Fishery Indicators
TypeMeasureValueUnitTime period
ProductionCatch 5118tonnes1990
Catch 3477tonnes1991
Catch 3474tonnes1992
Catch 4321tonnes1993
Catch 3196tonnes1994
Catch 3855tonnes1995
Catch 4397tonnes1996
Catch 3783tonnes1997
Catch 5749tonnes1998
Catch 4824tonnes1999
Catch 5069tonnes2000
Catch 5321tonnes2001
Catch 4992tonnes2002
Catch 4451tonnes2003
Catch 7559tonnes2004
Catch 9604tonnes2005
Catch 10025tonnes2006
Catch 11006tonnes2007
Catch 5836tonnes2008
Catch 7649tonnes2009
Catch 5891tonnes2010
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, with the exception of the Ivorian artisanal fleet. For data on catch of Dentex spp, the Working Group used the total catch series for 1990-2010. For the abundance index, the Pour l'indice d'abondance, les données des campagnes du R/V DR. FRIDTJOF NANSEN survey data for the 1999-2007 were used by the previous Working Group; but this series is not continuous, and that is why it is not used in the present assessment. The Working Group used eight 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 Côtte d’Ivoire and (viii) Industrial Benin. The initial input parameters are as follows: r (intrinsic growth rate) = 0.65; K (initial biomass)= 10 000 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 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 of the FAO was then used to determine the growth parameters (L∞, K, and M) for all the species. The parameters of the weightlength ratio (a and b) were obtained from the FishBase database.
Yield per Recruit Analysis (Y/R)
Overall Assessment Results

The Schaefer dynamic production model did not provide a satisfactory fit to the different series of abundance indices obtained from the fisheries of the four countries concerned. After the necessary adjustments, the diagnosis of the LCA model also did not give reliable results. The available data appear to be unreliable and no satisfactory results were obtained. It is noted that the results of the last assessmet indicated that the species has been overexploited.
Scientific Advice

As a precautionary measure and in expectation of more complete and reliable data series being collected in the future and knowing this species was considered to be overexploited during the last assessment and that the CPUEs are at a very low level, the Working Group recommends a reduction in fishing effort, and the catch should not be higher than the average of the last three years which is about 6 000 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
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