Fishery Resources Monitoring System

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West African croakers - Senegal and Gambia, 2006
Marine Resource  Fact Sheet
Status of stocks and resources 2007
West African croakers - Senegal and Gambia, 2006
Fact Sheet Citation  
Otolithe (Pseudotholithus spp) Senegal, Gambie 15°50''-12°;18''
Owned byFood and Agriculture Organization (FAO) – More
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Species:
FAO Names: en - West African croakers nei, fr - Otolithes nca, es - Corvinas africanas nep, ru - Горбыли-капитаны
Geographic extent of West African croakers - Senegal and Gambia
Main Descriptors
Considered a single stock: No        Spatial Scale: Regional
 
 
Habitat and Biology
Bottom type: Soft_bottom_muddy_or_muddy-sand; Soft_bottom_clean_sand.   Depth zone: Coastal (0 m - 50 m); Shelf - Uppershelf (up to 100 m); Shelf - Edgeshelf.   Horizontal distribution: Neritic.   Vertical distribution: Demersal/Benthic.  


The Pseudotolithus spp. consists of P. elongatus, P. typus, P. senegalensis and P. brachygnatus. These are coastal species distributed over the whole region. They are found on muddy, sandy and rocky bottoms. Smaller individuals can be found along the coast, but rarely in estuaries. The species feeds mainly on fish, shrimp and crabs.

Geographical Distribution
Jurisdictional distribution: Shared between nations

Water Area Overview
Spatial Scale: Regional

Geo References
Resource Structure
Considered a single stock: No


Croakers are mainly distributed and exploited in the southern part of the region that is Senegal and The Gambia. Consequently, the Working Group decided to consider them as a shared stock between The Gambia and Senegal and to assess them as a single stock for both countries.
Exploitation
 

Due to their generally elevated market value, coastal demersal resources are very sought after in all four of the northern CECAF zone countries (Morocco, Mauritania, Senegal and The Gambia). They are exploited by artisanal and industrial fleets (national and foreign). The fisheries are multi-purpose and demersal fish species often represent bycatch of other specialized fisheries such as the cephalopod, hake or shrimp fisheries.

The demersal fish to be assessed this year are the Pagellus bellottii, Pagellus acarne, Pagellus spp., Dentex macrophthalmus, Pagrus caeruleostictus, Sparus spp., Arius spp., Pseudotholitus spp. and Epinephelus aeneus. Overall catch for these species fluctuates between around 20 000 and 37 000 tonnes.

Demersal fish resources in Morocco are exploited by a heterogeneous fleet of Moroccan cephalopod freezer trawlers (Ceph. N), coastal fishing vessels: trawlers and longliners (coastal), artisanal boats (artisanal), leased boats and Russian vessels operating under the Morocco-Russia fishing agreement. Only the longliner and some of the artisanal boats target demersal fish, other vessels catch them as bycatch.

In Mauritania exploitation of demersal resources is carried out by various types of trawler: foreign cephalopod (Ceph. E), national cephalopod (Ceph. N), foreign and national hake (Hake), foreign and national shrimp (Shrimp), foreign pelagic trawlers (Pelagic) and foreign and national demersal fish trawlers (Fish).

In Senegal demersal resources are mainly caught by artisanal boats using fishing lines. Two categories exist: motorized line canoes (MLC) carrying out daily trips and ice canoes (IC) equipped with ice that do trips lasting several days. These resources are also caught by Senegalese and foreign trawlers fishing under fishing agreements. Each of these fleets is made up of freezer and ice trawlers. The artisanal fleet is currently composed of 12 619 canoes and the number of Senegalese trawlers was 100 in 2005.

In the Gambia, it is foreign freezer trawlers (PI) and artisanal canoes that exploit demersal resources.


Assessment
 
Data

The catch series of Dentex macrophtalmus for Morocco, Mauritania and Senegal and the abundance index for the surveys in Mauritania was used as inputs to the model.

Many countries do not separate all the various Dentex species and other Sparidae species in their catch reporting and it could be that what is reported as Dentex macrophtalmus is in fact one of the other Dentex species, hence causing a mismatch between the reported and true catch of this species.

Several other abundance series were considered by the Working Group, but given that Dentex macrophtalmus is not a targeted species and that the species is found principally in deeper waters, it was thought that none of the other abundance indices available to the Group would give a good indication of the abundance of this species. For instance the cephalopod trawlers in Morocco cover mainly the coastal area up to 100 m depth and thus cover mostly the juvenile part of the population, as observed from the length distribution of the catches (not presented to the Working Group).
Assessment Model
Type:  Biomass-aggregated
Schaefer dynamic production model

The Schaefer dynamic production model, implemented in an Excel spreadsheet, was used to assess the state of the stock and fisheries of Pseudotholitus spp (FAO, 2007).
Results


The input data used in the model did not provide a good fit. The CPUE could not explain the catch as there were sharp oscillations in annual landings. This could be attributed to the fact that Pseudotolithus spp. is caught together with high value fish species targeted by industrial fleets in both countries.

While the fit to the model was considered poor, observations of the croaker landings indicate that the effort targeting these species is increasing due to the existence of a market. The Working Group also noted, that in spite of uncertainties relating to the yields of this group of species, the general trend observed was a gradual increase characterized by oscillations.
Assessment Model
Type:  Size-structured
Length Cohort Analysis (LCA)

Length Cohort Analysis (LCA) was used with length composition data of the artisanal fisheries in Senegal.
Results


The Length Cohort Analysis (LCA) on Pseudotolithus senegalensis indicated an inconsistency due to length frequency samples not raised to population size. The results of the LCA are therefore not suitable for management advice.


Scientific Advice

for Management considerations

Croakers, Pseudotolithus spp. are considered to be subject to high fishing pressure as exerted on all demersal fish species. Although the assessment was inconclusive due to inadequate catch and effort data available to the Working Group, it was recommended that, as a precautionary approach, fishing effort should not exceed the current level.
Source of information
 
FAO Fishery Committee for the Eastern Central Atlantic/Comité des pêches pour l’Atlantique Centre-Est. “Report of the Working group on the assessment of demersal resources, Sub-Group North” Banjul, The Gambia, from 6 to 14 November 2007. “Rapport du Groupe de travail FAO/COPACE sur l’évaluation des ressources démersales dans la zone Nord” Banjul, Gambie, du 6 au novembre 2007. Rome, FAO . 2010. .
Bibliography
 

The bibliographic references are available in the report included in "Source of Information".
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