Habitat and Biology
Bottom type: Unspecified. Depth zone: Coastal (0 m - 50 m); Shelf - Uppershelf (up to 100 m); Shelf - Edgeshelf. Horizontal distribution: Neritic. Vertical distribution: Demersal/Benthic.
The white grouper (Epinephelus aeneus
) is a coastal demersal species belonging to the serranid family. Its bathymetric distribution extends from 20 to 200 m in depth, but the main fishing zone is between 30 and 60 m. The species lives on rocky bottoms of the continental shelf.
The young individuals (less than 30 cm) are mainly found in coastal zones, particularly in estuaries. After this they are found at greater depths (between 30 and 100 m) both in rocky zones and above all in very sandy zones.
The two main reproduction zones are the Petite Côte in Senegal and south of the Baie du Lévrier in Mauritania. The highest concentration of juveniles is found in the mangrove estuary of the Sine Saloum central delta in Senegal.
It is a voracious predator feeding on fish, cephalopods and crustaceans.
Jurisdictional distribution: Shared between nations
Considered a single stock: Yes
A single management stock of Epinephelus aeneus
was considered for the three countries (Mauritania, Senegal and The Gambia).
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
spp., Dentex macrophthalmus
, Pagrus caeruleostictus
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.
For catch data, the Working Group combined the total catches of all the fleets from the three countries (Mauritania, Senegal and The Gambia). For the abundance indices’ series, the ice canoes CPUE series from the Senegalese artisanal fishery gave the best fit.
Schaefer dynamic production model
The Schaefer dynamic production model implemented in an Excel spreadsheet was used to assess the state of the stock and the fisheries of Epinephelus aeneus
. This model is described in detail in Appendix 2.
The fit of the model using the ice canoe CPUE was judged to be satisfactory.
The results indicate that the stock is becoming extinct. Current biomass is below that corresponding to the B0.1 biomass. Current fishing effort is greatly above that producing maximum sustainable yield at current biomass levels (Table 1).
Table 1: Indicators on the state of the stock and the fishery of Epinephelus aeneus in the northern CECAF zone
|| F cur /F SYcur
|| B cur /B 0.1
|| F cur /F 0.1
|| B cur /B MSY
|| F cur /F MSY
|Epinephelus aeneus (Mauritania, Senegal and The Gambia)/CPUE Senegalese ice canoes
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.
Bcur/B0.1: Ratio between the estimated biomass for the last year and the biomass corresponding to F0.1.
Fcur/F0.1: Ratio between the observed fishing mortality coefficient during the last year of the series and F0.
Bcur/BMSY: Ratio between the estimated biomass for the last year and the biomass coefficient corresponding to FMSY.
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.
The results show that the Epinephelus aeneus stock in the region is at risk of extinction. These results agree with the abundance indices from the scientific surveys in Mauritania and the results obtained during the last Working Group. Declared catches in Senegal probably come from neighbouring waters.
Scientific Advicefor Management considerations
Taking into consideration the results from the assessment and the trends in the CPUEs, as well as those of the abundance indices from the surveys, the Working Group considers the stock to be at risk of extinction and reiterates it recommendation that all fishery directed at this species be halted.
Biological State and Trend
Exploitation state: DepletedExploitation rate: Fcur/F0.1= 970%
Abundance level: Bcur/B0.1= 5%
Stock at risk of extinction.
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
The bibliographic references are available in the report included in "Source of Information".