Habitat and Biology
Bottom type: Hard rocky bottom. Depth zone: Coastal (0 m - 50 m); Shelf (50 m - 200 m); Slope (200 m - 1000 m). Horizontal distribution: Neritic; Oceanic. Vertical distribution: Demersal/Benthic.
The large-eye dentex is distributed over the whole sub-region. The adults are normally found at between 100–300 m depth, although juveniles can also be found in shallower waters.
Jurisdictional distribution: Shared between nations
Considered a single stock: Yes
The large-eye dentex (Dentex macrophthalmus
) is found in Morocco, Mauritania, Senegal and The Gambia. Due to the lack of detailed information the Working Group decided to consider a single stock for the whole sub-region.
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.
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).
The Schaefer dynamic production model, implemented in an Excel spreadsheet, was used to assess the state of the stock and fisheries of Dentex macrophtalmus
. The model is described in detail in Appendix 2 (FAO, 2007).
Overall Assessment Results
The available data were not sufficient to obtain conclusive results for the assessment of Dentex macrophtalmus
The model did not provide an acceptable fit to the data. The poor fit of the model resulted from the difficulty in explaining the observed high catches given the very low abundance index in recent years.
Although no reliable result was obtained from the model, care should be taken in the management of this species as the survey abundance index from Mauritania indicates very low levels of this species.
Scientific Advicefor Management considerations
The quality of the fit did not allow precise conclusions to be drawn on the state of the stock. However, given the low catch rates observed in recent years in the surveys in Mauritania a precautionary approach would consist in not increasing current fishing effort on this species.
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".