Habitat and Biology
Bottom type: Unspecified. Depth zone: Coastal (0 m - 50 m); Shelf - Uppershelf (up to 100 m). Horizontal distribution: Littoral. Vertical distribution: Demersal/Benthic.
Jurisdictional distribution: Unspecified
Considered a single stock: No
spp. group consists of: Arius heudolotii
, Arius gambiensis
, and Arius mercatoris
. The Marine catfishes, Arius
spp. in the shelves of Senegal and The Gambian are considered as a single stock and therefore, the Working Group decided to assess the stock as a single management unit.
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.
Input data into the model was total catch of marine catfishes in both The Gambia and Senegal, with different abundance indices from the PIS CON, PIS GLA fleets in Senegal and all other fleets operating in the two countries.
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 Arius
spp. (FAO, 2007).
Several runs of the model using the above data have revealed that the available data were not sufficient to obtain conclusive results for assessment of marine catfishes in both countries. The model gives inconsistent results.
The poor fit of the model could be explained by the fact that the CPUE used are not a true reflection of stock abundance but represent more the fishing strategies employed by the fleet operating in the continental shelves of The Gambia and Senegal. Marine catfishes are not considered the main high value species targeted by the industrial fleet but are nonetheless landed as bycatch. They are coastal species and are not targeted.
Length Cohort Analysis (LCA)
Length Cohort Analysis (LCA) was used with length composition data of the artisanal fisheries in Senegal.
The Length Cohort Analysis (LCA) results were also not reliable and could not be used for any management decision.
Scientific Advicefor Management considerations
Considering the large catches recorded over the last few years, any increase in effort should be avoided until more detailed assessments are available.
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".