Biological State and Trend
Merluccius ssp. (Mauritania)
Merluccius ssp. (Senegal)
Habitat and Biology
Bottom type: Soft bottom - clean sand; Soft bottom - muddy or muddy-sand. Depth zone: Shelf (50 m - 200 m); Slope (200 m - 1000 m). Horizontal distribution: Neritic; Oceanic. Vertical distribution: Demersal.
Two species of black hake, both found only in the East-Central Atlantic, live along the Moroccan, Mauritanian and Senegalese coasts. The Senegalese hake (Merluccius senegalensis
– Cadenat, 1950) is found between 33 °N and 10 °N, whilst the Benguela hake (Merluccius polli
– Cadenat, 1950) is found between 20 °N and 18.5 °S (Lloris, Mattalana and Oliver, 2005).
At a taxonomic level it is very difficult to differentiate between the two species and for this reason they are not separated in commercial statistics. The maximum length is however different for the two species, 87 cm for the Senegalese hake and 80 cm for the Benguela hake (Lloris et al., 2003).
According to studies carried out by Boukatine (1986) and by Overko, Boukatine and Ly (1986), the most abundant species on the Mauritanian coast is the Senegalese hake. Studies carried out during IMROP scientific surveys in 2000 and 2001 (FAO, 2006) as well as results from scientific observers surveys on board Spanish trawlers and hake longliners between 2003 and 2007, show that M. senegalensis
is found at depths of less than 500 m whereas M. polli
is found more at greater depths of up to 1 000 m (Fernández et al., 2007). Observations in Senegal also confirm that M. senegalensis
is found more in coastal waters and M. polli
in deeper waters (Caverivière et al., 1986; FAO, 1986).
Both species spawn during the cold season, between October and March (Wysokinski, 1986; Sobrino, Cervantes and Ramos, 1990). It would also appear that both species migrate latitudinally (García, 1982).
Jurisdictional distribution: Shared between nations
Considered a single stock: No
No detailed studies are available on black hake stock identity.
Catch and effort series for black hake from the IEO, IMROP and CRODT databases were used to analyse the Mauritanian and Senegalese stocks.
The Spanish hake trawler CPUE series from the IEO for both zones were used as an abundance indice.
Furthermore, the model was adjusted to take into account catches by Spanish freezer trawlers.
Schaefer dynamic production model
The dynamic Schaefer production model implemented on an Excel spreadsheet was used to assess the state of the black hake stock. This model is described in detail in Appendix 2.
For both stocks (Mauritania and Senegal), the production model fits the CPUE series of the Spanish fleet quite well. The results show that both stocks are overexploited. The biomass of black hake in both zones is below that producing maximum sustainable yield. Current fishing effort is 26 percent greater than the F0.1 level (Table 1).
Table 1: Summary of the results on the state of the Merluccius spp. stock 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
|Merluccius ssp. (Mauritania)/ Spanish fresh fish trawlers
|Merluccius ssp. (Senegal)/ Spanish fresh fish trawlers
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 of the assessment show that both stocks are overexploited. In Mauritania, current biomass is below the B0.1 target biomass and current fishing effort is around 25 percent above the effort corresponding to the target biomass. In Senegal biomass is also below the target biomass. Current effort is however below the effort corresponding to the target biomass.
Scientific Advicefor Management considerations
The Working Group recommends not increasing current effort for both stocks. Catch of both stocks should not exceed 7 000 tonnes in Mauritania and 600 tonnes in Senegal.
for Future research
The Working Group gives priority to the following recommendations:
- Improve the follow up of bycatch of black hake by other fleets in Senegal.
- Establish a programme of observation at sea in order to break down catches of black hake by species in Senegal and Morocco and to continue with the current IEO programme in Mauritania.
- Study in greater depth the influence of environmental parameter on the abundance of resource in the subregion.
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".