Biological State and Trend
Ethmalosa fimbriata – Senegal and Gambia
Ethmalosa fimbriata - Mauritania
Habitat and Biology
Climatic zone: Temperate. Bottom type: Unspecified. Depth zone: Coastal (0 m - 50 m); Shelf - Uppershelf (up to 100 m); Shelf - Deepshelf (100 m - 200 m). Horizontal distribution: Neritic. Vertical distribution: Pelagic.
Jurisdictional distribution: Shared between nations
Considered a single stock: Yes
The assumption that the West-African bonga shad stock is a single stock was maintained by the Working Group. A detailed description of the stock is given in the 2007 report of the FAO Working Group. According to the synoptic presentation of biological data on the bonga shad by E. Charles Dominique (1982), the bonga shad (Ethmalosa fimbriata) is mainly concentrated in The Gambia, Mauritania and Senegal.
The bonga shad is mainly exploited by the artisanal fisheries in The Gambia and Senegal and recently in Mauritania. It is mainly fished using surround gillnets.
As in the last two years, the largest catch of bonga is found in Mauritania constituting about 56 percent of total catches of this species in the region. The bonga fishery is a major source of feed for the new fishmeal factories in Nouadhibou since 2008. Total catches
The total catches of the bonga resource in the subregion are presented in Table 7.2.1 and Figure 7.2.1.
Since 2007 the data from Mauritania have been included in Figure 7.2.1.
In Mauritania, a correction was made to the catch data series on bonga from 2007 to 2010 based on the results of surveys carried out with fishmeal factories in Nouadhibou. This updated data was complemented by the 2011 data. Overall, total catches of bonga in the subregion have been relatively stable in the last three years of the catch series between 2009 and 2011, with a slight decrease between 2010 and 2011. Prior to this period, catches were declining, from 49 000 tonnes in 2001 (the largest catch in the series) to about 21 000 tonnes in 2006 (Figure 7.2.1). Overall, total catches of bonga have been increasing in the subregion since 2008. Catches of bonga in The Gambia and Senegal have been on a downward trend since 2003 despite fluctuations in catch levels. A stable state of annual catch levels was observed in The Gambia in the last four years while in Senegal the catches slightly oscillated during the same period. However in Mauritania, there has been a sharp increase in catches since 2008; the estimated average catch of this series in the last five years amounts to around 35 797 tonnes. The marked increase in catches of bonga in Mauritania since 2009 has been attributed to the establishment of several fishmeal factories four of which are functional. About ten other factories are presently under construction. Fishing effort
In Mauritania, the effort data from 2006 to 2010 has been included based on surveys conducted with the factories and databases of SSPAC (APAM: GCP/MAU/032/SPA) of IMROP, complemented by the 2011 data. The artisanal fisheries targeting bonga use surround gillnets in The Gambia and Senegal, but also the purse seiner in Mauritania. Effort data for the region are presented in Table 7.2.2 as number of fishing trips. Recent developments
The marked increase in catches of bonga in Mauritania since 2009 has been attributed to the establishment of several fishmeal factories four of which are functional. Another ten factories are presently under construction.
A length frequency average based on the total catch in the areas concerned was used. The growth and mortality parameters used (Table 7.6.1) in the two models were estimated by the Group based on the analysis of the modal progression using the FISAT II - Version 1.2.2 software (FAO-ICLARM Stock Assessment Tools) (Gayanilo, Sparre and Pauly, 2005). The parameters of the length-weight ratio used come from the FishBase data base.
Overall Assessment Results
The results of the LCA and yield-per-recruit in Senegal-Gambia and Mauritania were satisfactory (Figures 7.7.1 and 7.7.2).
In Senegal–Gambia, the model results show that the level of exploitation is below F0.1. This indicates that the stock is overexploited. This level of exploitation mainly concerns the small fish.
For Mauritania, the results show that the exploitation is close to F0.1. The stock is fully exploited and exploitation mainly involves the large fish.Discussion
This model was achieved based on the existence of two stocks. However, the Working Group emphasized the lack of information needed to make assumptions on the stock identity of bonga in the subregion and its geographical distribution as well as the paucity of biological data on the different fisheries. Accordingly, the results obtained from the analysis should be taken with caution.
The Working Group could not make projections for the next five years due to the unreliable results.
Scientific AdviceFuture research
The discussions on the two previous years’ recommendations and the available data revealed that countries in the region conducted acceptable biological sampling, and that problems noted were only limited to The Gambia.
The recommendations made in 2010 were carried out by Mauritania and Senegal in 2011, The Working Group noted the progress achieved and therefore maintained the following recommendations:
for Management consideration
- Develop a strategy in Mauritania, Senegal and The Gambia to monitor the biological data of bonga in the different fisheries (including the standardization of length measurements).
- Estimate the biological parameters of bonga and prepare length frequency distribution series for analysis before the next meeting of the Working Group.
- Initiate biological sampling of bonga in The Gambia in order to have length frequency data on this species.
- Review and complete the catch series and fishing effort on bonga in the subregion.
As a precautionary measure, the Working Group recommended that the current fishing effort on bonga should not be increased in 2011 in the northern unit of Mauritania and that the fishing effort on bonga in the Gambia and Senegal should be reduced.
Source of information
Report of the FAO Working Group on the Assessment of Small Pelagic Fish off Northwest Africa./Rapport du groupe de travail de la fao sur l’évaluation des petits pélagiques au large de l’afrique nord-occidentale. Dakar, Senegal, 21–25 May 2012. http://www.fao.org/docrep/019/i3346b/i3346b.pdf