Habitat and Biology
Climatic zone: Tropical. Bottom type: Unspecified. Depth zone: Unspecified. Horizontal distribution: Unspecified. Vertical distribution: Pelagic.
Jurisdictional distribution: Shared between nations
In the region, anchovy is mostly exploited by beach seines and purse seines which are non
Anchovy is found in waters with strong upwelling, which explains the availability of this species in different territorial waters of the countries in the region during the upwelling season. In certain countries, anchovy consumption is part of the eating habits of the population. This is the case in Ghana, Togo, Benin and Congo where large quantities are landed by beach seine and purse seine. In other countries, anchovies are mixed with other small species in landings. Identification is therefore very difficult. This is the case in Nigeria and Cameroun where the species is present, but no data are available. In Guinea, anchovy is considered a non valuable bycatch and is consequently discarded. Catch
Six countries in the region have catch data for this species. These are Sierra Leone, Ghana, Togo, Benin, Angola and Congo. The data from 2006 to 2008 for Congo have not been provided because the scientist from Congo was absent. These catch data, divided by zone, are given in Table 4.2.1 and Figure 4.2.1. These stocks are the northern stock (Guinea and Sierra Leone), the western stock (Ghana, Togo and Benin) and the southern stock (Congo and Angola).
The northern stock is only represented by Sierra Leone. The catch data varied widely between 2002 and 2008. However, they peaked in 2006 with 151 tonnes.
For the western stock, the total catch of Engraulis encrasicolus
varied from 82 220 tonnes and 48 415 tonnes from 1990 to 2008 with peaks in 1996, 2000 and 2003. Generally there is a decreasing trend in the western stock and the graph that shows this trend is identical to that of the anchovy catch in Ghana, the biggest fishery.
The southern stock comprises the catch from Congo and Angola. Averaging around 499 tonnes yearly this catch has not undergone any major fluctuation.
The catch from Angola fell from three tonnes in 1998 to one tonne in 2003. This species does not seem to be a target species for the semi-industrial and industrial fisheries of Angola. They constitute bycatches. In 2002, the increase in catch observed in Congo is probably due to the increase in beach seine units. Effort
Effort over the whole region is expressed in fishing days as shown in Table 4.2.2 and Figure 4.2.2. Most of this effort came from the purse seine and the beach seine, the latter being used in the nursery area. A beach seine can be used up to twice a day. When a beach seine makes good catches, this encourages others to go out as well.
The vessels used in this fishery are generally monoxylous Ghanaian canoes of between 14 and 18 metres in length in the western stock and 6 to 18 metres in the northern and southern stocks. Most are powered by 10 or 25 hp engines. In some countries, some of the beach seines are not motorized.
The time series of landings of Engraulis encrasicolus
for the western stock (Côte d’Ivoire, Ghana, Togo and Benin) from 1990 to 2008 were used for the production model.
To test the data quality for the assessment, the subgroup carried out a preliminary analysis of the available data. The abundance index from Ghana was used for this analysis while that from Togo was chosen to adjust the model
The Schaefer dynamic production model was used on an Excel spreadsheet (the model is described in Appendix II).
Schaefer dynamic production model
The model did not provide reliable results with the abundance index from Ghana.
For Engraulis encrasicolus
, the model shows a varying abundance over the years (Figure 4.6.1) and the Working Group accepted the CPUE for Togo because the data adjustment was acceptable.
The results show that current biomass represents 77 percent of the biomass corresponding to B0.1
and the observed fishing mortality in 2008 is 89 percent of the fishing mortality F0.1
. At the end of this assessment, it appears that the stock is fully exploited.Table 4.6.1
: Summary of the state of the stock of Engraulis encrasicolus
|Stock ||Bcur/B0.1 ||Fcur/FMSY ||Fcur/F0.1 ||Fcur/FSYcur |
|Engraulis encrasicolus (Western/CPUE Togo) ||77% ||80% ||89% ||69% |
: Ratio between the estimated biomass for the last year and the biomass corresponding to F0.1
: Ratio between the fishing mortality coefficient observed over the last year of the series and the coefficient that would provide a maximum sustainable yield over the long term.
: Ratio between the fishing mortality coefficient observed over the last year of the series and F0.1
: Ratio between the fishing mortality coefficient observed over the last year of the series and the coefficient that would provide a sustainable yield at the current biomass level.Discussion
The model results should be considered with precaution for the western stock. They show that the stock is fully exploited in its current state. But, in reality, strong fishing pressure has been put this resource. There are also fluctuations in the western stock probably due to environmental factors. This species, as previously discussed, is essentially caught by beach seines and purse seines whose fishing effort increases continuously. Furthermore, these fishing gears are not selective.
It is worth noting that the surveys carried out by the R/V DR. FRIDTJOF NANSEN show a decline in the biomass of the western stock after 2004.
The artisanal catches from Côte d’Ivoire are not available. Consequently, the absence of this data could influence the results of the assessment.
Scientific AdviceFuture research
for Management consideration
- Ensure the collection of catch and effort data relating to gears that exploit anchovy to make a better stock assessment.
- Côte d’Ivoire should provide the relevant data.
- Continue acoustic surveys by the R/V DR. FRIDTJOF NANSEN and make biomass estimates for anchovy.
- Carry out national surveys and take into account depths below 15 m using appropriate methods.
As a precautionary measure for the western stock (Ghana, Togo and Benin), catches should not exceed the average recorded over the last three years (40 000 tonnes).
Biological State and Trend
Engraulis encrasicolus West (Côte d’Ivoire, Ghana, Togo and Benin)
Engraulis encrasicolus South (Congo)
Source of information
Report of the FAO/CECAF Working Group on the Assessment of Small Pelagic Fish – Subgroup South Accra, Ghana, 19–28 October 2009./Rapport du Groupe de travail FAO/COPACE sur l'évaluation des petits poissons pélagiques – Sous-groupe Sud Accra, Ghana, 19-28 octobre 2009. http://www.fao.org/docrep/018/i2909b/i2909b.pdf