Habitat and Biology
Climatic zone: Unspecified. Bottom type: Unspecified. Depth zone: Coastal (0 m - 50 m); Shelf (50 m - 200 m); Slope - Upperslope (200 m - 500 m). Horizontal distribution: Unspecified. Vertical distribution: Pelagic.
Jurisdictional distribution: Shared between nations
Considered a single stock: NoEngraulis encrasicolus
, commonly called anchovy, is found in the southern CECAF region between Guinea and Angola. A pelagic species often found in large shoals, Engraulis encrasicolus
lives in shallow waters and sometimes in depths to 400 m.
Anchovy represents one of the characteristic species of the upwelling. The juveniles are found in the coastal fringe and represent the dominant pelagic species in catches. Anchovy is also found in estuaries.
In the region anchovy is mostly exploited by beach seines and purse seines which are non-selective gears.
Anchovy is found in waters with strong upwelling which explains the availability of this species in the 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 for 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 Cameroon where the species is present, but no data are available. In Guinea anchovy is considered a non valuable bycatch and is consequently discarded.
Five countries in the region have catch data for this species. These are Sierra Leone, Ghana, Togo, Benin and Congo. 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 catches varied strongly between 2002 and 2005. The decline observed in 2003 and 2004 can be attributed to the lack of availability of data due to logistical problems. Catch in 2005 was 41 000 tonnes.
For the western stock, total catch of Engraulis encrasicolus
varied from 42 000 tonnes to 105 000 tonnes between 1990 and 2004, with an average of around 76 000 tonnes annually and 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 anchovy catch in Ghana, the biggest fishery.
The southern stock comprises the catch from Congo which totalled around 5 500 tonnes for the period 1998–2005. Averaging around 500 tonnes yearly, this catch has not undergone any major fluctuation. Nevertheless, in 2002, the increase in observed catch 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. Most of this effort came from the purse seine and the beach seine, this last being used in the nursery area. Fish is probably important. A beach seine can be used up to twice a day. When a beach seine makes good catches, this incites the 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 Schaefer logistic production model was used on an Excel worksheet.
The time series of landings of Engraulis encrasicolus in the western stock (Ghana, Togo and Benin) from 1990 to 2004 where used for the production model.
To test the data quality for the assessment, the sub-group carried out a preliminary analysis. The results obtained using the abundance index from Togo was thought to reflect the situation in the fishery in the western stock.
Thus the abundance indices from the commercial fisheries in Togo were used to estimate the model parameters.
Data from the Côte d’Ivoire were not considered during the assessment.
Overall Assessment Results
For Engraulis encrasicolus
, the model shows a varying abundance over the years (Table 1).
The results show that current biomass is below that at B0.1 and that current fishing mortality is below the sustainable level at this level of biomass.
Table 1: Summary of the state of the stock
|Engraulis encrasicolus/CPUE Togo
Bcur/B0.1: Ratio between the estimated biomass for the last year and the biomass corresponding to F0.1.
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.
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.
Fcur/F0.1: Ratio between the observed fishing mortality coefficient during the last year of the series and F0.
According to the assessment, it appears that the stock is fully exploited. It should be noted that the R/V DR. FRIDTJOF NANSEN surveys show a decrease in stock after 2004.
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 on this resource. This species, as with that previously discussed, is essentially caught by beach seines and purse seine whose effort increases continuously. Furthermore, these gears are not selective due to the mesh size.
Scientific AdviceFuture research
for Management considerations
- Harmonize the system of data collection on effort for the gears that exploit anchovy to better be able to assess the stock.
- Continue biomass estimates for anchovy during the R/V DR. FRIDTJOF NANSEN acoustic surveys and national surveys if possible.
- Continue acoustic surveys of depths of less than 15 m using appropriate methods.
It is recommended that a system of effort regulation be put in place for beach seines and purse seines and that the mesh size of these gears be regulated.
As a precautionary measure, catch level should not exceed the average level of the 5 last years
(78 000 tonnes for Western stock, 530 tonnes for Southern stock).
There was no assessment of the Congo stock, but the CPUEs of the last two years are stable. The acoustic abundance was estimated at 2 000 tonnes in 2005. It is therefore recommended that precautionary measures be adopted and that catches should not exceed the average of the last five years (530 tonnes).
Biological State and Trend
Western stock (Ghana, Togo, Benin)
Exploitation state: Fully exploitedExploitation rate: Fcur/F0.1: 92 %
Abundance level: Bcur/B0.1: 88%
Acoustic survey estimates showed a decrease in biomass in 2005 and 2006.
Southern stock (Congo)
No assessment made for Southern stock. Catch rates stable last 2 years. Acoustic estimates of 2000 tonnes in 2005.
Source of information
FAO Fishery Committee for the Eastern Central Atlantic/Comité des pêches pour l’Atlantique Centre-Est. “Report of the FAO/CECAF Working Group on the Assessment of Small Pelagic Fish – Subgroup South” Limbe, Cameroon, 25 September–1 October 2006
“Rapport du Groupe de travail FAO/COPACE sur l’évaluation des petits poissons pélagiques – Sous-Groupe Sud” Limbé, Cameroun, 25 septembre-1er octobre 2006
Rome, FAO . 2009
The bibliographic references are available in the report included in "Source of Information".