Habitat and Biology
Climatic zone: Tropical. Bottom type: Unspecified. Depth zone: Coastal (0 m - 50 m); Shelf - Uppershelf (up to 100 m). Horizontal distribution: Neritic; Oceanic. Vertical distribution: Pelagic.
Jurisdictional distribution: Shared between nations
Considered a single stock: No
Bonga (Ethmalosa fimbriata
), otherwise called shad is found along the West African coast and it is an important species as it is mainly found in coastal waters (15–45 m depth), estuaries and sometimes in rivers. It is largely targeted by the artisanal fisheries sector but some catches are recorded in the industrial sector. Bonga in the southern region was grouped into four stocks (northern, western, central and southern). Since there was no study on molecular biology of this stock, the stocks were mainly based on the catch and effort trend of the fisheries. The stocks were grouped into the northern stock (Guinea Guinea-Bissau, Liberia and Sierra Leone), the western stock (Côte d’Ivoire, Ghana, Togo and Benin), the central stock (Nigeria, Cameroon) and the southern stock (Gabon, DR Congo, Congo and Angola).
Bonga has been intensively exploited for a long time in the subregion. As a coastal and estuarine species, bonga is mainly exploited by the artisanal fisheries and is a very important species in Guinea, Sierra Leone, Nigeria, Cameroon and Gabon. Although the stock is exploited by other countries (Guinea-Bissau, Liberia, Côte d’Ivoire, Benin, Congo and DR Congo), very little catch and effort data were reported. No data were reported by Togo, Sao Tome and Principe and Angola.Northern stock
A range of fishing gears such as ring gillnets, purse seines, beach seines and bottom driftnets are utilized. The canoes used vary from 6 to 18 m and means of propulsion vary from sails, paddle and 15–40 hp outboard motors. Over 70 percent of the total artisanal landing in Guinea and Sierra Leone is bonga.
Fishing gears such as ring gillnets, purse seines, beach seines and surface driftnets are used. The canoes used vary from 12 to 18 m with 25–40 hp outboard motors as a means of propulsion. Bonga constitutes a low percentage in the total artisanal landings for Ghana and Benin.Central stock
The gears used include purse seines, surface drift gillnets, encircling nets and beach seines. The canoes used vary from 5–9 m and 12 to 20 m. The means of propulsion range from sails, paddles and 8–40 hp outboard motors. Bonga constitutes about 15–20 percent of the total artisanal landings in Nigeria and Cameroon. Southern stock
This species is largely caught in Lobito, Angola and is targeted by the artisanal fisheries exclusively employing surface drift gillnets. The canoes are 6–7 metres in length and driven by paddles and 15–25 hp outboard motors. No data on catches were provided by Angola. Bonga constitutes about 6–10 percent of the total artisanal landings for Congo. Catch
Total annual catch of bonga by countries, fleet and stocks are presented in Table 3.2.1. No catch data were provided by Sao Tome and Principe, Angola and Togo, which was due to the insignificant quantity landed or not reported as the case in Angola where the catches are discarded at sea. Figure 3.2.1 shows the total catch of bonga per stock (north, central, west and south). For the northern stock, the catches for years 1990 to 1994 were so low as a result of no contribution in catch data from all the countries in this zone except Guinea-Bissau. From then on, there has been an increasing trend in catches of bonga with interannual fluctuations reaching a total of 86 004 tonnes in 2006. The total catch of the western stock fluctuates from year to year but the highest value was recorded in 1992. It shows a steady decrease in values from 1998 with a little fluctuation in 2000 and 2006. The total catch in the central stock has an increasing trend with some fluctuations from 1990 to 1995. There was decreasing trend till 2002 and an increase from 2003 to 2007. This probably was due to increased catches for Cameroon as result of the Bakassi conflict during which many fishers crossed over and the installation of a good data collection system through the SOWEDA project. The total catch in the other stocks (southern) have been maintained at slightly constant production level with very little fluctuation.Effort
Effort data for bonga are presented in Table 3.2.2 and Figure 3.2.2 as well as the number of trips, of fishing days or of days at sea. It should be noted that the effort presented here was for the total artisanal fisheries from respective countries and the effort from industrial fisheries from Liberia, Sierra Leone and Ghana (inshore). The effort from Guinea-Bissau was the efforts recorded from foreign fleets from the Russian Federation and Germany.
The effort data for the artisanal fishery in Sierra Leone and Ghana were measured as number of fishing trips, the rest of the countries provided effort data in number of fishing days for all fleets. No effort data were provided by Togo, Nigeria, Sao Tome and Principe, and Angola. Various trends could be observed from the efforts recorded by countries with the trends starting from the years that data were available. The overall trend for all countries was fairly stable from 1995 to 2007, except for Cameroon and Sierra Loene which have increased efforts reported. The changes in the Cameroon series could be attributed to the same reasons as mentioned in the catch trends.
DataQuality of data
In order to test the quality of the data available for the assessment, the Subgroup carried out an exploratory analysis of the catch and effort data. At a stock level for west and central, limited effort data series were available hence no CPUE) was calculated. For the northern and southern stocks the CPUE calculated from the catch and effort data of Guinea and Gabon artisanal fleets respectively targeting bonga were used separately for the assessment. Input data
The model requires complete time series of data in total catch as well as an index of stock abundance. The estimates of total catch were obtained by adding the catch estimates of all the fleets in each country and were used as total catch series. For an abundance index, one time series was used. The CPUE from Guinea (1997–2007) and Gabon (1995–2008) artisanal fisheries were chosen. For bonga, the artisanal CPUE was considered more appropriate than the industrial series
To estimate the total catch for the time series of the northern stocks, FAO catch statistics for 1997 to 2001 for Sierra Leone (artisanal) were added to the series. For the southern stock, the catch for the last three years (2006–2008) were not available for Congo. The catch for this country for the period 2006–2008 was assumed to be the same as that recorded in 2005.
The dynamic production model, implemented on an Excel spreadsheet was used. This model is further described in Appendix II.
The results obtained from northern and southern stocks were satisfactory. However, the data from western stock gave poor fit to the model.
The fitted model using the artisanal CPUE from Guinea and the total catch from the northern stock was considered satisfactory. It manages to follow the main trends in abundance indices, reacting to the variation in catches (Figure 3.6.1).
The fitted model for the southern stock (using Gabon artisanal CPUE) also provided an acceptable adjustment to the data (Figure 3.6.2).
The model results indicate that the current biomass for northern stock is close to the biomass at B0.1, and that the current fishing mortality is below that at F0.1. This stock is considered fully exploited (Table 3.6.1). The model for the southern stock shows similar results to that of the northern stock. Table 3.6.1
: Summary of the current status of the stock and the fishery for bonga Ethmalosa fimbriata
|Ethmalosa fimbriata (North/CPUE Guinea artisanal)
|Ethmalosa fimbriata (South/CPUE Gabon artisanal)
: Relationship between the estimated biomass for the last year and the corresponding biomass at F0.1
: Relationship 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.
: Relationship between the fishing mortality coefficient observed over the last year of the series and the coefficient that would provide a sustainable yield over the long term.
: Relationship between the fishing mortality coefficient observed over the last year of the series F0.1
The lack of contrast in the catch time series and abundance indices decreases appreciably the reliability of the result obtained in the modelling. The reliability was also affected by lack of complete data from the different countries. Therefore, care must be taken when interpreting these results. However, the modelling results indicate that the northern and southern stocks are fully exploited.
The data available did not fit the model for the western stock. In this zone, bonga is the secondary target species sardinella is most preferred.
Scientific AdviceFuture research
for Management consideration
- To collect and improve data collection (catch and effort) for E. fimbriata in Nigeria, Cameroon, Côte D’Ivoire, Guinea-Bissau, Guinea, Gabon, DR Congo and Benin.
- Given the absence of biological sampling for bonga in the subregion, countries are urged to collect biological data on E. fimbriata to enable better analysis of the status of the stock and the effect of the fishery on the stock.
- It is proposed that countries targeting bonga should carry out research for data/information on the bonga fishery.
As a precautionary measure, catch level should not be increased for the northern stock and not exceed the average of the last five years (79 000 tonnes). For the southern stock as a precautionary measure catch level should not exceed the total average year’s catch (11 000 tonnes).
This Working Group could not produce results on the assessment of the central stock as a result of lack of discontinuous effort data from Cameroon and no effort data from Nigeria. It was therefore recommended that efforts should not increase over the average of the last five years (58 000 tonnes).
For the western stock, there is no recommendation due to insufficient data from countries within this zone.
Biological State and Trend
Ethmalosa fimbriata North (Guinea and Sierra Leone)
Ethmalosa fimbriata Central (Nigeria and Cameroon)
Ethmalosa fimbriata West (Ghana, Togo and Benin)
Ethmalosa fimbriata South (Gabon, Congo, DR Congo and Angola)
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