Habitat and Biology
Bottom type: Unspecified. Depth zone: Coastal (0 m - 50 m); Shelf - Uppershelf (up to 100 m). Horizontal distribution: Neritic. Vertical distribution: Demersal/Benthic.
Data on Penaeus notialis
were provided by surveys carried out by the research vessels in Mauritania in 2005 and 2006. No sampling of commercial landings for biological study has been carried out in Mauritania over the last few years.P. notialis
has a long reproduction period in Mauritania (mature females have been found by the Spanish fleet from July to April). Length at first maturity is estimated a 17.75 mm (total length) for males and 38.46–46.14 mm for females. It is important to underline that this study is being continued, even if it is not conclusive (fertile females were not found either in 2005 or 2006).
The main biological characteristics of this stock have been presented in previous CECAF Working Group reports on demersal fish.Penaeus notialis
reaches a length of 1.8 cm (total length) at the age of 3–4 months. At this age, the species migrates from the fluvial estuaries to the sea where it grows until the age of 22 months, at which age it reaches its maximum length (around 20 cm total length) (Garcia, 1976).
Length sampling of Penaeus notialis
catches by the Spanish fleet operating in Mauritania were carried out by the IEO, but length composition of this species was not presented to the Working Group.
Jurisdictional distribution: Unspecified
Considered a single stock: No
Two different stock units of P. notialis
were identified in the zone. One reproduction and breeding zone is situated in the Banc d’Arguin (Mauritania) and another at the mouth of the Senegal river. The unit associated with the Senegal river is considered to be composed of four sub-units associated with the Senegal, Saloum, Gambia and Casamance rivers. However, it is not possible to obtain broken down information (landing and effort) on these different sub-units. For this reason the Working Group decided to assess only two units, one in Mauritania and the other in Senegal and The Gambia.
Due to their generally elevated market value, coastal demersal resources are very sought after in all four of the northern CECAF zone countries (Morocco, Mauritania, Senegal and The Gambia). They are exploited by artisanal and industrial fleets (national and foreign). The fisheries are multi-purpose and demersal fish species often represent bycatch of other specialized fisheries such as the cephalopod, hake or shrimp fisheries.
The demersal fish to be assessed this year are the Pagellus bellottii
, Pagellus acarne
spp., Dentex macrophthalmus
, Pagrus caeruleostictus
spp. and Epinephelus aeneus
. Overall catch for these species fluctuates between around 20 000 and 37 000 tonnes.
Demersal fish resources in Morocco are exploited by a heterogeneous fleet of Moroccan cephalopod freezer trawlers (Ceph. N), coastal fishing vessels: trawlers and longliners (coastal), artisanal boats (artisanal), leased boats and Russian vessels operating under the Morocco-Russia fishing agreement. Only the longliner and some of the artisanal boats target demersal fish, other vessels catch them as bycatch.
In Mauritania exploitation of demersal resources is carried out by various types of trawler: foreign cephalopod (Ceph. E), national cephalopod (Ceph. N), foreign and national hake (Hake), foreign and national shrimp (Shrimp), foreign pelagic trawlers (Pelagic) and foreign and national demersal fish trawlers (Fish).
In Senegal demersal resources are mainly caught by artisanal boats using fishing lines. Two categories exist: motorized line canoes (MLC) carrying out daily trips and ice canoes (IC) equipped with ice that do trips lasting several days. These resources are also caught by Senegalese and foreign trawlers fishing under fishing agreements. Each of these fleets is made up of freezer and ice trawlers. The artisanal fleet is currently composed of 12 619 canoes and the number of Senegalese trawlers was 100 in 2005.
In the Gambia, it is foreign freezer trawlers (PI) and artisanal canoes that exploit demersal resources.
The total landings time series of P. notialis
in Mauritania, Senegal and The Gambia were used to assess each of the stocks. For the Mauritanian stock, the CPUE of the Spanish freezer trawlers was used as an abundance index. For the Senegal–The Gambia stock the CPUE series of the Senegalese industrial fishery trawlers (less than 250 GRT) was used.
Schaefer dynamic production model
The Schaefer dynamic production model implemented in an Excel spreadsheet was used to assess the state of the stock and the fisheries of P. notialis
. The model is described in Appendix 2 to this report.
The dynamic production model fits the data of both stocks relatively well.
The Mauritanian stock of Southern pink shrimp P. notialis is fully exploited. Current biomass is close to the target biomass B0.1 (Table 1).
For Senegal and The Gambia, the results show that the Southern pink shrimp stock is overexploited (Table 1). Current biomass is below the target biomass B0.1. It was also observed that current fishing effort is above the target effort F0.1. With respect to the 2004 assessment, the stock situation has further deteriorated.
Table 1: Indicators on the state of the stock and the fishery of Penaeus notialis in the northern CECAF region
|Stock/abundance index|| F cur /F SYcur|| B cur /B 0.1|| F cur /F 0.1|| B cur /B MSY|| F cur /F MSY|
|Mauritania/Spanish freezer trawlers||131%||101%||129%||112%||116%|
|Senegal Gambia/Senegalese industrial trawlers||116%||30%||215%||34%||194%|
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.
For Mauritania, the landings’ series and the abundance indices show some variation which could be tied to environmental factors which play an important role in the stock dynamic, or to the CPUEs used, which do not represent true abundance indices of the stock. Even if the results from the model should be treated with caution, they highlight that the level of current fishing effort is not compatible with the biomass level producing the optimal yield of the stock.
In the case of Senegal and The Gambia, the model provides a good fit, showing a situation of overexploitation. If this situation is not corrected, there is a threat of collapse of the stock.
Scientific Advicefor Management considerations
Taking into account the results from the assessment, the Working Group recommends decreasing current fishing effort (2006) in Mauritania and drastically reducing current fishing effort (2006) in the Senegal–The Gambia zone.for Future research
The Working group made the following recommendations for future research into P. notialis
- Improve knowledge on the biology of this species.
- Continue the programme of biological sampling of the Mauritanian catches with the support of the Spanish fisheries office in Nouadhibou
- Improve information on catch and effort by fishing zone (Senegalese and Gambian fleets).
- Study stock identity.
- Study the possible relationship between environmental factors (SST, rain, etc.) and abundance of the species.
- Study selectivity of the trawls to reduce bycatch.
Biological State and Trend
Senegal and The Gambia stock
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".