Habitat and Biology
Bottom type: Soft_bottom_muddy_or_muddy-sand. Depth zone: Slope (200 m - 1000 m). Horizontal distribution: Neritic; Oceanic. Vertical distribution: Demersal/Benthic.
The linear growth and length-weight relationship parameters of deep-water rose shrimp were estimated from the Moroccan coastal trawler commercial catches in the landing ports.
Length at first sexual maturity was estimated at 23.44 mm to the carapace, corresponding to a total length of 11.20 cm. Weight at first sexual maturity was 6.41g and the corresponding age was 0.44 years.
Individual absolute fertility varies between 1 100 and 120 100 eggs per female for carapace lengths between 20 and 40 mm (between 9 and 17 cm total length). Relative fertility varies between 151 and 6 191 eggs per gram of shrimp.
The deep-water rose shrimp has a very varied diet. The Foraminifira are the preferred prey of this species. Plant debris, copepods, Mysidacea, amphipods, euphausids, the eggs and larvae of decapods and molluscs, crabs, gastropods, fish scales and eggs, grains of sand, radiolarians and sponges are all an important part of its diet. The biodiversity in the diet seems to increase with age and this increase is more apparent amongst females. The diet does not vary between sexes or season. Natural mortality is very high in deep-water rose shrimp. Fishing mortality is 1.52 per year for both sexes combined, 1.60 per year for males and 1.43 per year for females.Environmental effects
A first analysis of the possible effects of different environmental parameters and of the abundance of P. longirostris
in Mauritanian waters carried out by the IEO using the available indices of sea surface temperature (SST) and the north Atlantic oscillation (NAO) (Garcia and Sobrino, submitted), suggests that there is no correlation between stock abundance/yields and the overall SST, but that there is a correlation between yields and the NAO indices.
The level of salinity seems to have a direct effect on deep-water rose shrimp spawning. Recent studies (Benchoucha et al . in preparation) have effectively shown that spawning generally takes place at salinity values of between 35.6 and 36.5 psu, both in shallower depths (75–200 m) and in deeper zones (250–500 m). Spawning has been observed both in spring and summer in shallower zones. In winter, spawning takes place in both zones.
The deep-water rose shrimp (Parapenaeus longirostris
) lives on sandy and muddy bottoms at depths between 20 and 700 m.
Jurisdictional distribution: Unspecified
Considered a single stock: Yes
This species is found between the northern limit of Cap Spartel (35°47’ N) and the southern region of Sidi Ifni (29°22’ N).
Considering the fact that P. longirostris
is found in different geographic zones, the Working Group adopted three stocks: Morocco, Mauritania and Senegal–The Gambia.
No fishery targets P. longirostris
between Agadir and Cap Blanc. In Mauritanian waters, P. longirostris
is targeted mainly between 21° and 19° N. The fishery targeting P. longirostris
in Senegalese waters from 16°N is developing.
A time series of total catch of deep-water rose shrimp Parapenaeus longirostris
by fishing zone was used by the Working Group.
For Morocco, two abundance indices series were adopted, the CPUE series from the shrimp freezer trawlers and the abundance indices series from the surveys. The global model fits both abundance index series. The group decided to retain the abundance indices series from the INRH scientific surveys in Morocco which better reflects the actual abundance of the stock.
For Mauritania, the CPUE series form the Spanish shrimp freezer trawlers operating in Mauritania were used.
The CPUEs from the Spanish shrimp freezer trawlers were also used to assess Parapenaeus longirostris
in the Senegal–The Gambia fishing zone.
Schaefer dynamic production model
The Schaefer dynamic production model implemented in and Excel spreadsheet was used to assess the state of the stock and the fisheries of Parapenaeus longirostris
. The model is described in Appendix 2 to the report. Given the availability of length composition data between 2002 and 2006, the analytical model was also used for the deep-water rose shrimp stock in Morocco.
The model provided acceptable fits to the data for the Moroccan and Mauritanian stocks (Figure 4.3.4), but not for the Senegal–The Gambia stock.
In Morocco, the deep-water rose shrimp stock is overexploited (Table 1). Current biomass is below the target biomass B0.1. This situation was confirmed by the yields obtained during the INRH scientific surveys in 2006. With respect to the 2004 assessment, the situation has deteriorated. It was also noted that current fishing effort is higher than the target effort F0.1.
In Mauritania, the model showed that the Parapenaeus longirostris
stock is fully exploited. Current biomass is close to the target biomass B0.1 (Table 1).
Table 1: Indicators on the state of the stock and the fishery of Parapenaeus longirostris in the northern CECAF zone
|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|
|Morocco /INRH survey index||297%||11%||618%||12%||556%|
|Mauritania/Spanish freezer trawlers||85%||106%||79%||116%||71%|
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.
Taking into account the difficulties encountered in fitting the models due to the random fluctuations in recruitment, the results should be treated with caution. Nevertheless, the results agree with those from other fishery indicators in the sector (abundance indices from the surveys and commercial vessel yields), which reinforces confidence in the reliability of the results overall.
For Morocco, the results are similar to those obtained during the 2004 assessment (FAO, 2006). The recommendations issued during that assessment regarding a reduction in effort have been largely ignored, which has consequently led to a renewed decrease in the biomass of the species.
For Mauritania, the assessment results show that the stock of deep-water rose shrimp is fully exploited with a biomass close to BMSY.
The fitted models for the Senegal–The Gambia zone were not acceptable and were therefore discarded.
Scientific Advicefor Management considerations
Taking into account the results from the assessments, the Working Group made the following recommendation for the three stocks:
- Strongly reduce current effort (2006) in order to obtain a level of sustainable catch to allow the stock to be rebuilt.
- Encourage the use of separator trawls.
- Do not increase current fishing effort.
- Do not increase fishing effort until new assessments are available.for Future research
The Working Group made the following recommendations for future research into P. longirostris
- Strengthen the biological sampling programme in place for landings of coastal trawlers and industrial shrimp trawlers in the Moroccan ports.
- Continue the programme of biological sampling of Mauritanian catches with the support of the Spanish fisheries office in Nouadhibou.
- Improve knowledge on the biology of this species.
- Carry out selectivity studies to reduce bycatch.
- Strengthen the follow-up on exploitation (catch and effort) of the stock in the Senegal–The Gambia zone.
Biological State and Trend
Exploitation rate: Fcur/F0.1=618%
Abundance level: Bcur/B0.1= 11%
Exploitation state: Fully exploitedExploitation rate: Fcur/F0.1= 79%
Abundance level: Bcur/B0.1= 106%
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".