Title: Assessing the North-west African stock of black hakes (Merluccius polli and Merluccius senegalensis) using catch-msy and length-based spawning potential ratio models.

Author(s): Kamarel BA
Type:
Final project
Year of publication:
2019
Publisher:
GRÓ-FTP
Place of publication:
Reykjavík
Number of pages:
31
Supervisors: Pamela Woods

Abstract

Shared by three countries (Morocco, Mauritania and Senegal), the black hakes (Merluccius polli and M. senegalensis) stocks are some of the most important resource exploited in northwest African waters. Since they resemble each other and are caught together in high proportions, the fisheries statistics record them as one species. The catches were high in the 1970s before sharply declining since 1980 as a result of an intense exploitation by the domestic and foreign vessels using bottom-trawls and longlines. Each of these countries has its own records about catch, efforts, CPUE and catch composition which generally led to pooled stock assessments during CECAF Working Groups. This study attempts to perform stock assessments using regional data (catches in metrics and in length composition) from FAO reports and data-limited methods such as Catch-MSY and Length-Based Spawning Potential Ratio (LBSPR) model as a preliminary work in order to compare reference points with existing literature and consolidate them for the fisheries management purpose. The objectives of this study were to (1) obtain information about life history parameters of both species from literature review, (2) estimate natural mortality rate M and M/k using data-limited methods, (3) provide recommendations based on assessments of black hakes using Catch-MSY and LBSPR models. Sensitivity analyses were also performed to test the reliability of the results according to some changes in the input parameters. The results from Catch-MSY assessments showed that the MSY ranged between 19,400 and 29,150 tonnes, according to the scenarios. The BMSY values were very high (137,000- 352,000 tonnes), resulting in a high carrying capacity K. However, the intrinsic growth rates were very low (0.12 to 0.30). For the LBSPR assessments, the spawning potential ratio appeared too low (SPR < 0.2) for most cases suggesting recruitment overfishing. Finally, this study recommends to update life history parameters (L50, L95, k, L∞, t0 and M) regarding both species for stock assessment purpose and separate the two species in the fisheries departments statistics (catches, effort, CPUE and length frequencies) which could help scientists to assess them individually and give management advices based on accurate data.

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