Title: Stock assessment and the influence of environmental parameters on the distribution of mackerel scad (Decapterus macarellus) in Cabo Verde waters.

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Mackerel scad; environmental factors; biomass; growth parameters; decline.


Makerel scad is one of the most important small pelagic fisheries in Cape Verdean waters, having enormous social and economic importance, and is used as bait and food and in the canning industry. INDP official landing data recorded between 1989 to 2015 indicate that mackerel scad made up almost 40 % of Cabe Verdean total catches at the peak of its fishery in 1997 and 1998. After this peak the catch decreased significantly, especially in the last six years, representing only 6.6 % of landings in 2015 or 642 tonnes. The main goal of this study was to assess if the fluctuations and recent decline in mackerel scad catch in Cape Verdeans waters are caused by harvesting or by changes in environmental parameters. The data analysed was provided by reconstructed catch data during the time frame 1950 to 2014 from the research initiative Sea Around Us, official landing and effort data from INDP in the period from 1989 to 2015, biological data from INDP in the period 1989 to 2018, and sea surface temperature and chlorophyll-a from satellite observation. The growth parameters K and L∞, the recruitment pattern and the total mortality were computed in the software FISAT II, the biomass was estimated by the Shaefer model using the Sea Around Us reconstructed catch data and CPUE data from INDP for both fleet, and simple linear regression was applied to see the correlation between the catch data and environmental parameters. The growth parameters computed from FISAT II indicate L∞ = 40.6 cm, K = 0.450 year-1, Z = 3.23 year-1, F = 2.31 year-1, M = 0.92 year-1. The biomass estimated by the Shaefer model indicate an MSY of 5,619 tonnes using the Sea Around Us catch and artisanal CPUE from INDP, and 5,686 tonnes using the Sea Around Us catch and industrial CPUE from INDP. The correlation between catch and environmental parameters, showed an R2 = 0.043 when catch is correlated with sea surface temperature, and R2 = 0.21 when catch is correlated with chlorophyll-a. There are indicators that the stock is declining, but not conclusive, hence the fishing effort should be reduced until more information is known. The stock did not show strong links to environmental factors, further studies and improved sampling procedures are recommended to get more information on the stock.

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