Abstract
The coastal regions of the Gulf of Guinea constitute one of the major marine ecosystems, producing essential living marine resources for the populations of Western Africa. In this region, the Ivorian continental shelf is under pressure from various anthropogenic sources, which have put the regional fish stocks, especially Sardinella aurita, the dominant pelagic species in Ivorian industrial fishery landings, under threat from overfishing. Here, we combine in situ observations of Sardinella aurita catch, temperature, and nutrient profiles, with remote-sensing ocean-color observations, and reanalysis data of wind and sea surface temperature, to investigate relationships between Sardinella aurita catch and oceanic primary producers (including biomass and phenology of phytoplankton), and between Sardinella aurita catch and environmental conditions (including upwelling index, and turbulent mixing). We show that variations in Sardinella aurita catch in the following year may be predicted, with a confidence of 78%, based on a bilinear model using only physical variables, and with a confidence of 40% when using only biological variables. However, the physics-based model alone is not sufficient to explain the mechanism driving the year-to-year variations in Sardinella aurita catch. Based on the analysis of the relationships between biological variables, we demonstrate that in the Ivorian continental shelf, during the study period 1998–2014, population dynamics of Sardinella aurita, and oceanic primary producers, may be controlled, mainly by top-down trophic interactions. Finally, based on the predictive models constructed here, we discuss how they can provide powerful tools to support evaluation and monitoring of fishing activity, which may help towards the development of a Fisheries Information and Management System.
Highlights
Upwelling ecosystems provide more than 40% of the world fisheries catch, they occupy less than 3% of the ocean’s surface [1]
Our results showed that the peaks of chlorophyll concentration, upwelling index, and wind-induced turbulent mixing generally coincide with low sea surface temperature (SST)
A regression model based on physical variables has been shown to explain 78% of the catch of Sardinella aurita in the following year when the annual mean upwelling index and mean wind-induced turbulent mixing in the months of Jun to Dec of the current year are known
Summary
Upwelling ecosystems provide more than 40% of the world fisheries catch, they occupy less than 3% of the ocean’s surface [1]. Since the 1980s, the Ivorian continental shelf has been subject to strong anthropogenic pressures associated with increased population size, as well as economic development, urbanization, wastewater discharge, and other localized pollution, habitat degradation, unsustainable fishing practices, and global climate change. These changes have put the regional fish stocks (especially Sardinella) under threat from overfishing [7,8]. An assessment of the regional risks and vulnerabilities of the marine environment is essential for responsible management of fishery resources. This requires that the biological and physical variables influencing fishery resources be identified
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