Hypoxia [O2 < 2.0 mL L−1 (87 μmol kg−1)] and severely hypoxic water masses [O2 < 0.5 mL L−1 (21.8 μmol kg−1)] are increasing in coastal marine ecosystems due to eutrophication and warming. Here, we investigate the response of the suboxic-tolerant endemic fish, Sufflogobius bibarbatus, to variations in the thermal and oxygen environment, as well as to predation pressure, using 22 yr worth of satellite and in situ data. We show that environmental variation and predation pressure affect the goby population, which has expanded over the last decade while that of horse mackerel has contracted. These changes co-occurred with a general warming in the north and central shelf areas (north of 24.5°S). Spring warming positively affected both goby and hake abundances, but not the horse mackerel, suggesting different responses to surface temperature. The goby habitat contracted when predators were abundant, particularly in the north, which is the fringe of its distributional area. The implications of the differential tolerance of gobies and their predators for climate variations are discussed.

No abstract

No abstract

This work compiles hydroacoustic recordings and catch data over Senegambia (Senegal and The Gambia) from assessment surveys on the major clupeid species to identify sources of bias in abundance estimates caused by their horizontal distribution. The latitudinal distribution of small pelagic fish is often well known, while their “across shelf” distribution on the continental shelf is less understood. The southern part of the Senegambian shelf has a wide shallow water (<10 m) area that makes up 20% (1500 NM2) of the total shelf surface, while the northern part accounts for 3% (200 NM2). These areas are not assessed by conventional fisheries acoustics surveys and therefore increase the uncertainty of the assessment of these species. Our findings show that this likely introduces a bias in the assessment of Sardinella maderensis, while for S. aurita no major estimation-error is caused by their horizontal distribution. The data confirm that Ethmalosa fimbriata and Ilisha africana are challenging to assess by conventional surveys, due to their mostly inshore distribution. We emphasise the usefulness of assessing S. aurita through fisheries independent hydroacoustic surveys, and propose alternative methods to survey shallow water areas to reduce biases in biomass estimates and distribution mapping.

No abstract