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We provide substantial evidence on how short-term changes in environmental conditions activate and deactivate spawning activities in small pelagic fishes. An ichthyoplankton survey was conducted along the southernmost part of the Canary Current upwelling ecosystem in May 2013, covering the area twice within 20 d. This period coincided with a strong environmental change from a cold productive upwelling regime to a warmer and less productive upwelling relaxation event. This change triggered a shift in spawning activity from European anchovy Engraulis encrasicolus to round/flat sardinella Sardinella spp. We used zero-altered negative binomial regression models with a generalized additive structure based on integrated nested Laplace approximations to link early larval distribution patterns to the 2 different regimes. The models confirmed 2 species-specific temperature spawning windows, suggesting a spawning pause of anchovy during upwelling relaxation while simultaneously activating spawning in sardinella. Observing immediate spawning responses to the 2 environmental regimes underlines the assumption that windows of spawning opportunity are the main drivers of small pelagic fish fluctuations in upwelling regions. The duration of a specific environmental condition can, therefore, increase or decrease the chances for reproductive success. The observations of this study may explain why certain small pelagic fish species can dominate over others during a particular period and might also apply to other upwelling regions of the world oceans where upwelling and relaxation events alternate.

International audienceThis work investigates the effects of changes in both fishing pressure and the environment on the trophic dynamics, abundance and diversity of species in the artisanal commercial fisheries off the northern coast of Senegal. Using artisanal commercial fishing data (provided by the Centre for Oceanographic Research of Dakar-Thiaroye [CRODT] in Senegal), we identify changes in the catch per unit effort, mean trophic level, biomass trophic spectrum and species diversity between two fishing periods (1990-1999 and 2000-2009). Decreases in mean trophic level, the biomass of high trophic level species and indices of species diversity between 1990 and 2009 were observed in commercial catches. These decreases were then related to changes in fishing pressure, fishing strategy and the combined effects of fishing and environmental factors (as derived from satellite observations). This paper helps to better inform the management of fisheries resources by providing decision makers with more effective biological indicators that incorporate the effects of fishing pressure and environmental change and that are applicable at local, regional and global scales