Summary:
Marine fishes employ specialized reproductive tactics in response to hydrographic fluctuations in their spawning habitats. Unprecedented environmental conditions induced by climate change will challenge these behavioral and physiological adaptations. Taking into account the key drivers of stock productivity, my PhD thesis aimed at assessing the reproductive adaptations of a clupeid fish species, Ethmalosa fimbriata, towards hydrographic alterations in its spawning habitats: the upwelling area at the Senegalese South Coast and the inverse hypersaline Sine Saloum estuary. Obtained results show that E. fimbriata's is adapted towards increasing its reproductive investment at high water temperatures (26–30°C) and at salinities (42–51), which by far exceed marine conditions, in an effort to maximize recruitment success. Examination of oocyte fatty acid profiles revealed that oocytes spawned inside the estuary under these high temperature/high salinity conditions were likely to develop normally. Investigation of spawning energetics and otolith microchemistry evidenced distinct stock spawning components, which are characterized by delimited home ranges and specific productivity. Because of this complex stock structure and by employing auspicious reproductive tactics the species is so far likely to benefit from the severe impacts of climate change on its spawning habitat. The adaptations described herein potentially allow for outcompeting other pelagic fish species with lower adaptive potential. All in all, high plasticity in reproductive traits combined with high fecundities and small generation times in clupeid fishes such as E. fimbriata may lead to an enhanced fitness during rapid environmental changes.