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The giant clam Tridacna maxima has been largely overexploited in many tropical regions over the past decades, and was therefore listed in appendix II of the Convention of International Trade in Endangered Species (CITES) in 1985. In French Polynesia, several atolls and islands harbor the world's highest stocks of giant clams in very shallow and accessible areas, which are therefore highly vulnerable to fishing pressure. The local fishery authority (i.e., Direction des Resources Marines or "DRM") implemented several management schemes in 2002 to control and regulate fishing pressure. However, for further decisions DRM was missing a sensitivity analysis on the effectiveness of the possible management actions. Here, we report on the use of a deterministic Viable Population Analysis (VPA) and spatially-explicit age-based population model that simulated the 30-year trajectory of a Tridacna maxima stock under different management approaches. Specifically, given various scenarios of intra-island larval dispersal, we tested which of No-take-Areas (NTAs), rotational closures, size limits, quotas, and restocking schemes would lead to the highest future stocks in Tubuai and Raivavae, two exploited islands of the Austral archipelago. For both islands, stock abundances were estimated in 2004/2010 and 2005/2010 respectively, and natural mortalities were assessed previously only in Tubuai. When compared to field data, the model successfully predicted the 2010 stocks for Tubuai, but proved to be less reliable for Raivavae, where natural mortality rates may well be different from those on Tubuai. For Tubuai, the spatial model suggested that reducing fishing effort (through fixed quotas) and banning fishing below the 12 cm size limit (as currently implemented) were the most effective management actions to sustain T. maxima populations into the future. Implementing NTAs was of poor effectiveness. NTAs increased giant clam stock inside the protected area, but also increased overfishing in the neighboring areas, and were ineffective overall.

Fish exhibit impaired sensory function and altered behaviour at levels of ocean acidification expected to occur owing to anthropogenic carbon dioxide emissions during this century. We provide the first evidence of the effects of ocean acidification on reproductive behaviour of fish in the wild. Satellite and sneaker male ocellated wrasse ( Symphodus ocellatus ) compete to fertilize eggs guarded by dominant nesting males. Key mating behaviours such as dominant male courtship and nest defence did not differ between sites with ambient versus elevated CO 2 concentrations. Dominant males did, however, experience significantly lower rates of pair spawning at elevated CO 2 levels. Despite the higher risk of sperm competition found at elevated CO 2 , we also found a trend of lower satellite and sneaker male paternity at elevated CO 2 . Given the importance of fish for food security and ecosystem stability, this study highlights the need for targeted research into the effects of rising CO 2 levels on patterns of reproduction in wild fish.

ABSTRACTMarine animal forests (MAFs) are benthic ecosystems characterised by biogenic three‐dimensional structures formed by suspension feeders such as corals, gorgonians, sponges and bivalves. They comprise highly diversified communities among the most productive in the world's oceans. However, MAFs are in decline due to global and local stressors that threaten the survival and growth of their foundational species and associated biodiversity. Innovative and scalable interventions are needed to address the degradation of MAFs and increase their resilience under global change. Surprisingly, few studies have considered trophic interactions and heterotrophic feeding of MAF suspension feeders as an integral component of MAF conservation. Yet, trophic interactions are important for nutrient cycling, energy flow within the food web, biodiversity, carbon sequestration, and MAF stability. This comprehensive review describes trophic interactions at all levels of ecological organisation in tropical, temperate, and cold‐water MAFs. It examines the strengths and weaknesses of available tools for estimating the heterotrophic capacities of the foundational species in MAFs. It then discusses the threats that climate change poses to heterotrophic processes. Finally, it presents strategies for improving trophic interactions and heterotrophy, which can help to maintain the health and resilience of MAFs.

The stock of the Senegalese flat sardinella, Sardinella maderensis, is highly exploited in Senegal, West Africa. Its growth and reproduction parameters are key biological indicators for improving fisheries management. This study reviewed these parameters using landing data from small-scale fisheries in Senegal and literature information dated back more than 25 years. Age was estimated using length-frequency data to calculate growth parameters and assess the growth performance index. With global climate change there has been an increase in the average sea surface temperature along the Senegalese coast but the length-weight parameters, sex ratio, size at first sexual maturity, period of reproduction and condition factor of S. maderensis have not changed significantly. The above parameters of S. maderensis have hardly changed, despite high exploitation and fluctuations in environmental conditions that affect the early development phases of small pelagic fish in West Africa. This lack of plasticity of the species regarding of the biological parameters studied should be considered when planning relevant fishery management plans.

Abstract Along the coast of North-West Africa, fish supply is important at both socio-economic and cultural levels while threatened by climatic changes. To assess the impact of climate change on the distribution of small pelagic fish, a comprehensive trend analysis was conducted using data from 2,363 trawl samplings and 170,000 km of acoustics sea surveys spanning the period 1995–2015. The approach included estimating eight northern small pelagic species' presence and acoustics spatial distribution of the sardinella. The analysis incorporated key environmental variables, including sea temperature, chlorophyll-a concentration, and a wind-based Ekman upwelling index. The Southern Canary Current Large Marine Ecosystem (CCLME) was divided into five distinct ecological areas, extending from Morocco to Senegal, providing a spatialized perspective on the dynamic changes unfolding within these characteristic areas. Then, yearly averages of the monthly data per area were calculated. Strong warming is reported in all five areas. Over 34 years, from 1988 to 2021, several discernible trends emerged, with the southern CCLME experiencing increases in both wind speed and upwelling intensity, particularly in areas where the coastal upwelling was already the strongest. Despite upwelling-induced cooling mechanisms, sea surface temperature increased in most areas, indicating the complex interplay of climatic-related stressors in shaping the marine ecosystem. Concomitant northward shifts in the distribution of sardinella and other species were attributed to long-term warming trends in sea surface temperature (SST). As a result, the abundance of Sardinella aurita, the most abundant species along the coast, has increased in the subtropics (north part) and fallen in the intertropical region (south part). Independent environmental and ecological observational time series confirm a northward shift of around 180 km in one decade for S. aurita, while S. maderensis did not move significantly. Spatial shifts in biomass from 30 to 145 kilometers were observed for six other exploited small pelagic species, similar to those recorded for surface isotherms. An intensification in upwelling intensity within the northern and central regions of the system is documented without change in marine primary productivity. In contrast, a stable upwelling intensity is reported in the southern region (Senegal), which is associated with a decline in primary productivity. These environmental differences were associated with several small pelagic species beyond national boundaries whose recent overexploitation adds a new threat to their sustainable future in the whole region. Such changes must motivate common regional policy considerations for food security and sovereignty in all West African countries sharing the same stocks.

Fisheries management is an important strategy for ensuring sustainable use of resources. However, in West Africa, in the absence of quality data for many stocks and effective stock assessment models, the cases where this has been truly successful are notable for their rarity. In West Africa, small pelagic fish are of great socio-economic importance, as well as good indicators of fish stressors. Here, historical data (2004–2019) of five small pelagic species (Sardina pilchardus,Ethmalosa fimbriata,Trachurus trecae,Scomber coliasandMugil cephalus) were collected in Senegalese waters. TheB/BMSYresults showed stocks to be collapsed (B/BMSY= 0.13 and 0.1 forM.cephalusandS.pilchardus, respectively) and heavily overfished (B/BMSY= 0.24;E.fimbriata). OnlyS.coliasandT.trecaestock were considered to be in good condition (B/BMSY= 1.7 and 1.4 respectively). TheLc/Lc_optratio was ≤ 1 forE.fimbriataandM.cephalus, suggesting that the individuals caught for these species were too small. To reverse these bad stock statuses, catching individuals atLc_opt, 25, 21, 43 and 18 cm forS.colias,E.fimbriata,M.cephalusandS.pilchardus, respectively should be a natural guarantee against recruitment failure and allow individuals to ensure the long-term survival of populations, in a context of data poor fisheries. In conclusion, this study shows that, despite limitations, the LBB model can provides indicators of stock status for species to encourage management measures, especially in data poor countries. It is hoped that these results can help to better assess many stocks currently considered too data poor to be assessed or at least encourage data collection effort on stocks discerned as in bad or critical status.