London, United Kingdom - July 03, 2024 A new study underscores the dire consequences of climate change on shark populations, revealing a significant decline in embryo survival rates under projected future environmental conditions. Led by Noemie Coulon, a PhD student at France's Laboratoire de Biologie des Organismes et des Ecosystemes Aquatiques, the research marks the first to highlight the critical role of monthly temperature fluctuations in shark embryo mortality. The study focused on small-spotted catsharks (Scyliorhinus canicula), a prevalent species in European waters already grappling with habitat loss. Coulon and her team simulated three climate scenarios: a control using historical data and two future scenarios based on UN climate models. Under the moderate SSP2 scenario, with a predicted 2.7°C temperature rise and 0.2 pH drop by 2100, embryo survival remained relatively high at 83%. However, under the more severe SSP5 scenario, with a projected 4.4°C rise and 0.4 pH drop, survival plummeted to a mere 11%. This stark difference underscores the vulnerability of shark embryos to intensified ocean warming and acidification. The study observed that higher temperatures during critical egg-laying periods, particularly in August, drastically reduced hatching success. Embryos in the SSP5 scenario showed slower growth and lower yolk consumption, critical for their development. These findings suggest that even modest increases in global temperatures could devastate shark populations, disrupting marine ecosystems. Coulon emphasized the study's dual message of caution and hope. "It's a stark warning for species sensitive to environmental change," she noted. "Yet, it also shows that adhering to more moderate emission scenarios like SSP2 could mitigate these effects, offering a lifeline for species like the small-spotted catshark." The research, supported by the Save Our Seas Foundation, underscores the urgent need for climate action to safeguard marine biodiversity. It will be presented at the Society for Experimental Biology Annual Conference in Prague, highlighting its significance in shaping conservation strategies amid a changing climate.