Sharks have been patrolling the oceans since before dinosaurs arrived on scene. Despite their 400 million years of adaptations and survival, they’re not in the greatest shape at the moment. With overfishing, bycatch, and habitat issues, they – along with rays – have seen a 71% population decrease since 1970. Currently, about one in three species is threatened with extinction. A new study shows how a warming climate could make the issue even worse.

Researchers at Laboratoire de Biologie des Organismes et des Écosystèmes Aquatiques in France recently examined how increased water temperatures and acidification – two climate change impacts – could affect embryo survival in the small-spotted catshark. The species is common in Europe and has a reproductive method that can give good insight into climate change impacts on our marine species.

Noémie Coulon, PhD student and the study’s first author, explains, “The embryos of egg-laying species are especially sensitive to environmental conditions. The hatching success of embryos is a crucial factor for population dynamics. In the case of skates and sharks, which have a slow pace of life, low hatching rates could be critical for population renewal.”

To conduct their study, published in the journal Marine Environmental Research, Coulon and her team subjected catshark embryos to three different water conditions. The first were baseline temperature and pH levels from 1995 to 2014. The second two were projected year 2100 climate scenarios from the UN’s Intergovernmental Panel on Climate Change’s Sixth Assessment Report from 2021. One scenario projects what would happen if there’s slow progress made toward climate goals but net zero is not achieved, which would involve a temperature increase of 2.7 degrees Celsius and a pH drop of 0.2. The second projection is what would happen with continued and accelerated use of fossil fuels, which would mean a temperature rise of 4.4 degrees and a pH decline of 0.4.

After monitoring the embryos weekly for four months, the researchers found that hatching success was comparable in the first two scenarios. The control group had an 81% success rate, while the more moderate projection group was at 83%. However, only 11% of the embryos in the more extreme conditions survived. Those that didn’t make it displayed lower yolk consumption, lower growth rates, and failure to transition to internal gills. That stage of transition may be especially vulnerable to seasonal temperature fluctuations.

Coulon says, “This mortality was most pronounced in August, coinciding with the highest temperatures (reaching 23.1°C), and during a stage of development where embryos undergo gill reabsorption.”

The 11% that survived had different growth patterns than the others. The team says that understanding these successes and variations among individuals may help scientists better predict the species’ future success.

While the findings suggest another iconic animal may be heavily impacted by climate change, much like polar bears and orcas, the study also shows that doing anything to try to address the problem may still help.

Coulon explains, “Firstly, it serves as a warning about the responses of other species that may be even more sensitive to environmental change. Secondly, our findings demonstrate that the more moderate… scenario can limit the damage inflicted on species like the small-spotted catshark, which gives us a positive incentive to reduce our greenhouse gas emissions.”

If you’d like to do what you can to help shark species at large, join us in our efforts to tackle overfishing!