Climate change may be on the horizon for some sharks, new research suggests. The study found that eggs of the spotted catshark are significantly less likely to survive under the worst-case climate scenario in 2100. The findings still suggest that these sharks could continue to thrive under less dire climate conditions.
The research was led by scientists from the Biology of Aquatic Organisms and Ecosystems (BOREA, for short) Lab in France. It was published earlier this April in the magazine Research into the marine environment The scientists will present their findings Wednesday at the annual conference of the Society for Experimental Biology.
The small spotted catshark (Scyliorhinus canicula), also confusingly known as the sandy or small spotted dogfish, is generally doing well at the moment, with good numbers found along the northeastern Atlantic Ocean around Europe. But according to the scientists behind the new study, the species is showing signs of becoming more vulnerable in an increasingly warm world.
“The small catshark is already experiencing habitat loss in coastal areas, especially during the summer months when egg laying is at its peak,” lead researcher Noémie Coulon, a PhD candidate at BOREA, said in a rack of the Society for Experimental Biology.
To better understand how these sharks will fare in the future, Coulon and her team raised and monitored batches of their eggs under three different scenarios. These scenarios were distinguished by the temperature and pH of the water in which the eggs were stored. The latter variable is especially important because increasing ocean acidification is one of the major complications of rising carbon dioxide emissions. The team checked these eggs every week for four months (catshark cubs usually come out After 5 to 11 months, the newborns were then monitored for another six months.
The first scenario was a control, with eggs kept under roughly the same baseline temperature and pH conditions as they are today (based on data collected between 1995 and 2014). In the other scenarios, the team changed the water to match what would happen under two sets of climate projections developed by the United Nations, known as the shared socioeconomic pathways (SSPs): SSP2 and SSP5.
Under SSP2, the most extreme scenario, the average global temperature would rise by about 4.9 degrees Fahrenheit (2.7 degrees Celsius) while the pH of water would fall by 0.2 by 2100. Under SSP5, the most extreme scenario, temperatures would rise by almost 8 degrees Fahrenheit (4.4 degrees Celsius) and the pH of water would fall by 0.4.
In the worst-case scenario, only 11% of the little spotted shark eggs hatched, compared to the 81% and 83% survival rates seen under the control and SSP2 conditions, respectively. The embryos in these eggs consumed less yolk, grew more slowly and were less able to successfully form their internal gills. There was no difference in survival rates between the groups after the sharks hatched, which was likely due to falling water temperatures as the year progressed, the authors say.
This is just one study from one team, so more research is needed to verify their findings. But if the team’s projections bear fruit, an SSP5 world could certainly be catastrophic for these fish and others like them, including rays, close relatives of sharks.
“Embryo hatching success is a critical factor for population dynamics. In the case of rays and sharks, which have slow lifespans, low hatching rates can be critical for population renewal,” Coulon said.
That said, many experts say that an SSP5 scenario unlikely that this will happen (although some still believe it is still so very likely). The team’s overall results can therefore be seen as somewhat reassuring, the researchers say. If humans can prevent the worst possible climate future, these fish will still be around and to kick swimming.
“First, it serves as a warning of the responses of other species that may be even more sensitive to environmental change,” Coulon said. “Second, our findings show that the more moderate SSP2 scenario could limit damage to species like the spotted catshark, giving us a positive incentive to reduce our greenhouse gas emissions.”