Thursday, July 18, 2024

Shark Eggs May Simply Stop Hatching Under Climate Change

Climate change may be coming for some sharks, new research suggests. The study found that eggs belonging to the small-spotted catshark are substantially less likely to survive under the worst case climate scenario by 2100. The findings still indicate that these sharks can continue to thrive under less disastrous 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 journal Marine Environmental Research and the scientists are set to 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 lesser spotted dogfish, is currently doing fine for the most part, with ample numbers along the northeast Atlantic Ocean surrounding Europe. But according to the scientists behind this new research, the species has shown some signs of becoming more vulnerable in an increasingly warming earth.

“The small-spotted catshark is already experiencing habitat loss in coastal areas, particularly during the summer months when egg-laying is at its peak,” said lead researcher Noémie Coulon, a PhD student at BOREA, in a statement from the Society for Experimental Biology.

One of the catshark embryos that the researchers monitored during their study, growing inside its egg.
Photo: Noémie Coulon

To better find out 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 that the eggs were kept in. The latter variable is especially important because increasing ocean acidification is one of the major complications of rising carbon dioxide emissions. The team checked in on these eggs every week for four months (catshark pups usually hatch after 5 to 11 months), then tracked how the newborns fared for another six months.

The first scenario was a control, with eggs kept under roughly the same baseline temperature and pH conditions as today (based on data collected between 1995 to 2014). In the others, 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, considered the middle-of-the-road scenario, the average global temperature would rise by about 4.9 degrees Fahrenheit (2.7 degrees Celsius), while the water pH would drop by 0.2 by 2100. Under SSP5, the most extreme scenario, the temperature would rise by nearly 8 degrees Fahrenheit (4.4 degrees Celsius) and the water pH would drop by 0.4.

In the worst case scenario, only 11% of the small-spotted shark eggs hatched, compared to the 81% and 83% survival rate seen under the control and SSP2 condition, respectively. The embryos inside these eggs consumed less yolk, grew at a slower rate, and were less able to successfully form their internal gills. There was no difference in survivability between the groups once the sharks hatched from their eggs, which was likely due to water temperatures falling as the year went on, the authors say.

This is only one study from a single team, so more research is needed to verify their findings. But should the team’s projections bear fruit, a SSP5 world could certainly be catastrophic for these fish and others like them, including skate fish, close cousins of sharks.

“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,” Coulon said.

That said, many experts say that a SSP5 scenario is unlikely to happen (though some do still believe it remains highly plausible). So the team’s overall results could be taken as somewhat reassuring, the researchers say. If humans can prevent the worst climate future possible, then these fish will still be around and kicking swimming.

“Firstly, it serves as a warning about the responses of other species that may be even more sensitive to environmental change,” said Coulon. “Secondly, our findings demonstrate that the more moderate SSP2 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.”

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