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Even hefty shark pups struggle on degraded reefs

Sept. 17 (UPI) — It’s better to be born small and grow up around healthy coral reefs than born big and be relegated to degraded reefs.

According to a new study, bigger, heavier shark pups that live near struggling reefs fare worse than their smaller peers living near healthy reefs. In the battle of genes versus nature, the influence of nature wins out.

For the study, researchers followed the growth patterns of two populations of newborn reef sharks: one living near St. Joseph atoll in the Seychelles and the other living near Moorea, a French Polynesian island northwest of Tahiti.

“We found that although shark pups are born larger, heavier and better conditioned in Moorea, they soon lost their physical advantage over the pups in St. Joseph,” Jodie Rummer, a scientist with the ARC Center of Excellence for Coral Reef Studies at James Cook University, said in a news release.

The coral reefs that make up the St. Joseph atoll are healthy, free from environmental damage, whereas Moorea’s reefs are still recovering from a massive die-off. Five years ago, more than 90 percent of the coral surrounding the island died.

The latest research suggests the coral degradation is still affecting local wildlife, including the health of shark pups.

Sharks are on their own as soon as they’re born. To give them the best chance of survival, mom’s give their pups extra fat reserves.

“These energy reserves sustain them during the first days and weeks after birth,” said Ornella Weideli, researcher at the Center of Island Research and Observatory of the Environment in France. “The ‘energy boost’ is important, as sharks are independent from their mothers from the moment they are born.”

Scientists caught and measured the weights of more than 500 sharks during their first few weeks of life. They found sharks were being born bigger in Moorea, but that they were losing that weight more quickly.

“Against our expectations, the larger pups from Moorea that received greater energy reserves started foraging for food later in life, which resulted in considerable declines in their body condition,” Weideli said. “On the contrary, despite being smaller and lighter for their size, the pups from St. Joseph started foraging for food earlier in life and became more successful predators than their Polynesian counterparts.”

Researchers surmised that the bigger sharks of Moorea are struggling as a result of the degradation of the local reefs. Sharks hunt the many smaller fish that rely on the food chain anchored by the coral. It’s also likely that many of the same stressors that caused the reef’s degradation in the first place — over-fishing, climate change and coastal development — have directly impacted local fish and shark species.

Scientists published their research Tuesday in the journal Scientific Reports.

“Sharks are at risk from human-induced stressors because they may not be able to adapt fast enough to keep pace with the changes that are happening in their environment,” Rummer said. “They are slow growers and take a long time to reach sexual maturity. When they do reach sexual maturity, they only have a few babies. Even fewer survive.”

Previous studies have suggested bigger, slow-growing species, which typically reproduce at slower rates, are especially at risk of climate change and other human-induced stressors — and therefore, may warrant stronger protections than smaller, faster-reproducing endangered species.

“Not enough generations are being born fast enough to make the genetic changes to adapt to what’s going on in their habitats,” Rummer said. “Mitigating human-induced stressors, especially during shark pupping season, is key to protecting these species and the ecosystems they support.”

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