Baby sharks are born smaller, thanks to climate change

James Marshall
January 13, 2021

"We tested shark embryos in waters up to 31°C and the hotter the conditions, the faster everything happened, which could be a problem for the sharks", said Carolyn Wheeler, a PhD candidate at James Cook University, in Queensland, Australia.

Baby sharks will find it hard to survive on the Great Barrier Reef by the end of the century, scientists say, with climate change and warmer oceans leading to the creatures being born smaller, exhausted and undernourished.

The research team found that in warmer waters, shark embryos grew faster and used their yolk sac - their only source of food in this developmental stage - quicker. The researchers also measured the fitness of the baby sharks, and found that it peaked at 29C but then fell sharply at 31C.

'This led to them hatching earlier than usual, ' she explained - adding that the baby sharks were thus not only smaller, but also were born needing to feed nearly straight away while also lacking significant energy reserves.

Researchers have found a unique species in the Great Barrier Reef that spends up to 25 days in its egg cases.

'The study presents a worrying future given that sharks are already threatened, ' commented Ms Wheeler. Wheeler said the hatchlings were not only smaller, but they needed to feed nearly immediately while lacking significant energy.

Co-author and associate professor Jodie Rummer explained in the release that this makes it hard for the species to survive as the epaulette sharks don't care for their eggs after they are laid.

The epaulette shark is widely considered to be among the more resilient species, raising concerns for other animals that are more sensitive to temperature change and ocean acidification.

Three new born sharks cuddling up together in a tray
Rising ocean temperatures are presenting a massive problem for baby sharks

Co-author and Associate Professor Jodie Rummer, Wheeler's co-supervisor at James Cook University, says the waters of the Great Barrier Reef will likely experience summer averages nearing or even exceeding 31°C/87.8°F by the end of the century.

"If this shark is having trouble coping with ocean warming conditions, that's going to be a really big problem for other shark species that are less tolerant and not as robust to changes in their environment", she said.

Sharks and other species from the Elasmosbrancii family, such as rays and skates, grow extremely slowly, and don't reproduce as regularly as other fish.

"Sharks are important as predators because they take out the weak and injured and keep the integrity of the population strong", Rummer said.

The study suggests that sharks will be born, or hatch, into environments that are already at the warmest temperature they can tolerate, decreasing their chance of survival. "Without predators, whole ecosystems can collapse, which is why we need to keep studying and protecting these creatures", Wheeler said in the release.

"The ocean faces increasing threats from humans, such as the effects of climate change, and it is vital to conduct scientific research to help strengthen the management and protection of those ocean species most negatively impacted and vulnerable", Mandelman said.

To find out how temperature changes will affect epaulette eggs, scientists at the New England Aquarium in Boston monitored 27 epaulette shark eggs. The New England Aquarium has a successful breeding program for epaulette sharks.

Other reports by Click Lancashire

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