Warming oceans due to the climate crisis mean baby sharks emerge into the world smaller, exhausted, undernourished and into environments which are already becoming increasingly difficult for them to survive in, scientists have warned.
As the world’s seas heat up, so too does shark embryo development, but this faster process is putting sharks, which already face catastrophic levels of persecution by humans, at greater risk.
A team of Australian scientists studied the effects of increased temperatures on the growth, development and physiological performance of epaulette sharks - an egg-laying species found only on the Great Barrier Reef.
“We tested shark embryos in waters up to 31C,” said lead author of the study Carolyn Wheeler, a PhD candidate at James Cook University and the University of Massachusetts.
“The hotter the conditions, the faster everything happened, which could be a problem for the sharks.
“The embryos grew faster and used their yolk sac quicker, which is their only source of food as they develop in the egg case. This led to them hatching earlier than usual.”
This meant the baby sharks were not only smaller than they should be, but also that they needed to feed immediately, while lacking significant energy.
Co-author associate professor Jodie Rummer, also from James Cook University, said the waters of the Great Barrier Reef will likely experience summer averages close to or even in excess of 31C by the end of the century.
Since sharks don't care for their eggs after they are laid, a shark egg must be able to survive unprotected for up to four months.
Though the scientists only examined the impact of rising ocean temperatures on epaulette sharks, they said the results are particularly concerning as the species is highly adaptable in comparison to other sharks - both those which lay eggs and those which have live young.
“The epaulette shark is known for its resilience to change, even to ocean acidification,” Dr Rummer said.
“So, if this species can't cope with warming waters then how will other, less tolerant species fare?” she said.
Sharks and the class of animals they belong to, which includes rays and skates, are slow growing. They also don't reproduce as often as most other fish. The populations of these creatures are already threatened across the globe.
The study suggests the sharks of the future will be born, or hatch, not only at a disadvantage but into environments that are already at the warmest they can tolerate.
“The study presents a worrying future given that sharks are already threatened,” Ms Wheeler said.
“Sharks are important predators that keep ocean ecosystems healthy. Without predators, whole ecosystems can collapse, which is why we need to keep studying and protecting these creatures.”
“Our future ecosystems depend on us taking urgent action to limit climate change,” Dr Rummer said.
The research is published in Nature Scientific Reports.
