Sharks Born Prematurely, Weaker in Warmer Ocean Temperatures

An epaulette shark pup.

An epaulette shark pup. Courtesy of E. Moothart

As ocean temperatures rise, baby sharks will be born prematurely, undernourished, and into harsh environments difficult for them to survive in, according to a new study of epaulette sharks — an egg-laying species found on the Great Barrier Reef — published in the journal Scientific Reports.

The research tested epaulette sharks’ embryotic development and physical performance after hatching in temperatures up to 31 degrees Celsius (87.8 degrees Fahrenheit) — conditions similar to what climate models project summer averages will be in the Great Barrier Reef by the end of the century.

“The hotter the conditions, the faster everything happened, which could be a problem for the sharks,” lead author of the new study Carolyn Wheeler, a PhD candidate at the ARC Centre of Excellence for Coral Reef Studies at James Cook University and the University of Massachusetts, said in a statement. “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.”

In normal conditions, epaulette sharks spend 125 days in their eggs developing. But scientists found that in 31-degree water, this dropped by 25 days. Those premature sharks emerged smaller and weaker, necessitating that they feed right away, but lacking the energy to do so and in an environment already at the extreme of what they can tolerate.

“The epaulette shark is known for its resilience to change, even to ocean acidification,” said co-author Jodie Rummer, also from the ARC Centre. “So, if this species can’t cope with warming waters then how will other, less tolerant species fare?”

The researchers told The Guardian they see three options for sharks — both egg-laying and live-bearing species — in the coming decades: They shift poleward to cooler climes, though they would also need to find the right habitat; they could genetically adapt to living in warmer temperatures, though this could be difficult for a species that reproduces so slowly; or they could disappear.

“The study presents a worrying future given that sharks are already threatened,” Wheeler said.