Baby sharks are born smaller, thanks to climate change

Future too warm for baby sharks.

A new study by the ARC Centre of Excellence for Coral Reef Studies examined the effects of increased temperatures on the growth, development, and physiological performance of epaulet sharks. Scientists studied the sharks as embryos and as hatchlings.

The study suggests that climate change causes the world’s oceans to warm, baby sharks are born smaller, exhausted, undernourished. Most important, they are born into environments that are already difficult for them to survive in.

Lead author of the study Carolyn Wheeler, Ph.D. candidate at the ARC Centre of Excellence for Coral Reef Studies at James Cook University (Coral CoE at JCU) and the University of Massachusetts, said, “We tested shark embryos in waters up to 31°C.”

“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 food source as they develop in the egg case. This led to them hatching earlier than usual.”

“This meant hatchlings were not only smaller; they needed to feed almost straight away—while lacking significant energy.”

Shark embryo
Shark embryo. Credit: M.Johnson

Co-author Associate Professor Jodie Rummer, also from Coral CoE at JCU, says, “the Great Barrier Reef waters will likely experience summer averages close to or even over 31°C by the end of the century.”

“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. Rising ocean temperatures as a major concern for the future of all sharks—both egg-laying and live-bearing species.”

“The epaulette shark is known for its resilience to change, even to ocean acidification. So, if this species can’t cope with warming waters, then how will other, less tolerant species fare?”

As compared to other fishes, sharks don’t reproduce that often. The populations of these creatures are already threatened across the globe.

The study suggests the sharks of the future will be born—or hatch, in this case—not only at a disadvantage but into environments that are already at the warmest they can tolerate.

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

“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.”

Dr. Rummer said“Our future ecosystems depend on us taking urgent action to limit climate change.”

Journal Reference:
  1. Wheeler C, Rummer J, Bailey B, Lockwood J, Vance S, Mandelman J. (2020). ‘Future thermal regimes for epaulette sharks (Hemiscyllium ocellatum): growth and metabolic performance cease to be optimal.’ Scientific Reports, 10: 79953. DOI: 10.1038/s41598-020-79953-0

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