Nursery grounds can provide protection and ample food sources for young sharks, but they can also be hazardous according to a new study by Ian Bouyoucos, a Ph.D. student at the ARC Centre of Excellence for Coral Reef Studies at James Cook University.
These shallow water habitats can be ‘extreme’, with dramatic changes in temperature and oxygen levels. The study, which was conducted in the French Polynesian shark sanctuary, found that with blacktip reef sharks, only one in four newborns survives.
“There are already extreme fluctuations and extreme highs going on in the shallows—and the conditions are only getting worse,” Bouyoucos said.
“It’s not a nice place really, in terms of environmental conditions,” said co-author Associate Professor Jodie Rummer. “Essentially from the day they are born, these sharks have to be pretty tough in how their bodies work in order to tolerate these harsh environmental conditions.”
Newborn sharks have a narrow window of time in nursery habitats, where they have to grow, learn to hunt, and not get eaten. Climate change may make this window even smaller.
“If these ecosystems disintegrate under climate change, the baby sharks fall into a ‘trap’,” Dr. Rummer said. “If they choose less harsh habitats, they lose their food and protection. If they remain within the safe, shallow nurseries, they suffer the effects of warming waters and decreasing oxygen levels.”