As ocean temperatures have soared, new research [1] shows that some sharks are abandoning coral reefs.
The study
[1] found that, as
coral reefs heat up, grey reef sharks are spending significantly less time around them; wjth some sharks not returning to these reefs for more than 16 months, after a major heatwave.
It was likely that high temperatures drove the sharks away immediately; but that the impact of the heat on the health of the reef kept them away.
Between 2013 and 2020, researchers tracked more than 120 grey reef sharks, in the Indian Ocean’s
remote Chagos archipelago. They found that while it took months for the sharks to return to most of the reefs, sharks also spent more time sheltering in healthier and more resilient reefs.
Sharks are cold-blooded, and their body temperature is linked to
water temperature. If it gets too hot, they’re going to need to move
offshore, into deeper, and cooler waters.
Sharks play an essential role in maintaining the biodiversity, and
health of coral reef ecosystems. By eating both herbivorous and smaller predatory
fish, they help to keep coral from being overgrazed or overgrown by algae.
Reef sharks are a key part of the highly diverse and delicate ecosystem, which could become dangerously unbalanced, without them.
Yet, reef sharks have already disappeared from nearly 20% of coral reefs globally
[2], due to overfishing [about 100 million sharks are estimated to be killed each year, for their fins and meat; often using destructive
fishing practices, such as longlines and gillnets], and other threats; and this new finding has the potential to exacerbate these trends.
Fortunately, the shark population was relatively high on Australia’s Great Barrier Reef, the world's largest coral reef system.
Places like the
Bahamas, and
Australia had features which the scientists associated with "increased abundances of reef sharks". These places were seen to be "well-governed and having strong management" of shark fisheries or sanctuaries - areas that forbid
commercial fishing.
[1] “Environmental stress reduces shark residency to coral reefs” ~ by Michael J. Williamson et al
➥
https://www.nature.com/articles/s42003-024-06707-3
[2a] “Half a century of rising extinction risk of coral reef sharks and rays” ~ by C. Samantha Sherman et al
➥
https://www.nature.com/articles/s41467-022-35091-x
[2b] “Global status and conservation potential of reef sharks” ~ by M. Aaron MacNeil et al
➥
https://www.nature.com/articles/s41586-020-2519-y