Unexpected increase in shark numbers - 'fantastic fun'

The numbers of aggressive bull sharks has increased sharply in a coastal area in the United States. Scientists link it to rising water temperatures – and predict more shark-human interactions as the planet warms.

The bull shark is counted – along with the white shark and tiger shark – among the shark species that are behind the most attacks on humans. It lives in warm coastal waters in, for example, North America, but can also swim far up rivers.

Now an American study, carried out in Mobile Bay in Alabama in the USA, points to a fivefold increase in the number of young bull sharks in the area between 2003 and 2020. This despite increased urbanization along the coasts which can stress the fishermen.

“Fantastic fun,” writes Fredrik Jutfelt, who is professor of zoophysiology at the University of Gothenburg and who read the study, in a comment to TT.

Threats to sharks

The researchers analyzed how several environmental factors changed in the area during the period. The average surface water temperature had increased from 22.3 to 23 degrees, and according to computer modeling, temperatures above 22.5 degrees were associated with an increased presence of bull sharks.

Researchers believe it could both affect local fisheries and lead to more “interactions” between sharks and humans. At the same time, the bull shark plays an important role in ecosystems.

Climate change is generally seen as a threat to sharks and, together with overfishing, can lead to more species being red-listed.

But the researchers behind the study, published in the journal Scientific Reports, believe that at least young bull sharks appear to be more resilient as temperatures climb. Although the study cannot establish any causal relationship, Fredrik Jutfelt agrees that it points to the sharks benefiting from warmer water.

“Deadly Heat Waves”

Meanwhile, the Gulf of Mexico, where Mobile Bay is located, had its hottest year on record last year with temperatures well above what the sharks can handle, according to Jutfelt.

“The weakly positive effect of warmer water can be completely counteracted by the downright deadly heat waves we see in the oceans last year,” he writes.

The number of sharks worldwide has declined sharply since industrial fishing took off, according to the World Wide Fund for Nature (WWF).