Climate-Challenged Whale Sharks Flocking to Island Chain

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Whale sharks are flocking to waters off of the Azore islands, a Portuguese archipelago in the North Atlantic Ocean, a new study has found.

Whale sharks tend to enjoy warmer temperatures, but even this species has been affected by climate change, according to the study, which is published in the latest issue of the journal PLoS ONE.

It appears to be a Goldilocks effect where the sharks prefer temperatures that aren’t too hot or too cold. Things must be just right — at least for the momen t– in the Azores, which is becoming whale shark central.

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Pedro Afonso of the University of the Azores and his colleagues wrote that the “occurrence of the whale shark in the wider Azores region increased drastically in 2008. Prior to this, and for a full decade, these large animals had only been sighted sporadically,” but the sharks keep coming.

Whale sharks, the world’s largest sharks, are slow-moving filter feeders known for their large mouths. They usually inhabit tropical and warm-temperate seas, preferring temperatures from 78.8 degrees Fahrenheit to 86 degrees.

In Portugal, the authors note that “whale sharks — local name ‘pintados’ — are known by Azorean fishermen to sometimes occur during the summer and associate with tuna, and have been used for a long time as an aid to locating and fishing the tuna schools.”

But the sharks have been coming even more often than that, to the point that "whale shark watching" tourism has become a growing business in the region.

The researchers analyzed a 16-year (1998-2013) observer data set from tuna fishermen around the region. They also used models to investigate the movement of the sharks in relation to factors such as food, sea surface temperature and seafloor features.

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Since 2008, whale shark presence around the Azores has been steadily increasing, which appears to coincide with water temperature changes.

Usually the Azores fall into the colder side of the sharks’ preferred range, but water temperature rises at this location are proving to be a draw for sharks. Conversely, temperatures that are too hot or too cold in other spots are becoming less desirable for them.

The temperature increase in the Azores correlated with larger amounts of chlorophyll — a, a type of whale shark food.

The researchers also found that whale shark populations are higher in areas of increased seafloor slope and closer to seamounts. That’s because these regions tend to be richer in chlorophyll-a.

“Our findings underline the potential for an increase of the wider Azores region’s importance as an oceanic habitat for the whale shark in the North Atlantic in years of exceptionally high water temperature, and for a concomitant shift in the whale shark distribution within the Atlantic Ocean, as predicted by global modeling studies,” Afonso and his team concluded.

“In the future, such shifts need to be placed in the context of decadal and very long-term changes in this ocean.”

Photo: A whale shark. Credit: ThinkStock

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