‘Goldilocks’ water temperature for tiger sharks may have implications on future human attacks

A recent study published in the journal Global Change Biology on Thursday, March 8, found that tiger sharks are most active and most abundant in coastal waters of around 71 F (22 C).

Tiger sharks are a particularly dangerous species for swimmers. The species is second only to the great white in recorded attacks on humans and has a notorious reputation for eating anything, according to the study’s press release.

The species are found mainly in tropical and temperate waters, especially around the central Pacific islands.

Researchers from the United Kingdom, Australia, United States and Japan were involved on this collaborative study, according to Study Author Dr. Nicholas Payne of Queen's University Belfast and the University of Roehampton.

The international team of researchers collected data from tiger sharks in Hawaiian and Australian waters.

“We collected a variety of different types of data on tiger sharks: catch rates from long-term culling programs, accelerometer tags that measure body activity of the sharks and both satellite and acoustic tags that measure location of the sharks,” Payne said in an email.

The researchers found that the swimming activity levels, such as how much ‘effort’ they put into swimming, and coastal catch rates, which are an indication of abundance, of tiger sharks were both highest at the same temperature, around 71 F.

“Because of this thermal optimum, tiger sharks are more likely to be seen in winter at warm tropical beaches but in summer in cooler climates, such as in Sydney, Australia,” Payne said.

The study specifically focused on tiger sharks. The researchers were interested in the species because it is a large apex predator that plays an important role in subtropical and tropical marine ecosystems, Payne said.

The researchers hope that these results will be helpful for predicting when and where tiger sharks will be in the future.

“This will be important for managing the ecological impact of changes in tiger shark distribution, but also for managing risks associated with human interactions with this species,” Payne said.

The ability to use water temperature to better predict occurrences of tiger sharks could help with the ability to develop management strategies that reduce the risk of shark attacks, according to Payne.

The study shows that temperature has a strong influence on how sharks behave and where they go. Therefore, increases in ocean water temperatures related to climate change may have a significant impact on shark behavior and whereabouts.

“As the oceans warm, we predict that tiger sharks will track their thermal optimum, meaning that they will start becoming more common at places and times where they were not regularly seen before,” Payne said.

For example, Sydney’s popular beaches currently see some tiger sharks in summer, but rarely in winter. If the seas around Sydney warm by a couple of degrees then tiger sharks may be just as common in winter as in summer in that location, according to Payne.

It's highly likely that there is going to be an increase in the total number of shark attacks, but not necessarily the rate of shark attacks, according to Director Emeritus of the Florida Program for Shark Research at the University of Florida George Burgess.

"The reason being with warmer waters and warmer air temperatures, people are more likely to go into the water in areas that they may not have before," Burgess said.

For example, people in the Northeast in places like Long Island may become more likely to go into the water because it's warmer. Therefore, you have more people in the water and an increase in the number of hours of humans in the water.

Ocean waters will also be warmer in these previously cooler climates, so there may also be more sharks in the water.

For example, during El Niño years when the waters are warmer farther north along the East Coast, certain species of sharks were seen farther north than usual in places like New York.

"The total number of attacks certainly will rise with warmer ocean temperatures and air temperatures, but the rate may not because you may be putting the same number of people in the water in those areas as you're also getting more sharks, so the chance of the two coming together won't have changed, it is just a greater area covered," Burgess said.

Temperature preference of shark species plays a large role in shark whereabouts and, ultimately, the likelihood of human attacks.

However, there are a number of other factors that play a role in shark distribution and the number of attacks on humans. For example, the availability of prey also plays a large role in shark distribution, according to Burgess.

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