Tiger Shark Migration Pattern May Help Prevent Attacks in Hawaii

Tiger sharks are some of the most dangerous fish in the oceans with their powerful jaws. In fact, this species of shark is one of the most likely to attack humans, which makes tracking their movements crucial. Now, scientists have learned a bit more about these sharks; they've discovered the migration of mature female tiger sharks, which could provide insight into attacks near the main Hawaiian Islands.

In 2012, there were 10 reported tiger shark attacks in Hawaii. In 2013, there were eight attacks with a fatality that occurred in August--the first to have occurred since 2004. In order to help prevent these attacks in the future, the researchers decided to track the movements of tiger shark migration.

"We have previously analyzed data to see which sharks are hanging around shark tours with cage divers on Oahu, and one of the things we noticed was that you'd get a spike in how many tiger sharks are seen in October, which would match our predicted model that you're having an influx of big, pregnant females coming from the northwestern Hawaiian Islands," said Yannis Papastamatiou, a marine biologist, in a news release. "There even tends to be a spike in the number of shark bites that occur during that season."

In order to track shark movements, the researchers used a series of new techniques. They tagged more than 100 tiger sharks and then used passive acoustic telemetry to gather the findings. Collecting seven years of data, the scientists then created a model. They found that only a portion of the tiger shark population migrates at one time and that there is a higher probability for females to arrive on the main Hawaiian Islands between September and October.

"We believe approximately one-quarter of mature females swim from French Frigate Shoals atoll to the main Hawaiian Islands in the fall, potentially to give birth," said Papastamatiou. "However, other individual sharks will also swim to other islands, perhaps because they are trying to find a more appropriate thermal environment, or because there may be more food at that island. So, what you see is this complex pattern of partial migration that can be explained by somewhat fixed factors, like a pregnant female migrating to give birth in a particular area, and more flexible factors such as finding food."

The findings may allow the researchers to better track the movements of these sharks. This, in turn, could help beaches decide whether or not to remain open to swimmers and could allow those in nearby waters to take precautionary measures.

"At least now we have an inkling as to how males and females behave differently and how these behaviors vary with resource changes or environmental changes," said Christopher Lowe, a professor of biological sciences who was not involved in the study, in a news release. "It gets us a step closer to the ability to better understand why incidents occur."

The findings are published in the journal Ecology.