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Conservation

Maui: The Tiger Shark’s Paradise

Article

Habitat geography around Hawaii’s oceanic islands influences tiger shark (Galeocerdo cuvier) spatial behavior and shark bite risk at ocean recreation sites. (2018). DOI: 10.1038/s41598-018-23006-0. https://www.nature.com/articles/s41598-018-23006-0

Background

The U.S. state of Hawaii is an archipelago of eight major islands, of which Maui is one of the major islands, also considered the second most populated. The island is known for its high number of shark incidents in the Hawaiian State. Over the past 20 years, Maui had twice as many shark bites incidents than Oahu, the most populated island of Hawaii.

Tiger Shark by Albert kok – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=8969258

Local scientists say that most of these incidents were caused by tiger sharks, which approach the Hawaiian Islands to give birth and feed, especially during late summer to early fall.

Dr. Carl Meyer and his team had a guess about the causes that leads Maui to have a higher number of shark bites than Oahu. They believed that it could be occurring because the population of tiger sharks on Maui was higher than on Oahu or because these sharks have visited human ocean recreation sites more often around Maui compared to other islands. To answer these questions, Dr. Meyer and his colleagues used electronic technologies to understand tiger shark movements around the Hawaiian Islands.

 

The study

Dr. Meyer and his team captured 41 tiger sharks at four Hawaiian Islands from 2013 to 2015. The sharks were equipped with electronic devices such as satellite and acoustic telemetry tags, which provided a detailed overview of their movement around the main Hawaiian Islands.

The results show that tiger sharks from different islands have similar movements. Most of the animals tagged for this study made large open-ocean excursion, including tours between and outside the Hawaiian Islands, but the majority seem to go back to their “home” island. The study’s tracking data show that during the winter, which is known mating season for tiger sharks in Hawaii, the tiger sharks go to Maui to mate.

Tiger shark’s ID codes emitted from tags can be detected by acoustic receivers. (photo: Jim Abernethy)

The authors believe that because of the large protected ocean shelf, the high availability of food, mating partners, and perfect habitat for pups make Maui a paradise island for tiger sharks.

During the fall season, adult females go to Maui to give birth, where they can have as many as 80 pups in a litter. These sharks are the only species in its family that are viviparous with yolk-sac, meaning that they have pups through a combination of laying eggs and giving birth to pups. An adult female develops eggs inside their bodies but doesn’t lay them. The eggs hatch inside the female’s body and develop for 16 months before being born.

Behind the good habitat quality for sharks

The real problem behind these amazing shark’s encounters and all the perfect conditions for the mother and her babies on Maui is that tiger sharks are using areas near popular recreation beaches, causing what the authors called an “overlap core”. Using the acoustic detections, Dr. Meyer and his colleagues discovered that home range areas around Maui are closer to high-use recreation sites than areas documented around Oahu. The authors believe that all combinations of factors explain why Maui has had more shark incidents than other Hawaiian Islands.

Location of shark bites incidents (yellow points) along high recreational- use (pink) and low recreational-use coastlines (dark blue).

Because of the shark attacks, Hawaii had historically allowed tiger shark culling to minimize public fears about getting bitten. Many specialists worked against this decision and made a change in conservation awareness about sharks. Scientists demonstrated that this strategy was not effective as they had more shark incidents occurring in the aftermath of culling than before.

According to Florida Museum of Natural History, Hawaii averages out to a shark attack every 1.59 years. Despite the natural presence of large sharks that use recreation sites in Maui waters, the island hosts over 2 million tourists per year, which shows that the risk of shark bite is relatively low and the number of ocean recreation activities on Maui is not the primary cause of incidents. Dr. Meyer’s study suggests tiger sharks are mostly disinterested in or even avoiding people.

Maui Nui insular shelf is an important natural habitat for Hawaii marine life, consequently large tiger sharks are frequently present in recreational sites. A good approach to avoid shark bites is to inform tourists about ocean recreation by raising awareness of the natural presence of these predators in Hawaii waters. Sharks are part of the environment and preventive measures could be taken to avoid unexpected encounters, such as staying out of the water if it’s murky, swimming with others and staying close to shore.

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