Male Tiger sharks, as this one seen here, showed signs of mating abrasions on their pelvic claspers (shown inset)

Researchers from the University of Hawai‘i at Mānoa’s Hawai‘i Institute of Marine Biology completed the second phase of a project to observe the movements of tiger sharks caught and tagged around Maui, UH reported last week.

In response to an uptick in the number of shark attacks recorded on Maui, the state Department of Land and Natural Resources is funding a study on the movements of tiger sharks caught and released around the Valley Isle. DLNR plans to use the results of the study to guide future decisions regarding management of shark populations in the state of Hawai‘i.

Lead scientists Carl Meyer and Kim Holland report that in early 2014, their team caught and released nine tiger sharks in waters off Maui, according to UH. Six of these sharks were equipped with satellite transmitters to track their movements; five off the north coast, and one off Olowalu in West Maui.

The near-real-time tracks of these sharks will be added to the eight tracks already on the Pacific Islands Ocean Observing System Hawai‘i Tiger Shark Tracking webpage.

All of the six new tags are reporting back via satellite, but so far only two have provided messages clean enough to glean location fixes. This may be due to weather (rough seas mean less dry time for the tag, even when the shark is swimming at the surface), shark behavior (sharks may be swimming at the surface less often), limited satellite coverage, or a combination of these factors. To help scientists keep track of tiger shark movements when satellite tags are not providing many fixes, all sharks are also implanted with acoustic tags that transmit to underwater receivers deployed on the sea floor at sites of interest around Maui.

Tiger shark fin HIMBThe most recent tagging trip off Maui was timed to coincide with the tiger shark mating season, a time of year when large males are easier to catch. All six sharks tagged in January bore fresh mating scars. As part of the study, researchers hope to determine whether major biological events such as pupping and mating draw tiger sharks to Maui, and whether those sharks leave afterwards.

In addition to the research funded by DLNR, Holland and Meyer have an existing data set for more than 150 electronically tagged tiger sharks captured at multiple islands and atolls throughout the Hawaiian archipelago. Previous tiger shark tagging locations include Hawai‘i Island, O‘ahu, Mokumanamana, French Frigate Shoals, Pearl and Hermes Reef, and Kure Atoll.

Some of the historical data are available on the PacIOOS Voyager at pacioos.org/voyager, an interactive map interface.

Tiger shark tagging Luiz Rocha

Rolling sharks onto their backs promotes a trance-like state called ‘tonic immobility,’ thus allowing researchers to implant transmitters into sharks.

Visit goo.gl/1E1LoR for a direct link to the tiger shark distribution layer in PacIOOS Voyager. In addition to these historical data, the team has multiple, electronically tagged tiger sharks currently swimming around various locations in the Hawaiian chain. These include sharks that they have been tracking for more than five years.

“We are also planning additional satellite tagging for the island of O‘ahu and intend to make these data available to the public in near-real-time via the PacIOOS website,” Meyer said. “These O‘ahu data will provide a concurrent record for comparison with sharks tagged around Maui.”

The track of one tiger shark tagged off Kāne‘ohe, O‘ahu at the same time as tagging was occurring on Maui in January 2014, is available on the PacIOOS website.

Visit pacioos.org/projects/sharks/ for more information.

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