Tracking Tiger Sharks

Aloha,

My name is Danny and I am one of the Teaching Assistants for the Marine Ecology & Evolution Lab this Spring. Last week, I along with other members of the Shark Research Team of the Hawai’i Institute of Marine Biology headed to Maui for the second trip of a two-year study focusing on tiger shark (Galeocerdo cuvier) movements around Maui, and comparing their behavior to that of known movement patterns around the other main Hawaiian islands. This study, funded by the Hawai’i state Department of Land and Natural Resources, Division of Aquatic Resources, was launched in early October 2013 and is led by principal investigators Dr. Carl Meyer and Dr. Kim Holland.

Tiger Shark SPOT

SPOT tag on dorsal fin. Photo credit: HIMB

Each shark was “double-tagged” with an acoustic and satellite transmitter. Acoustic tags consist of uniquely identifiable ultrasonic transmitters that are surgically implanted into each shark to ensure longer retention. These transmitters are then detected by underwater receivers stationed at various locations on the sea floor. When a tagged shark comes within detection range of a receiver (detection radius is up to 1 km), its unique ID code is recorded, together with the date and time. The records from receivers at different locations are combined to create an overview of shark movement patterns. In comparison, satellite tags are detectable over broad geographic areas and remotely relay information to Argos satellite arrays. These tags utilize radio transmissions, requiring the tag to have contact with air to send data (hence satellite tags must be externally attached). For this study, Smart Position or Temperature Transmitting Tag (SPOT tags) were attached to the dorsal fins of tiger sharks. SPOT tags transmit a signal to the Argos satellite array whenever the dorsal fin breaks the surface of the water. These transmissions result in geolocation estimates with location accuracies that range from a few hundred meters to several kilometers. The combined data will be used to help determine whether sharks around Maui are more resident (“site-attached”) than they are around other islands, and whether they exhibit greater use of inshore habitats than in other locations.

DCIM100GOPRO

Underwater acoustic receiver. Photo credit: Mark Royer

Furthermore, a new web tracking page is available online from the Pacific Islands Ocean Observing System showing the movement of several tiger sharks that were previously fitted with satellite tags off Maui (http://oos.soest.hawaii.edu/pacioos/projects/sharks/). So far, the website features tracking of seven sharks – one male and six females – ranging in size from 9.3 feet to 14.2 feet. Six additional tiger sharks – two males and four females – were fitted with satellite tags last week.

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