Hawaii Tiger Shark Research

Active Tracking of Tiger Sharks in Hawaii

Principal Investigator: Kim Holland

Project Overview

The tiger shark, Galeocerdo cuvier (Peron & LeSueur), is a large (up to 4.6m or 15ft) predator found in tropical and subtropical waters worldwide. Tiger sharks are one of three main shark species known to attack humans, and are thought to be responsible for most shark attacks in Hawaii. Three or four shark attacks occur per year on average in Hawaii (compared to an annual average of 40 drownings) and most attacks are non-fatal. This attack rate is surprisingly low considering that thousands of people swim, surf and dive in Hawaiian waters every day. Despite these statistics, shark attacks remain a highly emotive topic in Hawaii.

Culled Tiger Sharks

Figure 1. Culled tiger sharks on the boat ramp in Haleiwa, Oahu.

During the latter half of the twentieth century, shark culling was carried out in an attempt to make the waters of Hawaii safer. From 1959 to 1976, the state of Hawaii culled 4,668 sharks (at an average cost of $182 per shark), including 554 tiger sharks, in a series of shark control programs. In spite of such efforts no significant decrease in rate of shark attacks was ever detected. The rationale for culling was a widely-held belief that tiger sharks were site-attached to small home ranges, with individual sharks preferring to remain along the same small stretches of coastline. This theory had never been empirically tested.

Following a series of fatal shark attacks from 1991-93, the State of Hawaii considered reviving the shark control program. This prompted a team of graduate students, led by Dr. Kim Holland of the Hawaii Institute of Marine Biology, to lobby the state legislature to instead fund scientific research aimed at increasing understanding of tiger sharks. During the mid 1990’s we tracked tiger sharks captured off Honolulu to test the hypothesis that tiger sharks are site-attached to small, coastal home ranges.

Methods

Active tracking involves capturing tiger sharks, equipping them with small ultrasonic pingers, then releasing and following them in a boat equipped with a directional hydrophone and acoustic receiver. To capture tiger sharks, we set ten hook lines baited with large tuna heads and fish scraps overnight in the waters south of Honolulu. Lines were recovered at dawn and captured tiger sharks were brought alongside a small boat for tagging.

Fishing for tiger sharks

Figure 2. Recovering shark fishing lines at dawn. Honolulu, Oahu, Hawaii.

Captured tiger sharks were restrained by tail-roping and inverting them (turning them belly side up). This procedure places sharks in a temporary, trance-like state referred to as ‘tonic immobility’. This allows researchers to indentify, sex and measure the sharks, and to surgically implant them with tracking pingers. We tracked 8 tiger sharks during this project (one on two occasions), each for up to 50 hours.

Tiger inverted

Figure 3. Rolling sharks onto their backs promotes 'tonic immobility' - a trance-like state. This allows researchers to implant transmitters into these large, powerful animals.

Results

Short-term (up to 50 h), active tracking of tiger sharks equipped with acoustic transmitters revealed direct movements of up to 35 km across a 500 m deep channel between oceanic islands, orientation to the bottom in depths < 300 m and to the mixed layer (0-80 m) in deeper waters with occasional brief dives as deep as 335 m. These data clearly showed previous assumptions of tiger shark site attachment to restricted coastal areas were incorrect, and shark culling programs are unlikely to be effective in catching sharks responsible for attacks as these individuals may move beyond the fished area within hours of the incident.

Figure 4. Composite plot of all nine tiger shark tracks, illustrating universal offshore movement following tag-and-release and predominant tendency for directed movements towards Penguin Banks (PB). Adapted from Holland et al. 1999.

Current Tiger Shark Research

We are currently focusing on learning more about the long-term movement patterns and swimming behavior of tiger sharks. You can learn more by clicking on the links below;


Hawaii Tiger Shark	NWHI Predator Tracking	Tri-axial Accelerometers

Project Publications

Holland KN, Wetherbee BM, Lowe CG, Meyer CG. 1999. Movements of tiger sharks (Galeocerdo cuvier) in coastal Hawaiian waters. Marine Biology 134: 665-675.

Project Sponsors

Sponsor DLNR

Sponsor DAR