Project: Movements and behavior of white sharks near a seal colony at Guadalupe Island, Mexico

Fig. 1. M/V Ocean Odyssey off of Guadalupe Island

Introduction:

Guadalupe Island is an important white shark (Carcharodon carcharias) aggregation site in the eastern Pacific. The present thesis focuses on the behavior of white sharks at Guadalupe Island and provides information that will help in the development of future management and conservation plans for this species in Mexico.

Methods:

Individual sharks are tagged with acoustic transmitters so that they can be detected and tracked. We use both simple beacons, which transmit pulses at a fixed rate and are used to identify the presence of an animal, and telemetry transmitters, which can be equipped with sensors. We use transmitters with combinations of two of three different sensors: depth, speed and temperature. Sharks are tagged from cages and small boats deployed from cooperating ecotourism vessels such as the M/V Ocean Odyssey (Fig. 1) and M/V Islander .

Progress:

Preliminary records of the movement patterns and swimming depths of juvenile and adult white sharks ranging from 1.8 m TL to 5 m TL have revealed the following: 

Fig. 2.White shark observed near Guadalupe Island

1) Horizontal movements are similar in juveniles, which stay close to shore during all day.

2) Adults move farther during the day while searching for prey and stay close to shore at night.

3) The rate of movement of adults exceeded that of the juveniles due to their capacity to maintain an optimal physiological operating temperature.

4) There is an exponential relation between total length and habitat range possibly related to their size and the distribution of their prey.

5) Depth and temperature records indicate a number of interesting behaviors, including a strong diurnal pattern, and behavioral differences across age classes, possibly due to different thermoregulation capabilities and prey preferences.

6) Ten potential prey species were identified for juveniles and four for the adults.

7) Ten well-documented records of predation events by white sharks on pinnipeds, the first such records at this location.

8) We recorded the maximum difference between the internal temperature of the stomach of a white shark and the surrounding water (16 °C) in the world, confirming the hypothesis of thermoregulation in this species.

9) Temporary social structures are formed with a dominance hierarchy based on size during predation events; similarly sized sharks can dissuade the competitor from eating its prey through displays (exaggerated swimming style) before a direct attack.

Personnel:

Mauricio Hoyos (lead)

Felipe Galvan-Magana, Ph.D.

El Centro Interdisciplinario de Ciencias Marinas (CICIMAR), La Paz, Baja California Sur, Mexico

Pete Klimley, Ph.D.

Department of Wildlife, Fish, & Conservation Biology, University of California, Davis, CA, USA

Funding Sources:

Absolute Adventures - Shark Diver

CONACYT

Nautilus Productions