photo credit Phillip Colla
Very few animals generate the mixture of fascination and terror as the great white shark. Unfortunately, the terror-associated, anti-shark sentiment has led to the unnecessary slaughter of many animals. White sharks have recently been listed for international protection under the Convention on International Trade in Endangered Species of Wild Flora and Fauna (CITES) Appendix II and were listed as vulnerable by the International Union for the Conservation of Nature. A thorough understanding of the white shark’s life history will allow us to readily identify the regions and life history stages that this species is most vulnerable. Scientists with the Marine Conservation Science Institute have been performing a comprehensive study of white sharks at Guadalupe Island, Mexico since 1999 using tools such as satellite tagging and photo-identification.
Dr. Domeier insert a pop-up satellite tag in a white shark off of Guadalupe Island
Pop-up satellite tags One type of tag we have used to study white sharks is the pop-up satellite tags. Pop-up satellite tags are inserted at the base of the dorsal fin as the sharks are lured close to the boat with large tuna carcasses. After a set period of time the tags detach from the shark, float to the surface and transmit collected data of light, temperature and depth. These tags have remained on the sharks for up to 1 year and have given us invaluable information on the behavior and movement of white sharks including swimming depths, temperatures encountered, daily patterns, and migratory movements. With this technology we have shown that the sharks can dive as deep at 1000m and that they spend as much as half the year away from land out in the middle of the Pacific Ocean. We have found that sharks tagged at Guadalupe Island spend autumn and winter at the island, begin an offshore migration in late winter to early spring, spend spring and summer offshore between Baja California, Mexico and Hawaii, and then return to Guadalupe Island in late summer. We know that they travel out to the middle of the Pacific Ocean, but what draws them out there is still a mystery.
Photo-identification In conjunction with our satellite tagging, we have also been studying the Guadalupe Island white sharks through an extensive photo-identification project. We derived a unique system for identifying individual sharks by their color patterns and currently have a catalog of 116 white sharks from Guadalupe Island. The vast majority of the sharks in our catalog have been sighted over multiple years, with many of them having been sighted every year since 2001. The photo-ID database is used to calculate an index of abundance for the Guadalupe Island white sharks. The data we collect from this helps to not only track individual sharks but also monitor the status of the overall Guadalupe white shark population to determine if the population is increasing, decreasing or stable. This is important data in white shark management and conservation. You can make a difference in shark conservation by allowing us to view your Guadalupe Island white shark photos. For more information on how you can help, contact Nicole.
Through the combination of pop-up satellite tags and tracking through photo-identification we have been able to show that male sharks return to Guadalupe Island year after year while mature females may disappear for 2-3 years before returning to the Island. This pattern is most likely associated with mating and giving birth, but where they go has been a mystery. Following the track of SPOT tagged mature female white sharks, we have been able to show that they stay offshore in the middle of the Pacific Ocean for as long as 15 months. We had one tagged mature female travel into the Sea of Cortez, possibly to give birth.
SPOT tags Pop-up tags provide great data with respect to habitat preferences (temperature and depth) and diving behaviors, but the location data are not very precise and the tracks are not longer than 1 year. By working with the electronic tag manufacturer, we have developed a new satellite tag to address the weaknesses of pop-up tags. These new tags, called SPOT (Smart position or temperature transmitting) tags, can send near real-time position data up to six years! The drawback is that the tag must be mounted to the dorsal fin of each shark, so the sharks must be captured, tagged and released. However, together with Chris Fischer and the crew of his M/V Ocean, we’ve developed handling methods that have proven to be safe and effective, and we are no answering research questions that can be addressed in no other way. Additionally, the opportunity to exam these live adult white sharks has opened the door to brand new avenues of research that we had never before even considered. We are currently collecting data relative to when and where these sharks may be mating, where the females go when they disappear from seasonal adult aggregation sites like Guadalupe and the Farallon Islands, and whey they may go to give birth. We are also using this technology with juvenile white sharks in order to track their movement and hopefully show how and when juveniles recruit to adult aggregation sites. White sharks continue to fascinate us, even after more than a decade of research. The more we learn about them the more we are surprised by what we learned and by how many new questions there are to address! For recent tracking data from our tagged white sharks click here.
photo credit Phillip Colla
By combining long term photographic identification of individual white sharks from Guadalupe Island, together with long term tracking of these same sharks, the researchers at the Marine Conservation Science Institute have put together the most comprehensive study of white sharks in the world. We are committed to protecting the Guadalupe Island white shark aggregation and increasing the overall knowledge of northeastern Pacific white sharks.
We gratefully acknowledge the support of The George T. Pfleger Foundation, Fischer Productions, the Offield Family Foundation, Guy Harvey Ocean Foundation, and the Guadalupe Island Conservation Fund.
Publications:
Nasby-Lucas N., H. Dewar, C.H. Lam, K.J. Goldman, M.L. Domeier. 2009. White Shark Offshore Habitat: A Behavioral and Environmental Characterization of the Eastern Pacific Shared Offshore Foraging Area. PLoS ONE 4(12): e8163. doi:10.1371/journal.pone.0008163
Domeier, M.L and N. Nasby-Lucas. 2008. Migration Patterns of White Sharks (Carcharodon carcharias) Tagged at Guadalupe Island, Mexico, and Identification of an Eastern Pacific Shared Offshore Foraging Area. Mar Ecol Prog Ser 370: 221–237.
Domeier, M.L. and N. Nasby-Lucas. 2007. Annual re-sightings of photographically identified white sharks (Carcharodon carcharias) at an eastern Pacific aggregation site (Guadalupe Island, Mexico). Marine Biology 150:977-984.
Dewar, H., M.L. Domeier, and N. Nasby-Lucas. 2004. Insights into young of the year white shark, Carcharodon carcharias, behavior in the Southern California Bight. Environmental Biology of Fishes 70:133-143.
