Ecology and Population Dynamics of White Sharks in the Eastern Pacific: a Case Study
- Barbara Block
- Salvador Jorgensen
End Date: December 31, 2009
White sharks (Carcharodon carcharias) are important predators occupying a vital position at the pinnacle of the ocean’s ecological food web. However, white sharks have been listed as ‘vulnerable’ to extinction by the World Conservation Union (IUCN Red List of Threatened Species), and are protected under Appendix II of CITES, the Convention on International Trade in Endangered Species of Wild Fauna and Flora. Despite broad concern for their conservation, relatively little is known about their distribution and ecology. Our goal is to gain a better understanding of white shark populations, as well as their migratory patterns, preferred habitats and physiology through tagging, photo identification and genetic analyses.
Our collaborative studies with Stanford University have revealed that adult white sharks in central California coastal waters seasonally migrate thousands of miles offshore to the Hawaiian Islands and to a mid-ocean area halfway between Baja California and Hawaii dubbed by scientists as “The White Shark Café.” Precisely why they visit these waters remains a mystery. When they return to the California coast they exhibit high site fidelity, consistently returning to the same local neighborhoods (pinniped rookeries) year after year.
We are now learning that great white sharks observed in California comprise a genetically distinct population. Our recent genetics data indicate that great white shark females in the northeastern Pacific have maintained long-term isolation from the other known great white shark populations (i.e. the major concentrations near South Africa in the southwestern Indian Ocean and Australia in the southwestern Pacific). Knowing that the population unit (northeastern Pacific) is distinct will enable us to census the population in order to determine its number, and know from year to year whether this population is increasing or decreasing. As an isolated population, it can be more vulnerable since it cannot be “rescued” or replenished via immigration from other populations. We will continue to study migratory pathways, habitat preferences and estimate the population size using photographic mark-recapture methods to insure that accurate and sufficient information is available for the effective management of great white sharks in the northeastern Pacific.
Satellite tagging technology is also enabling us to determine the critical habitat occupied by young-of-the-year great white sharks. In collaboration with Stanford University, the University of Hawaii, Centro de Investigación Científica y de Educación Superior de Ensenada, Mexico (CICESE) and California State University, Long Beach, we are learning about a great white shark nursery area that extends from the Southern California Bight down throughout Baja California. In this region, sharks up to three years of age inhabit shallow coastal waters and frequently move between U.S. and Mexican territorial waters. These results indicate where young great white sharks are vulnerable to bycatch in coastal fisheries of both countries and highlight the need for transnational collaboration in creating effective management plans.
Recent evidence suggests that great white shark bycatch is indeed landed and sold. Over a three-year period, 40 mummified juvenile great white shark carcasses were found by our great white shark team and research collaborators in a desert dump site surrounding a fish camp in Baja California. The DNA associated with the teeth of these carcasses can be analyzed to help determine the population structure of great white sharks in California and Mexico. We will continue our sampling of great white shark carcasses within this region through our collaboration with researchers at Mexico’s Laboratorio de Genética, Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México and Laboratorio de Ecología Pesquera, Departamento de Oceanografía Biológica, CICESE, and colleagues at Stanford University. Eventually, we will incorporate these DNA results into the larger picture of overall genetic diversity and uniqueness of great white shark populations in northeastern Pacific waters (California and Mexico).
Summary to DateIn 2009, Jorgensen et al. revealed how eastern Pacific white sharks adhere to a highly predictable migratory cycle. Individuals persistently returned to the same network of coastal hotspots (Tomales Point, Point Reyes, South East Farallon Island, and Año Nuevo Island) following distant oceanic migrations. White sharks sampled in California comprise a population genetically distinct from previously identified phylogenetic clades (South Africa and Australia/New Zealand). We hypothesize that the strong homing behavior revealed from tagging has maintained the separation of a northeastern Pacific population following a historical introduction from Australia/New Zealand migrants during the Late Pleistocene. Concordance between contemporary movement and genetic divergence based on mitochondrial DNA demonstrates a demographically independent management unit not previously recognized. This population’s fidelity to discrete and predictable locations offers clear population assessment, monitoring and management options.
For more information on the project's findings, the following peer-reviewed article has been published:
Jorgensen, S.J., Reeb, C.A., Chapple, T.K., Anderson, S., Perle, C., Van Sommeran, S.R., Fritz-Cope, C., Brown, A.C., Klimley, A.P. & Block, B.A. (2009) Philopatry and migration of Pacific white sharks. Proceedings of the Royal Society B: Biological Sciences. doi: 10.1098/rspb.2009.1155
- On August 20, 2012, the California Fish and Game Commission (Commission) received a petition to list the Northeastern Pacific population of white shark as threatened or endangered under the California Endangered Species Act (CESA). Pursuant to the requirements of CESA the Department prepared an evaluation of the petition which concluded that the petition contained sufficient scientific information to indicate listing may be warranted.
- On February 6, 2013, the Commission unanimously concluded that listing the Northeastern Pacific population of white shark as threatened or endangered may be warranted, and designated the species as a candidate under CESA. The Commission’s decision will take formal effect on March 1, 2013, when a notice of decision is published in the California Regulatory Notice Register. Within twelve months of this notice publication, the Department will provide a written report to the Commission indicating whether listing the white shark as threatened or endangered under CESA is warranted.
- Migration/movement patterns
Figures and Images
Figure 1. Tagged white shark.
Figure 2. The process of tagging a white shark.
Figure3. Global distribution map of white sharks.
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