Migrations of the great white shark
In the world of sharks the great white has always been an outsider. It has a high media profile attention, and is the only shark that still carries that aura of brutal force, a ‘raw predator’ with its powerful body often covered with scars and its fearless approach of human visitors. It prefers open and cold waters, with Australia/New Zealand, South Africa and the North Eastern Pacific as the mostly frequented locations. UW photographers that visit Guadalupe island in Mexico in autumn or early winter have a good opportunity to get some nice pictures of this legendary shark. The island is the home base of the elephant seal which makes it a favorite place for foraging in that season. Unfortunately, being locked up in a cage is still the only safe option for UW photographers to get close to the great white. In South Africa at Seal island, another hotspot for meeting great whites visitors can even join great white shark breaching trips combined with cage diving. Great whites are attracted by a seal decoy pulled behind the vessel and occasionally jump with lightning speed with unbelievable precision and accuracy to take the decoy.
Upper picture: Location data for four satellite-linked radio-telemetry-tagged female white sharks leaving from Guadalupe island during their offshore migration. Adapted from **
Lower picture: Site fidelity of all satellite tagged white sharks to three core areas including the North American continental shelf waters and the waters surrounding the Hawaiian Island Archipelago and the ‘White shark Café’.Yellow circles represent position estimates from light- and SST-based geolocations, red circles satellite tag endpoint positions respectively. Adapted from ****.
Apart from the white sharks disputed reputation as a man eater and spectacular sightings we know very little of its behavior: its migratory routes, breeding grounds, socialising behavior, how it attracts a mate and what drives its search for a prey. Getting to know how and were they travel is one the challenges for marine biologists as well shark conservationists. The great white is on the red list of theathened animals of the World Conservation Union, and research that clarifies their immigration patterns, mating and pupping grounds could indeed have important implications for their conservation. Are great whites like other apex predators, that often alternate long trips in the wide ocean with visits to specific aggregation areas?
Bio-telemetry is the tool that has shed more light on these questions in the last decade. It implies detection of a shark from a certain distance with an electronic receiver that picks up a signal from a shark implanted ‘tag’. Often used are acoustic listening receivers placed at at the ocean floor at hot spots near the coastline. Whenever a tagged shark comes within a distance of say 800 feet of a receiver, a code or ‘ping'' for that particular shark will be received and transmitted. Its a useful tool to detect the presence of a shark in specific areas. More advanced sattelite based tools are PAT (Pop-up Archival Transmitting) and SPOT (Shark Position and Temperature) tags. PAT or Popup archival tags are normally active for maximal one year and provide approximate location data, making it most useful for tracking long-distance migrations. These tags remain inactive as long as the shark is submersed, until the tag detaches itself from the shark and floats to the surface and starts transmitting its collected data. They do not have to be physically recovered for the data to be obtained. Popup tags are relatively non-invasive small transmitters. They are placed with a tag pole near the base of the dorsal fin, mostly when the sharks come close to a diver or takes a bait from a small boat drifting with the shark on the surface. In contrast, the more expensive battery operated SPOT tags will transmit information for several consecutive years, making it the first choice for studying long term migration periods. These tags do not work underwater but transmit a signal to a satellite receiver whenever the dorsal fin breaks the surface of the water. They are more difficult to deploy since the shark has to be caught and restrained while the tag is attached to the dorsal fin. Which requires hooking the shark with a line and bait supended from a vessel, hauling it on board of the vessel, where the transmitter is attached by drilling holes in the apex of the dorsal fin and secured with metal or plastic bolts. It certainly involves some form of mutilation of the shark, justified by the argument that it provides a more complete picture of the sharks migration routes than PAT tags.
GWs are pelagic as well as philopatric Some useful information has been collected with sattelite tagging in the past years on its migration and breeding sites. An important finding was that great whites are pelagic (go out in the open sea) as well as ‘philopatric’ (returning to the same sites). In the open ocean they often display long migration paths with strange and irregular patterns. Males and females also seem to differ with respect to the duration of their migration phases. Some more details are presented below.
South Africa In South Africa, great white sharks in False Bay do not stay at Seal Island year-round, although it provides their favorite food, cape fur seals*. Most of the PAT tagged white sharks revealed at least three different movement patterns, including wide-ranging coastal migrations up and down the eastern side of South Africa. Often they leave the island for long trips in the Ocean, even extending over thousands of miles and crossing oceans separating continents. Most notorious case is female shark Nicole (named after Nicole Kidman) that was tagged in Gansbaai South Africa and migrated 11,000 km to Western Australia. Nicole was first tagged in November 2003, near the Western Cape of South Africa where researchers affixed a pop-up archival satellite transmitting tag to her dorsal fin. This is not a unique event; there have also been a few other recorded incidents of great whites from South Africa migrating to Australia and back within a year. This also included return of females mating in Australia to give birth in South Africa.
Pacific white sharks: Guadalupe island migrations Most detailed information on great whites migratory patterns has been collected from northeastern Pacific white sharks, revealing a seasonal migration between a vast offshore region and coastal aggregation sites. The sharks spend roughly half of their time in the deep-ocean environment, sometimes traveling as far as the Hawaiian Islands before returning to the continent. Hawaii is likely to be an important foraging area for great whites. A study by investigators of the Marine Conservation Science Institute used satellite-linked radio-telemetry (SLRT) tags with a multi-year battery capacity on a limited group of sharks.** (see insert: upper figure for aggregated data of 4 females). It confirmed a strong seasonal philopatry of GWs to one of two aggregation sites in the northeastern area: one off central California, USA, and the other at Guadalupe Island. Mexico. There were also interesting sex differences. Females showed a 2-year migration period that rougly consisted of a offshore gestation period phase which began when the females departed Guadalupe island. They spent around 18 months patrolling in the great ocean between Baja California, Mexico and Hawaii before migrating back to the coastal regions of Mexico during the pupping season. During this phase, females remained in the coastal waters of Baja California, after which they returned to Guadalupe again for the autumn and winter months, probably with a double purpose: feeding on the seals and mating.
White shark ‘café’ Tracking data of this study also indicated that during the offshore phase mature males and females were spatially strictly segregated, but joined again during their concurrent seasonal presence at Guadalupe Island. For males the offshore migration phase lasted only one year. Curiously, males in particular had a strong preference to hang around at a location approximately halfway between the coast of Baja California, Mexico and the Hawaiian Islands, also called shared offshore foraging area (SOFA) or White shark Café. This area lies within the eastern boundary of the North Pacific Gyre. Their preference for this destination remains a mystery because it is presumed to have very little food for the animals; researchers describe it as the shark equivalent of a desert (see also ***)
North Pacific Californian coastline Another study was carried out on a much larger group of North Pacific sharks by biologists from the Department of Biology, Stanford University. **** They mainly focused on the migratory routes of great whites of the California coast, using satellite PAT tags in combinaton with passive acoustic monitoring via listening stations near the coastline. The Californian sharks also alternated site fidelity at hot spots along the Californian coastline with long-distance migrations to and from defined oceanic core areas (see insert: lower figure for aggregated data). This included the same foraging area (White shark café) visited by the Guadalupe island sharks. “What we know," said Salvador Jorgensen, who co-authored the study, "is that all of them leave the coast in the winter and all of them end up either in the cafe or offshore in Hawaii." By comparing overlap between male an female sharks the study suggests that mating might also occur at the Cafe. Observed overlap was minimal near Hawaii and ‘’no direct or indirect evidence of copulation at North American coastal sites has ever been reported, despite decades of observation’. So the issue of mating sites still remains a bit of an open question in both studies of north Pacific whites.
Sources and links
* Bonfil R, Meyer M, Scholl MC, Johnson R, O’Brien S, Oosthuizen H, Swanson S, Kotze D, Paterson M: Transoceanic migration, spatial dynamics, and population linkages of white sharks. Science 2005, 310:100–103
**Domeier ML, Nasby-Lucas N: Migration patterns of white sharksCarcharodon carcharias tagged at Guadalupe Island, Mexico, and identification of an eastern Pacific shared offshore foraging area. MarEcol Prog Ser 2008, 370:221–237.
***Domeier ML, Nasby-Lucas N, Palacios DM: The Northeastern Pacific white shark Shared Offshore Foraging Area (SOFA): A first examination and description from ship observations and remote sensing. In Global Perspectives on the Biology and Life History of the White Shark. Edited by Domeier ML. Boca Raton: CRC Press; 2012:147–158.
****Jorgensen, SJ; Reeb, CA; Chapple, TK; Anderson, S; Perle, C (2010), "Philopatry and Migration of Pacific White Sharks", Proceedings of the Royal Society B, 277: 679–688