Great white a regular visitor
|||Snorkeler survives encounter with shark|
By Jan TenBruggencate
Advertiser Science Writer
A great white shark, one of the biggest and most ferocious predators in the sea, can and does readily migrate between the California seal rookeries and the waters of Hawai'i, according to new satellite tagging research published today.
"It's amazing. It's a real curiosity as to what they're feeding on here," said Honolulu-based shark researcher Jeff Polovina, of the National Marine Fisheries Service.
Polovina conducted studies in 1994 that showed tiger sharks also range far from home.
The new findings about great white migrations were made possible by a new generation of computerized tags, which remain attached to marine animals for months, recording water temperature, depth and light levels, and then automatically detach, popping to the surface, where they transmit their data to the Argos satellite.
Researchers attached satellite archival tags to six great whites in 1999 and 2000 four off Southeast Farallon Island and two near Nuevo Island off the California coast near San Francisco.
One of the Farallon sharks migrated 2,280 miles to the waters around Kaho'olawe, and stayed in the Islands for four months of the winter and spring, and then returned to the Farallones.
The research sample was too small to know whether other great whites joined in this migration. Scientists were able to attach a new electronic tag to the shark at the Farallones in November 2001, and hope to learn whether it returns to Hawai'i.
The research on the great whites, by Barbara Block and Andre Boustany of the Tuna Research and Conservation Center, Peter Pyle and Scot Anderson of the Point Reyes Bird Observatory, and Burney Le Boeuf and Scott Davis of the University of California-Santa Cruz Institute of Marine Sciences, is published in today's issue of the journal Nature.
It answers, in part, two questions shark researchers have had: Where do California great whites go when they regularly abandon that coast, and where do the great whites seen occasionally around Hawai'i come from?
Great whites, while not common in Hawai'i waters, have been known to visit since before European contact. Some early Hawaiian tools used the teeth of great white sharks for cutting edges, and there are traditions of Hawaiians hunting man-eating sharks, called nuihi, although experts are unsure whether these are primarily great white or tiger sharks, or simply a name for any extremely large shark.
There are two confirmed reports of great white attacks on people in the Islands, according to a running tally of shark attacks kept by National Marine Fisheries Service biologist George Balazs.
In May 1926, a man named William Goins disappeared while swimming at Hale'iwa, and his remains were later found inside a 12 1/2-foot great white caught off Kahuku. In March 1969, surfer Licius Lee was bitten on the leg off Makaha by a shark that was identified as a great white from bite marks on his surfboard. A dead whale had been on a nearby beach about that time.
Reports of great whites around Hawai'i have occurred with some regularity in recent years. One was seen frequenting the area near Makua and Keawa'ula off O'ahu in July and August last year.
A great white was reported by a skin diver in August 1999 off Ma'ili on O'ahu, and a woman swimming off Ka'anapali, Maui, in March of that year was bitten by a shark whose species was not confirmed, but which was described by witnesses as a great white.
Great whites have been reported from the waters off the north end of Ni'ihau, around Lehua Island, in separate sightings in the summers of 1995, 1997 and 1999.
Deep-sea fishermen also occasionally report seeing great whites while fishing in waters around the Islands.
The California researchers tracked migrations of four of their six tagged sharks. One, a male which they nicknamed "Tipfin," came to Hawai'i for the winter. The other three, two females and a male, migrated to an area several hundred miles west of Baja California, and remained there for several months.
"What they were doing out there is a mystery. Since they were hunting for seals when tagged, such a long migration suggests a possible rendezvous for mating, or a move to feed on different prey," said researcher De Boeuf.
Three possible sources of food have been suggested in Hawai'i.
One report indicated the great white off Makua last summer may have been feeding on a pod of spinner dolphins that returns regularly to the area.
Ni'ihau is home to the largest concentration of Hawaiian monk seals in the main Hawaiian Islands. The great whites there may be attracted to the presence of immature seals in the water, suggested Keith Robinson, one of the owners of Ni'ihau.
Researchers have linked the 1969 attack on a surfer to a dead whale that had beached in the area. The whale had been removed from the beach, but the shark could have been attracted by its smell in the water.
The use of long-term satellite tags provides scientists with a remarkable new tool for tracking migratory species.
"A lot of the conventional tagging, you tag and recapture the animal in the same place" but don't know where it has been in the meantime, Polovina said.
The California researchers hope their continued satellite tagging will yield further results.
"We see the same sharks return to the Farallones again and again," Pyle said. "Males come back yearly, but females return every other year, which means they may be going farther afield than males as part of a two-year breeding cycle. So long-range data on females will be of particular interest."
The research into the long migrations of great white sharks reinforces information developed by Polovina in his early 1990s work on tiger sharks.
He tracked longline fisheries catches of tiger sharks and found that Hawaiian tiger sharks were sometimes caught hundreds of miles from shore on longline rigs. Previously, tiger sharks had been thought to be mainly coastal animals, regularly cycling between shallow and deep waters of individual islands. University of Hawai'i shark researcher Kim Holland, building on the information, has used long-lived electronic tags to show that tigers regularly migrate interisland.
"Electronic tagging and remote sensing technologies herald a new era for biological oceanography," said California researcher Block.
She and others have launched the Tagging of Pacific Pelagics program, which will seek to electronically track the behavior of as many as 4,000 fish, birds, marine mammals and large squid.
Reach Jan TenBruggencate at email@example.com or (808)245-3074.