April 4, 2013
Scientists Discover Secret Migration Patterns Of The White Shark
Lee Rannals for redOrbit.com — Your Universe Online
According to research published in BioMed Central's open access journal Animal Biotelemetry, satellite tagging has helped map the secret migration of white sharks.
Researchers using satellite tagging found that pregnant female sharks travel between a mating area at Guadalupe Island and a nursery in Baja California, which puts them and their young at risk from commercial fishing. White sharks live most of their life in the open ocean, but also return to the same places to find mates. The commute for females has been a mystery until now.
The team mapped the migration patterns of female white sharks using satellite-linked radio-telemetry tags. The sharks were found to follow a two-year migration pattern with four distinct phases.
During the first phase, the females left Guadalupe Island, Mexico and remained offshore for most of their 18-month gestation. This area was much larger than the foraging area used by males, and tended to avoid the male's foraging area while the males were present.
The second phase was a two-month journey in the coastal waters of Baja California where the sharks gave birth. After they left the nurseries, the sharks began a path back to Guadalupe Island to avoid males until ready to reproduce. The final phase was mating at Guadalupe Island, which lasted for up to four-and-a-half months before the two-year cycle began anew.
"During the mating phase both males and female sharks are seen with injuries. It's unclear whether males are fighting over food or females or both, but this aggression may be why the females avoid males at other times," said Dr Michael Domeier from the California-based Marine Conservation Science Institute (MarineCSI). "Our tracking has also highlighted a previously unknown period of vulnerability when the females are exposed to commercial fishing off the coast of North America."
Researchers reported in February in the online journal PLoS ONE that whitetip sharks regularly migrate to waters around the Bahamas. They found that the sharks spend about 68 percent of their time in Bahamian waters.
“While the oceanic whitetip shark is one of the most severely overexploited shark species, it is also among the least studied because it lives much of its life far from land in the open ocean,” said the study´s lead author Lucy Howey-Jordan, from the scientific tracking company Microwave Telemetry, Inc. “Before this study and our ongoing research, very few of these sharks had been fitted with satellite tags, and the data we obtained will help establish new conservation measures.”
Understanding shark migration not only helps getting a better grasp of the traveling patterns of these species, but also helps scientists get a better perspective before taking conservation measures.