January 9, 2014
Coral Reefs Help Track Migration Of Tiger Sharks And Predict Attacks
Brett Smith for redOrbit.com - Your Universe Online
A new study tracking the migratory patterns of tiger sharks in the waters near Australia revealed just how important coral reefs are to the survival of this feisty predator. The study was published in the journal PLOS ONE on Wednesday and showed that coastal marine parks provide only temporary protection for the sharks.
"In this study we looked at migratory movements and fidelity to specific reefs for tiger sharks tagged in New Caledonia, the east coast of Australia (the Great Barrier Reef) and oceanic reefs in the centre of the Coral Sea," said study author Jonathan Werry, a researcher at Griffith University in Australia.
"We found the monitored sharks utilised three dimensional activity spaces of between 503 and 2360 cubic kilometers (120,000 and 560,000 cubic miles) but the range of movement varied consistently with the age and sex of the animal," he added.
The study team tracked the movements of 33 tiger sharks across the Coral Sea over the course of four years.
"When it comes to traveling long distances adult females are the primary custodians for the 'across Coral Sea' migrations, and this is probably driven by triennial reproductive cycles," Werry said. "Pre-reproductive females and mature male tiger sharks on the other hand, were observed to demonstrate extraordinary year round residency in the oceanic Chesterfields reef, so this area appears to be a very important habitat for them."
Werry said his team’s findings highlight the importance of understanding the migration patterns of large sharks for reviewing the effectiveness of zoned areas of protection, as well as the exposure of these predators to human activities, environmental influences and the fisheries industry.
"Management strategies need to consider the wide-ranging movements of large (sub-adult and adult) male and female tiger sharks at the individual level, in particular when fidelity to specific coastal reefs may be consistent across groups of individuals," he said. “The importance of oceanic Coral Sea reefs should be a priority for future research."
Based on a seven-year study of tiger shark movements, marine biologists from the University of Hawaii and University of Florida discovered that about 25 percent of the mature female tiger sharks that normally patrol the waters around the Northwestern Hawaiian Islands embark for the Main Hawaiian Islands about 1,500 miles away in the late summer and fall.
The study researchers noted that the annual migration conveniently precedes the tiger shark birth season in September to early November – also the months with highest rates of shark attacks.
“We have previously analyzed data to see which sharks are hanging around shark tours with cage divers on Oahu, and one of the things we noticed was that you’d get a spike in how many tiger sharks are seen in October, which would match our predicted model that you’re having an influx of big, pregnant females coming from the northwestern Hawaiian Islands,” said study author Yannis Papastamatiou, a UF marine biologist. “There even tends to be a spike in the number of shark bites that occur during that season.”
“Both the timing of this migration and tiger shark pupping season coincide with Hawaiian oral traditions suggesting that late summer and fall, when the wiliwili tree blooms, are a period of increased risk of shark bites,” added co-author Carl Meyer of the University of Hawaii.