Great whites and now Tigers too? Yo-rific!

Thanks to researchers in California, South Africa, and Guadalupe we know that white sharks (Carcharodon carcharias) spend a lot of time yo-yo'ing through the water column. This behavior is often attributed to hunting activity with animals moving up and down in a straight line seeking prey items.

Tigers (Galeocerdo cuvier) on the other hand were thought to be generalized migrants, but all that has changed with an interesting study coming out of the University of Hawaiʻi at Mānoa where a join effort with University of Tokyo, the Japanese National Institute of Polar Research, and the University of Florida, is shedding new light on the hunting behavior of tiger sharks by studying their swimming dynamics off the west coast of Hawai‘i Island.

As it turns out Tigers yo-yo too, as described by lead scientist Dr.Carl Meyer:

"These findings are exciting because they have given us unprecedented new insights into the behavior of these huge and difficult to study marine predators," explains Dr. Carl Meyer, a researcher at HIMB and the lead U.S. scientist of the project. Meyer also emphasizes the importance of these results “although we have long debated the reasons for the yo-yo diving, we have only recently developed tools allowing us to directly measure the behavior in sufficient detail to understand what these animals are actually doing”.

Complete study here.

Site fidelity and movements of sharks associated with ocean-farming cages in Hawaii

" Site fidelity and movements of sharks associated with ocean-farming cages in Hawaii "

Abstract:

Sharks are found in association with main Hawaiian Island ocean fish farms more frequently and at higher densities than is typical for coastal Hawaiian waters. Sharks attracted to fish farms could potentially threaten human water users, interact negatively with other fisheries, and seasonal migrations could be disrupted if individuals become entrained around farms throughout the year. We hypothesised that smaller coastal species would reside near farms, whereas more wide-ranging species would associate with farms only for short periods. We utilised passive acoustic telemetry to monitor the movements and behaviour of sandbar (Carcharhinus plumbeus) and tiger (Galeocerdo cuvier) sharks adjacent to two open ocean fish farms in Hawaii. Approximately half the tagged sandbar sharks showed site fidelity to the farms, with some individuals being detected repeatedly for 2.5 years. Sandbar sharks moved seasonally to the west coast of Oahu, suggesting that fish farms are not disrupting natural seasonal cycles in this species. Tiger sharks tagged near the cages were more transient, and showed much shorter residence times although some individuals returned sporadically to the cages over the 3-year period. Ocean fish cages appear to aggregate sandbar sharks, but are only ‘visited’ by tiger sharks. Although threats to public safety are probably minimal, the ecological effects of aggregating top-predators are still unknown.

Published: 13 December 2010

Yannis P. Papastamatiou, David G. Itano, Jonathan J. Dale, Carl G. Meyer and Kim N. Holland.

Marine and Freshwater Research 61(12) 1366-1375 doi:10.1071/MF10056