White sharks flee feeding areas when orcas present

Electronic tag data reveals white sharks do not return until following season; elephant seals benefit

Date:  April 16, 2019

Source:  Monterey Bay Aquarium

New research from Monterey Bay Aquarium and partner institutions published today in Nature Scientific Reports challenges the notion that great white sharks are the most formidable predators in the ocean. The study "Killer Whales Redistribute White Shark Foraging Pressure On Seals" shows how the great white hunter becomes the hunted, and the elephant seal, the common prey of sharks and orcas, emerges as the winner.

"When confronted by orcas, white sharks will immediately vacate their preferred hunting ground and will not return for up to a year, even though the orcas are only passing through," said Dr. Salvador Jorgensen, senior research scientist at Monterey Bay Aquarium and lead author of the study.

The research team -- which included Jorgensen and Monterey Bay Aquarium scientist Scot Anderson, and research partners from Stanford University, Point Blue Conservation Science and Montana State University -- documented four encounters between the top predators at Southeast Farallon Island in the Greater Farallones National Marine Sanctuary, off San Francisco, California. The scientists analyzed the interactions using data from 165 white sharks tagged between 2006 and 2013, and compiled 27 years of seal, orca and shark surveys at the Farallones.

"The research in this paper combines two really robust data sources," said Jim Tietz, co-author of the study and Farallon Program Biologist at Point Blue Conservation Science. "By supplementing the Aquarium's new shark tagging data with Point Blue's long-term monitoring of wildlife at the Farallon Islands National Wildlife Refuge, we were able to conclusively show how white sharks clear out of the area when the orcas show up."

In every case examined by the researchers, white sharks fled the island when orcas arrived and didn't return there until the following season.

Elephant seal colonies in the Farallones also indirectly benefited from the interactions. The data revealed four to seven times fewer predation events on elephant seals in the years white sharks left.

Continued

Singing Humpback Whales Tracked On Northwest Atlantic Feeding Ground

Apr. 29, 2013 — Male humpback whales sing complex songs in tropical waters during the winter breeding season, but they also sing at higher latitudes at other times of the year. NOAA researchers have provided the first detailed description linking humpback whale movements to acoustic behavior on a feeding ground in the Northwest Atlantic.

Findings from the study, published April 10 in the journal PLOS ONE, demonstrate the potential applications of passive acoustic tracking and monitoring for marine mammal conservation and management. 

Co-author Sofie Van Parijs, who heads the passive acoustics group at the Woods Hole Laboratory of NOAA's Northeast Fisheries Science Center (NEFSC), says this study is not so much about biology, but about acoustic methods. 

"We have monitored and acoustically recorded whale sounds for years, and are now able to 'mine' these data using new computer software applications and methods, " said Van Parijs. "Passive acoustic tracking has enabled us to localize humpback whale song to study the movements of individual whales, and to relate the singing to specific behaviors. This has never before been accomplished for singing humpbacks on a northwest Atlantic feeding ground." 

"Passive acoustic tracking of humpback whales and other cetacean species provides an opportunity to collect data on movement patterns that are difficult―or impossible―to obtain using other techniques," said lead author Joy Stanistreet, who worked with Van Parjis and co-author Denise Risch at the NEFSC's Woods Hole Laboratory at the time of the study. Stanistreet is currently a graduate student at the Duke University Marine Laboratory in Beaufort, N.C. 

Since 2007, NEFSC researchers have used year-round passive acoustic monitoring to study ocean noise in the Stellwagen Bank National Marine Sanctuary, a feeding ground for humpback whales and other marine mammal species in the southern Gulf of Maine. Humpback whales typically frequent the sanctuary between April and December and feed on sand lance and other small schooling fish. Humpback whale singing in the sanctuary usually occurs from April through May, following the spring migration from southern waters, and from August to December before the return fall migration. During the summer, humpbacks remain in the sanctuary but generally do not sing while they feed.

More: http://www.sciencedaily.com/releases/2013/04/130429133658.htm