Study relates predator, prey populations

A fur seal dips below the ocean waves in pursuit of prey; a black-legged kittiwake, a member of the gull family, skims the surface and brings its catch home to its chicks; a thick-billed murre dives into the depths for food before taking to the air.

Oregon State University scientists Kelly Benoit-Bird, associate professor in the College of Earth, Ocean and Atmospheric Sciences, and Scott Heppell, assistant professor in the department of fisheries and wildlife, wanted to understand was how each of these three predators are related to the distribution of their prey in the Bering Sea.

According to Heppell, the Bering Sea pollock fishery is one of the largest fisheries in the world.

Benoit-Bird and Heppell were part of the Bering Sea Project, a unique collaboration of scientists from multiple disciplines funded by the North Pacific Research Board and the National Science Foundation. More than 100 scientists are involved in the $52 million project, as noted on the BSP website.

“The integration side is really fun and brought different views to the study,” Benoit-Bird said.  
“It brought marine-mammal scientists, seabird biologists, oceanographers and fisheries experts together to study an ecosystem rather than the individual parts,” wrote Andrew Trites, zoology professor at the University of British Columbia, in an email.

Trites was involved in studying the eating habits of fur seals, and was responsible for putting together the Patch Dynamics Team, in which Benoit-Bird and Heppell took part.  
“It was this integration of our collective areas of expertise and knowledge that brought these fresh new insights and discoveries about life in the Bering Sea,” Trites wrote.      
Benoit-Bird and Heppell conducted their research aboard two separate boats, using fine-scale acoustic mapping to find fish such as pollock in the water below and trawled to analyze samples.

Meanwhile, they coordinated with others studying the seabirds and fur seals on the islands around them who sent data on what the predators were eating and where they were going to find them.

What they found was a surprising link between all three predators. According to Benoit-Bird, the fur seals, kittiwakes and murres all focused on tightly packed patches of prey, rather than the overall prey abundance over a large area. Despite their different hunting strategies, the scientists found each species gave the same answer.

For example, fishermen head to areas with the highest biomass of fish, while fur seals are “keyed into overall distribution rather than density of prey,” Trites wrote.

Packed sources of prey represent “a large amount of energy packed into a tight space,” according to Heppell.

Heppell noted for seabirds such as kittiwakes and murres, the less you have to swim from fish to fish, the greater foraging efficiency.

Benoit-Bird added the revelation that these three predators focus on the patchiness of their prey and not the sweeping overall abundance has implications for balancing the competition between predators and the fishing industry, as well as future scientific research.

The discovery that predators prefer patchy groups of prey is “making us think differently about what to do next,” Benoit-Bird said.

The article titled “Prey Patch Patterns Predict Habitat Use by Top Marine Predators with Diverse Foraging Strategies” can be found online on the PLOS ONE online access journal website.   

McKinley Smith, news reporter
news@dailybarometer.com