In May, the beach is covered in seals. Even elephant seal researcher Sarah Kienle was impressed when she and her family drove south from Santa Cruz to give Cambrians an update on her work.
“I’ve been here in the offseason, so I’ve never seen them line the beach like this,” she said.
Kienle’s research focus is on how marine mammals feed in the deep. Elephant seals, which feed at 1,000 feet and deeper, are her target research subjects. She’s in the third year of what she expects to be six years to earning her Ph.D. at UC Santa Cruz.
“We know so little about what elephant seals eat that I get to be a discoverer,” she said. “There are thousands of species of fish and squid, and we don’t know what the seals are eating.”
Researchers have to be creative to study what’s going on that deep in the ocean. The advent of digital technology has been a boon. Up until the turn of the 21st century, scientists thought elephant seals were coastal animals. It wasn’t until they were able to follow the seals with satellite tracking that they learned that the seals hunt all across the North Pacific.
“Technology will shoot up in the future,” she said. A camera with the ability to record in red light in the lightless depths is in the works.
Satellite tags carry time/depth recorders that show the depth of dives and the shapes of the dives. A seal might dive straight for the bottom and hunt along there, or might chase prey around without getting all the way to the bottom. Tags also have sensors for conductivity, temperature and salinity.
Kienle is formulating some ideas about how elephant seals feed from preliminary data.
Males typically leave the beaches and head straight for their core foraging areas in Alaska, at the farthest reaches of their range. They stay on the continental shelf for three to four weeks, foraging continuously.
“It must be really great food up there,” she said. “When they need to come back, they just book it to come back.”
Females don’t have a typical dive. They meander around the ocean, spending three or four days in one area, then moving on to another place. They don’t have an end destination the way the males do.
“They are entire ocean basin predators,” she said.
Mapping the dive data over ocean characteristics shows that seals are able to key in on certain features, such as sea mounts. They can also follow the continuously changing gyre boundary and Northern Pacific Transition Zone, places where their prey congregates.
“We don’t know how they do it, but they reliably do it,” she said.
Some seals may be hunting specialists. Some prefer fish, some squid, and some eat both. Some females follow coastal routes, staying within 200 meters of the shore, more like males. About half the seals at San Benito Island off Baja California don’t migrate at all. They spend the same amount of time at sea as the northern ones, but stay within 500 kilometers of the island.
“I’m curious why they migrate at all if they can forage locally,” she said.
The elephant seals are doing well now, but inevitably they will be affected by climate change. She’s analyzing data collected during the past year’s El Niño, which usually affects female elephant seals in the year following the El Niño. Pregnant seals return to locations where they found food before, and it isn’t there.
“If we don’t know what they are doing when they are doing well, then we don’t know how it has changed when they are doing poorly,” she said.
Technology is revealing the secret lives of elephant seals.
“Invite me back in two or three years,” she said.
Christine Heinrichs’ monthly column is special to The Cambrian.