On Thin Ice

Harbor seals in Alaska's Glacier Bay have seen a dramatic decline in recent years, and biologists aren't sure why.

By Scott Kirkwood 

It's one of the longest-running games of hide-and-go-seek ever played, employing some of the most ingenious technology you could ever imagine, in one of the most stunning locales ever seen.

Glacier Bay National Park & Preserve is the site of a unique collaboration among the Park Service, Alaska 's Department of Fish & Game, National Marine Fisheries Service, and graduate programs of several universities. Equipped with global positioning systems, time-depth recorders, and radio transmitters, researchers track seals from boats, kayaks, and floatplanes. And they need every single tool they 've got. When seals aren 't lounging about on glacial haul-outs, they 're diving deep into ice-cold water, or swimming hundreds of miles over the course of days.

It took ten years to prove suspicions that harbor seals in the region had been declining precipitously, and that was just the start. To figure out why, researchers have surgically implanted radio transmitters into about 150 harbor seals, in the blubber just below the fur. These electronic devices, about the size of a roll of pennies, transmit a signal for four hours a day during mid-day, when seals are most likely to be hauled out and more easily located; they last about five years.

"When we capture the animals, we take a full suite of biological samples that assess their general health, their organ function, their contaminant level, their disease exposure, their stress-hormone level, their diet, and their nutritional physiology," says Gail Blundell, principal investigator with the Alaska Department of Fish & Game. "We then follow these animals over time to see what 's different between those who survive and those who don 't."

"We 've been looking at a number of different hypotheses associated with this decline with the understanding that we 're not likely to come up with a ‘smoking gun, ' because so few population studies ever do," says Scott Gende, a Park Service ecologist. "But we hope to examine some factors that could relate to potential management decisions, to make sure that those aren 't necessarily contributing to a decline or hindering the population 's growth rate."

One of the first questions they examined was whether seals were being displaced from optimal foraging habitat by cruise ships, which had increased well over 30 percent during the period that harbor seals had declined by 70 percent. But the early evidence reveals that seals are foraging on herring, sand lance, and capelin in shallow, nearshore areas that cruise ships avoid.

Of course, private boaters go much closer to the shore, and kayakers even use the same areas that harbor seals use to haul out. So a graduate student from San Jose State is now working to quantify the cost of those disturbances from a biological standpoint, determining, for example, how far seals swim from the haul-out, how deep they dive, and how long it takes them to return—all of which may affect their energy reserves and hint at broader threats to survival.

Technology helps answer some of these questions but not all of them. Radio transmissions travel only so far, and you 've got to have a pretty good idea where the seals might be before shelling out $400 an hour for a plane. So researchers jump into kayaks and use spotting scopes to record the number of vessels entering the area and the seals' response. Once the animals dive underwater, time-depth recorders (TDRs) attached to the animals track their depth; when the animals shed the TDRs with their summer molt, they 're recovered in the water, and the information is synched with written observations. Data are then compared to studies in other areas where seal populations are either stable or increasing.

Biologists are also taking a closer look at the food web, to determine whether harbor seals are getting their necessary nutrients. Blubber samples reveal long-term trends in diet, whereas scat collected from glacial haul-outs yields more short-term data. Studies of captive seals at Alaska 's Sea Life Center are also yielding some clues to the impact of a diet without plenty of fat—a reality that may emerge in nature if competition for prey heats up.

Researchers are starting to look more closely at the population's genetic makeup, too. Although there are thousands of harbor seals scattered throughout coastal Alaska, the preliminary results suggest that Glacier Bay 's seals may be genetically unique, which may afford them extra protection. And that may buy some extra time. For now, the cause of the harbor seals ' decline still eludes biologists, but the hope is they'll find some answers before it 's too late.

"A lot of people look at marine mammals and see these cute, warm and fuzzy animals, but I'm drawn to the challenge they present," says Gende. "It requires a certain degree of imagination and ingenuity, combining grunt work with high-technology, then putting all the pieces together."

Scott Kirkwood is editor of National Parks magazine.