My first forays to the Beaufort Sea, in the early 1980s, were in small aircraft to count ringed seals resting on the shorefast sea ice, track bowhead whales migrating through the leads, and dart polar bears in the pack ice for tagging. Colleagues and I sought to understand how offshore oil development was impacting those species, an understanding that required both monitoring the animals’ responses to industry and learning enough about their ecology to put those responses in meaningful context.
Most of what we knew then of the bowhead whale’s migrations were based on where they were harvested. To fill in the picture between harvest locations, Doug Wartzok put together a team to tag from a boat offshore of the MacKenzie River delta and another team – for which I was recruited – to track the tagged whales from a Twin Otter aircraft. The boat team was pessimistic about getting close to the whales in the large tugboat, the only vessel available at the time. But, they quickly discovered – as the Yankee whalers had 100 years earlier – that in the summer feeding grounds, the whales are nearly oblivious to the approach of vessels. Thus, they deployed their tags, and I spent three months following whales west across the Alaskan Beaufort Sea.
Flying surveys over the ocean can be dreadfully boring, but it isn’t when freeze-up is happening below. Seeing the progression from open water to grease ice to consolidated flows and vast aprons of shorefast ice was mesmerizing. Seeing the pack ice collide with the shorefast ice and push it up into huge ice mountains was as though I were seeing high-speed plate tectonics. And, I had a rare view of life in the moving ice. The whales continued westward in the lead system beyond the shorefast ice between Demarcation and Oliktok Point. The ice bordering those leads was regularly dotted with polar bears waiting for a seal to venture too close.
Helicopters and small planes also were effective for tagging and tracking polar bears via satellite-linked transmitters. Participating in that effort again took me back and forth across much of the same coast but now in spring when the shorefast ice was stable but the pack ice was still moving in the winds and currents.
Studying ringed seals from the air, however, was less satisfying. Observations were limited to daylight hours in good weather and then only for as long as we had fuel. From the aircraft, we could only count seals in a narrow window between the collapse of their snow dens and the break up of the ice. Ringed seals maintain dens in the snow above breathing holes in the ice, and their young are born and nursed in those dens. Beyond that, we knew few details of the seals’ behavior and ecology, and we needed more than an aerial view.
So, every spring for 10 years, we established a camp on the Midway Islands, north of Prudhoe Bay or on the ice itself. During and after freeze-up, these barrier islands protect the shorefast ice developing between them and the mainland from the push of the moving pack ice. Thus, there are few hummocks and pressure ridges in that ice, and we could readily transport tents and supplies on sleds pulled by snowmobiles. Camping on or near those ice-bound islands, we were able to study ringed seals for extended periods. Our most important instruments were the noses of Labrador retrievers. Those acute sensors could detect where seals had breathed or rested under the snow. Surveying the seals’ snow-covered breathing holes and dens quickly revealed that an area which aerial surveys suggested was little used is, in fact, an important denning area.
Additional insights came from mapping the distribution of holes relative to natural and manmade features on the ice. Those early efforts were challenging, as we had to rely on magnetic compasses and theodolites to map locations, a tedious process. Over the course of a field season, the maps would show the locations of 100 or more seal holes found by the dogs within 5–10 kilometers (3–6 miles) of our camp. We monitored the seal holes to determine which were still in use and which were frozen, indicating they had been abandoned. We found that breathing holes within 150 meters (500ft) of industrial activity were abandoned three times more often than were breathing holes farther from the activity.
Needless to say, the advent of hand-held GPS greatly improved our efficiency and safety. By that time, we were regularly trapping ringed seals in their breathing holes, fitting them with radio transmitters, and monitoring their use of snow dens. Inferences drawn from the aerial observations or the distribution of breathing holes and dens began to be confirmed or overturned. An early result of the radio tracking was quantification of the time spent in the dens – an average of 20 percent. That meant that 80 percent of the seals’ time was under the ice, and – since radio waves do not propagate through salt water – we were missing the majority of the seals’ behaviors.
We then turned to ultrasonic transmitters and an array of sub-ice hydrophones to track the seals under the ice, and our understanding of their use of the shorefast ice habitat became more complete. Again, some previous inferences were confirmed – each seal maintained several breathing holes – and others were refuted – female home ranges were larger, not smaller, than those of males.
The more complete understanding of ringed seal behavior and habitat use in the breeding season allowed us to better understand the implications of seals abandoning breathing holes whether in response to industrial activity or to an influx of hunting polar bears. The bears typically hunt ringed seals in the shorefast ice when they first emerge from their own dens, often on the barrier islands. Typically, however, the bears move quickly across the shorefast ice to the moving pack ice. Using a ski plane to access the moving ice, the seal-sniffing dogs and I followed bears hunting in that habitat. We learned that dens in which seals raise young are under snow so deep that the bears cannot readily crush the roofs. To catch a seal in those dens, the bears must tunnel in and wait patiently.
The more complete knowledge of the seals’ activity patterns also allowed us to better interpret the counts of seals made in aerial surveys. Over several years, we documented the fraction of the seal population visible on the ice in late spring by monitoring when seals carrying radio transmitters were on the ice. Each time one of the tagged seals came out of the water, a team member donned skis and a portable radio receiver and antenna to search for the animal that had come out of the water. It typically took a couple of hours to ski around the signal and determine where the seal was resting and whether it was concealed under the snow or resting in the open where it could be seen in an aerial survey. The work selected for crewmembers who enjoyed each other’s company sufficiently to share a small hut on the ice for a few months but who also enjoyed a few solitary hours on skis even in the middle of a cold, dark night.
Inevitably, the labors of the dedicated team were rewarded with some unexpected findings. The first was that the seals’ emergence from under the snow was shifting to earlier dates as snow melts advanced in the warming climate. The second was that seals were returning in successive years to the same small home ranges for the breeding season. When the ice breaks up in summer, the seals wander – sometimes over thousands of kilometers – in search of food. At the next freeze-up, however, they come back and establish breathing holes and lairs within a few meters of their haunts the previous year. Ringed seal pups depend on the snow dens for protection from cold and predators, and our observations suggest that the predictable stability of the ice and snow along this coast is important to successfully rearing young. It also suggests that ringed seals have GP’s as good or better than ours.
The views expressed in this article are those of the author and do not necessarily reflect the editorial policy of Arctic Deeply.
This article first appeared on Vital Arctic Ocean Areas, a blog about important marine areas in the U.S. Arctic.