Polar Bears and Ringed Seals: A Relationship in Transition

Disconnected sea-ice during the Svalbard summer (Source: Allan Hopkins/Creative Commons).

Along the tidal glacier fronts of Svalbard, an archipelago halfway between Norway and the North Pole, polar bears have changed their hunting practices. A recent study published in the Journal of Animal Ecology indicates the new behavior is a response to rapidly disappearing sea ice. Charmain Hamilton and other researchers from the Norwegian Polar Institute mapped changes in the spatial overlap between coastal polar bears and their primary prey, ringed seals, to better understand how the bears are responding to climate change. The results don’t bode well for the long-term survival of polar bear populations: as sea ice continues to shrink in area, ringed seals—calorie-rich prey that are high in fat— have become increasingly difficult to catch during the summer and autumn. The bears are now finding sources of sustenance elsewhere: in the archipelago’s thriving bird colonies.

The Arctic is warming at a rate three times the global average, and the sea ice in the Svalbard region is experiencing a faster rate of decline than in other Arctic areas. As Charmain Hamilton reported in an interview with GlacierHub, the findings could demonstrate what the future holds for the top predator elsewhere. “The changes that we are currently seeing in Svalbard are likely to spread to other Arctic areas over the coming decades,” she said.

A polar bear steps across a gap in the sea ice near Spitsbergen, Svalbard (Source: Thomas Nilsen/The Barents Observer).

Svalbard’s polar bears exhibit one of two annual movement patterns: some follow the sea ice as it retreats northward during the summer, while others stay local, inhabiting coastal areas throughout the year. Both groups of bears depend on sea ice as a platform to hunt ringed seals. Given a rapid decline of sea-ice levels that began in 2006, Hamilton and other researchers wanted to know if the coastal bears were still hunting ringed seals under the deteriorating conditions.

The researchers compared satellite tracking data for both polar bears and ringed seals from the periods 2002-2004 and 2010-2013 to assess whether the predator-prey dynamic had shifted. The data was analyzed according to season, with researchers paying careful attention to the dynamics of spring, summer and autumn.

In spring, access to fat-rich ringed seals is critical, particularly for mothers weakened from nourishing their young in winter dens. The study shows that coastal polar bears continued to spend the same amount of time near tidal glacier fronts in spring as they did when sea ice was more abundant. The authors conclude that the declines in sea ice in Svalbard have not yet reached the stage at which bears must find alternative hunting methods during the spring. This could help to explain why cub production is not currently declining.

A calving glacier in Svalbard (Source: Geir Wing Gabrielsen/Norwegian Polar Institute).

However, during summer and autumn, bears are spending less time in the areas around tidal glacier fronts. The study shows a significant decrease in the amount of time bears spent within 5 km of glacier fronts and a sharp increase in the distances they traveled in search of food per day. The ringed seals, on the other hand, have remained near the glacier fronts. As Hamilton reported to GlacierHub, “The reduced spatial overlap between polar bears and ringed seals during the summer indicates that the reductions in sea ice have made it much more difficult for polar bears to hunt their primary prey during this season.”

As sea ice recedes, ringed seals are increasingly relying on calved pieces of glacier ice as shelters and resting places. Since these pieces of calved ice are no longer connected to land-fast ice, polar bears can no longer walk up to the seals or wait by their breathing holes, but have to attack from the water. This involves swimming surreptitiously up to seals resting on calved glacier ice and bursting onto the platform to make a kill. But this specialty hunting technique has only been observed in a minority of bears.

A Svalbard polar bear eats a ringed seal on a calved piece of glacier ice (Source: Kit Kovacs and Christian Lydersen/Norwegian Polar Institute).

So where are the coastal bears getting their calories during summer and autumn? The study shows that along with the marked decline in sea ice, the coastal bears were spending more of their time around ground-nesting bird colonies. At present, these tactics seem to be working. The bears are benefiting from a large increase in the populations of several avian species in the region, which Hamilton attributes to ongoing international conservation efforts along migration routes. While an increase in the amount of time polar bears spend on land is considered a cause of deteriorating health in other bear populations, the adult bears and cubs of Svalbard have not shown marked signs of decline.

Have the bears found a lasting alternative? Jon Aars, a research scientist and one of the co-authors on the paper, doesn’t think so. In an interview with GlacierHub, Aars emphasized that while birds and eggs provide the bears with an alternative to burning fat reserves as they wait for the sea ice to return, the dynamic is not permanent. “It is not likely that switching to eating more birds and eggs is something that can save polar bears in the long run if sea ice is gone for the whole of, or most of, the year,” he said. “We do think the bears are still dependent on seals to build up sufficient fat reserves. And it is limited how many bears can utilize a restricted source of eggs and birds on the islands.”

A mother and her cubs look out across an ice-free stretch of bay as they hunt for birds and eggs (Source: Thomas Nilsen/The Barents Observer).

The bears have adapted to the current change in their environment but may not be able to adapt as well in the future. The authors of the paper point out that the increased rates of movement required to hunt avian prey increases the bears’ energy needs. Additionally, as more bears rely on avian prey, their high rate of predation means that bird populations on the archipelago will likely decline, causing bears to alter their hunting strategies again. Ringed seals have not changed their own spatial practices, and the authors propose that more bears could learn, or be forced to learn, the aquatic hunting method.

However, ringed seal populations are in decline due to the loss of sea ice, according to Hamilton. Thus, the future of both species in the region is uncertain. In sensitive environments like the Arctic, predator-prey dynamics are fragile, particularly for species of such high trophic positions. In the future, Hamilton would like to include other Arctic marine top predators in similar studies to better understand how Arctic marine mammal communities are being impacted.

Roundup: Clean Climbing, Subglacial Discharges, and Nepali Youth

Denali NPS Encourages ‘Clean Climbing’

From the National Park Service: “A decade of scientific research has produced conclusive results – human waste left behind by climbers is polluting the streams and rivers that flow out of the Kahiltna Glacier. Our ultimate goal is to require 100% removal of all human waste from Denali, and we will continually strive to develop practical, working solutions to achieve this goal. We will be learning from your participation how to best to manage this next phase of ‘Clean Climbing’ on Denali.”

You can read more about how the Park Service is encouraging these practices here.

Climbers who remove all of their own waste will receive this flag from the Park Service as a reward (source: National Park Service).

 

A Forager’s Paradise for Seabirds

From Scientific Reports: “We found that tidewater glacier bays were important foraging areas for surface feeding seabirds, kittiwakes in particular. Such sites, rich in easily available food and situated in the fjord close to colonies, are used as supplementary/contingency feeding grounds by seabirds that otherwise forage outside the fjord. For kittiwakes these areas are of great significance, at least temporarily. Such an opportunity for emergency feeding close to the colony when weather conditions beyond the fjord are bad may increase the breeding success of birds and buffer the adverse consequences of climatic and oceanographic changes.”

Find out more about why these areas are so abundant here.

Researchers mapped the foraging hotspots of Kittiwake seabirds (source: Scientific Reports).

 

Nepali Youth Appeal to Trump

From The Himalayan Times: “Nepali Youth and Mountain Community Dwellers have appealed to U.S. President Donald Trump to take back his decision to pull out of the 2015 Paris Agreement on Climate Change. An appeal letter was submitted to the U.S. embassy here on Monday by Nepali youth representing people living in the foothills of the Himalayan peaks, including the tallest Mount Everest.  The letter was handed over to deputy political and economic chief of the U.S. embassy Stephanie Reed.”

Read more about why Nepalese people are so concerned over Trump’s decision here.

President Trump has withdrawn the United States from the Paris Climate Accord (source: Gage Skidmore/Flickr).

Cruise Ships Cause Murrelets to Demur: Management and Tourism in Glacier Bay

Visitors aboard a cruise ship visit Margerie Glacier in Glacier Bay National Park (Source: National Park Service).

When the U.S. National Park Service was established by the Organic Act of 1916, just over 100 years ago, it was given two mandates: to protect the natural resources in its parks, while also allowing for enjoyment of those resources. Sometimes, these mandates conflict. In a May 2017 paper in PLOS One, Timothy Marcella and his co-authors describe one such case. The paper shows that cruise ship traffic in Alaska’s Glacier Bay National Park and Preserve disturbs two rare seabird species, Kittlitz’s and marbled murrelets.

Glacier Bay National Park and Preserve, a 3.3 million acre region of water and land in Southeast Alaska’s Inside Passage, is characterized by vast tidewater glaciers and the landscape created as they recede, a succession from bare rock to mature spruce and hemlock forests. The Park provides crucial habitat for Kittlitz’s murrelets, which nest on the ground in deglaciated terrain, drawn to tidewater glaciers and the marine invertebrates and fish that live in glacial outflow. Up to 37 percent of the global population of Kittlitz’s murrelets visits Glacier Bay in the spring and summer, and as much as 95 percent breeds in Alaska, as the authors indicate. Closely related to Kittlitz’s murrelets, marbled murrelets nest in old-growth forests, crucial habitat preserved by the Park.

Wildlife observers poised on the bows of cruise ships found that, in areas of the cruise track dominated by Kittlitz’s murrelets, 61 percent of all murrelets approached within 850 meters by a cruise ship showed signs of disturbance. For a seabird, this means changing from a “loafing” behavior like sleeping, preening or swimming, to either taking flight or diving. In areas of the park where marbled murrelets were more prevalent, the effect was even greater— 71 percent of birds dove or flew away.

A Kittlitz’s murrelet flies over Kachemak Bay, Alaska (Source: Alan Shmierer/Creative Commons).

However, Scott Gende, project lead and co-author of the PLOS One paper, believes these diving and flushing behaviors aren’t necessarily harmful. Speaking from Juneau, where he and his team prepared for a cruise to study disturbance in harbor seal pups, Gende pointed out that long-term monitoring of both species suggests that their populations within Glacier Bay are stable. “If the murrelets are living on the energetic margin (having only sufficient resources for survival, and no more), one more dive could make a difference— disturbance events could equate to a population effect. If we assume that the stable numbers of murrelets over the years is reflective of their ability to forage and breed successfully in Glacier Bay, it’s not likely that the disturbance events are so egregious that it’s causing the murrelets to have lower reproductive success or survival rates,” Gende told GlacierHub.

If the murrelets’ populations are healthy, is disturbing them inherently a problem? Gende doesn’t think so. “Parks are for people,” he quipped, and noted it is far easier to measure impact to a natural resource, like seabirds, than to measure the positive effect of people on the ship experiencing that resource.

“People are moved by Glacier Bay, seeing wildlife— bears on the beach, whales, the scenic wilderness. That can have a profound impact on their experience of national parks,” he said. Positive experiences in national parks are important not just to individuals, but to the protection and longevity of the national park system itself, which relies on public and congressional support. “Over the years I’ve been doing this research,” Gende reflected, “I’ve talked to hundreds of people, and I’m convinced the experience they have pays dividends to recognizing values of having national parks and these protected areas in general.”

In addition, the cruise ship presence in Glacier Bay directly creates an opportunity for wildlife biologists to collect information difficult to gather in many other parts of the United States. The data for this murrelet study was collected by observers who boarded cruise ships for the day, a valuable and rare method of studying marine wildlife.

A marbled murrelet displays what the PLOS One study termed “loafing behavior” (Source: U.S. Fish and Wildlife Service/Creative Commons).

The trick is to create policy that balances conservation and tourism, says Gende: “It boils down to value-based decisions, because it is a trade-off. Some would say only kayakers should be allowed in Glacier Bay, some would say more cruise ships should be let in. There’s a suite of values in people. The park service has done a great job balancing that range and minimizing impacts while maximizing conservation.”

The lessons of murrelet management extend to the entire national park system. All visitors, whether in Yellowstone or Denali, will impact resources, says Gende. “Even on a well-worn trail, you step on a plant, or create disturbance to soil, water or wildlife. The goal is to mitigate disturbance while providing a visitation experience,” he added.

In Glacier Bay, the Park Service’s mandates of conservation and visitation seem to be mutually supportive. Perhaps, in a time when public protection of wild lands is under debate, the reciprocally beneficial nature of these mandates can benefit other parks, too.

Photo Friday: Aleutian Islands from the Sky, Sea and Space

This week’s Photo Friday explores the Aleutian Islands in Alaska. The Aleutian Islands, which separate the Bering Sea from the Pacific Ocean, consist of a series of islands and islets that contain 40 active and 17 inactive volcanoes. These volcanic islands formed from the subduction of the Pacific tectonic plate beneath the North American tectonic plate, and some of the volcanoes are glaciated. Scientists have determined that many of the islands had glaciers at one period.

The Aleutian Islands are also part of the Alaska Maritime National Wildlife Refuge (AMNWR), which protects various seabird colonies. As the largest wildlife refuge in the United States, more seabirds nest on the islands than anywhere else in North America. Puffins, gulls, cormorants, cackling geese, and terns, among others, call the area home. See pictures of some of these birds and the Aleutian Islands from the air,  land, and sea below.

Aleutian Cackling Geese in flight over Amchitka Island (Source: USFWS).

 

Crested Auklets resting on a rocky ledge (Source: Pixnio/Wikimedia Commons).

 

Unusually clear skies allowed NASA’s satellite to acquire this image on May 15, 2014 in which 52 volcanoes are visible (Source: NASA).

 

Eruption of Mt. Cleveland (Source: NASA).

 

Chagulak Island in the Aleutian Islands (Source: U.S. Fish and Wildlife Service).

 

Hauling supplies on Attu Island in Alaska (Source: Adam/Wikimedia Commons).