8/28/2013 9:11:37 PM
A Tale of Two Bears: The Challenges of a Changing Climate
Polar bears from the three populations that inhabit Hudson Bay are faced with the same ecological problem: the sea ice melts completely in early summer every year, forcing them ashore for four-five months, during which time they largely live off stored fat reserves until the ice returns again in late fall.
In the Hudson Bay region, the ice-free season has been getting longer and longer as break-up comes earlier and freeze-up comes later. This means that the bears currently have several fewer weeks to hunt seals compared to 30 years ago. Consequences of this have already been documented for the Western Hudson Bay population that summers on land in Manitoba, including declines in body condition, reproduction, survival, and abundance.
Similar declining trends in body condition and survival have been documented for the Southern Hudson Bay population that summers on land in Ontario and on the islands in James Bay and eastern Hudson Bay near the Quebec coast. Declines in abundance have not yet been documented for the Southern Hudson Bay population, but are expected in the near future if the pattern of changes in sea ice continues.
James Bay is the southernmost area continuously occupied by polar bears during winter. Because declines in sea ice are occurring rapidly in James Bay, I started a study in 2012 to document detailed movement patterns, habitat use, and feeding patterns of those bears in collaboration with colleague Dr. Greg Thiemann of York University in Toronto, Ontario. Other members of the team are Brandon Laforest, Ph.D. student at York University, and Kevin Middel of the Ontario Ministry of Natural Resources.
In September 2012 our team deployed 10 GPS/satellite radiocollars on adult female polar bears accompanied by either cubs or yearlings on Akimiski Island in James Bay and along the Ontario coast of James Bay. We had collars from two manufacturers but, unfortunately, all five from one manufacturer failed, providing only a few months of data. Collars from the other manufacturer were more reliable. Below I provide two examples of the detailed information provided by such radiocollars and how such information helps us to understand the difficult challenges facing polar bears in Hudson Bay.
Bear One (X37097) is an adult female first captured by our team on September 19, 2012. Originally collared along the James Bay coast of Ontario south of Polar Bear Provincial Park, she walked about 125 kilometers north along the coast to Cape Henrietta Maria, where she went out onto the newly formed ice in mid-December. During winter, she traveled over a vast expanse of eastern Hudson Bay in the region north and west of the Belcher Islands, covering thousands of kilometres in her search for hunting opportunities (Fig. 1, below).
As the ice began to recede she remained on the residual ice, which was north of the Ontario coast of Hudson Bay, until about July 29th when her collar stopped transmitting. On that date, she was still 80 kilometers north of the Ontario coast on what little ice remained.
GPS satellite collars are unable to send signals to the satellites when the transmitting portion of the collar is in salt water, such as when a bear is swimming, so we were hopeful that was the case rather than a collar failure. On August 3rd we got some good news: at 1:00 a.m. on that day, her collar transmitted a location about 70 kilometers due south of her last location on the ice, and 10 kilometers offshore. She had swum 70 kilometers in four days! She may have been resting on an offshore gravel bar which enabled the collar to send a location on August 3rd.
The collar sent two more locations that day and by about 5 p.m. on August 3rd, she had reached shore safely a few kilometres east of the mouth of the Winisk River. When first radio-collared, Bear One was accompanied by a female yearling. Assuming she is following the normal polar bear reproductive cycle, she is now pregnant again and will head inland to a maternity denning site later in the fall.
Bear Two (X37090) is an adult female first handled by our team along the southeast coast of Akimiski Island on September 18, 2012. She was accompanied by one cub-of-the-year at that time. We monitored data from the collar occasionally during the fall and noted that her collar began transmitting stationary locations on December 5th when she was still on land, so we assumed she had dropped her collar.
When bears drop collars it is a major disappointment, but GPS collars are expensive so I asked members of the Ontario Ministry of Natural Resources goose research project on Akimiski Island to recover the collar for us in May of this year during their nest search efforts. Imagine their surprise, and ours, when they discovered that Bear Two had died. Since her body had been frozen all winter, the crew were able to examine it for any clues to her death. They determined that there were no signs of trauma to the body, but photographs showed that she was in very poor condition at the time she died. She was literally skin and bones; her pelvic girdle and ribs were easily seen.
Alarmed by this, we checked Bear Two's capture information. She was recorded as having the poorest body condition of any bear our team handled in 2012. When we checked her movement data, we saw that she remained near the original capture location until late October. Between that date and late November, she walked the entire coast of Akimiski Island to the far northwest coast and back again. In early December she ventured to a small island off the southeast coast of Akimiski Island then returned to Akimiski and stopped moving. Between September 18th and December 5th, she walked an astounding 650 kilometers along the coastline (Fig. 2, below).
Since most of this movement occurred in November and early December we assume that she was searching for the first landfast ice to form that would enable her to return to the ice to hunt seals. Sadly, the ice finally formed off the southeast coast of Akimiski Island about 10 days after she died; she had simply run out of reserves.
This is an example of the detailed information that researchers can obtain from GPS collars. However, to our team, X37090's story is an alarming and dramatic example of the consequences of changes in sea ice duration in James Bay, especially delays in freeze-up date. Such effects on individuals have been predicted but to have such a powerful example underscores to us the importance of the study we initiated in 2012.
Visit our Bear Tracker Map to follow polar bears on the sea ice. We've also developed a Bear Tracker Unit for classroom use.