© Dr. Andrew E. Derocher
5/16/2019 6:38:29 PM
Spring Fieldwork on Hudson Bay
This year’s spring field season got off to a jarring start when our plane banked on landing in Churchill, Manitoba, revealing western Hudson Bay devoid of sea ice. Our field work relies on helicopters landing on the ice—and no ice meant we couldn’t even begin to reach the polar bears we planned to study. Fortunately, the ice was only missing to the north and the next day we found a path to the main pack ice east of Cape Churchill. We lucked out and over the coming days a combination of east and north winds pushed the ice (and the bears) back closer to shore.
Our objectives this spring were simple: deploy 20 ear-tag satellite radios on a sample of subadult and adult bears. These small tags allow us to monitor movements and habitat use and to determine the all-important date when the bears come ashore at break-up.
The team deployed an ear tag radio on a tranquilized subadult female polar bear. The tag should last up to six months, providing scientists with invaluable data. Photo by Dr. Andrew E. Derocher.
For this study, our focus was on adult males as we already follow adult females with satellite collars. (The neck on an adult male is wider than their head so we can’t use collars on them.) Ear tags are a fairly new development that allow us to study males and younger bears, collecting valuable information on these little-studied groups.
While deploying the radios, we also document ringed and bearded seal locations. We map prey availability so we can relate the distribution of the bears to the distribution of seals. We also note every seal kill location and, if we can, land the helicopter and collect a tooth, claw, and tissue sample. From these samples, we can determine the age and sex of the seals killed. A similar study in the Beaufort Sea revealed that the bears kill both young and the old seals, but few studies have directly examined the polar bear’s prey (most use indirect methods such as looking at stable isotopes or fatty acids in the bears).
An adult bearded seal hauls out on the edge of an open lead. The team mapped the locations of all seals and seal kills; they'll later compare seal distribution with the distribution of polar bears. Photo by Dr. Andrew E. Derocher.
Over the past two years, we only managed to catch 10 bears per year. In 2017, the ice blew away from shore and took the bears far offshore. In 2018, we had unseasonable, heavy rain that melted all the snow and made finding polar bear tracks impossible. At first it wasn’t clear that 2019 was going to be a record-breaking year as the ice was dodgy and a pair of rain storms didn’t help. (It’s not “supposed” to rain in mid-April.) However, the rain was followed by a wonderful snow storm that blanketed the area in fresh snow.
This year, the sea ice of Hudson Bay presented some of the toughest working conditions I’ve ever been in. The ice was often more like a slushy than solid ice. The ice floes were in constant motion, reshuffling polar bear tracks into a confusing and disconnected puzzle that made tracking next to impossible. Despite this, 2019 was a great season. We caught our target of 20 bears, deployed all the tags, found lots of seal kills, and piloted our new studies.
Remains of a bearded seal pup killed by an unknown polar bear. Bearded seals pup in the active broken ice. When weaned, bearded seal pups are an easy and energy-rich option to ringed seals. Photo by Dr. Andrew E. Derocher
Perhaps the best finding was that the bears this spring were in very fine shape. Most of the bears were much fatter than in the previous two years. Why? That’s a mystery. Clearly, they were finding more seals to eat but how 2019 differed from 2017 and 2018 isn’t obvious. The Arctic gives up its secrets slowly, and it’s important to remember that it’s the long-term trend that matters. An up or down in any given year is like the difference between weather and climate.
On the cautionary side of things, we caught a lot of lone adult females (eight of the 20 bears). That’s unusual because most females should be with new cubs, yearlings, or just weaning two-year-olds. None of the adult females had nursed recently, suggesting that recruitment to the population remains low. Low cub survival has been an ongoing problem for the Western Hudson Bay population.
We’ll see what 2020 brings: Lots of lone females in good shape could create a bumper crop of baby bears next year. Speaking of babies, perhaps the neatest bear to see this spring was X33158. Now a fully-grown adult male, this bear was last seen in February 2007 when he left the denning area with his mother and female sibling. We know his sister survived but he was a mystery until now. We don’t know where he’s been the last 12 years but lots of fresh cuts and scars indicate he’s been looking for love and scrapping with other males for mating opportunities this spring.
The crew this year consisted of two M.Sc. students, Natasha Klappstein and Brooke Biddlecombe, from the University of Alberta, Drs. Nick Pilfold and Megan Owen from San Diego Zoo Global, and a guest appearance from BJ Kirschhoffer of Polar Bears International to help with our scavenger cams (more on that to come). We had a great new pilot, Ryan Mutz, and Eric Dubeau, the helicopter engineer, kept us flying. A great crew and a great year. Here’s hoping spring 2019 is as good to the bears as it was to us.
Thanks to Polar Bears International, Point Defiance Zoo and Aquarium, the Polar Continental Shelf Project, World Wildlife Fund, Environment and Climate Change Canada, and the Natural Sciences and Engineering Research Council of Canada for providing funding for the spring field season.