Keeping track of walruses
23 August 2017
Counting walruses is difficult, complex and labour intensive usually requiring repeat visits to haulout sites. Even then there are numerous variables swaying the numbers. MIKE HAMMILL says good record keeping is integral to good management of declining herds.
WEIGHING UP TO A TON, the walrus is the largest seal native to Canada. Good walrus habitat is characterized by relatively shallow water (ca 80 m or less) with a seabed that supports plenty of shellfish in areas not far from haulout sites. Walruses were once widely distributed in Canada and common south to the Gulf of St Lawrence and Sable Island. By the late 1700s, commercial whaling in the Gulf of St Lawrence was already in decline as whales became harder to catch. Whalers began searching out new areas for harvesting and shifted their attention to other species to fill their holds. By the end of the century, Atlantic walruses (Odobenus rosmarus rosmarus) had been killed off from the Gulf of St Lawrence and sites on Canada’s east coast such as Sable Island. Today, walrus distribution is limited to Hudson and James bays, and areas to the north into the central and High Arctic.
An understanding of abundance and population trend is needed to make informed decisions for harvest management, evaluating industrial impact and understanding how this species responds to climate change. Walruses are a challenging species to enumerate due to a combination of factors including: a highly clumped distribution; movements between haulout sites; variability in detection probabilities depending on whether animals are hauled out on land, on the sea ice, or are in the water; and uncertainty in the fraction of the population hauled out when the survey is flown. In September 2017, the Canadian Department of Fisheries and Oceans is planning a survey to obtain information on walrus abundance along the southeast coast of Baffin Island, in Hudson Strait, around Southampton Island and along the northwest coast of Hudson Bay. This survey will also test some new developments to see if we can improve our estimates of abundance.
Walrus surveys are complex. The basic design is to fly over areas where they are resting and to photograph animals at the haulout sites for later counting in the laboratory. To determine which areas should be surveyed we review the literature to determine which islands they use as haulout sites and we build on this through consultations with hunters to determine if new sites have been colonized or if certain sites have been abandoned. The number of walruses hauled out at any single moment can be quite variable and is thought to be affected by local conditions, social behaviour, and environmental factors. At key haulout locations we plan to visit the site multiple times. Multiple counts will provide more information on how the number of animals at a site might vary. However, multiple visits are not always feasible, so we are proposing to install remote cameras at certain test sites. These will be programmed to transmit images of hauled out walruses via satellite which will allow for realtime data collection over multiple days. If successful, multiple counts from the remote cameras will provide greater insights into the numbers of walruses using a haulout site and how these numbers might vary in a way that is not feasible using an aerial survey aircraft. Multiple installations could also offer long term monitoring opportunities which might be more cost effective than using aircraft to cover large areas at considerable expense.
MIKE HAMMILL is a research scientist with the federal Dept. of Fisheries & Oceans in Canada
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