Polar bear Ursus maritimus use of the western Hudson Bay flaw lead

Abstract

Flaw leads (FLs) and polynyas are recurrent areas of open water within sea ice that provide habitat for a diversity of Arctic species. The western Hudson Bay FL is a major, predictable habitat feature; however, its importance to polar bears Ursus maritimus has not been examined. We mapped the FL using synthetic aperture radar (resolution 62.3 × 121 m) from December to May, 2009-2018, and assessed FL use by 73 adult female polar bears tracked using satellite telemetry. Maximum FL width varied from 4 km in March to 145 km in May. Bears were closest to the FL in May, which coincided with their hyperphagic period and the seal pupping season. Only 31.5% (n = 23) of the bears used the FL, and they travelled faster, with lower turning angles along the FL (16° turns at 101° and -69° relative to the FL), suggesting the feature acted as a corridor that could increase prey encounters. Bears were closer to and crossed sections of the FL that were 68% narrower than those not crossed, indicating that a wider FL deters crossing. Abundant prey likely attracts some bears to the FL, but most bears avoid the FL between hunts, likely to conserve energy on consolidated ice or to reduce intraspecific interactions. Increases in open water resulting from climate warming might make the FL more challenging for bears to cross, but could make it more attractive if open-water prey densities increase.