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

• Author / Creator

  Henderson,Erin

• Polynyas and leads are recurrent areas of open water within sea ice that are important to many Arctic species, including marine mammals; however, the importance to polar bears (Ursus maritimus) has not been examined. The western Hudson Bay flaw lead (hereafter lead) is a major, predictable habitat feature within the home range of the Western Hudson Bay polar bear population. The lead may provide hunting opportunities, but equally, could represent barriers to movement. We assessed use of the lead by 73 adult female polar bears tracked using satellite telemetry from December 2009 – May 2018 by measuring 1) distance to the lead, 2) movement direction relative to the lead, 3) first passage time, 4) turning angles, and 5) crossing rate of the lead. The use of the lead was compared 1) temporally, 2) spatially, and 3) based on reproductive status. The lead was mapped using synthetic aperture radar (resolution 62.3 m x 121 m) to differentiate between ice and water in Hudson Bay. The width of the lead varied temporally, from 4.5 km in March, up to 145 km in May. Polar bear use of the lead varied temporally, spatially, and based on reproductive status. Polar bears were closest to the lead in May during seal pupping season when polar bears are hyperphagic, and furthest from the lead in December. Polar bears had faster, more directed movements along the lead (moving on average with 16° turning angles at 101° and -69° relative to the feature) when closer to narrower sections of the feature, suggesting the feature acts as a corridor to increase prey encounter rate. Bears were consistently closer to narrow sections of the lead, and females with cub(s)-of-the-year were on the narrowest sections. Furthermore, while the bears crossed the lead 50% of the time overall, crossings occurred more often in January – March (80% of crossings) than in April or May (39%) when the feature was less prominent. These results suggest that a wider lead might deter crossings and restrict bear movements, particularly for mothers with cub(s)-of-the-year. When females of all reproductive classes were ≤1 median step length from the lead, however, lone females spent more time close to the lead than mothers with cub(s)-of-the-year and yearling(s). Prey likely attracts polar bears to the lead, but bears might limit their time in the area because of the higher energetic costs of travelling in unconsolidated ice and retreat to habitat further from the lead between hunts to conserve energy. Furthermore, mothers with cub(s)-of-the-year might limit their time on the lead to reduce the risk of infanticide by males that are attracted to areas with lone females for mating purposes, or because of prey availability. An increase in open water resulting from climate warming might make the lead a more challenging environment for bears, yet possibly more attractive as the spring feeding period decreases and energy intake declines, or as harbour seal density increases in the area.

• Subjects / Keywords

  • Synthetic Aperture Radar
  • Ursus maritimus
  • Arctic Sea Ice
  • Flaw Lead
  • Hudson Bay
  • Polar bear

• Graduation date

  Spring 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-rsnk-xm48

• License

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