Abstract
Between 2005 and 2008, 31 walruses were tagged with Argos satellite transmitters at their wintering grounds at Store Hellefiske Banke, Central West Greenland (N=23), and at their summering grounds off the coast of Southeast Baffin Island, Canada (N=8). Two male walruses moved along the Greenland coast from Store Hellefiske Banke north to Disko Banke, where contact was lost. Two other males went further north, up to the Upernavik area. Contact was lost with one of these tags, but the other animal travelled southward again and went towards SE Baffin Island. Eight of the tagged walruses moved between West Greenland and Baffin Island, demonstrating a connection between walruses at these sites. Walruses left the Store Hellefiske Banke during the period 7 April to 17 May and on average used 7 days to swim the 400 km across Davis Strait. The migration routes were quite similar; they travelled over the shallowest areas at the narrowest part of the strait. The timing of the spring dispersal and migration towards Canada was closely linked to the extent and timing of the retreat of the pack ice edge. One flipper tagged male that was marked off South Baffin Island was recovered in a hunt on Store Hellefiske Banke, documenting that the reverse migration also occurs. Off West Greenland satellite tagged walruses spent a lot of time around the Store Hellefiske Banke (55.0o-56.5o W), using this shallow area as feeding grounds irrespective of the ice cover in this area. Partial sexual segregation was observed. Despite a tendency in West Greenland for males to occur farther offshore, farther from the ice edge and at greater depths, only their preference for denser ice cover (64% ice cover) differed significantly (P=0.019) from the habitat preferences of females (52% ice cover). Coast dispersal was more condensed and the segregation between males and females was more pronounced during autumn along the Southeast Baffin Island. Females remained farther north (P<0.001) and farther east (P=0.006), and males were more often located offshore in areas with greater water depths (P=0.024). Males had also had larger home range than females during both seasons.
Highlights
Walruses occur during the winter and spring in Central West Greenland, but are absent from this area during the open water period
Duration of contact and tag type comparison The average duration of the puck (14 d) and the implant (36 d) tags deployed in the pack ice in West Greenland was comparable to the average longevities for walruses that were tracked in the Bering Sea (20 and 22 days, respectively; Jay et al 2006)
Premature transmission stops in the matchbox transmitters is likely due to tearing out of the skin or damage to the units as the walruses move through the dense pack ice and haul out on ice during the spring
Summary
Walruses occur during the winter and spring in Central West Greenland (between ca. 66.50° and 70.75° N), but are absent from this area during the open water period (i.e. summer; Born et al 1994). Walruses in Central West Greenland are to a large extent genetically and geographically separate from walruses farther north (i.e. the Baffin Bay stock in the Smith Sound area; Andersen et al 2014), but do not differ genetically from walruses along SE Baffin Island across Davis Strait (Andersen et al 2014, NAMMCO 2009). Prior to this study no information on the movements of walruses from these two banks to the sites they occupy during the open water period has been available. Understanding the movement and stock discreteness of walruses is important for several reasons. Information about movements obtained from satellite telemetry is an important tool in developing an understanding of stock delineations
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