Summer diving behavior of male walruses in Bristol Bay, Alaska

Pacific walruses (Odobenus rosmarus divergens) make trips from ice or land haul-our sites to forage for benthic prey. We describe dive and trip charac teristics from time-depth-recorder data collected over a one-month period d uring summer from four male Pacific walruses in Bristol Bay, Alaska. Dives were classified into four types. Shallow (4 m), short (2.7 min), square-sha ped dives accounted for 11% of trip time, and many were probably associated with traveling. Shallow (2 m) and very short (0.5 min) dives composed only 1% of trip time. Deep (41 m), long (7.2 min), square-shaped dives accounte d for 46% of trip time and were undoubtedly associated with benthic foragin g. V-shaped dives ranged widely in depth, were of moderate duration (4.7 mi n), and composed 3% of trip time. These dives may have been associated with navigation or exploration of the seafloor for potential prey habitat. Surf ace intervals between dives were similar among dive types, and generally la sted 1-2 min. Total foraging time was strongly correlated with trip duratio n and there was no apparent diel pattern of diving in any dive type among a nimals. We found no correlation between dive duration and postdive surface interval within dive types, suggesting that diving occurred within aerobic dive limits. Trip duration varied considerably within and among walruses (0 .3-3.4 d), and there was evidence that some of the very short trips were un related to foraging. Overall, walruses were in the water for 76.6% of the t ime, of which 60.3% was spent diving.