An estimation of walrus (Odobenus rosmarus) predation on bivalves in the Young Sound area (NE Greenland)

Abstract

The total consumption of bivalve prey by walruses (Odobenus rosmarus) in the important inshore summer feeding area Young Sound (about 74° N) in Northeast Greenland was estimated. To determine relative area use, the movement and activity of three adult male walruses carrying satellite transmitters were studied during the open-water season in 1999 and 2001. Because one of the animals was tracked during both years the study covered a total of four “walrus seasons”.
 Overall, the animals spent c. 30% of their time in the water inshore in Young Sound between Sandøen and Zackenberg. The remaining time was spent along the coast north and south of Young Sound and offshore in the Greenland Sea. The total amount of bivalve food consumed in Young Sound by the walruses during a total of 1620 “walrus feeding days” was calculated from information on the total number of walruses using the area (n=60), occupancy in the study area, and estimates obtained from satellite telemetry on the number of daily feeding dives (118-181/24 h at sea). Depending on the applied estimator of number of feeding dives, the estimated consumption by walruses of shell-free (SF) bivalve wet weight (WW) during the open-water period ranged between 111 and 171 tons.
 Based on estimates of mean total body mass (TBM: 1000 kg) of walruses using the area and daily per capita gross food intake (6% of TBM), the corresponding estimate of consumption by walruses is c. 97 tons SF WW. It is suggested that the two lowest estimates of total consumption are the most plausible.