Seasonal distribution and abundance of killer whales around Lofoten and Vesterålen Islands, northern Norway

Abstract

Killer whales (Orcinus orca) have been pohotoidentified around Lofoten and Vesterålen islands northern Norway during fall-winter (October-February) and summer (June-August) in 1990 and 1991. Some background data exists from 1983-1989. To date 302 killer whale individuals belonging to 44 different groups have been identified. The yearly distribution and abundance of whales is closely related to the distribution of springspawning herring (Clupea harengus) in the area. Since 1987 nearly all of the sexually mature herring in this stock spend the winter in Tysfjord, Ofotfjord and Vestfjord area, and killer whales are most abundant in the area during this time. Based on a capture-recapture estimate, about 500 killer whales are present in the overwintering area of herring. Most of the whales leave the study area in January when herring migrate to the spawning grounds 700 km farther south. Five killer whale individuals have been identified both in the overwintering and in the spawning grounds of herring. Based on the seasonal distribution, killer whale groups can be divided into three different types; whales present in fall-winter ( 25 groups), whales present both in fall and summer (12 groups) and whales present in summer (six groups).