Estimating abundance of killer whales in the nearshore waters of the Gulf of Alaska and Aleutian Islands using line-transect sampling

Authors

Alexandre N. Zerbini, Washington Cooperative Fish and Wildlife Research Unit, School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, WA
Janice M. Waite, National Marine Mammal Laboratory, NOAA Fisheries, Alaska Fisheries Science Center
John W. Durban, National Marine Mammal Laboratory, NOAA Fisheries, Alaska Fisheries Science Center
Rick LeDuc, Southwest Fisheries Science Center
Marilyn E. Dahlheim, National Marine Mammal Laboratory, NOAA Fisheries, Alaska Fisheries Science Center
Paul R. Wade, National Marine Mammal Laboratory, NOAA Fisheries, Alaska Fisheries Science Center

Date of this Version

2007

Comments

Published in Mar Biol (2007) 150:1033–1045.

Abstract

Killer whale (Orcinus orca Linnaeus, 1758) abundance in the North Pacific is known only for a few populations for which extensive longitudinal data are available, with little quantitative data from more remote regions. Line-transect ship surveys were conducted in July and August of 2001–2003 in coastal waters of the western Gulf of Alaska and the Aleutian Islands. Conventional and Multiple Covariate Distance Sampling methods were used to estimate the abundance of different killer whale ecotypes, which were distinguished based upon morphological and genetic data. Abundance was calculated separately for two data sets that differed in the method by which killer whale group size data were obtained. Initial group size (IGS) data corresponded to estimates of group size at the time of first sighting, and post-encounter group size (PEGS) corresponded to estimates made after closely approaching sighted groups.