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

• Main Authors: Alexandre N. Zerbini, Janice M. Waite, John W. Durban, Rick Leduc, Marilyn E. Dahlheim, Paul R. Wade
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2007
• Subjects: Gulf of Alaska; Killer Whale; Alaska; Aleutian Islands; Killer whale
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.183.4008; http://www.fakr.noaa.gov/sustainablefisheries/sslmc/april-06/ZerbinietalKWabundance.pdf

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 (CDS) and Multiple Covariate Distance Sampling (MCDS) methods were used to estimate abundance of different killer whale ecotypes, which were distinguished based upon morphological and genetic data. Abundance was calculated separately for two datasets 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. ‘Resident’-type (fish-eating) killer whales were more abundant than the ‘transient’-type (mammal-eating). Abundance estimates of resident killer whales (991 [95 % CI = 379-2585] [IGS] and 1587 [95 % CI = 608-4140] [PEGS]), were at least four times greater than those of transient killer whales (200 [95 % CI = 81-488] [IGS] and 251 [95 % CI = 97-644] whales [PEGS]). The IGS estimate of abundance is preferred for resident killer whales because the estimate based on PEGS data may show an upward bias. The PEGS estimate of abundance