[MARMAM] new article on killer whales

Alexandre Zerbini azerbini at u.washington.edu
Sat Aug 19 14:32:47 PDT 2006


Dear Marmamers,

The following paper has just been published in electronic format:

Alexandre N. Zerbini, Janice M. Waite, John W. Durban, Rick LeDuc, 
Marilyn E. Dahlheim and Paul R. Wade. 2006. Estimating abundance of 
killer whales in the nearshore waters of the Gulf of Alaska and Aleutian 
Islands using line-transect sampling. Marine Biology: 
http://dx.doi.org/10.1007/s00227-006-0347-8

Abstract:
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. ‘Resident’-type (fish-eating) killer whales were more abundant 
than the ‘transient’-type (mammal-eating). Abundance estimates of 
resident killer whales (991 [95% CI = 379–2,585] [IGS] and 1,587 [95% 
CI = 608–4,140] [PEGS]), were at least four times greater than those of 
the 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 is likely more 
accurate for transients. Residents were most abundant near Kodiak Island 
in the northern Gulf of Alaska, around Umnak and Unalaska Islands in the 
eastern Aleutians, and in Seguam Pass in the central Aleutians. This 
ecotype was not observed between 156 and 164°W, south of the Alaska 
Peninsula. In contrast, transient killer whale sightings were found at 
higher densities south of the Alaska Peninsula between the Shumagin 
Islands and the eastern Aleutians. Only two sightings of ‘offshore’-type 
killer whales were recorded during the surveys, one northeast of 
Unalaska Island and the other south of Kodiak Island. These are the 
first estimates of abundance of killer whale ecotypes in the Aleutian 
Islands and Alaska Peninsula area and provide a baseline for quantifying 
the role of these top predators in their ecosystem.

A pdf copy is available from the following website (for authorized 
users): <http://www.springerlink.com/content/bm1771q4qx169684/> 

or upon request to Alex Zerbini (azerbini at u.washington.edu)

Best regards,

-- 
Alexandre N Zerbini
Washington Cooperative Fish and 
 Wildlife Research Unit
School of Aquatic and Fishery Sciences
University of Washington
Box 355020
Seattle, WA  98195-5020, USA
phone: (206) 221-5453
email: azerbini at u.washington.edu





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