[MARMAM] Recent publication on transient killer whales

Orcamom1 at aol.com Orcamom1 at aol.com
Fri Nov 5 09:00:04 PDT 2010

Ecological  aspects of transient killer whales (Orcinus orca) as predators 
in  southeastern Alaska 

Wildlife Biology, Volume 6, No. 3:  308-322 
Marilyn E. Dahlheim, National Marine Fisheries Service,  Alaska Fisheries 
Science Center, National Marine Mammal Laboratory, 7600 Sand  Point Way NE., 
Seattle, Washington 98115. USA.  E-mail:  _marilyn.dahlheim at noaa.gov_ 
(mailto:marilyn.dahlheim at noaa.gov/)        
Paula  A. White, Museum of Vertebrate Zoology, 3101 Valley Life Sciences 
Building,  University of California, Berkeley, California 94720.  USA.   
In this study we present empirical data on predator numbers, movements  and 
area usage, and predation obtained from tracking transient killer whales  
(Orcinus orca) throughout the inland waters of southeastern Alaska, USA.  
During 1991-2007, we documented 155  transient killer whales via 
photo-identification methodology within this large  study area (27,808 km2).  Transient  
killer whales were distributed throughout southeastern Alaska and were 
present  during all seasons, although not all individuals were seen each year.  
Resighting data suggested that within  southeastern Alaska, maternal groups 
may partition area  usage of their environment.  By  following whales for 
1,467 km, we calculated a mean travel speed of 7.2 km/h  with mean daily 
movements of 134 km ± 88 km/24 hours and ranging within 59-240  km/24 hours.  
Photographic matches  demonstrated that most (86%) of the transient killer whales 
identified in  southeastern Alaska also utilized British Columbia and 
Washington State waters.  In contrast, photographic matches  between whales in 
southeastern Alaska and  whales seen off of California,  USA, were rare, 
suggesting that  different transient killer whale stocks occupy these two 
regions.  Transient killer whales preyed upon  Dall’s porpoise (Phocoenoides 
dalli), Pacific white-sided dolphins  (Lagenoryhncus obliquidens), harbor porpoise 
(Phocoena phocoena), minke whales  (Balaenoptera acutorostrata), Steller 
sea lions (Eumetopias jubatus), harbor  seals (Phoca vitulina), and seabirds.  
Potential prey species available, but not targeted, included humpback  
whales (Megaptera novaeangliae), elephant seals (Mirounga angustirostris), and  
sea otters (Enhydra lutris).  Prey-handling techniques varied depending upon 
the prey being targeted  with no evidence of prey specialization.  During 
114 encounters totaling 332.5 hours of direct observations of  transient 
killer whales, we documented 36 predation events for a calculated kill  rate of 
0.62 prey items/24-hour period/whale.  The data we present in this article  
provide a foundation of transient killer whale ecology aimed at improving 
our  ability to understand the impact of transient killer whale predation on  
southeastern Alaska prey populations.  
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