Grey whales (aka gray whales), Eschrichtius robustus, calve in southern California and Mexico and every year make the longest migration of any mammal to feed in the rich waters of the Chukchi Sea. The species was heavily hunted in the 1800’s and was almost extinct by the early 1900’s. Officially protected in 1936, the species has rebounded and now numbers approximately 20,000. 
 

Unimak Island Transient Killer Whale Research

 

The Background

In 2002, Dr. Lance Barrett-Lennard and colleague Craig Matkin began a research project to investigate the ecological role of Biggs (transient) killer whales in the remote Aleutian Islands of Alaska.  The Aleutians were of particular interest because two marine mammal species, Steller sea lions and sea otters, had gone through striking and worrisome declines in the area over the previous 10-20 years.  Some researchers had suggested that Biggs (transient) killer whales might have played a role in the decline, but there was little evidence for or against this theory.


 

After an initial field season surveying in the Aleutian Islands and around Kodiak Island, Lance and Craig decided to investigate the area around False Pass, a tiny Aleut community located in the passage between the tip of the Alaska Peninsula and Unimak Island, the first island in the  Aleutian chain.  They reasoned that this might be a hot spot for Biggs (transient) killer whales in the spring when  grey whales, which are preyed on by Biggs (transient) killer whales, pass through the area on their annual migration from southern calving areas to feeding grounds north of Bering Strait.  Fishers familiar with the area confirmed that killer whales were common in the area early in the year.

 

 

The Local Area

Lance made the first trip to the area in May 2003 with biologists Damian Power and Laurie Mazzuca.  They chartered the Lucky Dove, a local salmon driftnet boat run by local fisherman Buck Laukitis.  They found everything about the area spectacular.  The weather was bitingly cold, howling winds interspersed with brief periods of calm, rain, snow, and –rarely--sunshine.  The scenery---when they could see it---was spectacular…gravel beaches, rocky headlines, jagged snow-covered mountains with sweeping, grass-covered foothills, even a smoking volcano.  Brown bears fresh out of the dens turned over stones on the beaches and eagles, gulls, fulmars and other seabirds wheeled overhead.  Most importantly for Lance and his crew, the area abounded with Biggs (transient) killer whales single-mindedly attacking and feeding on grey whales.  By the end of the month they had photo-identified almost 80 Biggs (transient) killer whales, only three of which had been photographed by researchers before.

Photo: Lance Barrett-Lennard
Biggs (transient) killer whales in Alaska

 

What They Found

Lance and Craig returned every May for the next four seasons, usually with their collaborators Dr. John Durban and Eva Saulitis, photo-identification expert David Ellifrit, and boat skipper Mike Britain.  Some of their keys observations were as follows:

  • At least 160 transient killer whales visit the area during the grey whale migration some or most years.
  • The killer whales usually attack and kill young-of-the-year and yearling grey whale calves.
    The grey whale's principle defense is to move into very shallow water along the shorelines where killer whales are reluctant to press the attack. The killer whales also give up when mothers defend their calves particularly aggressively.
  • Most grey whales are attacked in waters 10-20m deep and sink to the bottom after death.
  • After an initial feeding, killer whales leave the site for 24 hours or more before returning to feed again - the first such food storing behaviour that has been reported in whales.
  • Grey whales killed by killer whales provide an important source of food for other predators including Alaskan brown bears and sleeper sharks.

 


Photo: John Durban, Lance Barrett-Lennard
Transient killer whale attacking a grey whale; transient killer whale with grey whale flesh over it's head; brown bear on Unimak Island feeding on a grey whale carcass

 

The Significance

This study is the first to report killer whales feeding principally or entirely on grey whales for extended periods of time and to describe killer whales leaving the remains of prey that they have killed and later returning to feed on them.  Lance and his team estimate that transient killer whales may take up to a third of the calves born to the Eastern Pacific grey whale population each year.  Through these direct observations, researchers have begun to recognize the dramatic impact killer whales have on other aquatic life.  This not only includes major impacts on the size and behaviour of prey populations, but also on the size and distribution of populations of scavengers such as sleeper sharks and brown bears.

Lance, Craig, John and Eva hope to return to the area in future years to document changes in both the killer whale and grey whale populations, and to determine whether the killer whales follow the grey whales north in the early summer, or whether they disperse to feed on other prey species.