Who Researched:
John K.B. Ford, Graeme M. Ellis, Lance G. Barrett-Lennard, Alexandra B. Morton, Rod S. Palm, and Kenneth C. Balcomb III
When Researched:
1973 to 1996
Published in the Canadian Journal of Zoology in 1998
Where Researched:
Nearshore waters of Vancouver Island, mainland British Columbia, the Queen Charlotte Islands, and the coastal waters of Washington State and southeastern Alaska
Research Methods Used:
Field observations of predation: Most observations of predation were seen from boats, ranging from 5 to 20 meters, patrolling waters that killer whales often frequent. Different whales were identified as resident or transient based on their dorsal fins and tails. The killer whales were observed throughout the year; however, most observations of feeding behavior took place during the summer (June through September).
When predation or attempted predation was observed (rapid acceleration, sudden direction changes, circling), the researchers would collect the prey remains by sweeping the water, in which the hunting just took place, with a fine-mesh dip net. The remains were then analyzed for species identification and age identification.
Analyzed the stomach contents of stranded killer whales: A total of 14 beached Orca carcasses were examined. The stomachs (and mouth, esophagus, and intestine when possible) were either taken out and examined later or were examined at the scene of the beaching. Remains of mammalian prey (teeth, claws and vibrissae) were identified from a reference collection at the Pacific Biological Station. Remains of fish prey (skeletal remains) were identified from a reference collection by Pacific Identifications Limited, Victoria, B.C.
What Was Found:
Resident-type killer whales showed a distinct preference for salmon prey (96% of the prey documented); however, a total of 22 species of fish and one species of squid were documented in the resident-type killer whale diet. 12 of these species were previously unknown to be in the Orcinus orca diet. Similar to the resident-type orcas, the transient-type killer whales showed a preference for a certain species. Over half of observed transient-type killer whale attacks were on Harbor seals; however, their diet was quite diverse. They were observed to prey on pinnipeds, cetaceans and seabirds.
The differences in diet between resident-type and transient-type killer whales were known before this study but the diversity of their diets was unknown. The differences in their diets are also key to understanding the differences between transient-type and resident-type killer whales.