Killer Whale Population Assessment

By Dena Matkin, North Gulf Oceanic Society

Is the killer whale population growing or declining? How does it correlate with fluctuating populations of prey species?

Project Dates

Ongoing since 1986

Did you Know?

Killer whales live in highly complex matrilineal societies; social bonds among the resident types are especially strong and stable. Resident pods are composed of a matriarch and her male and female offspring, sometimes including several generations. Transient types have less stable societies and usually stay with their mothers.
Orca researcher Dena Matkin
Dena Matkin and her trusty boat the Kingfisher have been plying Southeast Alaska waters in search of killer whales for more than thirty years.

Introduction


Two main ecotypes of killer whales cruise the coastal waters of Southeast Alaska. One type, called residents, feeds exclusively on fish, while the other, called transients, feeds exclusively on marine mammals. A third ecotype, the offshores, is seen infrequently and feed on sharks. Although their ranges overlap, the three groups rarely interact. They have been genetically isolated for so long—perhaps a million years—that some researchers suspect they may be different species, or at least sub-species.

More likely it is something other than genetics that keeps them separate. As Dena Matkin says in her new memoir, researchers “have begun to refer to these three ecotypes as distinct “cultures” as their food habits are passed down from one generation to the next.” Killer whales apparently do not recognize anything other than their preferred prey as food, or whales outside their ecotype as potential mates.

Dena has been fascinated with these powerful apex predators for decades. Transients—specifically, West Coast Transients—are the type she sees most frequently in Glacier Bay and Icy Strait, and the type that interests her the most. To better understand them and their role in the marine community, Dena follows them (at a respectful distance) to document their feeding behavior and gather information on population size, structure, range and social behaviors. She collects photographic, acoustic and prey data, compares it with past data and shares information with other marine mammal researchers in Glacier Bay and adjacent waters. In collecting photo-IDs, Dena contributes to the long-term photographic record, which is the basic tool of killer whale research.

Glacier Bay provides important habitat for killer whales, even as killer whales play a profound role in structuring the dynamic Glacier Bay marine ecosystem. Dovetailing with long-term research on killer whale prey species, this study seeks to further our understanding of complex predator-prey relationships in Glacier Bay.
orca
Similar to the flukes of humpback whales, the dorsal fins of killer whales can be used to identify individuals. Photo ID is the basic tool of research on both species.

Methods


Dena conducts surveys from her 20-foot boat to collect three types of data: dorsal fin and saddle patch photographs, acoustic recordings and observations of predation. She photographs the left side of each whale, recording details of the dorsal fin and saddle patch. Observing predation takes patience and perseverance. Being careful not to disrupt their normal behavior, she follows the killer whales at a slow, constant speed at a distance of 200 yards or more. Observing a possible predation event, she approaches to within 100 yards and documents any signs of a possible kill. It is usually difficult to observe an actual kill of smaller animals. She attempts to identify the prey species using visual observation, photo documentation and the recovery of prey fragments for genetic analysis.

All data collected is added to existing databases in Glacier Bay, Prince William Sound and British Columbia. Identifiable whales are recorded, catalogued and compared to existing catalogs of whales from the west coast of North America.
unique orca fin
Dena first encountered “T2” in Icy Strait in 1986. He is a regular Glacier Bay visitor, striking up temporary alliances with other transients, occasionally preferring to hunt alone.

Findings


From 1986 through 2015, Dena and her colleagues identified 168 Southern Alaska Residents, 260 West Coast Transients, 25 Gulf of Alaska Transients and 23 Offshore killer whales in Southeast Alaska. In all years West Coast Transients were the most frequently encountered population in the Glacier Bay and Icy Strait region.

Analysis of prey revealed that harbor porpoise comprised 32% of the kills, harbor seals 28%, Steller sea lions 22%, seabirds 8%, sea otters 7%, Dall’s porpoise 4%, and minke whales 2%. Historically, harbor seals have been the primary prey in Glacier Bay, but populations have declined drastically. It appears that the harbor porpoise is replacing the harbor seal as the most frequent observed prey.

Learn More:


“The Mammal-Eating Killer Whales of Glacier Bay: Hunting with the Strong Silent Types” by V. Deecke et.al. Alaska Park Science vol. 5 no. 2, 2006.

“Killer Whale Feeding Ecology. . .in the Glacier Bay Region” by D. Matkin, J. Straley and C. Gabriele, in Proceedings of the Fourth Glacier Bay Science Symposium 2007;

“Killer Whale: The Top, Top Predator” Robert Pitman, ed., Whalewatcher 2011;

“Alaskan Love Stories: A Researcher’s Life” by D. Matkin, 2013.

“An Orca Story: Predation and one Killer Whale’s Family” by D. Matkin 2015

Last updated: February 19, 2018