Not so black and white

Understanding the role of killer whales in the Aleutian Islands

Processed with MOLDIV

August 22, 2017
Kristin Campbell

Biologist

 

As I peer through the binoculars, a jet-black, triangular dorsal fin slowly arcs over the ocean’s glassy horizon. There is no mistaking it… we found killer whales!

NOAA Fisheries. Permit No. 20465

For centuries killer whales have captured the human imagination. Although arguably one of the most recognizable species, there is a lot we still do not know about them… but we are learning! NOAA Fisheries’ Cetacean Assessment and Ecology Program has been studying killer whales in the Aleutian Islands of Alaska since 2001. As researchers, our goal is to better understand the abundance (how many whales there are), distribution (where the whales are), social structure, and feeding behavior of killer whales in the Central and Western Aleutian Islands. The information we learn about these populations can help us understand the role of killer whales within this fragile ecosystem. We are particularly interested in how, or if, Bigg’s (“mammal-eating”) killer whale predation or resident (“fish-eating”) prey competition may be impacting Steller sea lion recovery in the Western Aleutian Islands.

Transient killer whale predation on marine mammals in the Aleutian Islands has rarely been observed. However, on this year’s cruise we happened upon a predation event in-progress at Hasgox Point on Ulak Island.

During this year’s Steller sea lion cruise, killer whale biologist, Dr. Paul Wade, and I conducted cetacean (whale, dolphin, and porpoise) surveys from the highest point of our research vessel, the flying bridge. We spent hours scanning the horizon with our binoculars as our ship traveled from one Steller sea lion site to the next. When we sighted whales or porpoises we noted the species, group size, and their GPS location. This year we saw many cetacean species on our voyage including sperm whales, fin whales, humpback whales, Dall’s porpoise, beaked whales, and others. Surveys give us information about whale population abundance and distribution within the Aleutian Islands.

dorsal fin

When we encountered killer whales, we suspended our survey in order to collect photographs of the killer whale’s dorsal fins and adjacent saddle patch pigmentation. We are able to make an initial determination of ecotype (“fish-eating” resident or “mammal-eating” Bigg’s) in the field based on physical characteristics of the dorsal fin and saddle patch, group size, and behavior. However, photographs allow us to later confirm the ecotype designation and even identify individual killer whales from their natural markings. If conditions permitted, we launched a small vessel for closer approaches to collect tissue biopsies or deploy satellite tags.

Campbell_photographs.jpg

Transient killer whale predation on marine mammals in the Aleutian Islands has rarely been observed. However, on this year’s cruise we happened upon a predation event in-progress at Hasgox Point on Ulak Island. We observed two transient killer whales methodically “working” the sea lion rookery. The killer whales closely approached sea lion groups on the shore and in the water.

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These killer whales may seem menacing, but Steller sea lions are not defenseless! Steller sea lions are large, agile in the water, and have big teeth that could harm killer whales. Even though many sea lions were in the water, the killer whales were not successful in making a kill and eventually moved on. The next morning we observed another group of four Bigg’s killer whales at Ulak Island. This group was more active, they hunted further away from the rookery, and displayed exciting behaviors like tail slaps, spy hops, and even porpoising.

Image credit: NOAA Fisheries. Permit# 20465 MML/AFSC/NMFS/NOAA

This year we successfully deployed two satellite tags on Bigg’s killer whales. Satellite tags give us information about where the whales travel and how deep they dive, unlocking the mysteries of their daily activities. Previous satellite data from Bigg’s killer whales in the Western Aleutians has revealed distinct foraging patterns. The tagged Bigg’s killer whales made shallow dives around Steller sea lion rookeries in the early mornings and repetitive deep dives (to almost 400m!) in the evenings. This data has revealed that Bigg’s killer whales in the Central and Western Aleutians forage on both marine mammals and squid!

NOAA Fisheries. Permit No. 20465

We look forward to analyzing the data we have collected this field season (including photographs, remote camera images, satellite tag data, and survey data) and discovering more about whales in the Aleutian Islands of Alaska.


I am a volunteer researcher for NOAA’s Marine Mammal Lab studying killer whales and for the Burke Museum of Natural History and Culture studying sea otter morphology and foraging behavior. I earned my B.S. from the University of Washington in Biology. I plan to attend graduate school in marine mammal science.

Author: Steller Watch

Blog for Steller Watch, a Zooniverse.org Project https://www.zooniverse.org/projects/sweenkl/steller-watch