“Seeing” What Killer Whales Visualize
Summary: Give a brief summary of your expedition’s mission. What are you planning to do?
Decline of prey, specifically Chinook salmon, has been identified as a threat to the recovery of the Southern Resident Killer Whale population in Canada and the US. However, little is known about whether there are enough fish for them to prey upon. Our mission is to determine how many Chinook are present and how the fish are distributed in areas where increasing and decreasing populations of fish-eating killer whales travel and feed. The drone will contribute to the recovery of Southern Resident Killer Whales by allowing us to see and verify the fish visualized by our sounder so we can confidently assess the availability of prey in habitats used by killer whales.
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Background: Tell us about your expedition background. What are you planning to do and what has already been done? This will be your first post.
We successfully completed our first field season to assess the availability of Chinook salmon for Southern Resident Killer Whales.
Our field work started in July in collaboration with sport fishing guides. These local fishermen volunteered their time to catch Chinook on hook and line to validate the acoustic signals we were observing on our sounder near Gabriola Island and Sooke, British Columbia. In 9 days, they caught 40 Chinook and 9 Coho salmon which helps us distinguish the echoes of Chinook from other species.
In August, we did large-scale hydroacoustic surveys along transect lines to compare the habitat of the increasing Northern Resident Killer Whales in Johnstone Strait with the habitat of the declining Southern Resident Killer Whales in Juan de Fuca Strait. We also followed 5 male northern resident killer whales in Johnstone Strait for 2 hours each while collecting sounder data to visualize the prey the whales were seeing.
We found the acoustic characteristics of prey present in Northern and Southern Resident Killer Whale habitats were quite different from each other. Johnstone Strait only had a few large acoustic targets, while Juan de Fuca Strait had larger targets that occurred in more structured depth layers.
In March 2019, we will return to the survey areas to see how the habitat differs between summer and winter.
During the first season, we learned how difficult it was to catch salmon to validate our hydroacoustic detections. Next year, we hope to use the OpenROV’sTrident drone to identify acoustic signals in real time and observe how Chinook salmon respond to killer whales and other predators.