“Seeing” What Killer Whales VisualizeLatest update August 4, 2019 Started on November 4, 2018
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. We are pursuing this goal using sound to visualize life beneath the surface water. Our study will contribute to the recovery of Southern Resident Killer Whales by assessing the availability of prey in habitats used by killer whales.
We finished all the CTD stations today. With a help of small capstan, Kiah Lee (undergraduate student majoring oceanography) deployed 42 casts over three weeks as deep as 400-m depth, rain or shine. The total length of rope she worked on was 13-km. Great job, Kiah!
We finally got a large Chinook (~ 75 cm) in Johnstone Strait! Jacob Lerner, Ph.D student, will look at how much calories they provide to killer whales and whether there is any difference in fat content of Chinook salmon we caught in southern and northern resident killer whale habitats.
Today, all of our fish on the lines got eaten! She showed up for lunch and dinner and we only got 1 fish at the end… We saw her taking a deep breath for a few times before long dives. She even ate our fish in front of us, while we were recovering the fishing lines.
(Photo credit: Kiah Lee)
After provisioning in Campbell River, we finally arrived in Johnstone Strait this afternoon. During the first hour of the acoustic surveys, we encountered a pod of killer whales!!! Over 5 days, we are going to study about their prey (how deep? how big? any hotspot?). Check out the amazing photo that Kiah Lee took!
We didn't observe any marine mammal in Haro Strait, and no fish was caught. But we did see the sign of fish in the hydroacoustics. Since our fishing gear is specifically targeting Chinook salmon, it is possible that other fish species were dominant in the water column.
In addition to the acoustics and fish sampling, we are also collecting environmental data using the CTD sensor which measures temperature, salinity, oxygen and phytoplankton abundance. These values will give us environmental conditions of where Chinook salmon hang out. The picture shows Kiah deploying the CTD over 180 m depth.
Gale Warning in effect in Juan de Fuca for the past couple of days. I had to stay on the deck for most of the time, fighting over the seasickness…. On the other hand, Kiah (Co-op student) and Jacob (Ph.D student) were enjoying the rough weather.
We got some interesting acoustic signals in Juan de Fuca Strait. The signals with an eye-browse shape (see photo) might be Chinook salmon. Using hook and line techniques, we are validating what kind of species in the water column. Even with the rough weather, Captain Dane successfully caught Chinook, Pink and Coho salmon! Jacob is collecting samples from Chinook to examine prey quality.
We are now on the F/V Carte Blanche heading toward Juan de Fuca Strait, while our students are looking for a sign of killer whales.
Our hydroacoustics are now attached to the side of the vessel. Using the sound from different frequencies, we can separate zooplankton, schooling fish, and large fish targets such as Chinook salmon. Working with the captain Dane Chauvel, we will validate the acoustic signals using hook and line technique.
We are getting ready for the second field season, studying whether a shortage of prey is the cause of the decline of southern resident killer whales. This summer, we match our field survey with the timing of Fraser Chinook return, so that we can examine the prey availability for southern residents during the peak season.
With the help of two undergraduate students, Kiah Lee and Kate Colson, we successfully tested the equipment and field gear. We are ready to get back to the field soon.
On Saturday (November 24th 2018), I presented my results from this summer at the B.C. Annual Marine Mammal Symposium. You can view the recordings of all the talks at: https://youtu.be/gyGB1m2DxTo
(Phillippe Roberge starts at 06:22:02, my talk at 06:31:04, and Prof. Andrew Trites’ talk at 07:03:24)
There were over 200 people gathered across B.C. to talk about issues related to marine mammals. I had some nice brainstorming conversation with salmon farmers and killer whale scientists over the coffee breaks. Now, I am excited to go back to my data analysis!
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 fish 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 sounder detections. Next year, we hope to use the OpenROV’s Trident drone to identify acoustic signals in real time and observe how Chinook salmon respond to killer whales and other predators.
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