VANCOUVER — UBC researchers will track chinook salmon as they navigate the summer feeding grounds of the southern resident killer whales to see if the whales’ dinner plate is empty or full.
About 100 mature wild chinook are being fitted with high-tech acoustic tags near Port Renfrew to see how they behave in the presence of the salmon-eating orcas — and, it’s hoped, help to determine why the whales appear malnourished.
Is there a shortage of chinook — their preferred food — or is noise from freighters and oil tankers interfering with the whales’ ability to catch enough fish to feed themselves?
“We know, mathematically, that there should be enough fish here for them, but we aren’t sure whether they can access them because of interference from vessels, whether it’s from noise or disruption,” said Andrew Trites, head of UBC’s Marine Mammal Research Unit. “Right now, it’s pure speculation.”
Data from the tags will be collected as the fish pass by underwater acoustic receivers placed at key points to record their movements while the southern residents are hunting.
Most of the devices are already in place for the Salish Sea Marine Survival Project organized by the Pacific Salmon Foundation, which has contributed $150,000 to the chinook study.
“We will be able to see how fast they are moving and their depth,” said Scott Hinch, director of the Pacific Salmon Ecology and Conservation Lab at UBC. “We are interested to see how their behaviour changes when there are predatory whales in the vicinity.”
Data about the presence of orcas from other research groups will be overlaid with the chinook data to see how they were behaving, he said.
Scale and tissue samples from each fish will allow them to determine the health and energy density of the chinook, while genomic testing will pinpoint its river system of origin, so researchers can determine if it survived to return to its spawning ground.
The southern resident killer whales and seven of B.C’s 13 chinooks stocks are rated as endangered under the Species at Risk Act.
Trites will also conduct hydro-acoustic surveys by ship to build maps of the presence of chinook salmon.
Hydro-acoustic devices employ essentially the same technique that whales use to find chinook: a razor-thin, cone-shaped signal that moves through the water to capture the density and distribution of fish.
“We want to get an image of what the dinner plate of the killer whales looks like,” he said. “Does the plate look empty at this time of the year compared to the fall?”
Between the two techniques, it will be possible to see how and if the fish school, their depth and distribution, and how many survive.
“Ultimately, we want to relate that to their behaviour and the presence of boats and noise levels in the water,” he said. “If the fish are there, but the whales can’t feed, that raises a lot of issues.”
Vessel noise may interfere with the orcas’ ability to communicate with each other while they are hunting, he said.
“In a quiet environment, they would typically be quite spread out when they are feeding and looking for fish,” he said. “But if there is vessel noise and they can’t hear each other, they have to move closer together, which means they are scanning less of the water” for food.
The feeding behaviour of orcas is complex and culturally ingrained.
Killer whales are known to share fish with each other, especially mothers feeding their sons. The males are lifelong “momma’s boys” who tend to stay with their mothers their entire lives, said Trites.
“That may be because the mothers are sharing their food with them, and it could explain why males don’t tend to live long after their mothers die,” he said.
The Vancouver Fraser Port Authority Enhancing Cetacean Habitat and Observation (ECHO) program is monitoring for the presence of the southern residents as part of its voluntary vessel slowdown program, which is intended to reduce underwater noise levels.
The trial zone has been expanded this year to include the Haro Strait and Boundary Pass, which Fisheries and Oceans Canada has identified as key killer whale foraging areas.
A program was launched in June to move tug and barge traffic in Juan de Fuca Strait south and away from preferred southern resident feeding areas. A similar trial included deep-sea vessels last summer.