A Pacific great blue heron preys on a juvenile salmon in Cowichan Bay. A new study out of UBC suggests the birds removed between three and six per cent of the young fish every year from the Salish Sea region. (Photo supplied by Robert Stenseth)

A Pacific great blue heron preys on a juvenile salmon in Cowichan Bay. A new study out of UBC suggests the birds removed between three and six per cent of the young fish every year from the Salish Sea region. (Photo supplied by Robert Stenseth)

Blue herons identified as a significant predator of B.C.’s juvenile salmon

Surprising UBC findings may actually be beneficial to stability of salmon populations

It appears Pacific great blue herons have a much larger appetite for juvenile salmon than previously understood, potentially raising the complexity of salmon recovery strategies in B.C.

A new study out of UBC shows the birds are annually removing three per cent of the young fish heading to the Salish Sea. During years of low waterflows predation can shoot up to to six per cent.

“It doesn’t sound like a lot, but when you’re talking about millions of juvenile salmon moving out of these river systems into the Salish Sea, it adds up pretty quickly,” lead author, PhD student Zachary Sherker said.

“There is a study that showed reductions as low as five per cent can have a really significant impact on the overall recovery of salmon populations. But in this instance, it looks like the smaller juveniles are being preyed upon more heavily, and evidence suggests they have less chance of survival at sea — it could be they wouldn’t return as spawning adults anyway.”

READ MORE: Genomic study tracks 118 Northwest B.C. sockeye populations

The study was part of Sherker’s master’s research, published January in The Canadian Journal of Zoology. It is the first to quantify the portion of juvenile salmon preyed upon by heron in the southern streams. The findings suggest river-side heron rookeries need to be more closely monitored, with heron predation taken seriously for salmon recovery planning.

Knowing where and how juvenile salmon die has become an important scientific quest in B.C. amidst record-low salmon returns.

As juvenile swim to the ocean, about 50 per cent die from predation and damaged habitat. Sherker had set out to determine exactly how the fish were dying, looking for evidence from predators often linked to predation in Western scientific literature — raccoons, otters, king fishers and mink. On Vancouver Island he spent months raking the forest floor with a magnetic device, searching for scat containing tiny transponder tags that scientists years prior had implanted in the juvenile salmon to track their migration patterns.

After four months with zero results, he turned to the estuary expecting seals were responsible for the predation. That’s when a local Indigenous collaborator, Cowichan Tribes biologist Tim Kulchinsky, directed Sherker’s attention to numerous herons in their seasonal foraging ground at the river’s outflow.

In the heron’s fecal remains Sherker located 100 tags on the first day.

“The way it all came together is quite surprising,” Sherker said. “This is the first time we’ve been able to use this technology to peer into predation in the wild. It’s evaded researchers prior to that.”

Blue herons are regularly seen near salmon habitat, but are rarely listed among known salmon predators. Identifying the heron as a prolific predator was problematic in the past, partly because their digestive tracts break down every part of the salmon, including bones. It was also assumed predators that rely on their vision target large, easy-to-spot prey.

Finding the tags in heron scat proved this assumption too simplistic, as Sherker concluded the heron are most likely hunting the smallest juveniles for their young.

“These are really important prey items for the chicks in the early weeks, when they’re still gape-limited and still have a high hazard of choking on larger fish,” Sherker said.

Over two summers of field research, Sherker had found 10,000 tags, one per cent of the total implanted in fish moving through the Cowichan, Big Qualicum and Capilano rivers. The finding suggests up to 8.4 per cent of the chicks’ diet consists of juvenile salmon, removing between three to six per cent of the fish from streams.

READ MORE: Researcher investigates accumulation of microplastics in B.C. whales

Sherker said further studies are needed to pin down what this means for salmon abundance, but he is optimistic the predation may actually be beneficial.

“Herons may be taking out fish that were destined to die somewhere else along the way, but were going to live long enough to compete with other fish for potentially limited resources in the early marine environment. This predation could benefit salmon stocks by weeding out the weak and allowing for less competition and higher growth among other fish in these critical juvenile life stages.”

The study was completed in collaboration with the British Columbia Conservation Foundation and Cowichan Tribes, and was funded by the Pacific Salmon Foundation with support of a MITACS Accelerate grant.



quinn.bender@blackpress.ca

ConservationSalmonScienceWildlife

Get local stories you won't find anywhere else right to your inbox.
Sign up here

 

UBC PhD candidate Zachary Sherker uses a magnetic device to locate salmon tags in bird scat at at the Cowichan Bay heronry. Sherker’s study now suggests herons remove three to six per cent of juveniles in the Salish Sea region to feed their chicks. (Photo supplied by Zachary Sherker)

UBC PhD candidate Zachary Sherker uses a magnetic device to locate salmon tags in bird scat at at the Cowichan Bay heronry. Sherker’s study now suggests herons remove three to six per cent of juveniles in the Salish Sea region to feed their chicks. (Photo supplied by Zachary Sherker)

Just Posted

Elvira D’Angelo, 92, waits to receive her COVID-19 vaccination shot at a clinic in Montreal, Sunday, March 7, 2021, as the COVID-19 pandemic continues in Canada and around the world. THE CANADIAN PRESS/Graham Hughes
110 new cases of COVID-19 in Interior Health

Provincial health officers announced 1,005 new cases throughout B.C.

BGC Cranbrook will renovate a facility to relocate 24 existing spaces and add 24 new spaces with support from the Trust. Photo courtesy Columbia Basin Trust.
Grant funding to help create new childcare spaces in Cranbrook

Columbia Basin Trust providing $10,000 to BGC Cranbrook to help renovate new facility

Earlier this spring, the City of Cranbrook started positioning components of the Stormceptor system to carry storm runoff to Elizabeth Lake from the Innes Avenue neighbourhood. Photo submitted
Stormceptor will bring clean run-off to Elizabeth Lake

The City of Cranbrook is installing new infrastructure to handle the Innes Avenue neighbourhood, but go easy on Elizabeth lake

Interior Health nurses administer Pfizer-BioNTech COVID-19 vaccines to seniors and care aids in Kelowna on Tuesday, March 16. (Phil McLachlan/Kelowna Capital News)
69 new cases of COVID-19 in Interior Health

The total number of cases in the region is now at 9,840 since the pandemic began

Kelowna General Hospital (File photo)
Interior Health hospitals not strained by rising COVID case counts

While provincial hospitalizations rise, health care systems in the B.C. Interior remain robust, say officials

Rainbow trouts thrashing with life as they’re about to be transferred to the largest lake of their lives, even though it’s pretty small. These rainbows have a blue tinge because they matched the blue of their hatchery pen, but soon they’ll take on the green-browns of their new home at Lookout Lake. (Zoe Ducklow/News Staff)
VIDEO: B.C. lake stocked with hatchery trout to delight of a seniors fishing club

The Cherish Trout Scouts made plans to come back fishing soon

Royal Inland Hospital in Kamloops. (Dave Eagles/Kamloops This Week file photo)
RCMP intercept vehicle fleeing with infant taken from Kamloops hospital

The baby was at the hospital receiving life-saving care

Vancouver Police Const. Deepak Sood is under review by the Independent Investigations Office of B.C. after making comments to a harm reduction advocate Sunday, April 11. (Screen grab)
VIDEO: Vancouver officer convicted of uttering threats under watchdog review again

Const. Deepak Sood was recorded Sunday saying ‘I’ll smack you’ and ‘go back to selling drugs’ to a harm reduction advocate

Provincial health officer Dr. Bonnie Henry prepares a daily update on the coronavirus pandemic, April 21, 2020. (B.C. Government)
B.C.’s COVID-19 infection rate persists, 1,005 new cases Friday

Hospitalization up to 425, six more virus-related deaths

Premier John Horgan receives a dose of the AstraZeneca COVID-19 vaccine at the pharmacy in James Bay Thrifty’s Foods in Victoria, B.C., on Friday, April 16, 2021. THE CANADIAN PRESS/Chad Hipolito
B.C. Premier John Horgan gets AstraZeneca shot, encourages others

27% of residents in B.C. have now been vaccinated against COVID-19

The Nautical Dog Cafe at Skaha marina is getting its patio ready in hopes Mother Nature will provide where provincial restrictions have taken away indoor dining. (Facebook)
‘A lot of instability’: B.C. restaurants in layoff limbo

As COVID-19 cases stay high, restaurants in British Columbia are closed to indoor dining

Prime Minister Justin Trudeau looks on as Deputy Prime Minister and Finance Minister Chrystia Freeland responds to a question during a news conference on Parliament Hill in Ottawa, Tuesday, Aug. 18, 2020. THE CANADIAN PRESS/Adrian Wyld
Expectations high as Trudeau Liberals get ready to unveil first pandemic budget

The Liberals will look to thread an economic needle with Monday’s budget

Cannabis bought in British Columbia (Ashley Wadhwani/Black Press Media)
Is it time to start thinking about greener ways to package cannabis?

Packaging suppliers are still figuring eco-friendly and affordable packaging options that fit the mandates of Cannabis Regulations

Join Black Press Media and Do Some Good
Join Black Press Media and Do Some Good

Pay it Forward program supports local businesses in their community giving

Most Read