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

The entrance to the Lodge Property on Reef Point Road. (Nora O’Malley photo)
Virtual public hearing held for the Lodge Property in Ucluelet

Mayor and council to make a final decision during the April 14 regular council meeting

The Pacific Rim National Park Reserve’s Green Point Campground saw an unprecedented flurry of reservations last week. (Pacific Rim National Park Reserve photo)
Pacific Rim National Park Reserve’s campground sees ‘unprecedented’ interest as reservations open

Green Point Campground is scheduled to open from May 1 – Oct. 12 this year.

Kale is a classic in West Coast gardens.
COLUMN: Kale reigns supreme in West Coast gardens

In Tofino and Ucluelet, kale is a classic.

(B.C. Government photo)
POLL QUESTION: Are you in favour of B.C.’s three-week ban on in-restaurant dining?

Dr. Bonnie Henry called the three week stoppage a “circuit breaker”

A 3.0-magnitude earthquake occurred off Ucluelet just after 12:30 a.m. on April 10 and was reportedly felt as far south as Oregon. (Map via United States Geological Survey)
Quake off Ucluelet reportedly felt as far south as Oregon

Magnitude 1.5 earthquake also reported off Vancouver Island’s west coast hours earlier

Burnaby MLA Raj Chouhan presides as Speaker of the B.C. legislature, which opened it spring session April 12 with a speech from the throne. THE CANADIAN PRESS
B.C. NDP promises more health care spending, business support in 2021 budget

John Horgan government to ‘carefully return to balanced budgets’

Restaurant owners Oura and Kymon Giakoumakis visit the PQB News/VI Free Daily studio. (Peter McCully photo)
PODCAST: COVID-19 pandemic hits Island’s food service industry hard

Pair of Vancouver Island restaurant owners share thoughts and advice

A real estate sign is pictured in Vancouver, B.C. THE CANADIAN PRESS Jonathan Hayward
1 in 3 young Canadians have given up on owning a home: poll

Data released Monday says 36% of adults younger than 40 have given up on home ownership entirely

A Nanaimo man will serve nine months in jail for the sexual assault of a young girl he admitted to having committed more than 40 years ago. (News Bulletin file photo)
Nanaimo man sentenced for sexually abusing girl more than 40 years ago

Man, now 71, gets nine-month sentence for abuse of friend’s daughter

Dr. Bonnie Henry gives her daily media briefing regarding Covid-19 for the province of British Columbia in Victoria, B.C, Monday, December 7, 2020. THE CANADIAN PRESS/Jonathan Hayward
B.C. urges people to stay in their neighbourhoods, discourages out-of-household meet-ups

Dr. Bonnie Henry says there should be no travel, even to the next city over

Dr. E. Kwok administers a COVID-19 vaccine to a recipient at a vaccination clinic run by Vancouver Coastal Health, in Richmond, B.C., Saturday, April 10, 2021. THE CANADIAN PRESS/Jonathan Hayward
Most Canadians plan to get COVID-19 vaccine, but safety fears drive hesitancy: poll

This comes as confidence in governments is plummeting in provinces being hit hardest by the pandemic

Marathon of Hope runner Terry Fox is shown in a 1981. (THE CANADIAN PRESS/CP)
Terry Fox’s legacy of resilience resonates during COVID-19 crisis, says brother

Fred Fox said his brother’s legacy of resilience has taken on renewed resonance as COVID-19 rages on

A youth was arrested following a car crash on Wallace Street on Saturday, April 10. (Karl Yu/News Bulletin)
Onlookers laugh and jeer as B.C. teen beaten, then forced to strip and walk home

Police arrest older teen, call video shared on social media ‘disturbing’

A lady wears a sticker given out after receiving a COVID-19 vaccine at a clinic in Richmond, B.C., Saturday, April 10, 2021. THE CANADIAN PRESS
B.C.’s COVID-19 case count slows after last week’s peak

3,219 new cases since Friday, 18 additional deaths

Most Read