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

Nanaimo city council voted unanimously Monday to pass a bylaw establishing the foundation for a new downtown business improvement association. (Chris Bush/News Bulletin)
City of Nanaimo adopts bylaw to create new downtown business improvement association

Chamber of commerce says next steps will be a board of directors and five-year strategic plan

Nanaimo-Ladysmith school district teachers’ union, and its counterparts from Mount Arrowsmith district, seek stricter COVID-19 rules. (News Bulletin file)
Nanaimo-Ladysmith teachers’ union asks health authority for stricter COVID-19 measures

Teachers ask for vaccine, more online learning, mask mandate for primary students

B.C. Finance Minister Selina Robinson outlines the province’s three-year budget in Victoria, April 20, 2021. (B.C. government video)
B.C. deficit to grow by $19 billion for COVID-19 recovery spending

Pandemic-year deficit $5 billion lower than forecast

Chakalaka Bar & Grill remains open in defiance of orders from Island Health to close. (Cole Schisler photo)
Island Health seeks injunction against restaurant defying COVID-19 orders

VIHA says Chakalaka Bar and Grill also violating water and sewer regulations with RV hook-ups

Nanaimo Fire Rescue investigator Mark Jonah probes the scene of a blaze that destroyed two apartments on Sunday, April 18. The cause of the blaze has not been determined. (Chris Bush/News Bulletin)
UPDATE: RCMP say Wakesiah Avenue fire was arson, suspect has been arrested

35-year-old man arrested for allegedly starting fire lived in the complex

A man pauses at a coffin after carrying it during a memorial march to remember victims of overdose deaths in Vancouver. THE CANADIAN PRESS/Darryl Dyck
B.C. announces historic half-billion-dollar funding for overdose crisis, mental health

Of it, $152 million will be used to address the opioid crisis and see the creation of 195 new substance use treatment beds

Children’s backpacks and shoes are seen at a CEFA (Core Education and Fine Arts) Early Learning daycare franchise, in Langley, B.C., on Tuesday May 29, 2018. THE CANADIAN PRESS/Darryl Dyck
B.C. budget to expand $10-a-day child care, but misses the mark on ‘truly universal’ system

$111 million will be used to fund 3,750 new $10-a-day spaces though 75 additional ChildCareBC universal prototype sites over the next three years.

The City of Nanaimo will further investigate an initiative to set up two 12-cabin sites to create transitional emergency housing for people experiencing homelessness. (Black Press file photo)
City of Nanaimo will ask for expressions of interest to operate tiny cabin sites

Staff expresses concern about workload, councillor says sheltering people must take priority

Ambulance paramedic in full protective gear works outside Lion’s Gate Hospital, March 23, 2020. Hospitals are seeing record numbers of COVID-19 patients more than a year into the pandemic. (The Canadian Press)
B.C.’s COVID-19 infection rate declines, 849 cases Tuesday

Up to 456 people now in hospital, 148 in intensive care

Christy Clark, who was premier from 2011 to 2017, is the first of several present and past politicians to appear this month before the Cullen Commission, which is investigating the causes and impact of B.C.’s money-laundering problem over the past decade. (Darryl Dyck/Canadian Press)
Christy Clark says she first learned of money-laundering spike in 2015

The former B.C. premier testified Tuesday she was concerned the problem was ‘apparently at an all-time high’

Police executed a search warrant at the Devils Army Clubhouse on Petersen road in Campbell River on August 10, 2017.
Murder trial into 2016 Campbell River killing underway in Victoria

Ricky Alexander is charged with the first-degree murder of John Dillon Brown

Most Read