Unravelling a mystery: Coho reappear after 30-year absence

Thirty years ago, Coho salmon vacated Georgia Strait and did not return in substantial numbers until this spring. 

Their disappearance is still a mystery. As is their resurgence. 

“We have not found good correlates to explain why they suddenly started exiting the Strait at much higher rates, no clear links with things like herring abundance or water temperature,” said Dr. Carl Walters, who heads the University of British Columbia Institute for Oceans and Fisheries.

But there are theories, including changes in the salinity levels and a lack of food when baby Coho first enter the marine environment. Both warrant more study. 

There has always been an annual but variable ‘inside/outside Georgia Strait’ distribution of Coho but their ongoing absence from about the mid-1990s was unprecedented. 

‘Resident Coho’ used to be abundant in Strait

From 1975, when data was first collected, until 1980, a lot of Coho resided in the Strait, hence the term ‘resident Coho.’ During these years, Coho had excellent ocean survival rates and generated exceptional catches. 

Before 1995, commercial and recreational marine fisheries took over a million Coho from Georgia Strait’s waters each year, of which recreational catches ranged from 100,000 to 750,000 fish. Low catch numbers coincided with the years Coho migrated outside the strait. 

In the 1970s and 80s, fishers exploited much as 80 per cent of the total abundance of Coho, according to data from the Department of Fisheries and Oceans (DFO). But high exploitation rates don’t explain why so many Coho vacated Georgia Strait on masse.

Good ocean productivity conditions can support much higher exploitation; poor conditions cannot. Ocean survival rates dropped from as much as 15 per cent prior to 1980, to as low as one per cent in the 1990s. 

Fishing ban halted population decline

By the mid-1990s, ‘outside’ Coho migrations increased in frequency and magnitude. Then-federal Fisheries Minister David Anderson imposed a Georgia Strait Coho fishing ban to conserve wild interior Fraser River stocks. 

Fishing restrictions halted the decline, but were unsuccessful in boosting interior Fraser River escapements until recently. Which suggests factors other than fishing are negatively influencing Coho recovery. 

The ban is still in place with a few exceptions.

In the intervening years from the initiation of the ban until present, those few Coho that did return provided hope for a revival of the good old fishing days, even though those sporadic re-appearances represented a fraction of the abundances of the pre-1980s, according to Walters. 

“This year’s big run is probably nowhere near as high as the Coho runs of the late 1970’s,” he said. While “fishing is great,” it’s partly because fewer people are fishing now compared to the boom years.

‘Potentially back at square one’

Currently, DFO has set a high bar for lifting the ban on Interior Fraser Coho: there must be escapements in excess of 40,000 and a minimum three per cent marine survival rate for three consecutive years. 

According to Jeremy Maynard, co-chair of the Sport Fishing Advisory Board’s Chinook and Coho Working Group, this will be a difficult target to meet. 

“The 2022 marine survival preliminary estimate is less than three per cent, so we are potentially back at square one again,” Maynard said.

Ongoing Coho conservation measures reduced fishing exploitation rates to as low as five per cent and consisted almost entirely of incidental mortalities in fisheries that were targeting other salmon species. 

But over-fishing and incidental mortality concerns had been identified long before Minister Anderson’s tough Coho recovery measures came into effect. Unfortunately, the early warnings weren’t acted upon because of political pressure to keep fishing. High marine survival rates also had an impact because they masked the consequences of over-harvest.

Other factors suggested as possible causes for the departure of Coho from Georgia Strait are the loss of critical freshwater habitat from human activities and increased predation from expanding seal and sea lion populations. However, these are most likely to affect abundance, not distribution, even for reduced Coho populations. 

Seal and sea lion populations expanded rapidly after adoption of marine mammal protection laws in Canada and the US. Their current populations are stable but large, and there have been calls for annual pinniped harvests to bring their numbers into balance.

Meanwhile, habitat loss and pollution continue to be problematic, in spite of community efforts to restore streams and educate the public about fish habitat values and basic needs.

Research unraveling Coho mystery

Research will eventually unravel the mystery behind abrupt shifts in marine distribution of Georgia Strait Coho, said University of Victoria graduate student, Will Duguid, who has been studying the foraging habits of juvenile Coho and Chinook for several years. 

Using winter micro-trolling, a fishing technique with tiny lures designed to trigger strikes from first ocean year Coho and Chinook, Duguid retains salmon and analyzes their stomach contents. The research aims to discover if predictive mechanisms exist – like prey availability and preferences – to improve understanding of Coho inter-annual distribution shifts. 

Duguid, working with University student Micah Quindazzi, will also be studying the growth rings found on salmon otolith bones to see if baby salmon are physiologically tuned to remain in Georgia Strait, or migrate outside, depending on external factors. For example, do early feeding conditions produce larger juveniles causing them to remain in the Strait? Or are poor feeding conditions the reason they migrate outside?  

The answers could help DFO fine-tune fishing opportunities based on knowing the upcoming year’s distribution pattern. 

Dr. Dick Beamish has been studying Georgia Strait salmon patterns for decades. An emeritus scientist at DFO’s Pacific Biological Station in Nanaimo, Beamish developed a data-time-series based on standardized trawl sampling of Georgia Strait. 

The trawl surveys began in 1998 to study early marine distribution, condition, feeding and growth of juvenile salmon in the top 75 meters of Georgia Strait. Preliminary trawl survey data for 2023 shows the highest Coho trawl catches to date.

“[The surveys] give us the ability to examine how shifts in ocean climate impact that ecosystem of the strait,” explained DFO researcher, Chrys Neville, who works with Beamish. The surveys also allow scientists to compare today’s conditions with what occurred in previous decades.

Results suggest that the strong showings of Coho during their first year in the Strait are a result of significant prey availability, which promotes rapid early growth. The data also shows an abrupt turnaround in juvenile Coho abundance began in 2013 after years of poor trawl survey catches. 

The research being done by scientists should advance our knowledge of the underlying factors that alter the Georgia Strait eco-system, while hastening Coho recovery and providing a scientific basis for improving fishing opportunities.       

Anglers celebrate renewed Coho abundance

It’s been so long since Coho salmon were really abundant in Georgia Strait, few contemporary anglers understand how many were there, or the size of fisheries they supported. 

But some fishers remember.

“It’s the best since the 1970s,” said George Bates, owner of Bates Beach Resort, which hosted a few celebrity recreational anglers over the years, including former B.C. Premier Dave Barrett and his wife, Shirley.

“We don’t know what caused the shift back to inside waters, but it sure helped the sport fishery, given the (Chinook) restrictions in Georgia Strait,” Bates said. 

Bob Meyer has chartered near Gabriola Island for decades. He says this year’s Coho numbers were “a complete surprise.” Last year he said he only landed about 25 Coho all year. “This summer, clients have seen that many on a single trip.” 

Meyer worries it’s an aberration. “If it’s not, it’s the best news for our local fishery in 30 years.”

Clyde Wicks is a keen angler who regularly fishes the Nanaimo area. He also participates in the Avid Angler salmon DNA collection program, which provides valuable stock data to DFO. Wicks was credited as one of the first to report large juvenile Coho numbers near Nanaimo in early 2023. He echoes the benefit potential that comes from renewed Coho abundance. 

Long-time Vancouver charter captain, David Korsch, ranked 2023 as the best season in three decades. “Perhaps better than 1986 when Fisheries released extra Coho to boost fishing tourism during Expo ‘86.”

“Coho in our area has been wonderful for sport fishing,” said Rick Hackinen, president of the Campbell River Fishing Guides Association.

“It is a reminder of what it was like when Coho choose to stay in our inside waters.”