Skip to content
Join our Newsletter

Research finds bull trout, seals major salmon predators

Despite low Chinook numbers, progress is being made on salmon research and recovery
Tracking tags have been used on adult salmon for some time, but lately the tags have gotten small enough to be placed on juveniles as well. | Pacific Salmon Ecology and Conservation Laboratory

Pacific salmon may be more abundant today than they have ever been, since records were kept, but for some salmon species and populations in certain regions, it’s a vicious Darwinian competition where some species are faring much better than others – perhaps even at the expense of others.

But it’s not all doom and gloom for B.C.’s iconic salmon.

Some salmon stocks are doing better than others, and a number of important research projects have either been conducted or are underway that are helping scientists better understand the threats to salmon stocks and improve their chances of recovery.

While Fraser River sockeye declines were the biggest concern 10 years ago, today it’s Chinook that is causing the most angst, because of their importance to both the sport fishery and Southern Resident Killer Whales.

A paper published in April 2018 found that Pacific salmon are “more abundant than ever,” based on 90 years of catch and escapement data of sockeye, pink and chum salmon.

Pink salmon are the most abundant, and their numbers are boosted by industrial-scale hatcheries in Alaska, Russia and Japan.

Fraser River sockeye, meanwhile, have yo-yoed between extreme highs and lows over the past decade. This year’s Fraser River sockeye returns are expected to be around 11 million to 12 million – an eight-fold increase over 2017’s return of 1.5 million.

For the first time in two decades, coho in the Straight of Georgia have been increasing in number. Chinook, on the other hand, are in trouble. Generally, they have been declining in both size and number.

Thanks to recent research, scientists are starting to get a better understanding of what the biggest threats to salmon survival are.

A juvenile salmon tagging project lead by a University of BC researcher, for example, has determined that bull trout appear to be zeroing in on juvenile sockeye salmon infected with IHN virus.

A recently completed $23-million, five-year joint American-Canadian study of the Salish Sea’s ecosystem has found harbour seals responsible for 25% to 40% of the predation of Chinook.

And to get a better understanding of what happens to salmon after they make it into the open ocean, an international team of scientists will head to the Gulf of Alaska in February to conduct the first-ever comprehensive survey aimed at getting a better of understanding of ocean conditions and mortality rates.

While open-net salmon farms get all the attention when it comes to potential threats to wild salmon, they may be the least of wild salmon’s worries.

Scott Hinch, professor of Forest and Conservation Sciences Department at University of British Columbia, who recently won an exceptional leadership-professor award from Mitacs, has been using tracking tags to determine survival rates of juvenile salmon.

Only recently have these tags become small enough to attach to juvenile salmon. They use acoustic signals that can track the salmon for up 1,000 kilometres and can tell researchers where they are, and when they die.

Working with Pacific Salmon Foundation (PSF), the St’át’imc Eco Resources and BC Hydro, Hinch’s team has tagged and tracked thousands of sockeye juveniles. They also take biopsies to determine the fish’s health. The tagging shows very high mortality rates in the juvenile salmon in the early stages of their migration to sea.

“We would lose on the order of 20% to 40% in the first 50 kilometres of their downstream migration,” Hinch said. “When those fish got to the Fraser River and travelled another 600 kilometres, they survived perfectly.

“What we’ve learned in some of the first studies we did with the juvenile fish is that a naturally occurring virus was accounting for a large amount of the mortality in these fish before they got to the marine environment. Naturally occurring pathogens were correlated with their ability to survive to get to the oceans.”

The virus in question is infectious hematopoietic necrosis (IHN). When Hinch’s team overlayed the results of their tagging research with juvenile salmon over a similar tagging program with bull trout – which eat juvenile salmon – they discovered something interesting.

“What we found was that the large bull trout were queuing in on the fish that were carrying the virus,” he said. “We all talk about how predators pick the weak and the physiologically compromised. This is one of the first times anybody’s showed it.”

The Pacific Salmon Foundation has been involved in a number of other important studies, one of the most significant of which was a recently concluded five-year project, the Salish Sea Marine Survival Program, a $23 million joint effort between Canadian and American researchers.

Foundation CEO Brian Riddell said hundreds of studies have been done on specific species or populations of fish in the Straight of Georgia. But a comprehensive study of the entire ecosystem of the straight and Puget Sound had never been done before.

The results are still being analyzed. But initial findings have identified a couple of obvious concerns. One is water flows on the Cowichan River, which have led to poor survival rates.

“We happened to get two extraordinary drought springs and we saw very poor survival,” Riddell said.

The Salish Sea research project also found that harbour seals account for 25% to 40% of the predation of juvenile salmon – mostly Chinook and coho.

“There isn’t any question, from our research, that seals are a major predator of juvenile salmon,” Riddell said.

There are roughly 40,000 to 45,000 harbour seals in the Straight of Georgia and 18,000 to 20,000 in Puget Sound, and 100,000 coast-wide, Riddell said.

Riddell said research in Puget Sound suggests that harbour seals consume roughly the same volume of Chinook as orcas. He said one new research project being developed will use “predator tags” on adult Chinook that will tell researchers when and where the fish are being eaten by marine mammals, including orcas and sea lions.

Alaska, Japan and Russia have been very successful in boosting chum and pink populations to through commercial hatcheries. Hatcheries have been less successful in boosting Chinook numbers in B.C., however.

“Right now, we’re seeing very depressed production of Chinook almost coat-wide,” Riddell said. “So there is something in the marine environment that is limiting production of Chinook salmon. There are some areas that are doing quite well, like the Cowichan, for example, but in general the rates of production are relatively poor.”

One of the biggest knowledge gaps has been what happens when salmon go to sea. Addressing that question is the objective of a landmark ocean survey taking place this winter in Alaska.

Dick Beamish, a fisheries scientist emeritus at the Pacific Biological Station in Nanaimo, spearheaded $1 million privately funded expedition, in which scientists from Canada, Russia, the U.S, Japan and South Korea will spend several weeks at in the Gulf of Alaska, starting in February.

"We will do the first-ever survey of the abundance, species competition and overall health or condition of all species of salmon in the Gulf of Alaska after the first ocean winter," Beamish said. "And we expect that about one-third of all Pacific salmon are over-wintering in the Gulf of Alaska."

Beamish thinks the survey will allow for better predictions of salmon returns, and hopes to see such surveys become a regular part of fisheries management.

As for salmon habitat efforts, a number of projects have taken place in B.C. over the years, and one new one was just announced December 20.

Under the federal Ocean Protection Plan, Ducks Unlimited Canada and Raincoast Conservation Society will receive $2 million to remove barriers in the dyke and flood control system on the south arm of the Fraser River to improve access for salmon to the marshes of the Fraser River Estuary.

[email protected]