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Coho salmon: BC’s canary in the coal mine

Weird new discoveries about Coho salmon may have bigger implications for Pacific coast

New research this winter shows Coho salmon are BC’s signature fish, and can offer valuable insights into coping with climate change.

An international team of scientists spent a month at sea on a research voyage in the Gulf of Alaska studying wild salmon. They used new genetic tests to discover that most Coho salmon feeding in the north Pacific Ocean are almost exclusively from rivers and streams within British Columbia’s borders.

One of their most interesting discoveries was how far Coho salmon were from home.

“Coho continue to mystify the team. They’re supposed to be a coastal fish. Why then are they appearing more than 1,000 kilometres off the coast, far from their home rivers in BC and Washington State?” said Vladimir Radchenko, executive director of the North Pacific Anadromous Fish Commission, (NPAFC) at a recent media event.

Radchenko, along with fisheries scientists from around the Pacific Rim, spent the last half of February and first half of March at sea in the Gulf of Alaska aboard a Russian research ship. The unprecedented voyage, made possible by the dogged determination of Dr. Richard Beamish, did what few scientists have done before: observe wild salmon from multiple countries of origin as they interact in their shared North Pacific feeding grounds.

The international team included six scientists from Canada, nine from Russia, three from the USA, one from Korea, and one from Japan. Radchenko went as representative of the NPAFC. They visited 72 different sample locations in a month and came back tired, but excited about what they learned. They presented their results at the Vancouver Aquarium on March 18.

Until this voyage, data about what wild salmon do for most of their lives was limited. Scientists know about the beginning and the end of the lifecycle of wild Pacific salmon, but very little about what salmon do for the months, or even years, they spend feeding and growing in the North Pacific Ocean. At least one-third of all salmon feed and grow in the Gulf of Alaska region, which was the focus of the voyage.

In one month, researchers collected more than enough information to keep scientists in all five countries busy until the next expedition, already in planning. The data will help scientists understand the effects of climate change on salmon populations, their food supply, and migration patterns. It will also help them provide the most up-to-date science-based advice to fisheries managers.

Coho as an indicator species

So far, the research suggests BC’s Coho salmon may hold an important key to understanding broader trends in all salmon populations. Stock genetic identification at sea, developed specifically for this voyage, found that most Coho in the Gulf were from Northern BC. The second largest amount were from Queen Charlotte Strait and Johnstone Strait, and the third-largest from the Strait of Georgia. Very few Coho caught were from Washington or Alaska.

Coho salmon are often caught in other fisheries. That makes them a good indicator stock for the health of other populations; the Alaskans have been using Coho data this way for years.

Researchers found evidence to support this idea. They discovered that unlike other salmon, while feeding in the North Pacific Coho do not group by their streams of origin, or even by species. They intermingle with other salmon stocks and species, with almost no spatial separation by stock.

“I think this is the most interesting result we got,” said Dr. Evgeny Pakhamov, chief scientist on the voyage and a director with UBC’s Institute for the Oceans and Fisheries, speaking at the same media event as Radchenko. “Of course this needs to be verified, it’s very remarkable.”

Now that researchers know Coho on this coast are mostly from BC, they can use this information and new genetic testing methods be better able to track health and population trends in all BC salmon.

Coho prefer “potato chips of the sea?”

Not only do Coho range incredibly far from home for a coastal species, and not only do they seem to be the “social butterflies” of the salmon world, mixing with other stocks as individuals, but their food source is also different from other salmon species.

Researchers on the voyage analyzed stomach contents from the fish sampled and discovered that each Pacific salmon species has a unique, specific diet during their winter grazing season. Coho in particular prefer a diet of pteropods – “sea angels and sea butterflies” – tiny snails with wing-like appendages known as the “potato chip of the sea” because they are an abundant and important food source for huge parts of the Arctic food chain.

These “potato chips” made up at least three-quarters of the entire diet of all Coho salmon sampled.

In contrast, the research showed that pink and sockeye salmon both depend on ephausiids (krill) almost as much as Coho depend on pteropods, and that chum salmon eat pretty much anything and everything.

The voyage was only able to sample three Chinook salmon (a bit of a surprise, researchers said) and found their stomachs full of squid and other fish, but they cautioned that three fish are not a representative sample.

Pinks and sockeye don’t really compete

Another finding that Pakhamov declared “most remarkable” was clear evidence that pink and sockeye salmon eat the same food, but don’t share the same space.

Researchers on the voyage divided their sample sites into northern and southern zones. They found different species prefer different water temperatures. BC’s Coho prefer the warmer, southern range and so do pink salmon. Sockeye, on the other hand, like it cold. Chinook and chum salmon hover in the middle and don’t seem to have clear water temperature preferences.

So even though pink and sockeye salmon depend on the same food sources, they aren’t competing directly for food.

Plenty of food in the sea

In fact, there isn’t much competition for food at all, because there doesn’t seem to be any shortage of food for any salmon species, research from the voyage shows.

“Central to the survival of all salmon, of course, is their food supply. Zooplankton and phytoplankton are the staples of their diet and catches of these vital food sources have been relatively large considering it is still winter,” said Pakhamov. “Then add in gelatinous plankton, which has been extremely abundant throughout the survey area, then you have a clearer idea of the nourishment resources the salmon have access to.”

Strangely, even though food was abundant for all species, chum caught on the voyage were in poorer health than all other species, and many appeared to be skinny with nothing in their stomachs.

“Most of these chum are actually coming from (Russia) and Japan, in the East Pacific,” said Pakhamov.

The chum in poor health may represent hatchery fish that never learned how to forage for themselves in an oceanic environment, or may indicate some other trend researchers have yet to uncover.

Hatchery programs around the Pacific Rim release more than three billion chum salmon into the ocean every year, far more than any other salmon species released from hatcheries. Most of these releases are from Japan, which releases on average two billion hatchery fish each year.

Many researchers are concerned about the implications of pumping billions of biologically naïve hatchery salmon into the shared feeding grounds of all Pacific salmon species. However, research data from last month’s voyage seems to show that inter-species competition for food isn’t a major issue.

BC salmon under threat from oceanic “vacuum cleaners”

In the southern regions of the study zone researchers found a lot of gelatinous jellyfish called Salpa aspera, “which are vacuum cleaners essentially,” said Pakhamov.

The jellyfish were found mostly in the warmer, southern waters closest to BC, and that could be a problem.

“These are carnivorous organisms. They eat on zooplankton, more or less on the same prey as salmon eats,” continued Pakhamov. “We do not know the consequences of this, because if they are competing with the salmon, and we underestimate them by two orders of magnitude, we might be getting into some situation… where this jellyfish can impose very strong competition with the salmon.”

International scientists inspired to cooperate again

Plans are already being laid for the next voyage, and scientists have begun analyzing the thousands of samples taken on the voyage, which will take months.

Dr. Richard Beamish has worked as a fisheries scientist in Canada for decades. He was instrumental in assembling people and resources to make the research trip possible, and said at the media event that it’s exciting to see international scientists working together to better understand all wild salmon.

He’s optimistic about the future and what the voyage’s unprecedented findings will reveal. For example, scientists were able to estimate for the first time how many salmon really are in the sea.

Their preliminary estimates suggest there were about 55 million salmon in the Gulf during their voyage.

“We, over time, will see exactly what that means, but that [estimate] has never been done before,” Beamish said at the media event. “The science that is coming out of this expedition is going to be tremendous.”

The voyage was timed to coincide with the International Year of the Salmon, “an initiative to inform and stimulate outreach and research that aspires to establish the conditions necessary to ensure the resilience of salmon and people throughout the Northern Hemisphere.”

The voyage was one of several research projects and events happening this year to draw attention to salmon all around the world, and the importance of the species to nature and to humans.

Grant Warkentin is a born-and-raised BC boy who has won numerous awards for his journalism and photography. He has worked in community newspapers and corporate public relations for the past 20 years. He currently resides on central Vancouver Island and rarely complains about the rain.