The whole coastal ecosystem benefits from the iconic salmon runs

Salmon are rainforest ‘nutrient pumps’

Salmon runs in the Great Bear rainforest pump nutrients into coastal habitat, says rainforest biologist Dr. John Reynolds.

“All of our salmon on this coast die after spawning,” Reynolds told the Discovery Passage Aquarium Society’s lecture Feb. 2 at the Maritime Heritage Centre. “When this happens, you shouldn’t be too surprised that there might be some impacts on the local environment.”

The temperate rainforest on the West Coast is a nutrient poor habitat, despite the big lush forests that the area produces. The same factors that create these verdant forests also suck up every bit of nitrogen and phosphorous that’s available. At the same time, heavy rainfall leaches these nutrients out of the soil.

“We live in very nutrient poor habitats here,” Reynolds said.

Meanwhile, the salmon that return to coastal streams do most of their living and growing out at sea. Which means they are bringing nutrients up with them like a conveyor belt and when they die, they leave the nutrients inland.

“So, they’re little nutrient pumps,” Reynolds said.

Reynolds is one of the leading researchers in temperate rainforest ecology at Simon Fraser University and also holds the BC Leadership Chair in Aquatic Conservation. He has been studying biology in Britain and elsewhere but came back to B.C. recently to study coastal ecology.

His objective in his research is to try and connect habitats and different aspects of biological study.

Traditionally, research is divided up into separate disciplines that do their own studies in isolation.

They conduct their own research projects and publish results in their own journals but Reynolds decided to connect all of these areas of study and outlined those connections in his presentation as part of the Speakers Series put on by the Aquarium Society in front of about 100 attendees.

Reynold’s research and that of his graduate students follows the salmon and see what impacts it has on different habitats.

First off, Reynolds pointed out that what happens with the salmon and the environment doesn’t just happen on the B.C. coast.

Salmon are widely dispersed all around the North Pacific from North America to Asia and now into the Arctic Ocean due to global warming.

The Central Coast is one of the better places to be doing this work, Reynolds said.

There have been no major disturbances despite the diminishing forest cover due to logging in the rest of B.C.

Based in Bella Bella on the Central Coast, Reynolds is close to all the habitat he needs to conduct his research. Most of his work is concentrated on 50 streams in the Bella Bella area. The “two big players” are chum and pink salmon while on the predator side there are black and grizzly bears as well as the recently identified coastal wolves that predate on salmon and other intertidal life.

Reynolds’ research and his presentation mapped the impact salmon have on different aspects of the environment like other fish, birds and plants and the implications for conservation.

Pink and chum salmon do not stay in the stream.

That means that pink and chum salmon do not benefit future generations of pink and chum salmon.

But there are coho salmon that stay in the stream.

Does the pink and chum benefit the coho, Reynolds explored.

“The answer is yes, that is what seems to be happening,” Reynolds said.

A graduate student’s research has shown the statistical correlation between the number of coho salmon in streams and the pink and chum salmon, even though the pink and chums don’t linger in the habitat.

The implication is that even though pink salmon is not popular with people for eating, they pinks do have a positive impact on species – coho – that people do like to consume.

“So, that’s one example of an ecosystem connection involving salmon,” Reynolds said.

Reynolds then turned to the impact of salmon on bird populations. The first question is if you have more salmon in an estuary would you have more scavenging birds and, of course, the answer is yes. Ravens and eagle populations reflect the abundance of salmon.

That prompted Reynolds to joke that he tells Fisheries and Oceans Canada officials that they don’t have to count salmon in the streams, they could just count the birds.

“I haven’t gotten very far (with them), you’ll be surprised to hear,” Reynolds said.

An interesting side note regarding scavenging birds was that the eagle numbers were higher the more prevalent fresh carcasses killed by bears could be seen. It indicates eagles prefer fresher, bear-killed salmon to salmon that have died naturally and are, therefore, older and more rotten.

But the aspect of bird numbers that Reynolds was more interested in was the correlation to summer breeding bird populations – sparrows, chickadees, flycatchers, etc.

Again, statistical counts of pink and chum salmon numbers show an increase in the density of songbird populations corresponding to the increasing density of pink and chum salmon.

“Some of these birds never even see a salmon in their life,” Reynolds said.

These birds are migratory and come into the area in the spring when there are no salmon spawning in the streams and the carcasses are long gone.

What’s going on here, Reynolds said, is that the overall productivity of the stream habitat is enhanced by all the nutrients washing down the stream.

This fertilizes the soil and there are stronger insect population and that translates into increased density of birds.

Next, Reynolds turned to the impact of salmon on plants.

“We’ve done  a lot of work on plants,” Reynolds said.

They worked on the idea that salmon may be fertilizing plants.

One of the “silliest experiments” Reynolds has ever done involved collecting some really rotten salmon and hiking above a waterfall which would serve as a barrier to salmon.

This was in grizzly bear country and here they were hauling bags of rotten salmon upstream past a waterfall.

One researcher said, “I hope we don’t win a Darwin Award.” Darwin Awards are an informal thing that is awarded to people who remove themselves from the gene pool by dying doing something stupid before they have a chance to reproduce themselves.

They dropped the carcasses down and then tested for nitrogen near to where the carcasses were dropped and far from them. The hypothesis is that plants near to the carcasses should  show higher levels of nitrogen than plants far from the deposited carcass.

“In the spring you get a jump near the carcass and a little bit uptick far from the carcass,” Reynolds said. “So there’s a big boost in the nitrogen in the leaves we could detect.”

There was a similar impact when the density of plants are measured.

The implication of this research for salmon management is it allows managers to set targets for how many salmon should be allowed to return to streams to sustain different values in the ecosystem. Those values would be how many bears and other large predators do you want and how many plants and how many birds, etc..

Each segment of the ecosystem has different needs and require a certain level of salmon to return in order to sustain them.

Included in that is the number of salmon needed for human consumption via commercial fishing, etc.

This research that Reynolds is doing provides data for making decisions to benefit different parts of the ecosystem.

Making those decisions gets into the realm of social studies and that is beyond what Reynolds is doing.

He provides the science and the hard data but making decisions on what social values are to be met is the work of Fisheries and Oceans Canada.