Study finds that dead salmon can make plants bigger

A four-year-old SFU team, led by Allison Dennert, a salmon ecologist, pulled rotting salmon from a stream to determine how it would affect plant growth in a nearby salt marsh. These results have huge implications for the whole web of life.

An estimated 200 salmon swim up the river each year to lay eggs and then die. A scavenging bear or wolf might throw a carcass into a meadow. Some years, flooding could deposit the dead fish amongst the wildflowers, sedges, and grasses. However, the next step was not as clear until now.

Researchers have discovered the first causal link in a study that shows the power of salmon carcasses in fertilizing wildflowers. This is the foundation of an ecosystem that ripples up to bees, eagles, and voles.

Dennert said that First Nations people, such as the Hailzaqv, on whose territory flows the river, have known for a long time that fish are good fertilizer. Some observational studies have also supported the idea that salmon fertilize forests. The Burnaby resident claims that she only knows of two other instances when it has been measured.

SFU researchers also conducted a 2011 study that found that chum salmon carcasses were dropped on the forest floor near 11 streams along the central coast of B. C. They found that plants living in forest understories absorb nitrogen from the rotting salmon, which was a significant growing period for the plants.

Researchers published the results from a 20-year-old study in 2018 that involved pitching over 200k sockeye salmon carcasses along one side of a river in Bristol Bay. Researchers found that trees grew faster along the river side where the salmon were deposited.

Dennert's research took these experiments one step further. She and her research team wore waders for four years and walked into the stream near Bella Bella in order to collect old salmon carcasses. They would stuff them into mesh bags and then tie them to the ground.

Each year, they would return to collect the salmon carcasses and stuff them into sacks before staking them to the ground. They would measure the size of common wildflowers in the meadow every year.

Scientists discovered that fertilizing land with salmon increased the growth of two wildflower species, yarrow, and common red paintbrush, which in turn led to larger leaves. Some wildflowers also grew differently after the salmon was applied. For example, the common red paintbrush or the Douglas' aster were both affected by salmon carcasses. This encouraged the growth of larger flowers over most years.

Dennert and her colleagues have seen a 70% drop in chum salmon returns to the river they study, according to Dennert. Globally, the ability of predators to disperse salmon carcasses in nearby terrestrial ecosystems is now only 10%, as previous studies have shown.

In large parts of the Great Bear Rainforest, trophy hunting is prohibited. The ban should be extended to all of British Columbia. The researcher stated that it would be a big step in protecting the bears, wolves and salmon-carriers from the rivers to the land.

Dennert said that while federal and provincial governments have made efforts to turn the tide, they still stand in their own way. She claims that federal agencies are being asked to manage salmon and the provincial bodies to care for the land nearby. This creates an artificial barrier between species and hinders conservation efforts.