Sunday, November 19, 2017

Salmon - nitrogen bomb.

Yesterday, miraculously, our scheduled trip to the Fraser River Eagle Festival at Harrison Mills coincided with a break in the rain.  Today the weather throughout the region reverted to November.

Harrison Mills is at the confluence of the Harrison and Fraser Rivers, about 50 miles upstream from Vancouver.  Before joining the Fraser, the Harrison flows around the tip of a sandy peninsula, at Kilby Provincial Park.  In this picture, facing west, the river is flowing right to left around the point to meet the Fraser flowing west on its south side.  Notice the lumpules scattered along the shore.  The larger ones are the carcasses of chum salmon.

Back around the northern flank of the peninsula and a short distance upstream the Harrison  broadens and contains a silty delta known as the Chehalis Flats, created by deposits settling out from the inflowing Chehalis River and Weaver Creek, whose winding channels continue into the flats, producing a web of sand bars and channels.  Within the faster flowing watercourses, where the bottom is sufficiently gravelly, chum salmon spawn.  And here, on the flats, bald eagles feast, hundreds at a time.  

I took no eagle pictures.  I had only my phone to record the scene, and phone pictures of eagles would be sadly inadequate.  The following images from the Eagle Festival Flickr photostream show nicely what the birds looked like: Eagles on flatseagles in trees. 

Oblivious to bird and human, the salmon fulfill their biological imperative, having spent years at sea, swimming who knows where, surviving who knows what.  

After that? Struggle upstream into freshwater while undergoing dramatic alterations in form and physiology, spawn, and then die, but not easily.  Salmon have death throes too.

But that's just the start of things:

Bears and other large mammals drag salmon from streams up to 500 meters into the forest where the remains gradually decompose and act as fertilizer.  The elements in their tissues, and in the waste products produced by carnivores then become available to the ecosystem.

In Gwaii Haanas, Haida Gwaii, it was estimated that 3,611 salmon carcasses, 63% of an entire run, were transferred from the river into the surrounding forest by as few as 3 to 8 bears.

Eagle numbers and breeding success are correlated with the abundance of salmon carcasses left behind in spawning streams.

In some places the timing  and success of mink reproduction is related to the availability of salmon carcasses.

Coastal Alaskan Brown Bears obtain virtually all of their nitrogen and carbon from salmon.

Bottom-dwelling insects in salmon-bearing streams in interior BC obtained up to 60% of nitrogen content from salmon tissue.

      Vegetation near salmon streams contain significant amounts of marine-sourced nitrogen.

The more salmon in a run, the more nutrients available to the ecosystem, and the more productive it is.  This inevitably includes an increase in the invertebrate prey species that nourish developing larval salmon.

When a salmon stock diminishes all plant and animal species within their food web are to varying degrees impacted.  This includes salmon themselves, whose decaying carcasses influence the survival rates of future runs.

It's almost as if the ocean is the lungs, the rivers are the blood vessels, the forest is the living tissue, and the salmon are the corpuscles.  Unlike the circulatory system in a single animal, however, the fish only travel in one direction, and their vital cargo isn't oxygen, required for the fueling of life, but rather carbon, and, especially, nitrogen, elements essential for its construction.

Once you start to get salmon, you realize that we spend most of our lives in a bubble of remarkable ignorance, clueless of how the heck our world works and needs to keep working for the whole darn thing to stay alive.

Chum Salmon, blessed nitrogen bomb.


Susannah Anderson said...

Wonderful post! I'm going to share this with my students.

Hugh Griffith said...

Thank you Susannah.