Ecology’s bear necessities

I found an old box of slides recently, which took me on a nostalgic journey back to British Columbia in 1980 and, in particular, to a weekend fishing trip with my cousin Steve.  We travelled north from Terrace, where he lived, along a series of unsurfaced roads through dense pine forest, passing the ethereal moonscape of Nisga’a Memorial Lava Bed to the Nass River where we cast lures and caught the salmon which became our dinner a few hours later.   The following morning we followed the road past an impressive Piedmont glacier, through the small town of Stewart and, a couple of miles beyond, passed an unmanned border post and entered Alaska.

The tiny settlement of Hyder sat just beyond the border, beyond which the forests close in again around the gravel track that followed a small stream into the hills.   When we pulled up beside the road and got out, however, the overwhelming sensory experience was not the landscape or even the sound of the stream tumbling out of the hills towards the fjord behind us.  It was the stench of rotting fish.   We were witnessing the spawning and subsequent death throes of the Pacific Salmon.   Unlike the Atlantic Salmon (Salmo salar) which can repeat their migration from the sea to freshwater several times, Pacific Salmon (Onchorhynchus spp.) spawn only once in their lifetime.   Exhausted after the exertions of the migration and what is euphemistically referred to as “big bang reproduction”, the salmon become easy prey for bears, one of whom emerged from the forest a hundred metres or so upstream of where we were standing.

My first encounter with the USA.   The border is at the point where the metalled road ends and the gravel track starts.  The building on the left is the US Customs post.   

You can just make out the bear in the photograph at the top of the post (I’ve also circled in another version at the end).  At the time, my camera was a Kodak Instamatic, which had a semi-wide-angle lens.   We all have two appendages dangling from our hips that make up for many of the deficiencies of a wide-angle lens but, on that stream bank in Alaska, I decided that discretion was the better part of valour.   We watched from afar and the multisensory memory is rather more vivid than the somewhat faded Kodachrome slide that I found in the loft.

That would have been the end of the story except that, in the early years of the new millennium, scientific papers started to appear which turned this spectacle from an item on the wildlife tourist’s bucket list to an integral component of the engine that drives the forest ecosystems of the Pacific Northwest.    These forests, like most natural systems, are hungry for nutrients such as nitrogen and phosphorus and the salmon are, in effect, unwitting suppliers of the fertiliser that the trees need.   The Pacific Salmon spend up to five years in the ocean before moving to their spawning grounds.   Those strong muscles that they need to swim upstream and leap up waterfalls are largely protein which is built from nitrogen-containing molecules.  And nitrogen is, coincidentally, the nutrient that trees need most.

A view across Nisga’a Memorial Lava Bed in the Nass River valley, British Columbia.  The lava was the result of a volcanic eruption in about 1700.  This and other photographs in this post were taken with my Kodak Instamatic, which partially explains their poor quality.

By fishing the dying salmon from streams such as this (and even grabbing the leaping salmon before they get to their spawning grounds – see some spectacular footage from David Attenborugh’s Nature’s Great Events here) the bears become the agents by which the salmon’s nutrients are transferred from the Pacific Ocean to the forests.    It has been estimated that up to a quarter of the nitrogen needs of the forest around these streams is supplied in this way.   Indeed, some have suggested that this transfer of nutrients may be so essential to the functioning of this forest ecosystem that the salmon and bears are, in effect, “keystone species” and that their interaction has an effect that is greater than their contributions individually.

Brian Moss used to use this as a pithy illustration of the need to take a very broad view when managing ecosystems.   We all know that rivers flow into the sea but it is not always so obvious how the oceans can have an effect on terrestrial vegetation far inland.   Similarly, we understand how water flows across land and into stream channels but perhaps we have a hazier awareness of the movements in the opposite direction – from the river channel into the depths of the forest.   Salmon spawning in the Pacific Northwest is one of the world’s great wildlife spectacles, but it should also give us cause to pause and consider the complexities of interactions within natural habitats and, in turn, the dangers of meddling.

One more prosaic lessons that I learned from this short trip: if you are going to the USA, take a passport. Actually, I didn’t need one going into Alaska, but when we returned the Canadian border official had rolled out of bed after his Sunday lie-in  and almost didn’t let me back in!

Another species of hairy wildlife in search of salmon, this time on the Skeena River, British Columbia.   On this particular occasion, the salmon did not oblige and I had my first and only encounter with Kentucky Fried Chicken instead.  

References

Helfield, J.M. & Naiman, R.J. (2006).   Keystone interactions: salmon and bear in riparian forests of Alaska.  Ecosystems 9: 167-180.

Naiman, R.J., Bilby, R.E., Schindler, D.E. & Helfield, J.M.  (2002).  Pacific salmon, nutrients, and the dynamics of freshwater and riparian ecosystems.  Ecosystems 2: 399-417.

Quinn, T.P., Carlson, S.M., Gende, S.M. & Rich, H.B. (2009). Transportation of Pacific salmon carcasses from streams to riparian forests by bears.  Canadian Journal of Zoology 87: 195-203.

The scene near Hyder, Alaska, this time with the bear circled, just in case you didn’t believe me.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

w

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.