Beavers and Salmon – Page 5

[youtube:http://youtube.com/watch?v=jtEqN2Vfhyw]

Our wise beaver-salmon friend William Hughes-Games in New Zealand worries that fish-ladder devices create the impression that beaver dams obstruct passage when in fact we used to have millions more beavers and millions more salmon and they got along just fine, thank you very much. He’s working with the reintroduction in Scotland to help them realize they should invest only in watchful good will, so they can document that the salmon manage the dams, and see the population changes as they happen.

This particular video shows a waterless earthen dam, unusual perhaps because its an unnatural creek. I think William would say that there are some dams that may be salmon obstacles, (and there are solutions to deal with those) but there are far fewer than we imagine, and they benefits to young salmonids far outweigh the risks.

Here are some of his ideas offered in correspondence with concerned salmon watchers in Scotland:

I take your point and have full sympathy with your concerns regarding the effect of beaver dams on the upward migration of adult salmon. I also admit that the opinion held by people like myself that beavers greatly enhance salmon runs is based to a large extent on historical, sometimes anecdotal information and on logic. Let me state as someone who has worked as a marine biologist most of my life that I am very aware that simple logic, such as a physicist would depend on, doesn’t always serve the purpose when it comes to biology. Biological systems are complicated and as much as you apply logic, the only final criteria is observation of what actually occurs. You then apply logic in hindsight and we all know that hindsight is an exact science.

I think we have one common point of agreement if I read correctly between the lines of your last e-mail – namely that putting in devices to allow salmon to pass beaver dams is a non starter. In my case, I would disagree with putting in such devices because I don’t think they are needed. In your case (I would assume) you would not put them in because they are expensive and in that I quite agree with you. the only place I can see using any devices with beaver dams would be to stop the flooding of some vital road or facility but never to help salmon ovee the dam. For the most part, in most locations, that very flooding is what makes beavers so valuable in an ecosystem for a whole suit of reasons. I would add that if such devices are put in place and the salmon do pass, then everyone will assume that these devices are needed for salmon to pass beaver dams. That would put a totally unjustified cloud over the introduction of beavers.

There are a couple of places in the world, including Argyle where the effect of beaver dams on a variety of salmon species will be observed and documented. Hopefully this will be done without any effort to help salmon artificially over the beaver dams. It is a shame that in Argyle there is not a numerical base line already established for the extent of salmon runs although I am sure there is a body of anecdotal information available. If it is shown over the long term that the beaver dams that are built in these catchments have the detrimental effects on salmon as you believe, I will be the first to reverse my opinion on the relationship between these two animals. I’m sure the reverse is also true. In a decade or so, when the results are in, I’m sure we will be in complete agreement one way or the other.

My contention is partially based on the following. In pre-European North America, with beaver dams in every possible location where one could be built, the salmon runs of all the species that existed on both coasts were legendary. First People fertilized their fields with salmon, would you believe. The extirpation of the beavers from the Columbia catchment following 1818 caused a precipitous drop in the salmon runs at a time when none of the other factors were in place that we associate with the demise of the salmon.

I know we will both be watching the Argyle experiment and others of a similar ilk with great interest. Let the results observed in the field determine our future course of action.

Best wishes in your quest to enhance salmon runs
We both have the same goal
We only disagree on the path to that goal

Regards
William