I don’t know how much proof people need and why we need to spend our time publishing studies like “Beavers Don’t Cause Beaver Fever More than any Other mammal” or “Don’t eat fish”. Some things you shouldn’t HAVE to prove. But I was glad to see this headine anyway,
Field experiments to assess passage of juvenile salmonids across beaver dams during low flow conditions in a tributary to the Klamath River, California, USA
Although the use of beaver ponds by numerous fish and wildlife species is well documented, debate continues as to the benefits of beaver dams, primarily because dams are perceived as barriers to fish movement, particularly migratory species such as salmonids. In this study, through a series of field experiments, we tested the ability of juvenile salmonids to cross constructed beaver dams (aka beaver dam analogues). Two species, coho salmon (Oncorhynchus kisutch) and steelhead trout (O. mykiss), were tracked using passive integrated transponder tags (PIT tags) as they crossed constructed beaver dam analogues. We found that when we tagged and moved these fishes from immediately upstream of the dams to immediately downstream of them, most were detected upstream within 36 hours of displacement.
By the end of a 21-day field experiment, 91% of the displaced juvenile coho and 54% of the juvenile steelhead trout were detected on antennas upstream of the dams. In contrast, during the final week of the 21-day experiment, just 1 of 158 coho salmon and 6 of 40 (15%) of the steelhead trout were still detected on antennas in the release pool below the dams. A similar but shorter 4-day pilot experiment with only steelhead trout produced similar results. In contrast, in a non-displacement experiment, juveniles of both species that were captured, tagged and released in a pool 50 m below the dams showed little inclination to move upstream. Further, by measuring hydraulic conditions at the major flowpaths over and around the dams, we provide insight into low-flow conditions under which juvenile salmonids are able to cross these constructed beaver dams, and that multiple types of flowpaths may be beneficial towards assisting fish movement past instream restoration structures.
Finally, we compared estimates of the number of juvenile salmonids using the pond habitat upstream of the dam relative to the number that the dam may have prevented from moving upstream. Upstream of the dams we found an abundance of juvenile salmonids and a several orders of magnitude difference in favor of the number of juveniles using the pond habitat upstream of the dam. In sum, our study suggests beaver dams, BDAs, and other channel spanning habitat features should be preserved and restored rather than removed as perceived obstructions to fish passage.
Are you paying attention WISCONSIN? Or do you stop reading when you saw all those long words. Let me make it clearer with a little graph. How’s this?
Just to clarify, on the first day only ONE fish had cleared the beaver dam. But two weeks later most of them had. And we’re talking salmon AND steelhead. Or to put it in the simplest terms. Do you remember the Swedish chef from the muppets? I think he would put it something like
“Can dee fishy yump over de beever dam? “Dee fishy is var tasty und dee dam est var hi. Mork Mork Mork! Yes! We can see dat the fishies all yumped over the beever dam!“
Are you following along? Look about those fine scientists blowing up beaver dams so that salmon and trout can get by, JUST STOP IT. You got that?
Overall, we suggest that unless there is clear and compelling evidence that a beaver dam or BDAs are preventing the movement of fishes and that this is likely to have a population-level effect, such structures should not be removed. Options such as temporarily notching may be an alternative under some conditions, such as the presence of adult salmon stacking up below a dam, but guidelines need developing. For human-built structures such as BDAs and other weirs, we conclude that our data provide some guidance as to what constitutes a passable structure, but that more examples from the field are needed under a wider range of flow conditions.
Kind of mealy mouth for my tastes, I wish you didn’t have to be so cautiously scientific about everything. JUST STOP IT. That’s what I’d say. But then I don’t work for NOAA Fisheries and nobody pays my salary.
