Subject: [Tweeters] River Otters and Hunting Efficiency
Date: Feb 6 12:53:33 2007
From: johntubbs at comcast.net - johntubbs at comcast.net


Hi all,

Here's one more input on otters and predation. My experience with them in Central Oregon while fly fishing has led me to view them as incredibly fearsome predators (if you're below them on the food chain, at least). The Deschutes River in Central Oregon is a world-famous wild trout river in its middle stretches. One morning early while fishing, I observed a group of six otters cavorting effortlessly in a medium speed and depth riffle. They appeared to be simply playing and passing time with frivolity - that is until one would dive under the water after a fish. Literally every dive was successful - I never saw one surface without a fish in its jaws. After surfacing, they would orient and half crunch/half swallow the fish and within several gulps it was gone. Although impressive to watch, after observing a half hour of this, it seemed likely that the predation effect of a group this size could be highly significant. [My Deschutes fishing friends and I now refer to them!
as TVC
's (Trout Vacuum Cleaners).]

This was brought home even more clearly a year or so later on a small tributary to the Deschutes River, before our annual raft trip on the Deschutes. I fished a good mile of pristine water near my rafting friend's house, which was loaded with small wild fish but which was almost never fished because of better options for bigger fish in the area. In a morning of fishing, I landed (and released) 34 beautiful wild trout, mostly rainbows with a few brookies mixed in. The next year before the raft trip, I was anxiously looking forward to another great morning of fishing the same little stream. I fished it hard that year for an entire morning and caught and released a grand total of TWO fish. While racking my brain for possible explanations for my lack of success with relatively unsophisticated fish, the reason became apparent when I came upon a wider, deeper stretch of the stream and surprised a family of four otters that were clearly denning in the area (several otter 'slid!
es' wer
e in evidence on the bank). They had nearly depleted that stretch of stream of its fish population. I was told later by a wildlife biologist in the area that they are nomadic along small stream systems for the reason I saw - they are simply too efficient as predators, since they lack any significant predators of their own, to take up permanent residence on anything but a very large stream system. He said when a family of otters settles into a small stream like the one I was fishing, the fish population plummets in short order, then the otter family will pick up and move on to the next not-so-lucky group of fish. Of course, they never totally deplete a stream and in a number of years the fish population recovers, but their impact is very substantial, not marginal.

So...it's not surprising at all to me that an otter family would be an opportunistic predator relative to other species.


John Tubbs
Snoqualmie, WA
johntubbs at comcast.net
www.tubbsphoto.com