Tropical Storm Irene: How Did the Trout Fair?

     I was very glad to have attended a presentation at American Museum of Fly Fishing, by Ken Cox of the Vermont Department of Fish & Wildlife, regarding the effects of tropical storm Irene on Vermont’s trout streams. Ken had given a related lecture at the Museum in 2011, very shortly after the flood waters had retreated. His recent presentation recapped much of that information and added new insight into the future of trout waters throughout the state. Two main points discussed were the questionable methods of the post-Irene cleanup and the surprisingly beneficial consequences of large-scale flooding.
     As one would expect, the trout population plummeted as a result of Irene. The VDF&W conducts annual population surveys in many trout streams, several of which had been conducted shortly before Irene. These waters were immediately resurveyed after Irene and the trout population had dropped sharply. Much of this initial kill is attributed to trauma from fast, heavy current; infection and other health problems attributed to increased sediment suspended in the water column; and fish stranded in flood plains and other areas where slow-moving water pooled. After the flood waters subsided many fish were left to languish with it’s affects.
     The immediate aftermath of Irene saw a tremendous cleanup effort that, while generally enhancing protective measures in flood-prone areas from a property damage standpoint, also had devastating consequences for streams and their aquatic life. In many instances all of the structural features that give a stream it’s character and create habitable conditions for trout were completely removed. Boulders and logs were systematically cleaned out, banks artificially raised and stream channels were straightened. This might sound like a case of putting wildlife first and humans second, but many of the methods intended to make streams flood-resistant had already been proven to be minimally effective at best. Cleaning out stream channels has no effect on preventing floods and raising banks inhibits the natural pressure-relieving mechanisms of flood plains. Since the initial cleanup the VDF&W has compelled many towns and other overseeing entities to return trout waters to a more natural state by placing boulders and logs back in stream channels. In a matter of months the normal flow of water acting on these structural elements had started to return many streams and rivers to a more natural state. This change in attitude toward stream repair helped the trout population bounced back faster than it otherwise would have, but the flood itself proved quite beneficial as well.
     When a stream floods it typically has a renewing effect on the stream bottom. Years and even decades worth of sediment and detritus is scoured away from the stream bed, making ideal spawning conditions for trout. One year after Irene, the total number of trout counted in streams that had been surveyed immediately pre-Irene was many times higher. Two years after Irene the trout population had generally declined somewhat, but was still significantly higher than pre-Irene. Although much of this population increase is attributed to a greater number of eggs hatching, resulting in more fry overall, it still bodes well for trout populations.
     There is no way to predict what the long term effects of Irene will be, but much of the data collected so far suggests the trout population certainly did not suffer as much as many feared. The vigilance of the Vermont Department of Fish & Wildlife to remedy a faulty cleanup effort certainly seems to have paid off.

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