Effects of Rainbow Trout Removal on Trout Populations and Food Habits in Great Smoky Mountains National Park

The range of the brook trout (Salvelinus fontinalis) in the Great Smoky Mountains National Park has continued to recede since the 1930's in the face of expanding rainbow trout (Salmo gairdneri) and, more recently, brown trout (Salmo trutta) populations. Exotic salmonid populations have been controlled with relatively intense electrofishing efforts in streams having barriers to prevent reinvasion by these fish.

Two years of moderately intense exotic salmonid removal efforts were evaluated for a group of nine Park streams, eight of which had no effective downstream barrier. Food habits of adult sympatric book and rainbow trout collected from three of the streams both before and after the removal efforts were also examined.

Rainbow trout total catch decreased for seven of the removal streams over the study period while brook trout total catch increased. Mean density and standing crop of rainbow trout in these streams decreased significantly relative to three control streams. Mean density and standing crop of brook trout increased concurrently.

The total catch of rainbow trout for the other two removal streams increased 252% over the two years. Mean density and standing crop of rainbow trout in these two streams also increased markedly. These increases were attributed to excessive mean stream widths, deep pools, large numbers of pre-removal rainbow trout, and the lack of barriers.

Food habits of adult brook and rainbow trout were very similar both before and after removal efforts. No apparent shift in the diet of adult brook trout, due to an attenuation of competition, was noted.