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Saunders, W.C., P. Budy, and G. Thiede. 2014. Demographic Changes Following Mechanical Removal of Exotic Brown Trout in an Intermountain West (USA), High-Elevation Stream. Ecology of Freshwater Fish. doi: 10.1111/eff.12143. USGS FSP: IP-034361.

Abstract

Exotic species present a great threat to native fish conservation; however, eradicating exotics is
expensive and often impractical. Mechanical removal can be ineffective for eradication, but nonetheless may
increase management effectiveness by identifying portions of a watershed that are strong sources of exotics. We
used mechanical removal to understand processes driving exotic brown trout (Salmo trutta) populations in the
Logan River, Utah. Our goals were to: (i) evaluate the demographic response of brown trout to mechanical removal,
(ii) identify sources of brown trout recruitment at a watershed scale and (iii) evaluate whether mechanical removal
can reduce brown trout densities. We removed brown trout from 2 km of the Logan River (4174 fish), and 5.6 km
of Right Hand Fork (RHF, 15,245 fish), a low-elevation tributary, using single-pass electrofishing. We compared
fish abundance and size distributions prior to, and after 2 years of mechanical removal. In the Logan River,
immigration to the removal reach and high natural variability in fish abundances limited the response to mechanical
removal. In contrast, mechanical removal in RHF resulted in a strong recruitment pulse, shifting the size
distribution towards smaller fish. These results suggest that, before removal, density-dependent mortality or
emigration of juvenile fish stabilised adult populations and may have provided a source of juveniles to the main
stem. Overall, in sites demonstrating strong density-dependent population regulation, or near sources of exotics,
short-term mechanical removal has limited effects on brown trout populations but may help identify factors
governing populations and inform large-scale management of exotic species.

 

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Status

Published
April (2nd Quarter/Spring) 2014

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  1. U.S. Geological Survey