Multiple electrofishing as a mitigate tool for removing nonnative Atlantic brown trout (Salmo trutta L.) threatening a native Mediterranean brown trout population

Abstract

In the native range of the brown trout (Salmo trutta L.) in Europe, the hybridization of native populations by nonnative domesticated strains introduced by stocking is one of the most serious threats to the long-term conservation of diversity within this species. With the objective of conserving and restoring the native gene pool, fishery managers are beginning to implement various management strategies at the local scale. Nevertheless, few case studies have been published that investigate the effectiveness of the various different conservation strategies for native brown trout populations. In the Chevenne Creek, a small French mountain stream, we tested the strategy of removing nonnative individuals by multiple electrofishing carried out by fishery managers in order to evaluate its feasibility and effectiveness for eliminating a nonnative population threatening a native population. Electrofishing produced major reductions in the nonnative population between 2006 and 2009, with 82-100% of nonnative individuals being removed over a period of 4 years. Nevertheless, despite multiple-electrofishing campaigns, this nonnative population was not entirely eradicated, and some natural recruitment persisted. The young of the year and subadults were less effectively removed than the adults. The results suggest that repeated electrofishing campaigns can be used by managers to reduce the nonnative brown trout population with the objective of conserving the native gene pool, but the removal operation must be continued for at least 4 consecutive years. This strategy, which is feasible in small streams, has to be followed by complementary operations to allow the restoration of a new, native, self-sustainable brown trout population.

Early effects of the strategies of creating a genetic refuge and direct translocation for conserving and restoring populations of native brown trout

“…Fig. Three other studies performed on streams in the Rhô ne drainage area, and using genetic refuge policies for 5 and 13 years, gave similar results (Caudron et al, 2011a;Caudron & Champigneulle, 2011;C. stocked trout and trout from natural recruitment) and otolith-unstained angler's catches (i.e.…”

“…According to these authors, the genetic refuge policy failed to erase the footprint of past stocking practices in the 10 rivers studied. Three other studies performed on streams in the Rhô ne drainage area, and using genetic refuge policies for 5 and 13 years, gave similar results (Caudron et al, 2011a;Caudron & Champigneulle, 2011;C. R. Largiadèr, unpubl.…”

Evaluating a Permeable‐Style Fish Barrier to Prevent the Upstream Recolonization of Nonnative Trout during an Eradication Project

“…We achieved success with backpack removal electrofishing, whereas many studies merely have reduced nonnative fish densities without achieving complete eradication of the target species (Moore et al 1983;Thompson and Rahel 1996;Meyer et al 2006;Carmona-Catot et al 2010;Caudron and Champigneulle 2011). In cases where eradication has been achieved, the streams like Johnson Creek have been small, with limited habitat complexity (e.g., pools <1 m in depth, few undercut banks), and the effort has been extensive, including multiple removal passes over several years (West et al 1990;Kulp and Moore 2000;Buktenica et al 2013;Shepard et al 2014).…”

Invasive Aquatic Animals

“…An integrated approach to improve the status of competitive species, like brook trout, has begun in New York, NY, USA. Repeated electrofishing can selectively reduce brown trout, provided labor and equipment resources can be made available (Caudron and Champigneulle, 2011). Piscicides have been applied to kill brown trout in areas of golden trout habitat, then fish barriers were installed to isolate golden trout and exclude brown trout (Pister, 1991).…”