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Brook Trout: The Scourge and the Saint. Applying Lessons Learned from Both Eradication and Reintroduction Efforts across the West and East to Better Manage this Char

Proceedings from a symposium that was held during the 2019 American Fisheries Society/The Wildlife Society Joint Annual Meeting in Reno, Nevada.

Symposium Abstract
Depending on one’s perspective, Brook Trout Salvelinus fontinalis hold distinction as a scourge, invading trout habitat across the American West, or a saint, serving as a beloved symbol of the long lost wilderness of Eastern North America. As fisheries managers in the West struggle to eradicate the prolific and adaptable Brook Trout in order to protect vulnerable native cutthroat and bull trout populations, fisheries managers in the East struggle to successfully protect and reintroduce Brook Trout to their natal watersheds. How can the struggles and experiences of fisheries managers across the West and East shed light on the persistence and vulnerability of Brook Trout? What are the genetic, biological, demographic, habitat preference and interspecies behavioral characteristics that make Brook Trout such a menacing invader of coldwater aquatic systems in the West, and such a challenge to reclaim their former niche in the coldwater systems in the East? This symposium hopes to share relevant and perhaps novel information gleaned from the intense interest in this char that now more than ever captivates the attention of coldwater fisheries managers, scientists and advocates dedicated to native aquatic species conservation.

Symposium Summary
In the East, Brook Trout show high levels of genetic differentiation among populations and major clades. Recent work shows that some eastern populations respond to heat stress in different ways (i.e., patterns of gene expression). This work suggests that some populations may be better equipped than others to deal with stressful temperatures, and that genetic variation may help provide resilience to populations against warming conditions. However, widespread population fragmentation and genetic drift have decreased genetic diversity in wild Brook Trout populations and will likely continue to threaten the future outlook for many populations. Larger, more interconnected populations found in waters with higher baseflows and without the presence of non-native trout tend to have higher numbers of effective spawners. Despite widespread stocking, generally hatchery Brook Trout have not successfully interbred with wild Brook Trout and survived. Brook Trout have held their own against Rainbow and Brown Trout in Vermont since the 1950’s, and have returned to a number of lakes and ponds with improving pH and alkalinity in New York’s Adirondacks, yet less so for that region’s rivers and streams. Lab and field research found that Brook Trout do not compete successfully with Brown Trout in using coldwater refugia during the summer and maintaining body weight. Removal of Brown Trout from streams where they overlap with Brook Trout across different states in the East has resulted in greater survival of young of year Brook Trout, larger adult Brook Trout, and greater use of warmer, downstream waters. Brook Trout that use main stem habitats tend to grow larger, which may help them coexist with some Brown Trout populations.

Across the West, Brook Trout have exerted significant impacts to 10 different subspecies of native trout since their introduction in the 19th century. Eleven states are actively using piscicides to eradicate Brook Trout, often in concert with construction of or use of existing fish passage barriers, and more than half are experimenting with stocking of YY-male Brook Trout to reduce Brook Trout spawning success. Simulations have indicated the use of YY-males in combination with suppression is a viable strategy for eradicating Brook Trout. Removal of Brook Trout have corresponded to dramatic increases in Cutthroat Trout population abundance at all ages, and to a lesser degree more moderate increases in Bull Trout abundance. Suppression efforts through electrofishing rarely have achieved desired outcomes as Brook Trout populations levels return to pre-suppression levels in several years. Genetic monitoring with effective number of breeders can potentially improve the monitoring of brook trout suppression efforts. Yet recreational fishing for Brook Trout in the West is popular, and education and engagement of the public and stakeholders is key to the success of any project to suppress or eradicate local Brook Trout.

The Brook Trout’s ability to outcompete other trout in the coldest waters, thrive in headwater habitat, spawn and reproduce successfully in small headwater streams or lake inlets, tolerate acid water chemistry, survive in small populations with low genetic diversity, and colonize upstream habitat successfully (in one case scaling a 9 foot waterfall barrier in a flood event) have equipped them to be a survivor across many headwaters in its Eastern range, as well as to be a exceptional invader of coldwater habitat across most of the West. Research has demonstrated the importance of flood event timing for trout egg survival and young of year recruitment: flooding in February/March is generally bad for Brook Trout, and flooding in April/May is generally bad for Rainbow and Cutthroat Trout. Changes in flood patterns will likely continue to affect future native and non-native Brook Trout success. In the East, efforts to restore aquatic connectivity have been strong, but future climate resiliency efforts must simultaneously address the limiting factors of habitat loss, warming waters and competing fish species. Across the West, every state is working to balance the desire to provide sport fishing opportunities for Brook Trout while also creating, maintaining, and enhancing native trout populations by limiting the Brook Trout’s substantial competition, predation and hybridization impacts.

For the full symposium proceedings click here

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