Simulated Effects of YY‐Male Stocking and Manual Suppression for Eradicating Nonnative Brook Trout Populations

Abstract

Eradication of nonnative Brook Trout Salvelinus fontinalis populations is difficult to achieve with standard techniques, such as electrofishing removal or piscicides; new approaches are needed. A novel concept is to stock “supermale” hatchery fish with wild conspecifics. Supermales (MYY) have two Y‐chromosomes, resulting in offspring that are all males; over time, successful supermale reproduction could eradicate the wild population. We constructed an age‐structured stochastic model to investigate the effects of manually suppressing wild fish and stocking MYY fingerlings on the long‐term viability of hypothetical nonnative Brook Trout populations. In streams, an annual stocking rate of supermales equivalent to 50% of wild age‐0 Brook Trout density combined with an annual selective suppression rate equivalent to 50% of wild Brook Trout density resulted in a time to extirpation of only 2–4 years if supermale fitness was equivalent to wild male fitness. However, time to extirpation in streams was 5–15 years if supermale fitness was 80% lower than wild male fitness. In alpine lakes, higher supermale stocking rates and nonselective gillnetting were required to eradicate Brook Trout populations. If supermales were assumed to be as fit as wild males, however, any supermale stocking rate greater than 49% in alpine lakes or 60% in streams achieved eradication in 10 years or less, regardless of the suppression rate. Because manual suppression and the stocking of MYY fingerlings can readily be conducted at the levels assumed in our simulations, use of such an integrated pest management (IPM) approach could extirpate undesirable Brook Trout populations within reasonably short periods of time. Given the recent successful development of an MYY Brook Trout broodstock capable of producing large numbers of MYY fingerlings and given the positive results of the present simulations for both streams and alpine lakes, field testing of MYY stocking is warranted within an IPM program that includes manual suppression for eradicating undesirable Brook Trout populations. Received October 14, 2016; accepted June 10, 2017 Published online August 22, 2017

Survival and Reproductive Success of Hatchery YY Male Brook Trout Stocked in Idaho Streams

“…While it is tempting to use the results in Schill et al. () to predict how long eradication would take in our study streams, we avoid that for several reasons. Most importantly, Schill et al.…”

“…Most importantly, Schill et al. () simulated eradication times using fingerling hatchery fish rather than catchable‐size fish, and survival, size at maturity, reproductive fitness, and other important population metrics are obviously not equivalent between the two size‐classes. Second, the results from Schill et al.…”

“…Second, the results from Schill et al. () stem from simulated populations for which the entire population was treated, whereas our streams were not isolated and only a small portion of each stream was stocked with M YY fish. Moreover, wild Brook Trout from outside our study reaches may have recolonized the vacated habitat in our suppression streams, diminishing any positive benefit to the stocked M YY fish.…”

“…); the results have been mixed, however, and it has been questioned whether stream electrofishing removal by itself can make meaningful progress in Brook Trout eradication at the landscape scale (Schill et al. ). Most recently, tiger muskellunge (Northern Pike Esox lucius × Muskellunge E. masquinongy ) have been introduced into alpine lakes and have successfully eradicated Brook Trout in some (but not most) of them (Koenig et al.…”

“…For example, piscicides have been used with some success (Gresswell 1991;Lee 2001;Lentsch et al 2001;Hepworth et al 2002), but they have the drawback of negatively affecting native fish populations (Britton et al 2011) and other aquatic fauna (Hamilton et al 2009;Billman et al 2012) and are increasingly being restricted in some U.S. states (J. Carter, Arizona Game and Fish, personal communication). Multiple-pass electrofishing has also been used to physically remove Brook Trout from streams (e.g., Thompson and Rahel 1996;Meyer et al 2006;Shepard et al 2014); the results have been mixed, however, and it has been questioned whether stream electrofishing removal by itself can make meaningful progress in Brook Trout eradication at the landscape scale (Schill et al 2017). Most recently, tiger muskellunge (Northern Pike Esox lucius × Muskellunge E. masquinongy) have been introduced into alpine lakes and have successfully eradicated Brook Trout in some (but not most) of them (Koenig et al 2015).…”