Movement dynamics of MYY and wild Brook Trout in southern Rocky Mountain streams

ABSTRACT Objective The Trojan Y chromosome (TYC) approach uses fish with two Y chromosomes (MYY) to skew the sex ratio of a nonnative population to all males, theoretically resulting in eventual extirpation. Although the TYC approach has the potential to extirpate nonnative fish populations, the spatial distribution of stocked MYY fish throughout a system can influence their ability to reproduce with wild fish. Furthermore, understanding the movement dynamics of MYY fish is an important consideration for developing effective stocking strategies. Therefore, we evaluated the dispersal of MYY and wild Brook Trout Salvelinus fontinalis in three streams undergoing TYC treatments in northern New Mexico. Methods We compared the movement of adult MYY and wild Brook Trout stocked over 4 years. In addition, we assessed the short-term (3 months) and long-term (12 months) movement of age-0 MYY fish in relation to stocking method (i.e., point stocking, disperse stocking). Results In general, MYY and wild Brook Trout did not exhibit extensive movement in each of our study streams. For instance, adult MYY and wild Brook Trout moved less than 50 m regardless of the sampling period. Age-0 fish exhibited more variable movement dynamics in relation to stocking strategy but generally moved less than 50 m in a given stream. Conclusions The movement of MYY Brook Trout was generally minimal in our study streams. Therefore, the managers stocking MYY fish likely cannot rely on natural dispersal to distribute fish throughout a system. Instead, streamwide stocking of MYY fish is likely necessary to facilitate dispersal of MYY fish and ensure adequate overlap and reproduction with wild conspecifics.