Performance of Diploid and Triploid Rainbow Trout Stocked in Idaho Alpine Lakes

Abstract

Increased growth, improved survival, and genetic protection of wild stocks have been suggested as benefits of stocking triploid (i.e., sterile) salmonids for recreational fisheries. We examined the return rates and growth of mixed-sex diploid (2N), mixed-sex triploid (3N), and all-female triploid (AF3N) rainbow trout Oncorhynchus mykiss across 28 alpine lakes. Equal numbers of each treatment group were stocked in 2001 and 2003 and sampled 3–4 years later. During 2004 and 2005, a total of 75 2N and 36 3N marked rainbow trout were recaptured. Taken together, the 2N fish accounted for an average of 0.68 of the total marked fish caught, and the combined proportions of test fish (including netting and angling) differed significantly between the test groups and were consistent across survey years. During 2006 and 2007, a total of 60 2N, 31 3N, and 208 AF3N marked rainbow trout were recaptured. The mean length of the test fish was similar between test groups within sampling years. Overall, the return of 3N rainbow trout to alpine lakes in Idaho was low compared with that of 2N trout, whereas AF3N trout appeared to return in higher proportions than both of the other groups. The triploid stocks studied in this evaluation did not show any growth advantages over the duration of the study. Study design limitations may have contributed in part to some of the differences in the number of 2N and 3N rainbow trout captured. However, our results suggest that fisheries managers should consider all-female triploid rainbow trout as a low-risk option for maintaining alpine lake fisheries while minimizing the impact on native stocks.

Received January 27, 2010; accepted November 16, 2010

ACKNOWLEDGMENTS

We thank John Cassinelli, Lars Alsager, Mike Biggs, Matt Wilson, Brett High, Art Butts, Sarah Nelson, Matt Kreizenbeck, Travis Parrill, Dan Garren, Carl Stiefel, Alan Sievers, and Bob Esselman for their assistance during high mountain lake surveys. This research would not have been possible without the generous contributions of our resident hatchery personnel. Gene McPherson, Steve Kammeyer, and Joel Patterson reared and stocked the high mountain lake test groups in 2001. Dan Baker, Jeff Heindel, and Jeremy Redding reared the three test groups for stocking in 2003. Brett High, Lance Hebdon, and three anonymous reviewers provided helpful reviews and commentary that greatly improved the quality of this manuscript.

Notes

^aWhile 49 2N fish were captured, only 43 were actually measured.