Assessment of altered rearing environments on survival and performance of hatchery-reared trout : implications for cutthroat trout reintroduction programs

Abstract

Reintroduction of native fish stocks is an important management tool used to mitigate the effects of invasive species and loss of habitat. A common reintroduction tool is the use of hatchery fish to create or supplement native populations in areas of their historic range. However, the low survival and poor performance of some hatchery outplants is an issue for hatchery reintroductions, as broodstocks may be limited. As a result, there has been a recent effort to develop 'conservation hatcheries' that employ hatchery rearing strategies that might improve the effectiveness of hatchery reintroduction efforts. This study developed and evaluated the effectiveness of enriched hatchery rearing strategies on increasing effectiveness of hatchery reintroductions for inland salmonids. Three hatchery rearing treatments of varying complexity were developed for rearing trials using westslope cutthroat trout Oncorhynchus clarkii lewisi and rainbow trout Oncorhynchus mykiss. Fish were reared in the hatchery for 60 days and various performance assessments were compared to evaluate behavioral, morphological, and physiological differences among the rearing treatments. A second 60 day rearing period using westslope cutthroat trout was followed by an outplant assessment. Fish were reared in the same three hatchery treatments and at the end of the hatchery-rearing period fish were placed into rearing ponds. Outplanted fish were left in the ponds with no artificial feed or predation relief. After 2 months in the ponds, fish were removed and their survival and growth were analyzed. Growth and survival in the hatchery were similar among the rearing treatments for both species. The most complex treatment was associated with increased cover seeking behavior, reduced aggression, higher fin condition, and improved coloration. Survival results from the outplanted fish were compromised because of fish movement; however, there was evidence that the most complex treatment may have performed better as suggested by growth data and proximate analysis of lipid content. Our results suggest that alterations to the hatchery environment may improve the effectiveness of native species reintroduction efforts using hatchery-reared fish. Further research is needed to assess additional hatchery-rearing environment alterations as well as the long-term effects such alterations might have on hatchery outplanted fish.