Movement, not survival, differs between wild and hatchery-reared imperiled desert fishes

Objective: Stocking streams with hatchery-produced fishes is an increasingly common practice to restore native populations, but the fate of these fish is uncertain due to low survival or high emigration rates. Monitoring these vital population rates is needed to assess stocking and translocation of rare and endangered fishes to identify approaches that maximize persistence and survival and ultimately result in established populations.Methods: We quantified survival, emigration, movement directionality, and longterm (24 months) trends in apparent survival of stocked and wild-caught fish implanted with passive integrated transponder (PIT) tags. We PIT-tagged and tracked 1419 individuals, consisting of direct comparisons between two species of hatchery and wild fish, as well as four other wild-captured species, from 2020 to 2022 in three desert streams in Arizona and New Mexico.Result: We found that hatchery fish had high (>98%) estimates of survival after being released (<40 days) that was similar to all tagged wild fish. But hatchery fish had a fivefold higher emigration rate than wild conspecifics shortly (<40 days) after being released. Emigrating hatchery fish also tended to move downstream, whereas wild fish were more likely to move upstream. Additionally, apparent survival estimates were about 10 times higher for tagged wild fish than hatchery conspecifics 6 months after release; hatchery fish apparent survival approached zero after about 165 days but did not approach zero for wild fish until 690 days following tagging and release. Conclusion: Our results suggest emigration, rather than reduced survival, might limit the success of stocking efforts. Thus, choosing optimal stocking locations and the time of year of the stocking, such as upstream reaches during times near the species reproduction season, might improve retention and establishment of stocked fish.

Automated summary

This study aims to investigate the differences in survival rates, emigration rates, and movement directionality between hatchery-produced fish and wild fish after stocking. The results suggest that hatchery fish have high initial survival rates but higher emigration rates, with a tendency to move downstream. On the other hand, wild fish have lower survival rates but lower emigration rates, with a tendency to move upstream. The choice of stocking locations and timing can greatly impact the retention and establishment of stocked fish.