Evaluating the impact of captive ancestry on the growth and survival of Delta Smelt in a captive environment

Abstract

Delta Smelt Hypomesus transpacificus, is an endangered fish endemic to the California San Francisco Bay-Delta, USA. Extreme declines of the wild Delta Smelt population have prompted use of cultured fish to supplement the wild population since 2021 to prevent the extinction of the species. However, evidence of adaptation to captivity in the conservation hatchery has raised concerns about the use of captive-bred fish for supplementation and how these fish may differ from wild Delta Smelt. We conducted a study over two consecutive years to investigate the effects of varying levels of captive ancestry on the growth and survival of cultured Delta Smelt from two different domestication index (DI) groups, capturing high DI and low DI values. Fish growth and survival were monitored in the hatchery from larval to adult life-stages to determine differences between DI groups. Our findings indicate that DI can have a significant influence as we observed reduced growth and survival of low DI fish at multiple life-stages. The results suggest that the DI of released hatchery-reared Delta Smelt may affect the performance of their offspring in the natural environment. Further studies might be necessary to develop a better management strategy on the released fish to enhance the conservation efforts.