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Improving the status of endangered species can be challenging because the efficacy of conservation actions is often uncertain. Conservation aquaculture has been the main recovery action for endangered white sturgeon ( Acipenser transmontanus) in the Transboundary Reach of the upper Columbia River. Using long-term mark-recapture data (2002–2018), we predicted variation in growth rates due to genetic, environmental, and competition effects to evaluate the efficacy of the aquaculture program. Environmental conditions (by season and country) and competition had the greatest effects on growth. Growth, length-at-age, weight-at-age, and condition factor were higher for fish residing in reservoir habitats (US) compared to those in riverine habitat (Canada). Growth declined over the study period but growth in length for larger fish remained higher in the US as fish > 100 cm fork length in Canada were not growing. Small differences in growth among families indicate that differences in genetics among parents spawned in the hatchery had negligible effects on growth in the wild. Our estimate of substantive negative density-dependent growth in Canada is important for management of conservation aquaculture for sturgeons.

Few studies have quantified the repeatability of reproductive decisions by individuals or assessed their relationship with environmental variables over multiple seasons for long-lived iteroparous fish species. Using individual-based data collected for 678 lake sturgeon ( Acipenser fulvescens ) over 8 consecutive years, we evaluated hypotheses regarding spawning periodicity and repeatability of spawning location, spawning time, and environmental cues associated with spawning. At our study site (Upper Black River, northern Michigan, USA), interspawning interval differed between males (2.3 ± 0.08 years) and females (3.7 ± 0.16 years), but was not significantly related to age. Individual spawning behavior was highly repeatable with respect to spawning time (relative day within the spawning season) for both sexes regardless of size or age, but was less repeatable, though still significant, relative to water temperature, river discharge, and lunar phase. Breeding area was also repeatable, with individuals spawning earlier in the season selecting locations further upstream than those spawning later. Repeatability in spawning times and locations suggest that subpopulation differentiation may develop among different spawning groups, even within small and spatially contiguous areas.