Seaward migration behavior of juvenile second filial generation Chinese sturgeon Acipenser sinensis in the Yangtze River, China

Second filial generation (F2) Chinese sturgeon from hatcheries have been released to restock the endangered natural population of this fish ever since full-cycle artificial breeding was first achieved in 2009. However, our knowledge of the habitat use and migration tactics of hatchery-bred F2 Chinese sturgeon is poor, as is our understanding of the effects of releasing these hatchery-bred sturgeon on the natural population. Acoustic telemetry data and recapture information were therefore collected to study the seaward migration behavior and distribution of hatchery-bred juvenile F2 Chinese sturgeon. Acoustic monitoring showed that the released F2 juveniles dispersed gradually and migrated down the Yangtze River at a ground migration speed of 24.2–125.9 km/day (mean 88.5 km/day). The range of swimming depths used by the F2 Chinese sturgeon during downstream migration depended on the river reaches considered, but the mean depth was 10.4 m (range 0.2–32.3 m). It was found that F2 Chinese sturgeon juveniles prefer to swim in the middle and upper layers of the water. Twenty-one of the 61 (34%) acoustically tagged F2 juveniles arrived at the estuary area. Recapture information indicated that the cultured F2 Chinese sturgeon adopted a similar distribution strategy to the wild Chinese sturgeon larvae in the estuary area. Knowledge of the migration and distribution patterns of the hatchery-bred juvenile F2 Chinese sturgeon should help to illuminate the consequences of restocking the natural population of Chinese sturgeon with cultured F2 juveniles, and thus point the way to an effective protection strategy for this species in the Yangtze River.