Swimming behavior of Chinese sturgeon in natural habitat as compared to that in a deep reservoir: preliminary evidence for anthropogenic impacts

Unusually deep water due to dam construction has the potential to negatively effect endangered sturgeons, which lack a physiological mechanism to inflate their swimbladder and may be unable to remain buoyant under high pressure at depth. In a previous study, some juvenile sturgeons released in a deep (> 100 m) reservoir lost buoyancy and stayed nearly motionless on the bottom. However, it is not clear whether this behavior represents a negative effect of the dam, because natural sturgeon swimming behavior is unknown. In this study, we attached multi-sensor data loggers to nine wild adult Chinese sturgeons Acipenser sinensis in an unimpounded reach of the Yangtze River, China. The depth utilization, tail beating activity, swim speed, and body inclination of these fish were monitored for 1-3 days. Fish swam up and down successively in the water column (mean depth, 9.9 m) with a cycle of 100-1,000 s during 64 % of the time on average, and stayed at depth, presumably on the riverbed, during rest periods. Tail beats were continuous (mean frequency, 0.77 Hz) throughout the records, indicating that their buoyancy was maintained. These results contrast with the previous study, suggesting that the behavior observed in the reservoir is unusual and that deep water poses a risk of losing buoyancy for sturgeons. Furthermore, all fish intensively swam (maximum speed, 3.0 m s(-1)) to the river surface at a mean frequency of 0.35 times per hour-a behavior that could explain why ship strikes are a serious cause of mortality in sturgeons.