Implications of a Migration Impediment on Shortnose Sturgeon Spawning

Abstract

A population of shortnose sturgeon Acipenser brevirostrum was documented congregating at the base of Pinopolis Dam, Cooper River, South Carolina, during the February−March spawning season. Pinopolis Dam is a peaking hydroelectric facility and navigation lock located within the coastal plane, 77 km upriver of the mouth of the Cooper River at Charleston, South Carolina. In a 5-year radiotelemetry experiment, shortnose sturgeon did not pass upstream through the navigation lock but congregated at the base of the dam. As a result, a study was conducted to determine whether the tailrace was used as spawning habitat. The location is atypical of published descriptions of shortnose sturgeon spawning habitat in terms of a suite of characters, including distance upriver, tide, flow characteristics, and substrate. The river is tidally influenced for its entire length, and the bottom substrate in the tailrace is dominated by hard marl with negligible fine sediments such as silt and sand. Turbine discharge varies from 0 to 329 m3/s subdaily; current velocities during typical hydroelectric peaking discharge exceed 3 m/s. Egg sampling showed that successful spawning (i.e., fertilized eggs and developing embryos) occurred during the three spawning seasons sampled. Spawning was detected from 27 February through 29 March (1997–1999) at water temperatures ranging from 11.5°C to 19.0°C (mean = 14.5°C), reaching the highest levels published for shortnose sturgeon spawning. Active spawning and lack of upstream passage by shortnose sturgeon at this site suggest that physical blockage of migration may prevent fish from reaching preferred spawning habitat, probably to the detriment of the population.