Conditional Capture Probability of Pallid Sturgeon in Benthic Trawls

Abstract Long-term population monitoring assumes that relative abundance reflects trends in the population. Sampling efficiency and capture probability are assumed to be consistent so samples can be temporally and spatially compared. Benthic otter trawls are being used for a long-term monitoring project on the Missouri River. To estimate the capture probability of Pallid Sturgeon Scaphirhynchus albus, we used acoustic telemetry to locate and target tagged sturgeon with benthic otter trawls. Conditional capture probability (pi*) of a fish in a known location was only 0.08 on the first pass, increased slightly (pi* = 0.18) on the second pass, and again on the third pass (pi* = 0.26). Individual habitat parameters or their interactions did not explain when Pallid Sturgeon were successfully or unsuccessfully captured. Our study suggests that otter trawls are a highly inefficient gear for capturing Scaphirhynchus species. Therefore, relative abundance indices based on otter trawl captures need to be assessed cautiously for juvenile and adult Pallid Sturgeon, especially in highly variable conditions. Received December 4, 2014; accepted March 19, 2015