Conditional Capture Probability of Scaphirhynchus spp. in Drifting Trammel Nets

Pallid sturgeon Scaphirhynchus albus and shovelnose sturgeon S. platorynchus are commonly sampled using drifting trammel nets in the Missouri and Mississippi river basins. Despite the fact that drifting trammel nets have been used for decades to sample these species, little is known about the capture efficiency of this gear. We estimated conditional capture probability for drifting trammel nets over known locations of pallid sturgeon and shovelnose sturgeon. In addition, we examined several variables that were predicted to influence the success of capturing a pallid sturgeon or shovelnose sturgeon in a drifting trammel net. Conditional capture probability (the conditioning factor was known presence) varied from 0.37 on the first attempt to 0.51 on the second attempt. None of the variables measured were useful in explaining the success of sampling a fish in a drifting trammel net. Drifting trammel nets are relatively efficient, and we suggest that they continue to be used to sample pallid sturgeon and shovelnose sturgeon in large turbid rivers. The high variability in catch per unit effort associated with sampling pallid sturgeon and shovelnose sturgeon using drifting trammel nets reported in the literature is probably related to the their low abundance (primarily pallid sturgeon) and patchy distribution (both species). Thus, using sampling designs appropriate for species with low abundance or patchy distributions rather than sampling designs commonly used for abundant species with ubiquitous distributions will require less effort because drifting trammel nets are relatively efficient.