Increasing capture efficiency of pallid sturgeon Scaphirhynchus albus (Forbes and Richardson, 1905) and the reliability of catch rate estimates

This study evaluated the effects of environmental parameters on the probability of capturing endangered pallid sturgeon (Scaphirhynchus albus) using trotlines in the lower Mississippi River. Pallid sturgeon were sampled by trotlines year round from 2008 to 2011. A logistic regression model indicated water temperature (T; P<0.01) and depth (D; P=0.03) had significant effects on capture probability (Y=-1.75- 0.06T+0.10D). Habitat type, surface current velocity, river stage, stage change and non-sturgeon bycatch were not significant predictors (P=0.26-0.63). Although pallid sturgeon were caught throughout the year, the model predicted that sampling should focus on times when the water temperature is less than 12 degrees C and in deeper water to maximize capture probability; these water temperature conditions commonly occur during November to March in the lower Mississippi River. Further, the significant effect of water temperature which varies widely over time, as well as water depth indicate that any efforts to use the catch rate to infer population trends will require the consideration of temperature and depth in standardized sampling efforts or adjustment of estimates.