Gear bias in fyke netting: Evaluating soak time, fish density, and predators

Knowledge of gear bias is critical for conducting valid population and community assessments. We studied the biases in tyke netting by investigating the individual effects of soak time (fyke nets were fished for 6, 24, or 48 h), fish density (tyke nets were stocked with 0, 30, or 60 fish/net), and predators (tyke nets were stocked with one or zero bowfin Amia calva) on the escape probability and number of individuals captured (i.e., catch) for three fish species. Overall, escape probabilities were consistently lower for round gobies Neogobius melanostomus than for bluntnose minnows Pimephales notatus and banded killifish Fundulus diaphanus. Both escape probability and catch increased with soak time. Escape probabilities were lower at high fish densities and in the presence of a predator, whereas catch appeared to be unaffected by both factors. We documented predation on fish stocked in tyke nets by free-ranging bowfins and yellow bullheads Ameiurus natalis, which is a potential source of bias that will probably vary among systems. Of the factors we investigated, variation in soak time had the strongest effect on catch. Our results were consistent with catch being proportional to soak times of at least 24 to 48 h, although this relationship was highly variable. Thus, standardizing catch by soak time (e.g., net nights) can be appropriate when confronted with low variation in soak time (e.g., 1 d). Finally, our study highlights potential differences in escape probabilities among fish species, a factor that is probably important in determining which species are overrepresented and which are underrepresented in entrapment gear.