Gillnet Contact Selectivity and Correction Factors for the AFS Standard Gillnet Design

Gill nets are inherently size-specific due to the physics of how they capture fish.  Size selectivity can affect several fisheries metrics, including length frequencies and size indices. To examine contact selectivity of the AFS standard gill net, we sampled white crappie, white bass, hybrid striped bass, saugeye, and channel catfish in five Oklahoma reservoirs and used the SELECT method to model five log-linear selectivity curves (normal, normal location, log normal, gamma, and bimodal).  For all species, the bimodal model best fit the data and was used to adjust length frequencies and PSDs.  The adjustments were typically minor for moderate-sized fish and strongest for small fish (i.e., compensated for low retention of small fish).  Some species also required adjustments to compensate for low retention of large fish.  Unadjusted and adjusted length frequencies were not significantly different for any species; however, adjusted PSD and PSD-P values differed from unadjusted values by <u>></u> 5% for white crappie and white bass.  When the AFS standard net is used in systems similar to the ones we sampled, our bimodal selectivity curves could be used to adjust length frequencies and PSDs to better represent the fish that encountered the net.