Effects and Utility of Minimum Length Limits and Mortality Caps for Flathead Catfish in Discrete Reaches of a Large Prairie River

Abstract

Populations of flathead catfish Pylodictis olivaris in four reaches of the Kansas River, Kansas, were examined to evaluate the effects of three minimum length limits (305 (the minimum size that anglers are willing to harvest), 610, and 762 mm total length (TL)) on population size structure and number harvested over a 30-year simulation. We used electrofishing and hoopnetting to capture and tag flathead catfish throughout the Kansas River from 2005–2006. Current exploitation (u) based on tag returns was probably less than 10%, and total annual mortality A ranged from 14% to 28% across all reaches. Increased river access and promotion of this fishery may increase u in the future, so model simulations were conducted with conditional natural mortality (cm) and u ranging from 10% to 40%. Proportional stock density (PSD) and the relative stock density of preferred-length fish (RSD-P) substantially declined (by >25% and >15%, respectively) as u increased with the 305-mm TL limit over the 30-year simulation. The PSD showed similar trends across all reaches, indicating that use of different regulations among reaches was not necessary and that differences in growth among reaches were less influential than u and cm. No substantial differences were observed in size structure under the 610- and 762-mm TL limits among reaches, but under a 762-mm TL limit anglers would have to sacrifice about 42% of the number harvested under the current cm level. Mortality caps revealed that each reach could sustain an A of about 60% and 55% to maintain current PSD and RSD-P levels, respectively; this result suggests that quality flathead catfish size structure can be preserved. Our results show that the effects (or lack thereof) on flathead catfish and other sport fishes should be evaluated before harvest restrictions are implemented.