Exploitation of Smallmouth Bass from Selected Ozark Streams and Simulated Effects of Higher Minimum Length Limits
Chris Williamson, Nick Girondo, Paul Cieslewicz, Dave Knuth, Mike Reed, John Ackerson, A.J. Pratt, Sarah Peper, and Jen Girondo
Abstract.—Angler harvest and population characteristics of Smallmouth Bass Micropterus dolomieu were assessed through electrofishing surveys and tagging 3,027 fish with reward tags at six sites on five Ozark streams. Growth, exploitation, and mortality were estimated for each site. Predicted population responses to higher length limits were simulated using Fishery Analysis and Modeling Simulator software. Tag return rates ranged between 37% and 64%, angler release rates ranged between 63% and 94%, and annual exploitation ranged between 5% and 26%. The median time at-large for tags returned within one year of tagging ranged from 22 to 47 d of the tagging date. Growth rates were relatively slow, as mean time to reach 305 mm was 4.9 years and mean time to reach 381 mm was 7.8 years. Total annual mortality estimates ranged from 37% to 55%. Annual natural mortality estimates ranged from 13% to 33%. Predicted responses to higher length limits varied considerably by site because of differences in estimated rate functions. Although simulations predicted small increases (0.54–2.73 fish/100 recruits >381 mm) in the number of larger fish with the 381-mm length limit at five of six sites, predicted increases were substantial (17 fish/100 recruits >381 mm) and yield increased 6% at the Current River-Powder Mill site. Individuals in the Current River-Powder Mill site were not reaching their full growth potential due to growth overfishing, while simulations of the remaining five populations indicated no growth overfishing under current conditions and regulations. The combined effects of natural mortality and slow growth limited the effectiveness of higher length limits. Under most conditions, the statewide length limit of 305 mm was adequate to balance the desire of quality fishing and harvest opportunities on most Ozark streams. Our study indicates that fisheries at select stream reaches may be improved by higher length limits where exploitation is high, growth is adequate, and natural mortality is low.