Mandatory Catch and Release and Maximum Length Limits for Largemouth Bass in Minnesota: Is Exploitation Still a Relevant Concern?

Abstract

We evaluated the response of Minnesota populations of largemouth bass Micropterus salmoides to implementation of 305-mm maximum total length (TL) limits (three lakes) and mandatory catch-and-release regulations (six lakes). Responses were compared with population trends observed in nine reference populations where largemouth bass harvest was regulated by prevailing statewide regulations. Increased harvest regulation generally improved largemouth bass size structure, but statistically significant improvements in size structure indices were detected in only a few individual lakes. Increased regulation of harvest did not appear to influence electrofishing catch per unit effort (CPUE; fish/h) of largemouth bass less than 381 mm TL. Electrofishing CPUE of fish greater than or equal to 381 mm TL (CPUE-381) generally improved after more stringent harvest regulations were in place, but improvements were only significant for two of the three lakes where a 305-mm maximum length limit was implemented. With the exception of one lake, increased harvest regulation did not appear to reduce largemouth bass growth rates. Improvements in size structure and CPUE-381 were rarely observed in reference lakes. Our results suggest that despite increases in voluntary catch and release of largemouth bass, angler exploitation is still an important factor regulating size structure in some Minnesota lakes, and more intensive harvest regulations can improve size structure in some populations.