Evaluation of a 356-mm Minimum-Length Limit for Smallmouth Bass in Wisconsin Streams

Abstract
In 1989, a 356-mm minimum-total-length limit was instituted for sport angler harvest of smallmouth bass Micropterus dolomieu in the southern two-thirds of Wisconsin. Previously, there had been no minimum-length limit. We compared smallmouth bass abundance and size structure in six Wisconsin streams with good habitat quality from before (1987–1988) and after (1991–1994) the length limit was enacted. We also sampled a reference stream in northern Illinois that had no minimum-length limit during the study period. No significant changes in smallmouth bass abundance or size structure occurred at the reference stream. Conversely, five of the six Wisconsin streams showed significantly increased smallmouth bass abundance or improved size structure or both after 1989. Five sites had more sublegal-length (178–355 mm) smallmouth bass and two also had more legal-length smallmouth bass. Mean total length of smallmouth bass increased at four sites and decreased at one, and proportional stock density improved significantly at two sites. Our results suggest that the size limit has been beneficial for smallmouth bass populations in Wisconsin streams with good habitat. However, this conclusion is only tentative because the single reference stream may not have adequately represented the variation and trends in smallmouth bass populations that might have occurred in Wisconsin streams. Also, we have few data to determine whether the length limit actually changed angler harvest from the six streams.

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