Evaluation of a 356- to 457-mm Slot Length Limit for Largemouth Bass in 5 Texas Reservoirs

Following 6 years under a 356-mm minimum length limit regulation, poorly-structured largemouth bass populations at 5 Texas reservoirs were placed under an experimental 356- to 457-mm slot length limit in September 1993. The limit was designed to target angler harvest at the relatively abundant sub-slot fish and to increase angler catch rates within the protected length range. Largemouth bass populations were monitored at each reservoir by electrofishing at 4—8 shoreline stations in 1989-1992 (pre-change) and in 1995-1996 (post-change). A general linear model statistical procedure was used to determine any significant changes (P = 0.05) in the CPUE or RSD for fish below (203-355 mm), within (356-456 mm), or above the slot (≥457 mm) following implementation of the limit. Pre- and post-change Wr of fish below and within the slot as well as mean lengths of age groups at capture also were compared. In addition, spring creel surveys were conducted from 1993 to 1997 at 1 of the reservoirs. Significant changes in density were detected at only 2 reservoirs where CPUE203-355 and CPUE356-456 were significantly lower at one and CPUE356-456 was significantly higher at the other following implementation of the slot length limit. No significant changes in RSD values were found at any reservoir. Relative weight did not improve following the limit change. Results from the creel survey showed angler harvest of sub-slot fish was low, but did increase during the third and fourth year after the slot length limit was imposed when primarily 304-340-mm were harvested. Low fishing pressure and harvest of sub-slot bass most likely prevented the slot limit from producing the desired results at the creel reservoir and probably caused the failure at other study reservoirs as well. Other factors not related to the regulation could have potentially influenced population structure at any of the reservoirs.

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