Evaluation of a 23-cm (9-in) Minimum Length Limit for Black and White Crappies in Lake Alvin, South Dakota

The South Dakota Department of Game, Fish and Parks (SDGFP) implemented a 23-cm (9-in) minimum length limit for black Pomoxis nigromaculatus and white P. annularis crappies in 36-ha Lake Alvin , South Dakota beginning 1 January 1996. Both relative abundance [catch per unit effort (CPUE)] and size structure [e .g., proportional stock density (PSD)] increased following implementation of the length limit. However, these changes were more related to recruitment patterns than to regulation effects. Age structure and harvest of both crappie populations increased slightly after the regulation was enacted . However, relative weight (Wr) values declined with increasing length for both species, likely indicating limited prey availability for larger fish. Growth of both species declined after implementation of the length limit. In 1999, incremental growth of 6- to 19-cm fish was similar to or faster than growth from pre-treatment samples. However, annual growth increments of 20-cm and mortality will likely negate any benefits of the regulation. Harvest of legal-sized crappies has declined from 1998 to 1999, indicating that slowed growth has resulted in fish being unavailable to anglers. Therefore, the regulation was removed 1 January 2000 to allow anglers the opportunity to catch and harvest crappies that were stockpiling just below 23 cm