No abstract

The South Dakota Department of Game, Fish, and Parks instituted a 23‐cm minimum length limit for black crappie Pomoxis nigromaculatus and white crappie P. annularis in Lake Alvin on 1 January 1996 because an undesirable size and age structure indicated that these populations were being overharvested. Crappies were sampled annually using trap (modified fyke) nets from 1992 to 1999. Mean catch per unit effort (fish/net night) was higher in the postregulation years (1996–1999) than in the preregulation years (1992–1995) for both species. The mean length of age‐3 fish in the postregulation years was not different from that of the 1995 baseline for either species. The relative stock density of 23‐cm crappies did not increase after implementation of the length limit. Limited prey availability, which was inferred from the negative trend of relative weight with respect to length, was the likely reason that larger crappies did not appear. The 23‐cm minimum length limit was removed on 1 January 2000 to give anglers the opportunity to harvest smaller crappies.

No abstract

The routine assessment and monitoring of aquatic habitat characteristics, such as submerged aquatic vegetation (SAV), is a fundamental tool in fisheries management. The relative low cost and availability of recreation‐grade side‐scan sonar (SSS) systems has made capturing high‐resolution (<10 cm) underwater imagery a practical and viable tool for improving these assessments. Using Humminbird SSS and a boat‐mounted transducer, we determined our ability to produce classified maps of SAV within three reservoirs in Texas. Sonar recordings of photic zone habitat were collected and processed into georeferenced mosaic images by using SonarTRX SSS software for use in geographical information systems (GISs). The resulting raster images were interpreted to identify and map SAV, and a classification scheme was developed. Random‐point data was also used to develop a traditional error matrix and an accuracy assessment for each classified map. In the three reservoirs, 485 ha were classified, including 298 ha of SAV. The area estimates for 11 of 12 classes fell within the 95% CIs that were estimated from concurrent random‐point surveys. Overall classification accuracy ranged from 78% to 88% for the three reservoirs. The methods that were developed demonstrate an accurate procedure for calculating SAV coverage and producing a high‐quality map product for distribution to stakeholders.

We evaluated the efficacy of trap nets fitted with a batteryoperated, submersible light in the net mouth in increasing the catch rates of white crappies Pomoxis annularis by comparing the catch rate and size structure of white crappies collected by these nets with those of fish collected by standard (i.e., unlighted) trap nets in six Texas reservoirs. The catch rates of standard (mean = 16.3/netnight) and lighted trap nets (12.1/net-night) did not differ significantly. We found no significant difference in the catch of stock-size white crappies (≥130 mm total length [TL]) by standard (12.7 fish/net-night) versus lighted trap nets (9.9 fish/net-night); however, significantly fewer preferred sizes (≥250 mm TL) were taken by lighted (1.9 fish/net-night) than by standard sets (2.9 fish/netnight). The length-frequency distributions of the white crappies collected by each trap net treatment were similar and did not significantly differ in four of the five lakes tested. Our results suggest that trap nets fitted with artificial lights in the net mouth do not effectively increase catch rates for white crappies and may favor the collection of smaller size-classes than standard trap nets.