Effects of striped bass stocking on largemouth bass and spotted bass in Lewis Smith Lake, Alabama

Abstract

Striped bass Morone saxatilis have been introduced into over 100 USA reservoirs over the last several decades to provide additional sport fishing opportunities and to control abundant shad, Dorosoma spp. populations. Stocking of striped bass has been controversial and-non striped bass anglers have expressed two primary concerns; 1) striped bass consume sport fish including black bass and therefore reduce the abundance of catchable size fish; and 2) striped bass compete for limited prey with other piscivorous fish, which could reduce the growth rates and ultimately the abundance of black bass. The objectives of this study were to 1) compare food habits among striped bass, largemouth bass, and spotted bass; 2) estimate biomass and relative weights of all three species; and 3) predict consumptive food demand of all three species. Striped bass, largemouth bass Micropterus salmoides and spotted bass M. punctulatus were sampled every other month in Lewis Smith Lake, Alabama (8,583 ha) between October 2006 and August 2007. In addition, striped bass were sampled in November 2005, and April and June 2006. Striped bass and black bass stomachs were examined to describe food habits and striped bass were aged using otoliths to describe striped bass growth and survival. Growth and survival were estimated for largemouth bass and spotted bass from historically collected age data. Density and biomass of striped bass, largemouth bass, and spotted bass were estimated using striped bass stocking densities, black bass age-0 densities, and mortality rates and weight:length relations for each species. Fish bioenergetics models were used to estimate striped bass and black bass consumptive food demands. Striped bass diets (by weight) were dominated by shad (64%), while black bass and sunfish/crappie comprised 5% and 6% of the diet, respectively. Largemouth bass and spotted bass diets were dominated by crayfish 72% and 75%, respectively and sunfish 21% and 9%, respectively, while shad comprised 6 and 14% of the diets, respectively. Diet overlap values varied seasonally among species with highest overlap in June between striped bass and black bass, but relative weights of black bass did not decline. Black bass diets shifted from shad to crayfish in December when striped bass consumption of shad was the highest. Black bass relative weights were slightly depressed in December and indicated the potential for a competitive interaction between striped

bass and black bass. Partitioning of prey resources between black bass and striped bass was evident throughout the rest of the year and diet overlap was minimal. Striped bass and black bass biomass estimates were nearly equal between species groups and ranged from 0.7 to 9.4 kg/ha, and 1.4 to 8.3 kg/ha, respectively. Overall, consumptive prey demand was similar between striped bass and black bass. Bioenergetics modeling indicated striped bass consume between 3 to 28 kg/ha a year of shad and 0.2 and 2.3 kg/ha a year of black bass, while annually black bass consume between 1 to 3 kg/ha of shad, 7 to 25 kg/ha of crayfish, and 2 to 6 kg/ha of sunfish. All black bass consumed by striped bass were less than the 330-381 mm slot limit on Lewis Smith Lake, and striped bass consumption of these black bass provided an additional mechanism to reduce small black bass. Although striped bass did consume some black bass, impact on the black bass population was low, striped bass and black bass partitioned prey resources, and impact of striped bass stocking on the black bass population was low.