An evaluation of the seasonal abundance, catchability, and organic constituents of selected wild populations of crayfish

Abstract

PART I. Thirteen monthly crayfish samples were taken to evaluate the relative abundance and harvest potential of crayfish in a small southwest Virginia stream. Sixty-five and eight tenths percent of the crayfish were captured with a 0.5 by 1 m kicknet, 34.2% were captured with a hand seine, and less than 0.1% were captured with traps. Crayfish were most abundant in the stream from late spring through early fall. Sixty four and three-tenths percent of the crayfish were captured in stream run areas, 31.5% in riffle areas and less than 5% in pools. Population estimates based on long term mark-recapture were 9 crayfish/m2 , whereas those based on an intensive short term study were 5 crayfish/m2 . PART II. Thirteen monthly samples of tissues of Orconectes juvenilis were taken to develop data on indices of organic constituents for use in crayfish culture operations. The hepatopancreas and gonads of each of five males and five females were removed and analyzed for wet and dry weight, and water, lipid, glycogen, RNA, and DNA content. Changes in these organic constituents were compared to observed changes in molting activity, growth, and mating condition. Molting activity was reflected by low hepatopancreatic water concentration. Growth associated with molting activity was indicated by increases in RNA and lipid levels and rapid mobilization of glycogen. Lipid was the major organic reserve of Q. juvenilis and comprised up to 85% of the total dry weight of the hepatopancreas and gonads. Maturation of the gonads preceding the mating season was accompanied by changes in location of lipid from the hepatopancreas to the gonad. Maturation of the gonads was also indicated by an increase in hepatopancreatic water content.