The age, growth, and bathymetric distribution of Reighard's chub, Leucichthys reighardi koelz, in Lake Michigan

Abstract

Reighard's chub has come to be one of the most important species of the group since the serious decline in abundance of the larger representatives of the genus Leucichthys in Lake Michigan. An understanding of the biology of as many species of chubs as possible is essential if further depletion and the collapse of the fishery are to be prevented. The age and growth of 331 individuals taken in 1932 were determined. Each of the other phases of the study is based on more than 5,000 specimens collected during the three years, 1930–1932. Reighard's chub occurred most abundantly, when not spawning, in depths of 20 to 60 fathoms where the temperature of the water ranged from 38.8 to 40.6° F. It was taken at all depths where the nets were set from 12 to 97 fathoms, and in water that varied from 34.7 to 50.6° F. The abundance on the east shore was seven times that on the west shore and between two and three times that in the upper part of the lake. The data indicate the existence of separate populations on the two shores. The greater exploitation with smaller meshes in the western part of the lake probably accounts for the relative scarcity in those waters. Ecological factors are considered the probable cause of the lesser abundance in the upper lake. Spawning occurs during May and June at depths of 20 to 79 fathoms, over a wide variety of bottom materials at temperatures of 38.8 to 40.5° F. Age-group IV dominated in the samples of fish whose ages were determined and made up 50.2 per cent of the total. Age-groups V and III were the next largest groups in that order. Growth in length was most rapid during the first year of life. Growth in weight was most rapid during the first three years with the annual increment in weight about the same in each of those years. The sexes grew in both length and weight at approximately the same rate. Growth compensation occurs in the reighardi of Lake Michigan, but the first year differences were not removed entirely by the time of capture in the fifth year. The weight of the fish in the combined samples increased as the 2.468 power of the length. No relationship between condition (K) and rate of growth could be demonstrated. Condition (K) was better in 1931 than in either 1930 or 1932 and usually was better in 1930 than in 1932. The seasonal changes in relative heaviness followed the same general trend irrespective of the sex or stage of maturity of the fish. The females lost 8 per cent of their weight in spawning, but no loss of weight could be demonstrated for the males. The females were always strongly dominant in the samples except during May and June 1931 and May 1932 when the sexes occurred in about equal numbers. The relative abundance of the sexes did not change materially in age-groups II to V. There were no males assigned to age-groups VI and VII.