Fish Species Distribution in Relation to Water Quality Gradients in the North Branch of the Moose River Basin

The distribution of fish species in the North Branch of the Moose River (Lake Rondaxe to headwaters of Big Moose Lake) was determined by intensive netting and electrofishing surveys of lakes and streams in the watershed during 1982-83. A chronology of changes in fish species occurrence in the drainage system was reconstructed from earlier published surveys conducted in 1882 and 1931 and unpublished survey data obtained by the NYSDEC during the period 1948-1975. Native species present in 1882 were also collected in 1931. Smallmouth bass (Micropterus dolomieu) were introduced in the early 1900's and were present in collections made in 1931. Major changes in the fish community have taken place since 1931. The smallmouth bass and many of the native species found in the earlier surveys were either absent or restricted in occurrence to downstream sites (eg. L. Rondaxe and Moss L. sub-drainage) in 1982. Non-native species introduced after 1931 (yellow perch, Perca flavescens; central mudminnow, Umbra limi; banded killifish, Fundulus diaphanus) are currently widely distributed throughout the drainage system. In particular, the yellow perch is now a dominant species in the larger lakes of the basin. Comparisons of survival rates for caged fish transferred from high to low pH sites in the Big Moose drainage system demonstrated relatively greater acid tolerance of non-native species (yellow perch, mudminnow, killifish) than native cyprinids. Watershed acidity gradients (pH and aluminum concentrations) and relative physiological acid tolerance are major determinants of currently observed fish species distribution patterns in the North Branch of the Moose River. Differences in age and size structure of fish populations inhabiting acidic and non-acidic lakes of the drainage system were apparent, but difficult to interpret without additional information on population size and potential density dependent parameters such as age specific growth and survival rates. Differential hatching success was observed for yellow perch eggs reciprocally transferred between acid (Big Moose) and neutral (Moss L.) lakes. Eggs transferred from Moss L. to Big Moose L. exhibited poor hatching success as a result of alterations in egg membrane structure that inhibited normal egg expansion and the hatching process. This effect was not evident in eggs from the same parents reared in Moss Lake nor in eggs from the Big Moose parents reared in both lakes. These experimental observations suggested p