The Influence of Stream Order and Selected Stream Bed Parameters on Fish Diversity in Raystown Branch, Susquehanna River Drainage, Pennsylvania

Abstract

SUMMARY Consistent relationships among certain physical parameters with stream order have been shown (summarized in Platt 1974). These parameters in combination are significant in influencing fish population densities and species diversity. Diversity of fishes in Raystown Branch was correlated most highly with stream order; other physical data were significantly correlated with both diversity and stream order. Data from Raystown Branch support the hypothesis that stream order represents a multidimensional network of the physical parameters which comprise it and, as such, can be used as a satisfactory composite index. Stream classifications based on various physical, chemical and biological parameters have been advanced to explain changes in faunal diversity within streams. Shelford (1911) originally described the longitudinal distribution of fishes in temperate stream habitats in terms of the geologic age of stream beds. The concept of ranking streams based on bifurcation ratios, drainage density and stream length was advanced by Horton (1945) and applied by Kuehne (1962) to the fish distribution of Doe Run, a tributary of Kentucky River. Strahler (1957) extended the use of this dimensionless number system for geomorphic basin studies. The physiological effects of temperature on longitudinal fish distribution were included by Burton & Odum (1945) but no attempt was made to separate the effects of temperature and basin morphometry (Sheldon 1968). Trautman (1942) investigated the importance of gradient in distribution, abundance and stocking potential. Huet (1959) discussed the effects of both gradient and width as applied to Western European streams. Hocutt & Stauffer (1975) studied the effect of gradient and other physical features on the longitudinal distribution of fishes in Conowingo Creek, Maryland/Pennsylvania. Harrel & Dorris (1968) showed a high correlation between stream order and numerous stream basin dimensions. Platts (1979) used stream size obtained by interpolative width and depth from stream order to predict fish population structure. Correlation between the presence and absence of fish species was used by Gorman & Karr (1978) to illustrate the influence of habitat on fish populations of small streams. Horwitz (1978) tested the relationship between diversity gradients and variability patterns by studying gradients of variability of discharge. The purpose of this paper was to study the influence of stream order and selected stream