A Comparison of Fish Community Composition of Headwater and Adventitious Streams in a Coldwater River System

The river continuum concept is an overarching paradigm in stream ecology, but the concept makes no provision for adventitious streams (i.e., low-ordered tributaries to larger rivers). We examined the fish community and habitat of the fifth-order mainstem, two second-order adventitious tributaries to the mainstem, and three second-order headwater streams of the Pine River (Alcona County, Michigan) from May through August 2000. Fish species richness generally increased with increasing stream order and was higher in the adventitious streams than in the headwater streams. The fish species composition of adventitious streams was more similar to the mainstem than to the headwater streams but showed greater month-to-month variability than either the mainstem or headwater streams. Habitat conditions in headwater and adventitious streams were similar except adventitious streams were generally warmer. These results indicate that factors in addition to stream order, such as stream connectivity and temperature, are important determinants of stream fish assemblage.