Upstream Movement of Crayfish in an Intermittent Oklahoma Stream

Abstract

Weekly observations were made on a population of the crayfish, Orconectes nais, in an intermittent Oklahoma stream. The population density at the beginning of the study was about 1 crayfish for every 2 ft2 of stream bottom. The percentage of young-of-the-year crayfish in the total population increased as the summer progressed, indicating extensive mortality in older individuals. The life span of this crayfis'h is two years; thus it has a rapid population turnover rate. Migration of crayfish between three adjacent sections of the stream stopped when the falling water level isolated the sections from each other. The general pattern of migration was upstream. Physical and chemical conditions of the water were approximately the same for all sections. Crayfish migrated extensively upstream from a section with a silty substrate toward one with a rubble substrate. In contrast, upstream migration from a section with a rubble substrate into one with a silty bottom was much less pronounced. Drought obliterated the population that had migrated upstream into the rubble-bottomed pond. Thus survival in such extremely fluctuating habitats seems to be a matter of chance. Periodic floods tend to sweep crayfish downstream; perhaps their upstream migration acts as a compensating redistribution mechanism. INTRODUCTION Since inany of the streams in Oklahoma depend on surface runoff for their flow, they are reduced to isolated pools during the dry summer. A prolonged rainstorm can turn such a stream into a swiftly flowing torrent that can quickly deplete bottom fauna populations. Since crayfish are among the more mobile members of the bottom fauna, they may be able to rapidly recolonize such depleted areas by migration. I examined the movements of a crayfish population of just such a stream. Acknowledgments.-This study was conducted at the University of Oklahoma Biological Station during the summer of 1964. I wish to thank the Director, Dr. Carl Riggs, for use of equipment and laboratory space, Miss Mary Ann Roepke, who ably assisted in all of the field work, and Dr. David H. Stansbery, Department of Zoology and Entomology, Ohio State University, who criticized the manuscript. MATERIALS AND METHODS Weekly observations and collections were made at three selected stations located along a tributary of Glasses Creek, Marshall Co., Oklahoma (T5S, R5E, Sec. 32) 'for a seven-week period from 9 June to 29 July, 1964. The stream flows in a general north-to-south direction. Each of 1 Present address: Department of Zoology and Entomology, Ohio State University, Columbus 43210.