Smallmouth Bass Summer Habitat Use, Movement, and Survival in Response to Low Flow in the Illinois Bayou, Arkansas

—The southwestern edge of the natural range of smallmouth bass Micropterus dolomieu contains streams that become disconnected pools during summer primarily owing to hydrogeologic conditions, including high evapotranspiration rates. These conditions may complicate fisheries management by affecting fish behavior or mortality rates. The objectives of this study were to characterize summer habitat use by smallmouth bass, estimate the changes in the extent of available habitat, describe summer movement patterns, and estimate summer survival rates. Radio transmitters were implanted into 60 smallmouth bass during May 2006, and the fish were tracked until October in the forks of the Illinois Bayou, which drains a portion of the Ozark National Forest. Habitat characteristics were measured as the summer progressed, and during this time most riffle–run habitat dried completely, resulting in a series of disconnected pools. The decreases in wetted area exceeded 55% in certain 2-km study reaches; however, smallmouth bass were consistently found at a median depth of 0.80 m. Boulder habitat was preferred when it was available; however, cobble, gravel, and bedrock substrates were also used. By July, velocity was below detection levels and water temperature occasionally exceeded 308C. The average distance moved by smallmouth bass was 270 m in May, decreasing to 54 m by July. The distances moved were greater on average but more variable in streams with larger losses of wetted area, as fish moved away from drying areas. The survival rate was lowest in the stream most accessible to anglers. Dryness appeared to increase mortality, as survival estimates were lower than expected from published studies of streams with continuous summer flow. The effective management of fisheries under such hydrologic conditions may require preserving continuous surface flow and the quality of remnant pools as well as implementing more restrictive harvest regulations in summer. The southern parts of the range of smallmouth bass Micropterus dolomieu, such as northwestern Arkansas, contain streams that tend to lose surface flow (Hines 1975) during the summer when evapotranspiration is high. At this time, riffle–run habitats become rare (Homan et al. 2005). The surviving fish in these systems are forced to either congregate in remnant pools, where they must compete for available resources and are more susceptible to predators (Lowe-McConnell 1975; Harvey and Stewart 1991; Gagen et al. 1998), or move long distances to escape the drying stream reaches entirely. The populations of smallmouth bass in streams that experience seasonally discontinuous surface flow have lower production rates and abundance than those in streams with more continuous surface flow (Homan 2005). Thus, managing a sustainable fishery in this type of stream will probably require assessing the potentially elevated mortality, avoidance movements, and changes in habitat use associated with dryness. Smallmouth bass in lotic systems have been described as a sedentary species (Funk 1957; Todd and Rabeni 1989) with strong homing behavior after movement (Larimore 1952). Fajen (1962) found that the smallmouth bass in two small Ozark streams normally restricted their movements to one distinct pool. Lyons and Kanehl (2002) reviewed the available literature and concluded that during the summer smallmouth bass generally remained in localized areas, their net movements totaling less than 1 km. In Otter Creek and the Pecatonica River, Wisconsin, all movements were less than 200 m (Lyons and Kanehl 2002), and few long-range movements were observed during the summer in the Wolf and Embarrass Rivers of Wisconsin (Langhurst and Schoenike 1990). Although the movement patterns of smallmouth bass have been studied extensively, the loss of surface flow during summer could affect them in ways that are not well understood. * Corresponding author: [email protected] 1 Present address: Division of Forestry and Natural Resources, West Virginia University, 322 Percival Hall, Morgantown, West Virginia 26506 USA. Received August 16, 2008; accepted February 13, 2010 Published online May 13, 2010 604 North American Journal of Fisheries Management 30:604–612, 2010 Copyright by the American Fisheries Society 2010 DOI: 10.1577/M08-183.1 [Article]