RIPARIAN SHADING AND GROUNDWATER ENHANCE GROWTH POTENTIAL FOR SMALLMOUTH BASS IN OZARK STREAMS

Authors

  • Gregory W. Whitledge,

    1. Department of Fisheries and Wildlife Sciences, 302 Anheuser-Busch Natural Resources Building, University of Missouri, Columbia, Missouri 65211-7240 USA
    Search for more papers by this author
    • 4 Present address: Fisheries and Illinois Aquaculture Center, Department of Zoology, Southern Illinois University, Carbondale, Illinois 62901-6511 USA. Email: gwhit@siu.edu

  • Charles F. Rabeni,

    1. U.S. Geological Survey, Biological Resources Division, Missouri Cooperative Fish and Wildlife Research Unit, 302 Anheuser-Busch Natural Resources Building, University of Missouri, Columbia, Missouri 65211-7240 USA
    Search for more papers by this author
  • Gust Annis,

    1. Missouri Resource Assessment Partnership, University of Missouri, 4200 New Haven Road, Columbia, Missouri 65201 USA
    Search for more papers by this author
  • Scott P. Sowa

    1. Missouri Resource Assessment Partnership, University of Missouri, 4200 New Haven Road, Columbia, Missouri 65201 USA
    Search for more papers by this author

  • Corresponding Editor: T. Essington.

Abstract

Moderation of stream temperatures by riparian shading and groundwater are known to promote growth and survival of salmonid fishes, but effects of riparian shade and groundwater on to be growth of warmwater stream fishes are poorly understood or assumed to be negligible. We used stream temperature models to relate shading from riparian vegetation and groundwater inflow to summer water temperatures in Missouri Ozark streams and evaluated effects of summer water temperatures on smallmouth bass, Micropterus dolomieu, growth using a bioenergetics model. Bioenergetics model simulations revealed that adult smallmouth bass in non-spring-fed streams have lower growth potential during summer than fish in spring-fed streams, are subject to mass loss when stream temperatures exceed 27°C, and will likely exhibit greater interannual variation in growth during summer if all growth-influencing factors, other than temperature, are identical between the two stream types. Temperature models indicated that increased riparian shading will expand the longitudinal extent of thermal habitat capable of supporting adult smallmouth bass growth in spring-fed stream reaches when mean daily air temperatures exceed 27°C. Optimum growth temperature (22°C) will be present only in spring-fed streams under these conditions. Potential for increasing shade through riparian restoration is greatest for streams <5 m wide and along north–south reaches of larger streams. However, temperature models also indicated that restoring riparian shading to maximum levels throughout a watershed would increase the total stream mileage capable of supporting positive growth of adult smallmouth bass by only 1–6% when air temperatures are at or near average summer maxima; increases in suitable thermal habitat would be greatest in watersheds with higher spring densities. Riparian management for maintenance or restoration of the thermal habitat of adult smallmouth bass during summer should be focused in areas strongly influenced by groundwater. Restoring riparian shading along spring-fed warmwater streams will likely benefit adult smallmouth bass growth and may ultimately influence population sizes.

Ancillary