Larval gizzard shad characteristics in Lake Oahe, South Dakota: a species at the northern edge of its range

Abstract

Gizzard shad, Dorosoma cepedianum, have generally been restricted to the lower Missouri River impoundments in South Dakota. In recent years, gizzard shad numbers have increased in Lake Oahe, marking the northern-most natural population. These increases could potentially affect recreational fishes. Specifically, questions arise about larval gizzard shad growth dynamics and if age-0 gizzard shad in Lake Oahe will exhibit fast or slow growth, both of which can have profound effects on piscivore populations in this reservoir. In this study, we evaluated larval gizzard shad hatch timing, growth, and density in Lake Oahe. We collected larval gizzard shad from six sites from May to July 2008 and used sagittal otoliths to estimate the growth and back-calculate the hatch date. We found that larval gizzard shad hatched earlier in the upper part of the reservoir compared to the lower portion and that hatch date appeared to correspond to warming water temperatures. The peak larval gizzard shad density ranged from 0.6 to 33.6 (#/100 m³) and varied significantly among reservoir sites. Larval gizzard shad growth ranged from 0.24 to 0.57 (mm/d) and differed spatially within the reservoir. We found no relationship between the larval gizzard shad growth or density and small- or large-bodied zooplankton density (p > 0.05). As this population exhibits slow growth and low densities, gizzard shad should remain a suitable forage option for recreational fishes in Lake Oahe.

Keywords:

• Dorosoma cepedianum
• age-0
• zooplankton
• spatial variability
• population dynamics
• forage species

Acknowledgements

G. Adams Jr, B. Hanten, C. Longhenry, J. Lott, and K. Potter from South Dakota Game, Fish, and Parks and Dr. M. Brown, Dr. B. Fincel, Dr. D. James, W. Schrek, B. Swanson, B. VanDeHey, Dr. J. VanDeHey, Dr. D. Willis, Dr. M. Wuellner, and A. Wuestewald provided technical assistance, reviews of earlier drafts, and field and laboratory assistance. Funding for this study was provided by Federal Aid in Sport Fish Restoration, Project F-15-R, Study 1515, administered through South Dakota Department of Game, Fish, and Parks. The South Dakota Cooperative Fish & Wildlife Research Unit is jointly sponsored by the US Geological Survey, South Dakota Department of Game, Fish & Parks, South Dakota State University, and the Wildlife Management Institute. Any use of trade names is for descriptive purposes only and does not imply endorsement by the US Government.