Manipulations of Stocking Magnitude: Addressing Density-Dependence in a Juvenile Cohort of Common Snook (Centropomus undecimalis)

Abstract

We released hatchery-reared juvenile common snook (Centropomus undecimalis) to test the effects of augmenting age-1 abundance by 100% (high augmentation, n = 2) vs 10% (low augmentation, n = 2) in estuarine creeks of southwestern Florida. We monitored in-creek abundance of age-1 snook 1 month before releases in May 2002 to estimate wild snook density and stocking magnitude. All sampling used seining standardized for effort, gear efficiency, and depletion removal. After releases, sampling continued for 1 year. After 1 month, creeks with high augmentation showed a 126% and 74% increase in total age-1 abundance, and low augmentation creeks a 6% increase and an 18% decrease. Total age-1 abundance declined during fall in all creeks, but by winter, abundance increased again, comparable to earlier levels (132% and 67% above the pre-release estimates in high augmented creeks and 8% and 5% in creeks with low augmentation). While overall density was elevated in both high augmentation creeks, hatchery-reared snook in one creek experienced a 64–85% loss within 1 month after release; loss of hatchery-reared or wild snook was negligible in other experimental creeks. Pre-release density was not a good predictor of creek productive capacity, suggesting variation in habitat production and localized recruitment. Further work is needed to understand inter-cohort density-dependent interactions, food chain responses, and variation in habitat productivity.

Keywords:

• coded-wire tag
• competition
• elastomer
• habitat capacity
• predation
• snook
• stock enhancement

ACKNOWLEDGEMENTS

This manuscript was prepared in partial requirements of the first author's doctoral dissertation at the Department of Fisheries and Aquatic Sciences, University of Florida. He thanks his committee members (the two co-authors, W. Lindberg, M. Allen, T. Frazer, and C. Osenberg). Financial support was provided by the Florida Fish and Wildlife Conservation Commission (FWC) and the National Oceanic and Atmospheric Administration's Science Consortium for Ocean Replenishment (SCORE). We thank J. Bell, W. Lindberg, C. Osenberg, and anonymous reviewers for their editorial reviews and contributions toward strengthening this manuscript. We thank R. DeBruler Jr., D. Wilson, V. Mooney, A. Warner, J. Rock, B. Blackburn, G. Wahl, P. Simmons, G. Smith, and the many college interns and volunteers who assisted with field work, tagging, and release operations. We thank staff at Mote's Center for Aquaculture Research and Development for rearing snook used in this study. We also thank staff at the FWC Stock Enhancement Research Facility for providing equipment and assistance during tagging and release operations. We thank P. Hull, D. Doherty, and M. McLeod for assistance during snook spawning activities. W. R. Mote and FWC provided startup funds for snook stock enhancement projects at Mote Marine Laboratory.