Occupancy Modeling and Estimation of the Holiday Darter Species Complex within the Etowah River System

Abstract

Documenting the status of rare fishes is a crucial step in effectively managing populations and implementing regulatory mechanisms of protection. In recent years, site occupancy has become an increasingly popular metric for assessing populations, but species distribution models that do not account for imperfect detection can underestimate the proportion of sites occupied and the strength of the relationship with a hypothesized covariate. However, valid detection requires temporal or spatial replication, which is often not feasible due to logistical or budget constraints. In this study, we used a method that allowed for spatial replication during a single visit to evaluate the current status of the holiday darter species complex, Etheostoma sp. cf. E. brevirostrum, within the Etowah River system. Moreover, the modeling approach used in this study facilitated comparisons of factors influencing stream occupancy as well as species detection within sites. The results suggest that there is less habitat available for the Etowah holiday darter form (Etheostoma sp. cf. E. brevirostrum B) than for the Amicalola holiday darter form (Etheostoma sp. cf. E. brevirostrum A). Additionally, occupancy models suggest that even small decreases in forest cover within these headwater systems adversely affect holiday darter populations.

Received October 5, 2010; accepted June 19, 2011

ACKNOWLEDGEMENTS

We would like to thank Brett Albanese and Jim Peterson for providing invaluable insight on project design and analysis. Additionally, Seth Wenger was extremely helpful in evaluating the analysis used in this study. Members of the laboratory of Byron Freeman of the Odum School of Ecology, especially Christina Baker, Nicole Pontzer, and Amanda Neese, were essential in both the field and the lab. Funding was provided by grants provided to Byron J. Freeman from the Georgia Department of Natural Resources. Use of trade, product, or firm names does not imply endorsement by the U.S. Government.

Notes

Link magnitude is the number of first-order streams upstream of the location.