Otolith Chemistry to Determine Within-River Origins of Alabama Shad in the Apalachicola–Chattahoochee–Flint River Basin

Abstract

Recent fish passage work in the Apalachicola–Chattahoochee–Flint (ACF) river system has coincided with an increase in the abundance and population estimates of adult Alabama Shad Alosa alabamae. Juvenile Alabama Shad are now common in the Flint River and Lake Seminole above Jim Woodruff Lock and Dam where they have historically been absent. Fish passage work has successfully restored spawning adults to these habitats; however, whether these juveniles are contributing to the observed population increases is unknown. Our objective was to determine the natal origins of adult Alabama Shad returning to spawn in the ACF river system, specifically whether fish passage efforts at the dam were contributing recruits to the adult population. Juvenile otolith chemistry profiles were significantly different between nursery locations above and below the dam but were complicated by temporal variation. However, including short term temporal variation in a discriminant function analysis (DFA) resulted in 88% correct classification, indicating that for the ACF river basin, short-term temporal variability in otolith chemistry does not pose a significant problem for predicting natal origins from cohorts that were not sampled. This finding relied most heavily on strontium, which did not exhibit temporal variation. Our data show that juvenile Alabama Shad produced upstream and downstream of the dam in the ACF can be reliably discriminated with an otolith chemistry approach. This discriminant function was applied to 140 adult Alabama Shad collected during 2010 and 2011 from below the dam and indicated that 86% of adults returning to spawn in the ACF system recruited from the Flint River above the dam. Neither collection year, sex, nor age affected the shad origins. These data indicate that juvenile Alabama Shad are able to emigrate successfully downstream through at least one lock and dam and contribute to the adult stock.

Received April 12, 2014; accepted August 5, 2014

ACKNOWLEDGMENTS

We thank K. Anstead for assistance preparing otoliths for trace element analysis. Funding for this study was provided by The Nature Conservancy. We thank Georgia Department of Natural Resources personnel that assisted in collection and extraction of otoliths: Dean Barber, John Kilpatrick, and Rob Weller. We would also like to thank Rick Long for the collection of juvenile Alabama Shad from the Apalachicola River. This manuscript benefited greatly from reviews by two anonymous reviewers and the editors of this journal.