Comparison of Otolith-Based Growth Rates and Microchemistry in Red Drum before, during, and after the Deepwater Horizon Oil Spill

Oil from the Deepwater Horizon blowout reached the Gulf of Mexico coast in the summer of 2010 and potentially exposed species living in those areas to toxic chemicals. The purpose of this study is to examine otoliths from Red Drum (Sciaenops ocellatus) for evidence of oil exposure that could be related to reduced growth rates. Samples originating from various inshore locations in Louisiana and the Florida Gulf Coast were compared by applying dendrochronology-based methods to annual growth increments (annuli). Because somatic growth and otolith growth are directly related, differences in annulus measurements can indicate differences in annual somatic growth, which is a good indicator of overall fish condition and reproductive potential. Variation in growth during years affected by the Deepwater Horizon oil spill was combined with otolith microchemistry to determine if slow growth was associated with oil exposure, as indicated by oil-associated element presence within otoliths. Trace metal analysis showed elevated abundances spanning all growth years, indicating some oil exposure also occurred before the Deepwater Horizon spill. We found elevated abundances of oil-indicator elements at various locations in both Florida and Louisiana. Growth comparisons among exposed and unexposed fish are ongoing.