Graduation Year

2014

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Marine Resource Assessment (Marine Science)

Major Professor

Steven A. Murawski, Ph.D.

Committee Member

Don Chambers, Ph.D

Committee Member

Susan Lowerre-Barbieri, Ph.D.

Committee Member

Christopher Stallings, Ph.D.

Keywords

Otolith, Oil Spill, Increment Width Analysis

Abstract

The Deepwater Horizon blowout occurred on April 20th, 2010 and released nearly 5 million barrels of crude oil into the northern Gulf of Mexico causing pollution of the water and sediment inhabited by many fishes for at least 87 days while the wellhead went uncapped. Populations of the Gulf of Mexico Red snapper, Lutjanus campechanus, an important fish to the ecology and economy in the region, exhibit affinity to shallow water oil infrastructure such as the Deepwater Horizon making them especially vulnerable to crude oil contamination. The objective of this study is to determine growth of Red snapper before, during and after the DWH spill and to assess factors potentially explaining such growth variation. Sagittal otoliths were collected from individuals sampled in 2011 - 2013 from scientific, demersal long-line surveys in the northern Gulf of Mexico (GoM) and West Florida Shelf (WFS). Age and otolith increment width analyses were performed. No annual variation in von Bertalanffy growth parameters was determined among the three catch years. The L∞ , K and t0 estimated from the complete data set (2011-2013) were 82.91, 0.20 and 0.43, respectively. However, significant differences in otolith increment width-at-age were observed in increment numbers three - seven in years following the DWH event, with declines of 13%, 15% and 22% occurring in the fourth -sixth increments. To asses the potential significance of exogenous environmental variables to observed yearly growth variation I evaluated five parameters - meridional (V) winds, zonal (U) winds, wind stress curl which is a measure of upwelling, Mississippi River discharge, and mean sea level anomaly - using a linear mixed effects model. Hypothesis testing via reduced maximum likelihood estimates indicated that variation in U winds and River discharge could significantly explain the variation in increment width. However, further work must be done in order to determine the natural, inter-annual variability in age specific growth before the results from model fitting can be considered conclusive. Mean back-calculated weight-at-age measurements were obtained in order to assess potential variation in productivity changes. Results from forward difference and reverse helmert contrast-coding indicated that weight at age three+, four+ and five+ declined by 16%, 15% and 11% in 2010, respectively. These analyses indicate a significant decline in fish growth in 2010 coincident with the DWH event, followed by a return to pre-spill rates.

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