Effect of Trawling and Habitat on Mercury Concentration in Juvenile Red Snapper from the Northern Gulf of Mexico

Abstract

We evaluated mercury (Hg) contamination in juvenile red snapper Lutjanus campechanus (<250 mm total length) as an indicator of Hg pollution on the northern Gulf of Mexico (GOM) continental shelf. Specifically, we examined the effects of fish size, commercial shrimp trawling, and habitat type on total Hg concentrations and stable nitrogen isotope ratios (δ15N; a proxy for trophic position) in red snapper. Red snapper Hg concentrations and δ15N values were positively and significantly correlated with fish size. In addition, red snapper collected over trawled habitats had significantly higher Hg concentrations and δ15N values than did red snapper collected from similar, nontrawled habitats. Red snapper also exhibited habitat‐specific differences in Hg concentrations and δ15N values, but differences were size dependent and generally small. Our study suggests that the Hg concentrations of juvenile red snapper in the northern GOM are elevated in areas where commercial shrimp trawling occurs, possibly due to increases in both red snapper trophic position and bioavailable Hg in trawled areas. Additional studies are needed to determine whether Hg concentrations are elevated in fish from trawled areas in other marine ecosystems.

Regional variation in mercury and stable isotopes of red snapper (Lutjanus campechanus) in the northern gulf of Mexico, USA

“…Examination of d 15 N, d 13 C, and d 34 S allowed for the evaluation of whether variation in Hg concentrations could be caused by diet and trophic position differences of red snapper among regions. In the present study, a positive linear relationship existed between Hg concentrations and trophic position (d 15 N) with TL, suggesting the potential for bioaccumulation of Hg with increase in size and trophic position [40][41][42], as has been found in previous studies [6,10]. The average d 15 N values of phytoplankton, the dominant basal resource for red snapper (S.T.…”

“…No significant year ( p ¼ 0.813) differences were detected in the general linear model; therefore, year was combined in the models. Fixed-effects analysis of covariance models were computed to test for differences by region and habitat in red snapper Hg concentration (n ¼ 994), and TL was included as the covariate to correct for size-related differences in red snapper (as described in Wells et al [6]). Tukey's honestly significant difference test was used to detect a posteriori differences among means [27].…”

“…Total Hg analysis was performed on all red snapper tissue samples (n ¼ 994) and sediment samples (n ¼ 112) with a direct Hg analyzer (DMA-80; Milestone) using thermal decomposition, gold amalgamation, and atomic absorption spectrometry [24]. A detailed description of Hg analysis, including a description of standards used, was provided in a previous study [6]. Quality assurance included certified reference and duplicate samples.…”

“…Despite the importance of marine fish in human diets and high levels of Hg observed by monitoring agencies [2], much of the research that has been conducted on aquatic Hg cycling has occurred in freshwater ecosystems [3]. Studies of Hg bioaccumulation in marine ecosystems often examine fish collected from limited geographic areas [4][5][6][7]. How Hg concentrations in fish vary within ocean basins has not been well studied.…”

“…Typical of reef-associated fish, red snapper tend to aggregate near structured environments on the sea floor, including oil and gas platforms [19,20]. Thus, red snapper may be a good indicator species for assessing patterns of MeHg bioavailability and bioaccumulation in offshore environments (as indicated [4,6]), in addition to evaluating potential influences of Hg from oil and gas development.…”