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<p>Alligator Gar (<i>Atractosteus spatula</i>) are a species of conservation concern due to habitat alteration and harvest-oriented fishing activities. An additional concern is contaminant exposure, particularly mercury (Hg), which may pose reproductive risks to this long-lived predator. We quantified total mercury (THg:mg/kg wet weight) in Alligator Gar populations in one coastal and one inland region of the Brazos River, Texas, USA to explore accumulation patterns, consumption risks, and potential reproductive impairment. Furthermore, we included an analysis of stable isotopes of nitrogen (δ<sup>15</sup>N) and carbon (δ<sup>13</sup>C) to decouple trophic position and its influence on Hg accumulation within these two regions. We used generalized linear models (GLMs) to examine the effects of fish size (length, mm) and region (inland versus coastal) on Hg concentration, δ<sup>15</sup>N, and δ<sup>13</sup>C. Length had a significant positive effect on both Hg and δ<sup>15</sup>N. Further analysis accounting for the effect of length found both Hg and δ<sup>15</sup>N were significantly higher in the inland population (N = 45; mean ± SE = 0.232 ± 0.020 mg/kg ww and 18.8 ± 0.184‰, respectively) than the coastal population (N = 48; mean ± SE = 0.143 ± 0.012 mg/kg ww and 16.72 ± 0.291‰, respectively). We further estimated probabilities of Alligator Gar exceeding Hg screening thresholds set by the United States Environmental Protection Agency (EPA). Exceedance probabilities were 0.048 for coastal, and 0.276 for inland populations, however, when extrapolated to fish ≥ 2000 mm these climbed to 0.146 for coastal and 0.559 for inland populations. Furthermore, Alligator Gar may experience some level of reproductive toxicity because of sublethal Hg exposures. We observed that 39% (37/93) of Alligator Gar in our study exceeded 0.2 mg/kg, a threshold level associated with reproductive impairment, with inland region Alligator Gar representing a higher percentage of individuals over this threshold compared to the coastal population (64%, 29/45 versus 17%, 8/48). These findings highlight the effects of trophic position, location, and size (length) on Hg concentrations and should be accounted for when creating management decisions and consumption advisories for Alligator Gar.</p>

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Regional variation in mercury bioaccumulation of Alligator Gar (Atractosteus spatula): A case study from inland and coastal reaches of the Brazos River, Texas, USA

  • 期刊论文

  • 发表日期：

    2026年2月18日

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  • Zachary S. Moran,
  • Michael T. Penrose,
  • George P. Cobb,
  • Michael S. Baird,
  • Ryan S. King,
  • Cole W. Matson

摘要

Alligator Gar (Atractosteus spatula) are a species of conservation concern due to habitat alteration and harvest-oriented fishing activities. An additional concern is contaminant exposure, particularly mercury (Hg), which may pose reproductive risks to this long-lived predator. We quantified total mercury (THg:mg/kg wet weight) in Alligator Gar populations in one coastal and one inland region of the Brazos River, Texas, USA to explore accumulation patterns, consumption risks, and potential reproductive impairment. Furthermore, we included an analysis of stable isotopes of nitrogen (δ15N) and carbon (δ13C) to decouple trophic position and its influence on Hg accumulation within these two regions. We used generalized linear models (GLMs) to examine the effects of fish size (length, mm) and region (inland versus coastal) on Hg concentration, δ15N, and δ13C. Length had a significant positive effect on both Hg and δ15N. Further analysis accounting for the effect of length found both Hg and δ15N were significantly higher in the inland population (N = 45; mean ± SE = 0.232 ± 0.020 mg/kg ww and 18.8 ± 0.184‰, respectively) than the coastal population (N = 48; mean ± SE = 0.143 ± 0.012 mg/kg ww and 16.72 ± 0.291‰, respectively). We further estimated probabilities of Alligator Gar exceeding Hg screening thresholds set by the United States Environmental Protection Agency (EPA). Exceedance probabilities were 0.048 for coastal, and 0.276 for inland populations, however, when extrapolated to fish ≥ 2000 mm these climbed to 0.146 for coastal and 0.559 for inland populations. Furthermore, Alligator Gar may experience some level of reproductive toxicity because of sublethal Hg exposures. We observed that 39% (37/93) of Alligator Gar in our study exceeded 0.2 mg/kg, a threshold level associated with reproductive impairment, with inland region Alligator Gar representing a higher percentage of individuals over this threshold compared to the coastal population (64%, 29/45 versus 17%, 8/48). These findings highlight the effects of trophic position, location, and size (length) on Hg concentrations and should be accounted for when creating management decisions and consumption advisories for Alligator Gar.