Mercury bioaccumulation in elasmobranchs

by Nicholas Kutil and David L. Taylor.

ABSTRACT:

Mercury (Hg) is a toxic environmental contaminant that bioaccumulates in fish tissues,
including numerous marine species. Cartilaginous fish of the subclass Elasmobranchii are
important ecological constituents of marine ecosystems, yet the fate of Hg contaminants in
their body tissues is largely unknown. In this study, four species of elasmobranchs: little
skate (Raja erinacea), winter skate (R. ocellata), smooth dogfish (Mustelus canis), and
spiny dogfish (Squalus acanthias), were collected from the Rhode Island/Block Island
Sound, and the Hg content (ppm wet wt) of white muscle tissue was analyzed using
automated combustion atomic absorption spectrometry. Diet and feeding habits for each
species were also assessed by stomach content and stable nitrogen (δ15N) and carbon (δ13C)
isotope analyses. Mean Hg concentrations differed significantly among species, with highest
levels measured in smooth dogfish (mean Hg = 0.680 ± 0.107 ppm, n = 15), followed by
spiny dogfish (mean Hg = 0.312 ± 0.034 ppm, n = 44) and skates (mean Hg = 0.110 ± 0.008
ppm, n = 78 and 0.069 ± 0.005 ppm, n = 56 for little and winter skate, respectively). The Hg
concentration of skate muscle tissue did not vary by body weight, suggesting that Hg does
not bioaccumulate in these species. Conversely, smooth and spiny dogfish both
bioaccumulate Hg with respect to body size, although smooth dogfish have a higher Hg
content relative to spiny dogfish. The elevated Hg concentration of smooth dogfish may be
explained by their higher trophic level status, as determined from δ15N signatures (mean
δ15N = 13.29 ± 0.88, 11.82 ± 0.60, 12.33 ± 0.65, and 12.12 ± 1.06 for smooth dogfish, spiny
dogfish, little skate, and winter skate, respectively). The enriched δ13C values of skates and
smooth dogfish indicated benthic foraging (range of mean δ13C = -16.39 ± 0.32 to -17.42 ±
0.46), which was further confirmed by the dominance of decapods and crustaceans in the
stomach contents. Conversely, squid and butterfish were the principal prey of spiny
dogfish, and the contribution of these pelagic prey was reflected in the depleted δ13C
signature (mean δ13C = -21.97 ± 0.83). Future work includes researching the effect habitat
use and prey Hg to better understand bioaccumulation patterns in these species.

Presentation at the 2012 Winter Meeting of the Southern New England Chapter (SNEC).

January 26, 2012
University of Rhode Island

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