Mercury Accumulation in Pelagic Fishes

Total mercury (Hg) concentration was determined in the tissues of ten pelagic fishes, with a special emphasis on apex predators (Table 1). Highest Hg levels were observed in blue marlin, carcharhinid sharks (Genus Carcharhinus) and little tunny, ranging from ~1.0 to 10.5 ppm. Moderate to low concentrations (<1.0 ppm) were observed in blackfin tuna, cobia, dolphin, greater amberjack, king mackerel, wahoo, and yellowfin tuna. For the majority of species examined, Hg concentrations did not vary significantly between location (Texas vs. Louisiana) or collection period. Relationship between Hg concentration and fish size/weight were also explored for six taxa (blackfin tuna, carcharhinid sharks, dolphin, king mackerel, wahoo, yellowfin tuna), with each showing a significant positive relationships between Hg concentration and body size and/or weight. Natural dietary tracers, stable isotopes (δ¹⁵N, δ¹³C) and fatty acids, were used to evaluate the relationship between Hg and trophic position and the relationship between Hg and dietary history. Stable nitrogen isotope analysis showed that Hg concentrations in fish tissues were positively associated with trophic position. Based on the δ¹³C and δ¹⁵N values of pelagic fishes, three natural associations were identified and groupings were identical to those detected with fatty acid signatures. No connection between the three natural trophic associations and Hg was observed, and thus the bioaccumulation of Hg in these pelagic taxa was not related directly to prey selection patterns.

Table 1. Hg level of ten taxa of pelagic fishes from the NW Gulf of Mexico.
Common name	N	[Hg]total ppm wet wt.		Total length (cm)
		mean	range	mean	range
blackfin tuna*	48	0.64	0.00 - 1.41	73	22 - 87
blue marlin**	9	10.52	4.95 - 18.72	285	256 - 311
carcharhinid sharks **	9	1.61	0.46 - 4.08	69	15 - 96
cobia*	17	0.89	0.20 - 2.40	97	76 - 142
dolphin	57	0.07	0.01 - 0.49	79	38 - 135
greater amberjack*	44	0.60	0.24 - 1.07	84	689 - 112
king mackerel*	39	0.96	0.37 - 1.46	84	64 - 104
little tunny**	9	1.08	0.24 - 2.52	56	52 - 66
wahoo*	52	0.78	0.01 - 3.31	133	103 - 175
yellowfin tuna	103	0.18	0.07 - 0.87	112	54 - 159
N = Number of individuals. ** > FDA 2001 recommended criteria level (1.0 μg/g wet wt.). * > EPA 2002 recommended criteria level (0.3 μg/g wet wt.).

Copyright 2006, Pelagic Fisheries Conservation Program
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Texas A&M University at Galveston