Methylmercury Concentrations in Fish from Tidal Waters of The Chesapeake Bay

Abstract

Striped bass (Morone saxatilis), white perch (Morone Americana), and largemouth bass (Micropterus salmoides) were collected in the Chesapeake Bay mainstem and tributaries and analyzed for total mercury (Hg) and methylmercury (MeHg) content. Striped bass are anadromous, whereas white perch and largemouth bass are resident species, and the largemouth bass are also restricted to the tidal fresh portion of the Bay. Total Hg and MeHg concentrations in striped bass increased with fish size, and large fish (>7.5 kg wet weight) tended to have MeHg concentrations of 300 ng g(-1) or greater. On average, the striped bass MeHg concentration was 120 +/- 100 ng g(-1) and the fraction of the total Hg as MeHg was 65 +/- 22%. Reasons for the lower relative MeHg content are discussed. Otolith strontium/calcium ratios were also determined to examine whether migration had a significant impact on MeHg content in striped bass. Resident fish did appear to have a higher MeHg burden than the more migratory fish of similar size. Largemouth bass and white perch tended to have low MeHg content (respectively, 14 +/- 7 and 13 +/- 11 ng g(-1); all fish <1 kg wet weight), and the white perch also had a low %MeHg (28 +/- 14%), reflecting their mostly planktivorous lifestyle. A comparison of largemouth bass and striped bass MeHg concentrations for the estuarine fish with those of fish in Maryland reservoirs of similar size showed that the estuarine fish have much lower MeHg burdens. Differences in MeHg concentration in the estuarine waters compared to the reservoir waters likely account for much of this difference, although the importance of other factors is also discussed.