Mercury Strategy for the Bay-Delta Ecosystem - CALFED Bay-Delta ...

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(3) To provide fish-consumption advice to the public. Fish-consumption advisories can be
effective for reducing exposure of humans to methylmercury. Existing and monitoring data
should be analyzed to determine if a single regional fish-consumption advisory is appropriate or
whether spatial variation in contamination of fish warrants multiple advisories across the region.
(4) To transfer information through public outreach. The public benefits of this program would
be enhanced by active public outreach and by communication of findings to environmental
health professionals. Monitoring data, combined with information from special studies, can be
used to identify priority areas and target groups for outreach and education efforts, which should
also communicate the health benefits of eating clean fish.
(5) To perform special studies needed to support health-risk assessment and risk communication.
Ancillary studies may be needed to estimate rates and patterns of fish consumption, to identify
and characterize groups with potentially high levels of exposure, to identify optimal methods for
communicating advice, and to evaluate the effectiveness of fish-consumption advisories.
Goal 2 of this core component, to gage methylmercury contamination of the ecosystem, would
provide a performance measure for ecosystem restoration. Many factors can influence the
bioaccumulation of methylmercury in long-lived biota of upper trophic levels, greatly
complicating the detection and interpretation of patterns in mercury concentrations in large game
fishes. A biosentinel-based monitoring approach is, therefore, preferable for gaging
methylmercury contamination of aquatic food webs and for detecting spatial and temporal
patterns in contamination during restoration.
A biosentinel species should possess certain key attributes. It should be spatially widespread and
abundant throughout much of the ecosystem. Ecotoxicological relevance is enhanced if the
biosentinel is important in the diets of certain piscivores and substantially involved in the foodweb
transfer of methylmercury. The biosentinel should exhibit limited variation in diet and
trophic position; in other words, variation in mercury concentrations in the biosentinel should
result largely from variation in processes influencing the abundance of methylmercury in the
aquatic ecosystem, rather than to differences in diet or trophic position. Small whole fish, such
as 1-year-old yellow perch (Perca flavescens), have been widely used as a biosentinel of
methylmercury contamination of food webs in temperate lakes in the United States and Canada
(Frost et al. 1999, Wiener et al. 2003). During their first year, yellow perch occupy a low trophic
position, feeding on zooplankton and small zoobenthos, yet small yellow perch are regionally
important in methylmercury transfer in food webs supporting sport fish, piscivorous wildlife, and
humans who consume sport fish. Age-1 perch are also sensitive indicators of annual and spatial
variation in the abundance of methylmercury in aquatic food webs (Frost et al. 1999). Young-ofthe-year
fish may also be useful as a biosentinel.
Goal 2 should include the following two objectives.
(6) To monitor total mercury in biosentinel species to assess methylmercury contamination of
aquatic food webs. Sampling and analyses of biosentinel fishes (or other aquatic biota) would
provide a direct measure of methylmercury concentrations in aquatic food webs supporting
production of piscivorous fish and wildlife.
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