Exploring the Influence of Fish Body Size on Tissue Mercury Dynamics: Implications for Natural Resource Management and Human Health Risk

Mercury (Hg) contamination of aquatic biota has received much attention in recent years because of the adverse health effects that Hg poses to humans and wildlife, primarily through fish consumption.  However, less is known about perhaps the most important factor that links Hg accumulation in fish tissue to human consumption: fish body size.  In the context of fisheries management, body size is a basis for establishing recreational and commercial harvest regulations, directly influencing the fish that will be harvested for consumptive purposes.  Thus it is essential that we quantify the relationship between body size and Hg accumulation in fish tissue for more effective fishery policy.   We quantified this relationship for three commonly consumed freshwater sportfish of different trophic levels, bluegill (Lepomis macrochirus), largemouth bass (Micropterus salmoides), and black crappie (Pomoxis nigromaculatus) in lakes with different levels of Hg contamination.  Accounting for fish age and trophic position, we found strong and in most cases positive correlations between fish tissue Hg concentration and fish length.  Largemouth bass had the highest levels of Hg contamination.  In addition, the projected size at which largemouth bass reached the Environmental Protection Agency (EPA), North Carolina (NC), and Food and Drug Administration (FDA) action levels decreased with an increase in the level of lake contamination (determined by average fish tissue Hg concentration).  Our results also suggest that “high consumption risk” sizes for largemouth bass were below the fishery management minimum size limit in two of six lakes sampled, leaving only high risk fish as an option for anglers to take home.  In general, we found that larger and older largemouth bass and black crappie surpassed EPA and NC action levels.  We suggest that public health officials incorporate fish size into fish advisories to better inform health risks to fish consumers.  We also suggest that public health officials and wildlife managers work together to structure fishery size regulations that protect consumers from Hg exposure and help communicate the relative risk of fish consumption.