PARENT SESSION
Poster Session #23: Fish, Lakes, Streams, and Wetlands.
Wednesday, August 8, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

Mercury contamination of northern California fish: spatial and temporal patterns.

Davis, Jay¹, Greenfield, Ben¹, Ichikawa, Gary², Stephenson, Mark², Jarman, Walter³, ^{1 2 3}

ABSTRACT- The Sacramento and San Joaquin River watersheds in northern California are sites of intensive historic gold and mercury mining. As a consequence, mercury concentrations in sport fish of the region are above screening values that indicate a potential public health concern. In order to determine spatial patterns in this contamination, in 1999 we examined mercury concentrations in fish muscle at 31 river sites in the Sacramento and San Joaquin watersheds. Mercury concentrations in largemouth bass were lower in sites in the Sacramento-San Joaquin Delta than in the mainstem portions of the Sacramento River and San Joaquin River. Length, age, and ¹⁵N stable isotope data provided no evidence that these differences result from growth or trophic position differences. We also compared tissue concentrations between 1973 and 1999 to evaluate long term trends during this period. Graphical analysis comparing striped bass collected in the San Francisco Estuary before 1973 versus after 1997 indicated that mercury concentrations have not declined from historical levels. Our data indicate that mercury contamination in fish remains a long-term human health concern in this region but that concentration varies by drainage. Future research should focus on whether this spatial variation results from regional differences in total mercury levels, mercury methylation or demethylation rates, or fish diets.

KEY WORDS: mercury bioaccumulation, stable isotope, micropterus salmoides