Roger L. Hothem

Bioaccumulation of selenium in birds at Kesterson Reservoir, California.

This study was conducted to determine selenium (Se) concentrations in tissues of birds collected during the 1983–1985 nesting seasons at Kesterson Reservoir (an area receiving high-Se irrigation drainage water), compare them with birds from reference sites within Californias Central Valley, and relate them to food-chain Se concentrations at the study sites. Within years, Se in livers of adult birds collected early and late in the nesting season changed significantly at both Kesterson and the primary reference site (Volta Wildlife Area). These changes were related to the length of time birds had been present at the study sites and the associated accumulation (at Kesterson) or depuration (at Volta) of Se. All species showed significant location differences, which were greatest in species that occurred at Kesterson throughout the year or fed more consistently within the reservoir. There were few species differences in Se for birds at the reference sites (where food-chain Se levels were “normal” [⩽2 μg/g, dry wt]). At Kesterson (where bird foods generally contained >50 μg Se/g), species patterns varied by year, probably because of varying periods of residence and other factors. Se concentrations in kidneys and livers of American coots (Fulica americana) were significantly correlated (r=0.9845); Se concentrations in breast muscles and livers of juvenile ducks (Anas spp.) also were correlated (r=0.8280). Body weights of adult coots were negatively correlated with liver Se concentration. Lateseason resident breeding birds or pre-fledging juvenile birds reared at a site usually provided the best indication of sitespecific Se bioaccumulation.

Contaminants in foods of aquatic birds at Kesterson Reservoir, California, 1985

Plants, aquatic insects, and mosquitofish (Gambusia affinis) were collected from Kesterson Reservoir, Merced County, California, and a nearby reference site (Volta Wildlife Area) to compare concentrations of three contaminants found in 1985 with those reported in 1983 and 1984. Mean selenium concentrations in food-chain organisms from sites at Kesterson in 1985 ranged from 26.0 μg/g (dry wt) in water boatman (Corixidae) to 119 μg/g in mosquitofish. All mean selenium concentrations at Kesterson were significantly higher than those from Volta and were sufficient to have caused the impaired avian reproduction observed at Kesterson. Boron concentrations were also significantly higher at Kesterson, and, at one pond, the mean concentration in widgeongrass (Ruppia mari-tima) (1,630 μg/g) was high enough to impair avian reproduction. There were no differences in arsenic concentrations between locations, and concentrations in all food-chain organisms (<1.9 μg/g) were lower than those reported to cause adverse effects in wildlife. Within-location differences were observed for all three contaminants at Kesterson and for selenium at Volta, but there was no consistent pattern to these differences. Between-year comparisons showed that selenium concentrations in mosquitofish generally decreased at Kesterson, but remained about the same at Volta over the 3 years. Selenium concentrations in insects from 1985 were lower at Kesterson than 1983, but were similar to 1984. Concentrations in plants were generally higher in 1983 and lower in 1984 compared with 1985. Boron concentrations in plants were generally higher in 1985, but in mosquitofish and insects, boron concentrations remained about the same all 3 years. Most arsenic concentrations did not change significantly between years.

Bioaccumulation of selenium by snakes and frogs in the San Joaquin Valley, California

Livers of gopher snakes (Pituophis melanoleucus) from Kesterson Reservoir (Merced County, California) contained significantly higher mean selenium concentrations (11.1 g/g, dry weight) than those from two nearby reference sites (2.05 and 2.14 &g/g). Livers of bullfrogs (Rana catesbeiana) collected from the San Luis Drain at Kesterson Reservoir also contained significantly higher mean selenium concentrations (45.0 tg/g) than those from nearby reference sites (6.22 Ijg/g). The high levels of selenium bioaccumulation in these snakes and frogs at Kesterson Reservoir reflected the elevated levels found in their food organisms. We did not examine the snakes or frogs from Kesterson for signs of ill health, but the concentrations we found were sufficiently high to warrant concern about potential adverse effects in these animals and their predators.

Uptake of environmental contaminants by small mammals in pickleweed habitats at San Francisco Bay, California

Small mammals were live-trapped in pickleweed (Salicornia virginica) habitats near San Francisco Bay, California in order to measure the uptake of several contaminants and to evaluate the potential effects of these contaminants on the endangered salt marsh harvest mouse (Reithrodontomys raviventris). Tissues of house mice (Mus musculus), deer mice (Peromyscus maniculatus), and California voles (Microtus californicus) from nine sites were analyzed for chemical contaminants including mercury, selenium, cadmium, lead, and polychlorinated biphenyls (PCBs). Concentrations of contaminants differed significantly among sites and species. Mean concentrations at sites where uptake was greatest were less than maximum means for the same or similar species recorded elsewhere. Harvest mice (Reithrodontomys spp.) were captured only at sites where concentrations of mercury or PCBs were below specific levels in house mice. Additional studies aimed at the protection of the salt marsh harvest mouse are suggested. These include contaminant feeding studies in the laboratory as well as field monitoring of surrogate species and community structure in salt marsh harvest mouse habitats.

Diets of Three Species of Anurans from the Cache Creek Watershed, California, USA

Abstract We evaluated the diets of three sympatric anuran species, the native Northern Pacific Treefrog, Pseudacris regilla, and Foothill Yellow-Legged Frog, Rana boylii, and the introduced American Bullfrog, Lithobates catesbeianus, based on stomach contents of frogs collected at 36 sites in 1997 and 1998. This investigation was part of a study of mercury bioaccumulation in the biota of the Cache Creek Watershed in north-central California, an area affected by mercury contamination from natural sources and abandoned mercury mines. We collected R. boylii at 22 sites, L. catesbeianus at 21 sites, and P. regilla at 13 sites. We collected both L. catesbeianus and R. boylii at nine sites and all three species at five sites. Pseudacris regilla had the least aquatic diet (100% of the samples had terrestrial prey vs. 5% with aquatic prey), followed by R. boylii (98% terrestrial, 28% aquatic), and L. catesbeianus, which had similar percentages of terrestrial (81%) and aquatic prey (74%). Observed predation by L. catesbeianus on R. boylii may indicate that interaction between these two species is significant. Based on their widespread abundance and their preference for aquatic foods, we suggest that, where present, L. catesbeianus should be the species of choice for all lethal biomonitoring of mercury in amphibians.