skip to main content

Search for: All records

Creators/Authors contains: "Fisher, Nicholas S."

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. The importance of fish consumption as the primary pathway of human exposure to mercury and the establishment of fish consumption advisories to protect human health have led to large fish tissue monitoring programs worldwide. Data on fish tissue mercury concentrations collected by state, tribal, and provincial governments via contaminant monitoring programs have been compiled into large data bases by the U.S. Environmental Protection Agency’s Great Lakes National Monitoring Program Office (GLNPO), the Ontario Ministry of the Environment’s Fish Contaminants Monitoring and Surveillance Program (FMSP), and many others. These data have been used by a wide range of governmental and academic investigators worldwide to examine long-term and recent trends in fish tissue mercury concentrations. The largest component of the trend literature is for North American freshwater species important in recreational fisheries. This review of temporal trends in fish tissue mercury concentrations focused on published results from freshwater fisheries of North America as well as marine fisheries worldwide. Trends in fish tissue mercury concentrations in North American lakes with marked overall decreases were reported over the period 1972–2016. These trends are consistent with reported mercury emission declines as well as trends in wet deposition across the U.S. and Canada. More recently, amore »leveling-off in the rate of decreases or increases in fish tissue mercury concentrations has been reported. Increased emissions of mercury from global sources beginning between 1990 and 1995, despite a decrease in North American emissions, have been advanced as an explanation for the observed changes in fish tissue trends. In addition to increased atmospheric deposition, the other factors identified to explain the observed mercury increases in the affected fish species include a systematic shift in the food-web structure with the introduction of non-native species, creating a new or expanding role for sediments as a net source for mercury. The influences of climate change have also been identified as contributing factors, including considerations such as increases in temperature (resulting in metabolic changes and higher uptake rates of methylmercury), increased rainfall intensity and runoff (hydrologic export of organic matter carrying HgII from watersheds to surface water), and water level fluctuations that alter either the methylation of mercury or the mobilization of monomethylmercury. The primary source of mercury exposure in the human diet in North America is from the commercial fish and seafood market which is dominated (>90%) by marine species. However, very little information is available on mercury trends in marine fisheries. Most of the data used in the published marine trend studies are assembled from earlier reports. The data collection efforts are generally intermittent, and the spatial and fish-size distribution of the target species vary widely. As a result, convincing evidence for the existence of fish tissue mercury trends in marine fish is generally lacking. However, there is some evidence from sampling of large, longlived commercially-important fish showing both lower mercury concentrations in the North Atlantic in response to reduced anthropogenic mercury emission rates in North America and increases in fish tissue mercury concentrations over time in the North Pacific in response to increased mercury loading.« less
  2. Abstract

    Because seawater temperature is correlated with viscosity, temperature changes may impact small zooplankton through a mechanical pathway, separately from any thermally-induced effects on metabolism. We evaluated both viscous and thermal effects on copepod feeding in experiments where viscosity was manipulated separately from temperature using a non-toxic polymer. Two copepod species, Acartia tonsa and Parvocalanus crassirostris, feeding on two monoalgal diets (a diatom and a dinoflagellate) were compared. At constant temperature, increase in viscosity nearly always reduced feeding; at constant viscosity, changes in temperature had no effect on feeding. The effects of viscosity and temperature were more pronounced for the diatom than the flagellate prey. Overall, reductions in zooplankton feeding at cold temperatures can be explained primarily by the mechanical effect of viscosity. Q10 values for copepod feeding (1.0–7.9), calculated from the present data and from the literature, were generally higher and more variable than Q10 values from the literature for copepod respiration (1.5–3.1) indicating that, at cold temperatures, feeding is more dramatically suppressed than metabolism. We conclude that (i) high viscosity may inhibit copepod feeding, and (ii) this viscous effect on feeding (rather than a thermal effect on metabolism) may influence the cold-temperature bounds of zooplankton populations.