Prey fish sampling

Mercuiy concentrations in prey fish are useful indicators of relative MeHg levels in food webs snpporting the prodnction of sport fish and wildlife, information relevant to the pnblic and the policy community. There is a sizable scientific literature on MeHg in prey fish, bnt they have been monitored less extensively than sport fish. Effects of removal sampling on target populations would be insignificant in all but the very smallest lakes. 

In summaiy, prey fish are present in most surface waters, require moderate sampling effort, are important in the trophic transfer of MeHg in aquatic food webs, and probably indicate annual changes in exposure to MeHg. Given these attributes. 

The second factor is the temporal variation in concentrations in different ecosystem compartments. For example, sediments and prey fish exhibit less temporal variation in mercuiy concentration than do air or water, and thus statistically valid estimates of their status can be collected with less frequent monitoring (e.g., annual sampling for prey fish vs. daily or hourly sampling for atmospheric concentrations of mercury). 

Freshwater mammals such as heaver may leave odors on the surface of their ponds and olfactorily sample the water or layer of air immediately above it. Lipids on water may form micelles, small blobs of molecules (from Latin mica, a grain, crumb, morsel) that enhance evaporation into the air layer by increased chemical potential. Some seahirds hunt hy odor (e.g. Hutchison and Wenzel, 1980 Nevitt, 1999). They may respond to prey volatiles (from krill, squid, or fish) that rise to the water surface and evaporate into the air. The air-water equilibrium for dilute solutions can be expressed by using partition coefficients, relative volatility, or Henry s law (Thibodeaux, 1979). 

Any effects on populations may ultimately be manifested as effects on communities because, by definition, communities are collections of interacting populations of several species (e.g., an aquatic community may consist of populations of fish, worms, plants, insects). Individual populations within a community may interact by competing for resources (food, habitat, etc.) or by predator/prey relationships. Environmental contaminants can affect the structure of communities as well as the interactions of species within them. For example, it is well known that exposure to chemicals may cause a reduction in community diversity (e.g., relative number of species), and changes in community composition. In addition, the trophic structure of fish and invertebrate communities may also be affected by exposure to anthropogenic chemicals. Changes in community structure and diversity may be determined by field sampling or manipulative studies. Alternatively, computer simulations using food web or linked population models may be used to assess community-level effects. 

A fish depends of its senses of olfaction (smell) and taste to detect chemicals that are dissolved in the water. Smell helps a fish pick up clues about prey, even when it is distant. Taste is most often used to sample the source of the smell. Taste buds can be located on the skin, on barbels, and on the tongue. The degree of sensitivity to taste depends on the type of fish and its environment for example, a fish in murky water might be more dependent on chemical... 

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