High-Altitude POPs and Alpine Predators

Studies of glacial ice cores and fish caught in alpine lakes in the Rocky Mountains show that levels of persistent organic pollutants (POPs) generally increase with elevation, and that many small lakes and reservoirs fed by glacial runoff contain concentrations high enough to affect wildlife at the top of the food chain.

Chemical contaminants invade these seemingly pristine environments because they can move long distances in the atmosphere. Prevailing winds carry them to colder climates, where they condense out and are trapped in the snow or ice until they are released into the ecosystem in the spring melt. To determine the degree to which domestic and international sources are contributing to increased levels of high-altitude contamination, and how POPs bioaccumulate in organisms and are passed up through the food web, scientists at Environment Canada are measuring contaminants in Osprey eggs and nestling blood samples, and in their fish diet.

Since the birds are migratory, satellite transmitters are also being attached to Ospreys with elevated contaminant concentrations in their eggs so they can be tracked to their wintering sites in Central America. Mexican biologists are assisting in locating the birds, determining their feeding areas and diet, and collecting fish samples for analysis. The three-year study, funded by the federal Toxic Substances Research Initiative, is part of a broader effort to detect human and wildlife health concerns through fish sampling.

Ospreys are being used as an indicator species for several reasons. First, because these large raptors feed exclusively on fish, they are directly exposed to pollutants in the aquatic ecosystem. Second, they are a common breeding species in British Columbia, where the study is taking place, and typically lay an extra egg that is rarely fledged and can therefore be removed with minimal effect. They are also sensitive to the effects of chlorinated hydrocarbons such as pesticides on shell quality and embryonic viability, as proven in earlier studies of the impacts of contaminants on breeding success. Osprey eggs collected from 120 nesting sites in the Columbia and Fraser drainage basins between 1991 and 1997 showed that roughly a quarter had concentrations of the pesticide DDE that exceeded four parts per million: the threshold associated with reduced hatching success.

The sites for the current study include lakes and drainage areas at a wide range of altitudes, as well as sites with known agricultural outputs, such as the South Okanagan. Over the past two summers, fish sampling has progressed as planned, and eggs have been collected from some 50 nests at low and mid altitudes, as well as some high-altitude glacial lakes in the Rocky Mountains and reservoirs on the Upper Columbia River. Unfortunately, this year's very cold, wet spring caused many nest failures and poor productivity, particularly at high elevations, so fewer eggs were collected from these key sites than planned. The absence of chicks also made it more difficult to lure adults to their nests for trapping and tagging, and only three of five transmitters were successfully deployed.

Despite these difficulties, data have yielded some interesting results. One is that, so far, the fish with the highest contaminant concentrations-including any caught in Mexico-are from tiny lakes at the highest altitudes of the Rockies' Selkirk Mountains. Another is that a surprising concentration of DDE has been detected in Ospreys in some glacial-fed reservoirs and in areas like the South Okanagan, where past pesticide use was heavy.

Next summer, Environment Canada scientists hope to sample more nests at high-altitude lakes, attach more transmitters, and ensure that samples of Osprey eggs, nestling blood, and prey fish are taken from common sites. This will mean collecting more fish at sites where Osprey nests have already been found, and possibly installing Osprey nest platforms on lakes with contaminated fish. The study may also expand to the mountainous areas of the south-west Yukon, where fish have already been shown to have relatively high levels of chemical contamination.

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