Quantifying Temporal Variation in Harlequin Duck Cytochrome P4501A Induction, Prince William Sound, Alaska (1998-2002) - [UNFORMATTED]

CYP1A has been used widely as an indicator of exposure of vertebrates to polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), and the use of EROD activity as a measure of CYP1A has been validated and accepted as a standard method. EROD activity has been used since 1998 as an indicator of the degree of exposure of harlequin ducks to residual Exxon Valdez oil in Prince William Sound, Alaska. These data have proven to be extremely valuable for understanding the processes by which population recovery of harlequin ducks has been constrained following the Exxon Valdez oil spill. EROD activity data were collected in 1998, 2000, 2001, 2002, and 2005 from wintering harlequin ducks captured in Prince William Sound; one reason for collecting these data was to provide a time series with which changes in exposure could be tracked over years. However, the data reported from the laboratory varied dramatically in magnitude from year to year, to a degree far beyond what could be expected due to normal biological variation. Similar variation was observed across years in harlequin ducks held at the Alaska SeaLife Center under strictly controlled circumstances. Therefore, this project was initiated to determine the explanation for this interannual variation, and to apply laboratory analyses and data standardization to allow valid interannual comparisons. Additional data analysis of EROD activity of wintering harlequin ducks captured in Prince William Sound in 2005 through 2007 confirmed that individual attributes (age, sex, and mass) and season of capture did not explain observed variation in EROD activity. In review of the originally reported EROD values, it was discovered that some data were reported in incorrect units. However, even after these were corrected, the large interannual discrepancies were not completely resolved. Other potential factors, such as low protein yields, were considered; exclusion of samples with low protein values, along with application of appropriate units, considerably reduced interannual variation, although differences were still apparent that reduced confidence in interannual comparisons. EROD reanalysis of old samples resulted in data that were correlated (R2 = 0.53) with original data, but values were considerably different in magnitude, possibly as a result of sample degradation or annually varying lab techniques or equipment. Also, not all individuals had adequate sample volume remaining for reanalysis, reducing the power for detecting differences across areas and years if only reanalyzed data were used. In consultation with the laboratory, it was concluded that changes in analysis approaches and equipment may have led to the observed interannual differences and that, although within-year comparisons between areas were valid, between-year comparisons were not appropriate without corrections. Therefore, a method indexing CYP1A values was created that allows for interannual contrasts, in which average EROD activity for harlequin ducks captured at our unoiled/control area (Montague Island) is set to 1 for each year and all values are adjusted accordingly within
the same sample year. Therefore, for each year, the average indexed EROD activity for
birds from oiled areas is a ratio of oiled to unoiled averages. The average indexed values
can be compared across years to consider annual changes in oil exposure, under the
assumption that oil exposure at unoiled Montague Island was the same across years.
Further, the indexed values can be calculated for each individual, which allows
consideration of relationships between individual variation in oil exposure and variation
in survival.