Long Term Impacts of the Exxon Valdez Oil Spill on Embryonic Pink Salmon Resulted in Population Effects

Elevated pink salmon embryo mortalities were detected in 1989; not surprising given that beaches were heavily oiled for months following the spill.  However, ADFG continued to detect  elevated embryo mortalities for four years past the spill.  This was surprising in that oil was never visible in the spawning gravels, and was no longer visible on the banks of streams that crossed the oiled beaches.   A series of laboratory exposures confirmed that long-term low-level exposure of embryos to oil will result in mortalities and sublethal effects that decrease adult returns- thus corroborating the field observations.  Mortalities and edema were caused by exposures and were most evident at hatching.  Sublethal exposures can result in impacts on fitness and decreases in adult returns;  healthy appearing embryos exposed to low doses of oil and controls were coded-wire tagged and released to the environment for evaluation when adults returned 1.3 years later.  Doses as low as 5 parts per billion PAH (polycyclic aromatic hydrocarbons) caused a 20% decrease in adult returns.  Tests repeated in other brood years confirmed these results.  The results indicated that embryos are particularly sensitive to low parts per billion PAH—about three orders of magnitude more sensitive than short-term toxicity tests from the 1970s had predicted.  The controlled laboratory exposure tests, with releases to the environment, confirmed the low doses of oil can cause hard to detect effects that will result in population level effects.