Abstract-Research was conducted at the University of Idaho

Productivity of naturally spawning salmon populations is sometimes estimated by sampling incubating eggs from the spawning grounds to assess survival by pumping water or an air-water mixture into the stream gravel and collecting eggs displaced by the resulting agitation. General knowledge regarding embryo sensitivity to physical shock indicates that this procedure may kill eggs if conducted before embryo development has advanced beyond blastopore closure, which is up to day 12 postfertilization. In 1998, we assessed the impact of sample timing on egg mortality estimates of pink salmon Oncorhynchus gorbuscha in 10 spawning streams in Prince William Sound, Alaska, by hydraulically sampling the same streams in September and again in October. The mean egg mortality was significantly higher in the early sampling period (63.6%) than in the later sampling period (22.8%). Results from examining stage of advancement at the time of embryo death indicate that sampling with hydraulic techniques will elevate mortality among embryos that have advanced in development up to the early eyed stage, corresponding to day 20 in embryo development or approximately 50% longer than previously thought. To avoid induced embryo fatality, the sampling protocol should delay assessment of spawning ground survival until sufficient time has past to assure that the most recently spawned eggs have progressed well into the eye pigmentation stage.

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Abstract-It has been hypothesized that pink salmon eggs incubating in intertidal streams transecting Prince William Sound (PWS) beaches oiled by the Exxon Valdez oil spill were exposed to lethal doses of dissolved hydrocarbons. Since polycyclic aromatic hydrocarbon (PAH) levels in the incubation gravel were too low to cause mortality, the allegation is that dissolved high-molecularweight hydrocarbons (HPAH) leaching from oil deposits on the beach adjacent to the streams were the source of toxicity. To evaluate this hypothesis, we placed pink salmon eggs in PWS beach sediments containing residual oil from the Exxon Valdez oil spill and in control areas without oil. We quantified the hydrocarbon concentrations in the eggs after three weeks of incubation. Tissue PAH concentrations of eggs in oiled sediments were generally Ͻ100 ppb and similar to background levels on nonoiled beaches. Even eggs in direct contact with oil in the sediment resulted in tissue PAH loads well below the lethal threshold concentrations established in laboratory bioassays, and very low concentrations of HPAH compounds were present. These results indicate that petroleum hydrocarbons dissolved from oil deposits on intertidal beaches are not at concentrations that pose toxic risk to incubating pink salmon eggs. The evidence does not support the hypothesis that interstitial pore water in previously oiled beaches is highly toxic.

In the tenth year following the Exxon Valdez oil spill, differences of opinion still exist about injuries to pink salmon. It was alleged that exposure to oil reduced growth of fry and induced mortality in eggs. The authors reexamined the allegation that injury occurred and have concluded that insufficient consideration was given to other factors that affected results in the studies from which these allegations were drawn. The inability to track temperature differences and the unknown ages of fry precluded assessment of oil effects on growth during early marine residence. Reported higher egg mortality and long-term injury alleged to have resulted from oil exposure during incubation were confounded by the mortality of eggs that occurred as an artifact of the sampling procedure, unrelated to oil effects. The authors concluded that injury to incubating pink salmon embryos and reduced fry growth were based on an incomplete assessment of other factors that influenced these results. This evidence is supported by other research that has disclosed no oil effects on incubating eggs. Among these were studies that showed measured oil concentrations reaching the incubation substrate were 14 to 7,600 times below the lethal threshold. The seven largest runs in the history of Prince William Sound (PWS), Alaska have returned in the 10 years following the spill, which ultimately demonstrated the lack of measurable effect of the oil spill on pink salmon. The authors suggest that the allegation of oil-induced injury to PWS pink salmon needs to be reconsidered in light of these analyses.

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