The effects of exposure of incubating adult and young herring gulls to a simulated no. 2 fuel oil slick

Naturally incubating herring gulls (Larus argentatus) were exposed to No. 2 fuel oil. The gulls were treated either early (seven to ten days after clutch completion) or late (when the second egg of the clutch reached the pip stage) in incubation. Hatching success of eggs of adults oiled early in incubation was reduced at 321 ml oil/m² and survival of young to seven days post-hatch was reduced at both 107 and 321 ml/m². This decrease in survival at 107 ml/m² suggests that a concentration of oil which is not lethal to the embryos may have a sublethal effect which reduces chick viability. When adults were oiled late in incubation, the only effect noted was decreased hatching success at 321 ml/m². Chicks between five and nine days of age which were exposed to an artificial slick of 321 ml No. 2 fuel oil/m² exhibited decreased survival to seven days post-treatment. Since 107 ml/m² is more than 20 times the maximum thickness of No. 2 fuel oil slicks which have been measured on the Great Lakes, a single exposure of an adult at the incubation stages tested or of a young chick to a free-floating oil slick would probably not cause a significant reduction in hatching success or survival of young. The effects of repeated exposure to a fresh fuel oil slick are unknown.