Sunday, 27 February 2011

Injury to the early life history stages of Pacific herring in Prince William Sound after the Exxon Valdez oil spill

PROCEEDINGS OF THE EXXON VALDEZ OIL SPILL SYMPOSIUM. pp. 448-462. American Fisheries Society Symposium. Vol. 18. 

The Exxon Valdez oil spill occurred a few weeks before Pacific herring Clupea pallasi spawned in Prince William Sound. About half of the egg biomass was deposited within the oil trajectory, and an estimated 40 to 50% sustained oil exposure during early development. The resulting 1989 year-class displayed sublethal effects in newly hatched larvae, primarily premature hatch, low weights, reduced growth, and increased morphologic and genetic abnormalities. Genetic endpoints, especially anaphase aberration rates, were highly correlated with site-specific Exxon Valdez oil concentrations. Responses were specific and sensitive to this oil exposure. In newly hatched larvae, anaphase aberration rates were elevated at oiled sites, and in pelagic larvae genetic damage was greatest near oiled areas of southwestern Prince William Sound. Genetic damage in larvae from oiled areas progressively decreased during the 6-week study, but site-specific measures of instantaneous mortality suggest that a significant reduction (52.3%) in larval production occurred in 1989. Although approximately equal egg biomass was deposited in non-oiled and oiled areas, we estimated that oiled areas produced only 0.016 x 10 super(9) pelagic larvae compared with 11.82 x 10 super(9) non-oiled areas. Despite the estimated substantial decrease in larval production, reduced abundance in the 1989-year class recruiting as 4-year-old adults in 1993 could not be estimated because natural processes affecting recruitment are poorly understood; however, the 1989 year-class was a minority of the 1993 spawning population, one of the smallest cohorts observed in Prince William Sound, and it returned to spawn with an adult herring population reduced by approximately 75%, apparently because of a