The assessment of cause is a complex process during resource damage assessments because there are a range of anthropogenic and environmental factors contributing to adverse biological responses in urban estuaries. After the San Francisco Bay Cosco Busan oil spill in 2007, three years of field and laboratory data were compiled using Pacific herring (Clupea pallasi) as an indicator species. Pacific herring were chosen for this program because they have been used to document oil exposure for other programs and they spawn seasonally in San Francisco bay and could have been subjected to any lingering oil effects present after cleanup efforts were completed. The three-year study was focused on demonstrating whether Cosco Busan oil (CBO) or components of the fuel oil were the cause of adverse developmental effects or if other environmental factors may have contributed to the developmental defects observed in the naturally spawned larvae from 2008 just three months after the oil spill.
EcoAnalysts personel performed a secondary assessment of data collected in 2008 and 2009 by the natural resource trustees. A review of the 2008 and 2009 data indicated that early life stage abnormalities were likely due to environmental factors present during embryo development.
To demonstrate the effects of the environmental factors during the 2008 herring spawn, EcoAnalysts performed a laboratory simulation of the observed field conditions including temperature and salinity fluctuations, ultraviolet light exposure, donor gamete condition, and aerial exposure during extreme tidal conditions.
An assessment framework was used to examine the data collected over the three-year effort to determine probable cause of observed abnormalities. The outcome of the analysis concluded that CBO was not the primary cause of disrupted development in naturally spawned herring from 2008. There was no CBO signature present in embryos spawned in 2008 and collected from the intertidal areas. The chemical exposure signature was consistent with urban background and burned wood or creosote. Further the types of effects observed in 2008 namely a high incidence of yolk sac impairment and a low incidence of pericardial edema were consistent with outcome of the non-chemical environmental stressor study of 2010. The comparable responses between the 2008 and 2010 studies indicate that the combination of fluctuating temperature and salinity, UV exposure, quality of the donor gametes and aerial stranding during low tide events contributed significantly to the developmental defects observed in the naturally spawned herring embryos from the 2008 spawning season.