As of 2012, European shags nesting in areas oiled during the Prestige incident in 2002 were still rearing fewer chicks to fledging than shags in colonies not affected by the spill. Chronic exposure to residual oil and reduced food resources are suggested as possible reasons for this.
The study is one of the few done to assess the impacts of oil on wildlife where pre-spill data is available. Shag colonies along the coast of northwest Spain were being monitored starting in 1994, eight years prior to the Prestige oil spill which occurred in 2002. This allows for comparison of pre- and post-spill information on factors affecting the colony.
In the 18 years of the study more than six colonies were monitored on a regular basis. Prior to the spill reproductive levels were similar in the oiled and unoiled areas. In the first five years after the spill, however, shags in the oil-affected colonies had a 70% lower reproductive success rate, as measured by number of chicks surviving to fledging. Over the course of the study, reproductive rates remained 40% lower for oil-affected colonies.
The findings of the study make sense when reviewed in conjunction with other data coming from the area, including of reports superficial and subsurface oil in the intertidal areas of several beaches on each of nine years after the spill. The oil was fingerprinted and confirmed to have originated from the Prestige. Tar balls, also confirmed from this tanker. Another study (Velando, 2005) found that populations of a primary food source, sand eel (Ammodytes sp.), had not recovered from the spill as of 2005, suggesting another reason for continued low reproductive rates.
These findings are not surprising in light of other, older spills including the Tanker Bouchard 65 incident (Massachusetts, USA, 1974) which had continued negative impact on a local salt marsh for more than 30 years after the spill and the Exxon Valdez (Alaska, USA, 1989) where long term monitoring has shown that orca and five avian species affected by the spill are not yet considered recovered after 25 years.
Resources:
Barros, A´, A´lvarez D, Velando A. 2014 Long-term reproductive impairment in a seabird after the Prestige oil spill. Biol. Lett.10: 20131041. dx.doi.org/10.1098/rsbl.2013.1041
Bernabeu, A.M. 2013. Recurrent arrival of oil to Galician coast: The final step of the Prestige deep oil spill. Journal of Hazardous Materials 250-251:82-90. dx.doi.org/10.1016/j.hazmat.2013.01.057
Peacock, E. E.; Hampson, G. R.; Nelson, R. K.; Xu, L.; Frysinger, G. S.; Gaines, R. B.; Farrington, J. W.; Tripp, B. W.; Reddy, C. M. 2007. The 1974 spill of the Bouchard 65 oil barge: Petroleum hydrocarbons persist in Winsor Cove salt marsh sediments. Mar.Pol.Bul. 54(2)214-225 dx.doi.org/10.1016/jmarpolbul.2006.10.007
Velando, A., Munilla, I. & Leyenda, P.M. (2005). Short-term indirect effects of the Prestige oil spill on European shags at Illas Cíes (Galicia, Spain): changes in prey availability. Mar. Ecol. Prog. Ser., 302:263-274.