Contaminants and Common Murre Die-Offs

Investigation of Persistent Seabird Mortalities along the Oregon Coast

Summary

Photo - Collection (USFWS).From 1978 until 1997, Oregon experienced large annual die-offs of common murres (Uria aalge) from July to October. The mortality was predominantly among juveniles, but adults were impacted as well. Juvenile common murres require extensive parental care for several months, both at the colony site and at sea. At this stage they are vulnerable to natural and anthropogenic disturbances as well as changes in nearshore marine productivity. Given the vulnerability of birds at this age, exposure to contaminants may increase seabird mortality. However, aside from large oil spills, there was little information as to the potential contribution of contaminants to the annual die-offs.

In addition to annual die-offs, Oregon common murres experienced some of their worst reproductive seasons on record during that time. Poor reproduction coupled with high mortality could have serious impacts on the stability of common murre breeding populations in Oregon and elsewhere.

The primary objectives of this study were to determine concentrations of contaminants in common murres during the annual die-off, assess the importance of contaminants as causative agents in the die-off, and identify potential sources and pathways of these contaminants.

Concentrations of inorganic and organic compounds in common murres were not life threatening. However, murres are accumulating some inorganic and organic contaminants to low concentrations that may have sublethal effects. In addition, blood analyses and necropsy results were not suggestive of contaminant exposure or significant disease, but they provided further evidence that starvation from limited food resources is likely a significant contributor to die-off events.Photo - Necropsy (USFWS).

The tissue residue analyses suggest that common murres in Oregon are likely exposed primarily to non-point source pollutants (e.g., those from land runoff or atmospheric deposition), which are not readily controlled through direct management actions. Consequently, the only management recommendation from this study is to continue ongoing efforts in Oregon to decrease stress on common murres from disturbance (boats, aircraft, and people) which increase the potential for breeding colony abandonment and cause general stress that may exacerbate the effects of limited food resources, low levels of environmental contaminants, minor disease events, or any combination of these factors.


Report

Investigation of Persistent Seabird Mortalities along the Oregon Coast
(Dec. 2011)