8/9/2019 Pigeon Guillemots Are NOT Recovering From the Exxon Valdez Oil Spill

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Pigeon Guillemots are NOT Recovering from the Exxon Valdez Oil Spill

Injury Although pigeon guillemots are widely distributed in the North Pacific region, they do not occur anywhere inlarge concentrations. An estimated 2,0006,000 guillemots, representing 1015 percent of the spill area

population, died from acute oiling. Additionally, an increase in nest predation of pigeon guillemot chicks and

incubating adult birds occurred in the Sound after the spill. Researchers speculated that immediately after thespill, predators such as river otters and minks preyed more heavily on nesting guillemots due to heavy oilingand subsequent reduction of their customary shellfish prey.

Recovery Objective Pigeon guillemots will have recovered when their population is stable. Sustained or increasing productivitywithin normal bounds will be an indication that recovery is underway.

Recovery Status Pigeon guillemot populations were likely declining prior to the spill and this decline has continued through2008. The causes of the decline are unclear and the extent to which the spill has been a factor has not been

determined. From 1989 to 1991, pigeon guillemot abundance decreased more in oiled areas than in unoiledareas, and this accelerated decrease persisted in most years through 2001. Summer surveys along both oiled andunoiled shorelines of the Sound have indicated that numbers of guillemots continued to decline through 2005.March surveys reveal no significant trends in abundance although the data appear to suggest a decline at thistime of year as well.

As of 1999, adult pigeon guillemots in the oiled areas were still being exposed to oil as indicated by elevation of a biochemical marker of exposure, cytochrome P450. No differences were found between P450 activity inchicks from oiled and unoiled sites. The difference in P450 activity between adults and chicks is probably dueto the fact that pigeon guillemot chicks are fed primarily fish, while adults eat a combination of fish andinvertebrates. Invertebrates are more likely to sequester petroleum compounds, whereas fish metabolize them.

Data collected in 2004 indicated that there was no difference in P450 activity in adult pigeon guillemotscollected in oiled and unoiled parts of the Sound.

Lingering oil occurs in habitats used by pigeon guillemots. They feed on fish and invertebrates by diving and probing the substrate with their bills. Because their diet includes benthic organisms living in the intertidal zone,they could encounter subsurface oil while foraging. However, guillemots do not use the intertidal zoneexclusively and can travel several miles offshore to feed. Thus, their exposure to lingering oil is likelyintermittent.

Reduction in forage fish, specifically herring and sand lance, has been implicated in declines of pigeonguillemots. The extent to which the oil spill resulted in the depletion of these species could indirectly injure

guillemots and other seabirds by removing the food resources on which they depend. Other factors, such as predation and interactions with commercial fisheries, might be contributing to the negative population trend;however comprehensive studies including these variables have not been conducted.

The pigeon guillemot population continues to decline in both oiled and unoiled areas of Prince William Sound. Nest predation is a potential source of mortality that may be limiting recovery in some areas, implying that predator removals could prove an effective restoration option. More data on productivity levels is needed todetermine if the recovery objective of increasing abundance and productivity has been met.

8/9/2019 Pigeon Guillemots Are NOT Recovering From the Exxon Valdez Oil Spill

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