Why aren't pigeon guillemots in Prince William Sound, Alaska recovering from the Exxon Valdez oil spill?

• Main Author: Bixler, Kirsten S.
• Other Authors: Roby, Daniel D., Betts, Matthew G., Suryan, Robert M., Fisheries and Wildlife, Oregon State University. Graduate School
• Format: Master Thesis
• Language: English; unknown
• Published: Oregon State University
• Subjects: Minks > Food > Alaska > Prince William Sound; Pigeon guillemot > Effect of oil spills on > Alaska > Prince William Sound; Exxon Valdez Oil Spill; Alaska; 1989 > Environmental aspects; Predation (Biology) > Alaska > Prince William Sound; Pigeon guillemot > Mortality > Alaska > Prince William Sound; Pigeon guillemot > Predators of > Alaska > Prince William Sound; Smith Island
• Online Access: https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rb68xg25k

The Pigeon Guillemot (Cepphus columba) is now the only species of marine bird in Prince William Sound (PWS), Alaska that is listed as "not recovering" on the Exxon Valdez Oil Spill (EVOS) Trustee Council's Injured Resources List and has shown no sign of population recovery. During the 20 years since EVOS, the guillemot population in PWS has gradually declined by nearly 50% following the initial mortality event caused by direct contact with spilled oil. This decline has continued even though there is no longer evidence that guillemots are negatively affected by residual oil from EVOS. My objectives in this study were to (1) identify the primary factor now limiting Pigeon Guillemot population recovery at the Naked Island group, the most important historical breeding area for guillemots in PWS, and (2) determine whether guillemot population trends across PWS are consistent with my understanding of the primary limiting factor. I investigated two competing hypotheses for the lack of guillemot recovery at the Naked Island group: availability of high quality prey (i.e., schooling forage fish) and nest predation. The prevalence of schooling forage fish in the diet of Pigeon Guillemots at the Naked Island group has not recovered to pre- EVOS levels. However, data from both aerial surveys and beach seines provided evidence of an increase in abundance of schooling forage fish near the Naked Island group since the late 1990s. Yet between 1990 and 2008, there was a precipitous 12% per annum decline in the guillemot population at the Naked Island group, where mink are present, while at the nearby mink-free Smith Island group guillemot numbers were stable. The mortality rate of guillemot eggs and chicks at the Naked Island group was high during the late 1990s, largely attributable to predation by mink. The weight of evidence indicates that predation by mink is now the primary factor limiting the reproductive success and population recovery of Pigeon Guillemots at the Naked Island group. Differences in guillemot population ...