title: Evaluating signals of oil spill impacts, climate, and species interactions in Pacific herring and Pacific salmon populations in Prince William Sound and Copper River, Alaska.
abstract: The Exxon Valdez oil spill occurred in March 1989 in Prince William Sound, Alaska, and was one of the worst environmental disasters on record in the United States. Despite long-term data collection over the nearly three decades since the spill, tremendous uncertainty remains as to how significantly the spill affected fishery resources. Pacific herring (Clupea pallasii) and some wild Pacific salmon populations (Oncorhynchus spp.) in Prince William Sound declined in the early 1990s, and have not returned to the population sizes observed in the 1980s. Discerning if, or how much of, this decline resulted from the oil spill has been difficult because a number of other physical and ecological drivers are confounded temporally with the spill; some of these drivers include environmental variability or changing climate regimes, increased production of hatchery salmon in the region, and increases in populations of potential predators. Using data pre- and post-spill, we applied time-series methods to evaluate support for whether and how herring and salmon productivity has been affected by each of five drivers: (1) density dependence, (2) the EVOS event, (3) changing environmental conditions, (4) interspecific competition on juvenile fish, and (5) predation and competition from adult fish or, in the case of herring, humpback whales. Our results showed support for intraspecific density-dependent effects in herring, sockeye, and Chinook salmon, with little overall support for an oil spill effect. Of the salmon species, the largest driver was the negative impact of adult pink salmon returns on sockeye salmon productivity. Herring productivity was most strongly affected by changing environmental conditions; specifically, freshwater discharge into the Gulf of Alaska was linked to a series of recruitment failures-before, during, and after EVOS. These results highlight the need to better understand long terms impacts of pink salmon on food webs, as well as the interactions between nearshore species and freshwater inputs, particularly as they relate to climate change and increasing water temperatures.
authors.affiliation: Conservation Biology Division, Northwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Seattle Washington, United States of America.
authors.forename: Eric J
authors.identifier: http://orcid.org/0000-0002-4359-0296
authors.initials: EJ
authors.lastname: Ward
authors.affiliation: School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Juneau, Alaska, United States of America.
authors.forename: Milo
authors.initials: M
authors.lastname: Adkison
authors.affiliation: National Center for Ecological Analysis and Synthesis, Santa Barbara, California, United States of America.
authors.forename: Jessica
authors.initials: J
authors.lastname: Couture
authors.affiliation: Alaska Department of Fish and Game, Division of Commercial Fisheries, Juneau, Alaska, United States of America.
authors.forename: Sherri C
authors.initials: SC
authors.lastname: Dressel
authors.affiliation: Farallon Institute for Advanced Ecosystem Research, Petaluma, California, United States of America.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Litzow
authors.affiliation: Alaska Department of Fish and Game, Division of Commercial Fisheries, Cordova, Alaska, United States of America.
authors.forename: Steve
authors.initials: S
authors.lastname: Moffitt
authors.affiliation: Kasitsna Bay Laboratory, National Ocean Service, National Oceanic and Atmospheric Administration, Homer, Alaska, United States of America.
authors.forename: Tammy
authors.initials: T
authors.lastname: Hoem Neher
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington, United States of America.
authors.forename: John
authors.initials: J
authors.lastname: Trochta
authors.affiliation: Alaska Department of Fish and Game, Division of Commercial Fisheries, Juneau, Alaska, United States of America.
authors.forename: Rich
authors.initials: R
authors.lastname: Brenner
mesh_terms: D000818:Animals; D005399:Fishes / Q000502:physiology*; D012474:Salmon / Q000502:physiology*; D013045:Species Specificity