Daniel Cushing | Geology Reports

USGS2018

Timelines and mechanisms of wildlife population recovery following the Exxon Valdez oil spill

Research and monitoring activities over the 28 years since the T/V Exxon Valdez ran aground and spilled oil into Prince William Sound, Alaska have led to an improved understanding of how wildlife populations were damaged, as well as the mechanisms and timelines of recovery. A key finding was that for some species, such as harlequin ducks and sea otters, chronic oil spill effects persisted for at least two decades and were a larger influence on population dynamics over the long term than acute effects of the spill. These data also offer insights into population variation resulting from factors other than the oil spill. For example, while many seabirds experienced direct and indirect effects of the spill, population trajectories of some piscivorous birds, including pigeon guillemots and marbled murrelets, were linked to long-term environmental changes independent of spill effects. Another species, killer whales, suffered population declines due to acute spill effects that have not been resolved despite lack of chronic direct effects, representing a novel pathway of long-term injury. The observed variation in mechanisms and timelines of recovery is linked to species specific life history and natural history traits, and thus may be useful for predicting population recovery for other species following other spills.

Alaska↗

USGS2017

Patterns of distribution, abundance, and change over time in a subarctic marine bird community

Over recent decades, marine ecosystems of Prince William Sound (PWS), Alaska, have experienced concurrent effects of natural and anthropogenic perturbations, including variability in the climate system of the northeastern Pacific Ocean. We documented spatial and temporal patterns of variability in the summer marine bird community in relation to habitat and climate variability using boat-based surveys of marine birds conducted during the period 1989–2012. We hypothesized that a major factor structuring marine bird communities in PWS would be proximity to the shoreline, which is theorized to relate to aspects of food web structure. We also hypothesized that shifts in physical ecosystem drivers differentially affected nearshore-benthic and pelagic components of PWS food webs. We evaluated support for our hypotheses using an approach centered on community-level patterns of spatial and temporal variability. We found that an environmental gradient related to water depth and distance from shore was the dominant factor spatially structuring the marine bird community. Responses of marine birds to this onshore-offshore environmental gradient were related to dietary specialization, and separated marine bird taxa by prey type. The primary form of temporal variability over the study period was monotonic increases or decreases in abundance for 11 of 18 evaluated genera of marine birds; 8 genera had declined, whereas 3 had increased. The greatest declines occurred in genera associated with habitats that were deeper and farther from shore. Furthermore, most of the genera that declined primarily fed on pelagic prey resources, such as forage fish and mesozooplankton, and few were directly affected by the 1989 Exxon Valdez oil spill. Our observations of synchronous declines are indicative of a shift in pelagic components of PWS food webs. This pattern was correlated with climate variability at time-scales of several years to a decade.

Alaska↗