Pirouette above the sea,
dive fast on pleated wing
Sand lance for a meal
Why are we sampling?
Almost 30,000 dead marine birds were recovered following the Exxon Valdez oil spill. Based on modeling studies using carcass search effort and population data, an estimated 250,000 marine birds were killed in Prince William Sound and the northern Gulf of Alaska. We are continuing to monitor these marine bird monitoring and to synthesize our data with that of other monitoring projects to help determine whether populations injured by the spill are recovering, and if not, why not, and how other environmental variables such as anomalous warm or cold periods affect populations.
Where are we sampling?
We sample throughout all marine waters of Prince William Sound. Using a stratified random sampling design, we sample three strata: shoreline (within 200 m of land), coastal-pelagic (pelagic transects that intersect land), and pelagic (offshore transects). Because 351 transects were randomly chosen, and the same transects were sampled each survey, they represent the variety of coastal and offshore habitats that occur in PWS.
How are we sampling?
We conduct surveys in three strata every other year during the month of July, using three fiberglass boats traveling at low speeds (6-12 mph) to survey the area over a three-week period. Two observers and a boat operator record all marine birds and marine mammals within the transect “window” (100 m either side of the boat). Each team records species, numbers, and behavioral observations directly into a computer, which also records location (latitude and longitude) and environmental conditions. Having exact location information allows us to later overlay our observations and track lines with habitat data such as bathymetry, as well as satellite data on sea surface temperature and salinity.
What are we finding?
Marine bird communities in Prince William Sound are spatially primarily structured along a primary onshore-offshore environmental gradient and secondarily structured along an estuarine-marine environmental gradient. Abundance estimates for both marbled murrelets and Kittlitz’s murrelets decreased by more than two-thirds between 1989 and 2012 and the density (birds/km2) of marbled and Kittlitz’s murrelets continued a long-term pattern of decline through 2018. Additionally, densities of pigeon guillemots continue to decrease sound wide, even with the gradual increase in pigeon guillemots at the Naked Island group, where predator control has been successful. Also notable, complete or nearly-complete breeding failures of black-legged kittiwakes occurred in Prince William Sound 2016-2018 and kittiwake density has trended downward during the same period.