Pirouette above the sea,
dive fast on pleated wing
Sand lance for a meal
Why are we sampling?
Of the marine birds that overwinter in Prince William Sound (PWS), nine species were initially injured by the Exxon Valdez oil spill, including three species that have not yet recovered (marbled murrelet, Kittlitz’s murrelet, and pigeon guillemot). Long-term monitoring of marine birds in Prince William Sound during winter is needed to understand how post-spill ecosystem recovery and changing physical and biological factors are affecting bird abundance and species composition, as well as their distribution and habitat use.
Where are we sampling?
We conduct marine bird surveys throughout the open and nearshore waters of Prince William Sound, including in juvenile herring nursery bays such as Zaikof, Whale, Eaglek, Lower Herring, Gravina, and Simpson. These surveys provide coverage in four different quadrants of Prince William Sound.
How are we sampling?
We conduct surveys between mid-September and March following established U.S. Fish and Wildlife Service marine bird survey protocols. One observer records the number and behavior of birds and marine mammals occurring along a strip transect that is 300 meters wide (150 meters on both sides and ahead of the boat, in distance “bins” of 50 meters). Additionally, we record any noteworthy observations out to 1 kilometer on either side of the boat.
What are we finding?
We have recently examined the use of ecosystem indicators to understand the influence of environmental variability on marine bird populations in PWS. Our previous modeling efforts found that murres and murrelets demonstrate relatively consistent temporal patterns in PWS within winter; murres tend to be present in low densities during fall and high densities during spring, whereas murrelets tend to occur in low densities in early fall increasing to higher densities in late fall, and then occur in low densities during spring.
We examined anomalies in murre and murrelet densities over time as potential ecosystem indicators because, as piscivorous seabirds, murres and murrelets are particularly sensitive to changes in the marine ecosystem. Both murre and murrelet densities appear to be highly variable within months and across winters (Fig. 1). For murres, our surveys detected changes in densities and distribution in PWS during the months leading up to a prolonged die-off event that occurred along the Gulf of Alaska beginning during the winter of 2014-15 and ending in the spring of 2016. Our surveys recorded anomalously high densities in February 2015 (immediately preceding the onset of the die-off) and fall 2015 (immediately prior to the peak December 2015 die-off). This increased use of PWS by murres during the winter coincided with persistently high ocean temperatures in the Northeast Pacific Ocean beginning during the winter of 2013-14 and was strongest (with regional variability) through 2016 in the northeast Pacific, with positive temperature anomalies continuing through 2017 and 2018 in PWS (refer to Oceanographic Conditions in Prince William Sound). Since the die-off, we have observed murre densities below the long-term monthly averages during fall 2016-2018 surveys and spring 2018 surveys. Murrelet densities followed a similar pattern as murres and were also below long-term monthly averages for fall 2016-2018 and spring 2018.