Spatial and Oceanographic Factors Affecting Black-Legged Kittiwake and Thick-Billed Murre Distributions in the Southeastern Bering Sea
Master's Thesis (Open Access)
Master of Science (M.S.)
Moss Landing Marine Laboratories
James T. Harvey
The distribution patterns of Thick-billed Murres (Uria lomvia) and Black-legged Kittiwakes (Rissa tridactyla) in the southeastern Bering Sea were documented at sea during vessel-based surveys in July-August of 2008 and 2009. The relationships of murre and kittiwake densities with environmental variables were investigated using binomial generalized additive models (GAMs) to model the presence or absence of birds, and Gamma-error distribution GAMs to model the positive densities of birds. Environmental variables included oceanographic factors (Chlorophyll, Chlorophyll anomalies, Daily SST, Monthly SST), spatial factors (Distance to nearest colony, Distance to 300m shelf break, Depth), and a temporal factor (Year). Nocturnal surveys were also conducted in 2009 using a novel surveying protocol to quantify changes in seabird distribution patterns between day and night. Diurnal and nocturnal transects were modeled with environmental variables and acoustically derived measures of prey abundance, to investigate whether birds associated with different regions or food types between day or night. The association of murres with habitat variables did not differ greatly between years, and variability in murre distributions was primarily explained by spatial factors. When pooled between years, murres sighted closest to St. Paul were positively associated with chlorophyll concentrations and with the proximity to their colony, whereas murres from St. George were positively associated with the proximity to their colony, chlorophyll concentration, and a monthly sea surface temperature of 7° Celsius. In contrast, the association of kittiwakes with habitat variables differed significantly between year and when categorized by closest colony. In 2008, kittiwake densities were not strongly associated with any variables, but were most closely related to oceanographic conditions. In 2009, kittiwake sightings were more concentrated along the shelf break and northwest of St. Paul Island over the continental shelf. Kittiwakes sighted nearest to St. George were significantly associated with shelf break habitat in both years, whereas kittiwakes sighted nearest St. Paul were more closely associated with middle shelf habitat northwest of St. Paul. The distribution of murres did not differ between day and night, but kittiwake distributions shifted to deeper water at night. Kittiwakes were positively associated with juvenile walleye pollock abundance in the top 100m during the day, but were not clearly associated with pollock at night. The nocturnal distribution of kittiwakes over deep water and near the shelf break may have reflected other nearby prey resources (myctophids, smoothtongue) that were not well-quantified. In conclusion, 2008 and 2009 were both similar “cold” environmental years during which murres appeared to use consistent foraging patterns, whereas kittiwakes associated with different habitat variables between years and frequented distinct foraging areas between day and night.
Hoover, Brian, "Spatial and Oceanographic Factors Affecting Black-Legged Kittiwake and Thick-Billed Murre Distributions in the Southeastern Bering Sea" (2012). Capstone Projects and Master's Theses. 235.
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