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Distribution and oceanographic habitats of non-breeding Ardenna shearwaters within the northern California Current: combining environmental predictors with satellite telemetry and at-sea densities

Released: 2016
Citation:
Adams, J, J Felis, J Broughton, B Henry, P Hodum, JT Harvey, D Pereksta. 2016. Distribution and oceanographic habitats of non-breeding Ardenna shearwaters within the northern California Current: combining environmental predictors with satellite telemetry and at-sea densities. 6th International Albatross and Petrel Conference (IPAC6), Barcelona, Spain. 19-23 September 2016. [presentation]

During the summer-fall, southern hemisphere Pink-footed (Ardenna creatopus), and Sooty (A. grisea) shearwaters, travel to the California Current System (CCS) to overwinter. A. creatopus is a Chilean endemic that occupies shelf and slope waters of the CCS from March through October, with maximum abundance during July through September. A. grisea is one of the world’s most abundant seabirds; in the Pacific, it nests on islands off Chile and New Zealand. AdultA. grisea arrive to reside within the CCS during April through October during which time the species dominates the marine avian biomass. We used aerial survey data and satellite telemetry to compare at-sea habitats and environmental factors influencing the non-breeding distribution and abundance patterns in these 2 nonbreeding sympatric shearwaters. A. creatopus abundance was greatest in fall surveys (390 individuals; 0.39 ± 0.07 birds km-2), whereas fewer birds were seen in summer (June 2011 and July 2012: 33 individuals; 0.03 ± 0.01 birds km-2), usually occurring over outer continental shelf and slope waters. A. grisea was the most abundant bird in summer surveys (9225 individuals; 9.12 ± 1.97 birds km-2) and second most abundant in fall (2453 individuals; 2.43 ± 0.59 birds km-2). In June 2011, A. grisea was most abundant over inner-shelf (36.01 ± 11.15 birds km-2) and slope (7.71 ± 2.54 birds km-2) waters; most birds were observed over shelf waters off Washington and over slope waters off northern Oregon. Fewer A. grisea were observed in July 2012 (1061 individuals, compared with 8470 in June 2011) and average densities were less. We used a step-wise regression techniques to evaluate a-priori candidate model sets (bathymetric and oceanographic) to predict density for each species. Top-ranking models from these sets then were evaluated against models where we added independent measures of species-specific spatial intensity derived from satellite tracking data. We hypothesize that telemetry data can be used to improve density estimates for shearwaters at sea in areas not surveyed directly. By doing so, we evaluate a new approach to combine traditional vessel-based surveys of seabird density at sea with measures of individual space-use derived from telemetry.


This product is associated with the following project:
Pacific Continental Shelf Environmental Assessment (PaCSEA)

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