title: Spatial Distribution and Temporal Patterns of Cassin's Auklet Foraging and Their Euphausiid Prey in a Variable Ocean Environment.
abstract: Krill (Euphausiids) play a vital ecosystem role in many of the world's most productive marine regions, providing an important trophic linkage. We introduce a robust modeling approach to link Cassin's auklet (Ptychoramphus aleuticus) abundance and distribution to large-scale and local oceanic and atmospheric conditions and relate these patterns to similarly modeled distributions of an important prey resource, krill. We carried out at-sea strip transect bird surveys and hydroacoustic assessments of euphausiids (2004-2013). Data informed separate, spatially-explicit predictive models of Cassin's auklet abundance (zero-inflated negative binomial regression) and krill biomass (two-part model) based on these surveys. We established the type of prey responsible for acoustic backscatter by conducting net tows of the upper 50 m during surveys. We determined the types of prey fed to Cassin's auklet chicks by collecting diet samples from provisioning adults. Using time-depth-recorders, we found Cassin's auklets utilized consistent areas in the upper water column, less than 30 m, where krill could be found (99.5% of dives were less than 30 m). Birds primarily preyed upon two species of euphausiids, Euphausia pacifica and Thysanoessa spinifera, which were available in the upper water column. Cassin's auklet abundance was best predicted by both large scale and localized oceanic processes (upwelling) while krill biomass was best predicted by local factors (temperature, salinity, and fluorescence) and both large scale and localized oceanic processes (upwelling). Models predicted varying krill and bird distribution by month and year. Our work informs the use of Cassin's auklet as a valuable indicator or krill abundance and distribution and strengthens our understanding of the link between Cassin's auklet and its primary prey. We expect future increases in frequency and magnitude of anomalous ocean conditions will result in decreased availability of krill leading to declines in the Farallon Islands population of Cassin's auklets.
authors.affiliation: California Current Group, Point Blue Conservation Science, Petaluma, California, United States of America.
authors.forename: Suzanne
authors.initials: S
authors.lastname: Manugian
authors.affiliation: California Current Group, Point Blue Conservation Science, Petaluma, California, United States of America.
authors.forename: Meredith L
authors.initials: ML
authors.lastname: Elliott
authors.affiliation: California Current Group, Point Blue Conservation Science, Petaluma, California, United States of America.
authors.forename: Russ
authors.initials: R
authors.lastname: Bradley
authors.affiliation: California Current Group, Point Blue Conservation Science, Petaluma, California, United States of America.
authors.forename: Julie
authors.initials: J
authors.lastname: Howar
authors.affiliation: Department of Biology, Pomona College, Claremont, California, United States of America.
authors.forename: Nina
authors.initials: N
authors.lastname: Karnovsky
authors.affiliation: Department of Biology, University of South Florida, Tampa, Florida, United States of America.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Saenz
authors.affiliation: California Current Group, Point Blue Conservation Science, Petaluma, California, United States of America.|Department of Geography, San Francisco State University, San Francisco, California, United States of America.
authors.forename: Anna
authors.initials: A
authors.lastname: Studwell
authors.affiliation: California Current Group, Point Blue Conservation Science, Petaluma, California, United States of America.
authors.forename: Pete
authors.initials: P
authors.lastname: Warzybok
authors.affiliation: California Current Group, Point Blue Conservation Science, Petaluma, California, United States of America.
authors.forename: Nadav
authors.initials: N
authors.lastname: Nur
authors.affiliation: California Current Group, Point Blue Conservation Science, Petaluma, California, United States of America.
authors.forename: Jaime
authors.initials: J
authors.lastname: Jahncke
mesh_terms: D000818:Animals; D046091:Charadriiformes / Q000502:physiology*; D002980:Climate; D017753:Ecosystem; D004777:Environment; D033201:Euphausiacea / Q000502:physiology*; D009792:Oceans and Seas; D011156:Population Density; D013696:Temperature