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Petaluma, California, United States

Robinette D.P.,PRBO Conservation Science | Nur N.,California Current Group | Brown A.,California Current Group | Howar J.,PRBO Conservation Science
Marine Ornithology | Year: 2012

The Vandenberg State Marine Reserve (VSMR) was established in 1994 with the primary goal of protecting fishes and invertebrates targeted by fisheries. However, studies of other reserves have shown that effects cascade and benefit species at several trophic levels. We tested the hypothesis that the VSMR would provide benefits to nearshore foraging seabirds. We measured the foraging rates (mean number of individuals observed per hour) of seabirds at four plots (two inside and two outside the VSMR) over six years to test the hypothesis that foraging rates are greater inside the reserve than outside. The VSMR spans a coastal promontory, and we controlled for promontory effects by selecting plots at windward and leeward sites. All species showed either no difference or higher rates outside the reserve than inside. The consistency of our results over the six-year period illustrates predictable foraging behavior in these species. Piscivorous species foraged more in leeward plots than windward plots, while the benthic invertebrate specialist foraged more in windward plots. Our results reflect reported differences in community structure around coastal promontories; namely, windward habitats enhance biomass of suspension-feeding invertebrates while leeward habitats provide refuge for fish recruitment. Our results suggest that the VSMR is not protecting significant foraging habitat for nearshore foraging seabirds and that coastal geography should be considered when designing marine reserves to protect these species.

Manugian S.,California Current Group | Elliott M.L.,California Current Group | Bradley R.,California Current Group | Howar J.,California Current Group | And 7 more authors.
PLoS ONE | Year: 2015

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. © 2015 Manugianet al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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