Climate change has exacerbated the occurrence of large‐scale sea surface temperature anomalies, or marine heatwaves (MHWs)—extreme phenomena often associated with mass mortality events of marine organisms. Using a combination of citizen science and federal data sets, we investigated the causal mechanisms of the 2014/2015 die‐off of Cassin's Auklets (Ptychoramphus aleuticus), a small zooplanktivorous seabird, during the NE Pacific MHW of 2013–2015. Carcass deposition followed an effective reduction in the energy content of mesozooplankton, coincident with the loss of cold‐water foraging habitat caused by the intrusion of the NE Pacific MHW into the nearshore environment. Models examining interannual variability in effort‐controlled carcass abundance (2001–2014) identified the biomass of lipid‐poor zooplankton as the dominant predictor of increased carcass abundance. In 2014, Cassin's Auklets dispersing from colonies in British Columbia likely congregated into a nearshore band of cooler upwelled water and ultimately died from starvation following the shift in zooplankton composition associated with onshore transport of the NE Pacific MHW. For Cassin's Auklets, already in decline due to ocean warming, large‐scale and persistent MHWs might represent a global population precipice.

Monitoring beach litter is essential for reducing ecological threats towards humans and wildlife. In Monterey Bay, CA information on seasonal and spatial patterns is understudied. Central California's coastal managers require reliable information on debris abundance, distribution, and type, to support policy aimed at reducing litter. We developed a survey method that allowed for trained citizen scientists to quantify the types and abundance of beach litter. Sampling occurred from July 2009-June 2010. Litter abundance ranged from 0.03 to 17.1 items m(-2). Using a mixed model approach, we found season and location have the greatest effect on litter abundance. Styrofoam, the most numerically abundant item, made up 41% of the total amount of litter. Unexpected items included fertilizer pellets. The results of this study provide a baseline on the types and abundance of litter on the central coast and have directly supported policy banning Styrofoam take out containers from local municipalities.

Although seabird population biology is relatively well studied, little data exists on mortality at-sea. Beached bird surveys are used to identify patterns of seabird mortality, but resulting patterns are difficult to interpret without corresponding data on at-sea density. We examined seabird mortality relative to at-sea density in Monterey Bay, California over 10 yr by integrating data from monthly beachcast seabird and offshore seabird censuses. Beachcast seabird numbers were relatively constant (mean 2.82 ± 0.31 seabirds km -1 ) throughout the year. At-sea seabird density (mean 148.9 ± 16.12 seabirds km -2 ) peaked in the summer upwelling period and was least in the winter Davidson period. A principal components analysis of seasonal climatic, prey availability, and anthropogenic variables for Monterey Bay derived 3 significant principal components (PCs) (explaining 70% of variance) characterized by storm activity and low prey availability (PC1), river discharge and krill abundance (PC2), and oiling (PC3). These principal components were used in detailed analyses of the 2 most abundant seabird species and indicate that sooty shearwater Puffinus griseus relative mortality is greatest during decreased productivity and increased storm activity. While relative mortality of common murres Uria aalge cannot be explained by the derived principal components, relative mortality increased in late winter when prey availability decreased concurrent with the annual increase in reproductive stress. Beachcast seabird data is difficult to interpret in isolation; however, when linked to at-sea densities of seabirds, it becomes a powerful tool to examine the relative impacts of oceanography and direct human perturbations on seabird demography. KEY WORDS: Seabirds at-sea · Beached bird survey · Density · Mortality · Sooty shearwater · Common murre Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 392: [295][296][297][298][299][300][301][302][303][304][305] 2009 birds (Roletto et al. 2003, Fleet 2006, Harris et al. 2006, Heubeck 2006, Zydelis et al. 2006, Parrish et al. 2007). An advantage of this method over CMR studies is that beached bird surveys enable researchers to examine the seabird community as a whole, including residents and migrants, away from breeding colonies, and sampling can occur year-round. Few researchers, however, have studied the correlation of the number of birds at sea to the number of birds that wash ashore (Mason 1997, Camphuysen & Heubeck 2001. For example, in November 2003, Nevins & Harvey (2003 reported a mass mortality event of northern fulmars Fulmarus glacialis in Monterey Bay, California. Two possible scenarios explain the event: (1) it was a mass mortality event, or (2) mortality was normal and there was an extraordinary influx of northern fulmars into Monterey Bay. Scaling beachcast density to at-sea density as a per capita mortality rate allows us to discern between these 2 possible scenarios, which have different management implications,...

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