Linking Marine Birds to Forage Fish – Is Diet a Limiting Factor in Puget Sound? (Year 1)

Testing the Limits of Diet - Short-term Climate Effects on Seabird-Forage Fish Linkages in Puget Sound (Year 2)

Julia K. Parrish, School of Aquatic and Fishery Sciences, University of Washington

$34,417 (Year 1); $31,322 (Year 2)

Year 1 Abstract

We propose to use a suite of piscivorous marine birds to examine the degree to which prey quality within Puget Sound may be a significant driving factor affecting the distribution and abundance of marine birds within Sound waters. We will use three species of Alcids for which data on colony size, reproductive effort, and diet are historically available: Rhinoceros Auklets, Common Murres, and Tufted Puffins. We selected this suite of species because one or more members of the group breed in both Puget Sound and the outer coast, because historical diet data are available for seabirds breeding in Puget Sound and on the outer coast and because these species are declining, species of concern or indicator species. Specifically, we propose to use data mining in concert with contemporary on-colony data collection (diet composition and quality) to examine diet patterns in coastal and Puget Sound populations of these diving seabirds. We will examine the degree to which diet in these two locations may differ both spatially and temporally and, thus, potentially limit these diving seabirds. We will use diet data from an outer coast colony, Tatoosh Island located at the entrance of the Strait of Juan de Fuca, as a control against which longitudinal change in Puget Sound dietscan be assessed. Diet data for Puget Sound will be collected at Protection Island, located in the central sound. For example, a change in diet quality and composition within Puget Sound with no accompanying change along the coast would suggest that the observed diet changes are locally caused and not part of a regional shift in diet. We will also compare contemporary and historical coastal and Puget Sound diet collected both during and after the breeding season. If, for example, we find the quality of Puget Sound diet to be lower than coastal diet then prey base may be limiting marine birds within Puget Sound. Thousands of seabirds move into Puget Sound during the late fall and winter and presumably take advantage of abundant food resources to raise young and recondition after the breeding season. Examining changes in diet over time of these top-level predators in concert with changes in distribution and abundance of forage fishes provides a necessary link when examining the health and sustainability of the Puget Sound ecosystem. Information about the factors limiting populations of marine birds in Puget Sound waters is critical to organizations like SeaDoc and other participants in the research and natural resource management communities when addressing the root causes of marine bird declines.

Year 2 Abstract

We propose to extend and intensify dietary sampling begun in 2006, focusing on the Rhinoceros Auklet, Cerorhinca monocerata, a piscivorous marine bird nesting in Puget Sound and along the outer coast of Washington. This species has apparently declined in Puget Sound, both in number of colonies, and in number of birds at the largest colony – Protection Island. Our research in 2006 documented differences in the diet of Sound breeders (Protection Island) versus outer coast breeders (Tatoosh Island), suggesting that Sound breeders must work harder (more fish captures per trip) for a lower return to their chicks (lower bill load weights, lower energy content).  In addition, comparison with historic diet from Puget Sound suggests these birds currently favor sandlance at the expense of salmon, a richer forage resource.  However suggestive, these data should be interpreted with caution, as interannual variability can be large, as a consequence of chronic and cumulative human activities, and as a function of natural climate forcing. Because current oceanographic conditions are moderate El Niño, and this climate event is predicted to continue through summer of 2007, an additional year of data will provide the perfect ‘natural experiment’ to test the degree to which Puget Sound top predators, exemplified by Rhinoceros Auklets, are diet limited. We propose two alternate conceptual hypotheses: (1) Puget Sound buffers breeding seabirds from regional effects of El Niño, because the within-Sound processes affecting forage fish distribution and abundance are not solely dependent on seasonal upwelling. (2) Because seabirds in Puget Sound are already relatively food stressed, the addition of an El Niño stressor will have a larger observable effect relative to coastal colonies.  We will make at least four sampling trips each to Protection and Tatoosh Islands during the chick rearing season (July – September) to collect data on burrow occupancy, reproductive success, and to sample chick diet. We anticipate a minimum of 250 fish per site, but will target 600+ fish. Fish will be identified, weighed and measured, and sub-samples selected for determination of energy content.  The aim of our proposed (multi-year) research is to provide evidence to support – or refute – the hypothesis that changes in the prey base may be limiting the abundance and distribution of piscivorous marine birds in Puget Sound. Multi-year studies are crucial if the inherent variability in local environments and predator-prey linkages are to be determined.  In particular, climate events such as El Niño set limits on what coastal marine ecosystems in seasonally affected upwelling domains, such as the Pacific Northwest, can assimilate. Information about the factors limiting populations of marine birds in Puget Sound waters is critical to institutions, organizations, and planning efforts involved in natural resource management and conservation, including the Puget Sound Partnership, the Puget Sound Conservation and Recovery Plan, and SeaDoc.

Life on the Colony and Death on the Beach: Seabird Ecology in the Pacific Northwest. Shannon Point Marine Center, Anacortes, WA 2007.

Listening to the Birds: What are Seabirds Telling us about Coastal Ecosystem Health? Cruising Club of America, Seattle, WA 2007.

Listening to the Birds: Seabird Ecology and Conservation in Puget Sound. Skagit Audubon Society, Padilla Bay Interpretive Center, WA 2007.

Seabirds in Puget Sound, People for Puget Sound’s “Keeping Our Sound Alive” Seminar Series, Seattle WA 2007.

Seabird Ecology and Conservation. SeaDoc Society Marine Conservation Seminar Series, Orcas Island, WA 2007.