six times more productive (Sambrotto et al. 1984) and have 

 different ( more oceanic ) plankton composition { Springer ff «/. . 

 1989) than ACW, the productivity and food webs of SCW are 

 largely unknown. 



The southern Chukchi Sea Shelf is somewhat unique in 

 having unifomiiy shallow bathymetry and water masses aligned 

 across rather than along the shelf. Both northern fulmars and 

 short-tailed shearwaters exhibited greater along- as opposed to 

 across-shelf variability in abundance, and this variability 

 corresponded well to the locations of water masses (Table 2). 

 Other studies have related an opposite trend — that is, greater 

 across-shelf variability in seabird abundance — to across-shelf 

 gradients in bathymetry or water flow (e.g., Schneider et al. 

 1988). These studies, however, did not control for the cross- 

 correlation of water mass orientation and bathymetry. Shallow 

 areas of continental shelves frequently have distinct mixing 

 regimes because freshwater inputs, tidal, and atmospheric 

 forcing create and maintain different water masses than further 

 offshore in deeper areas of the shelf, where density forcing, or 

 geostrophic currents, may play greater roles (e.g., Atkinson 

 et ai, 1983). Relationships of seabirds to oceanographic 

 features can be determined with greater confidence if areas 

 lacking large numbers of intercorrelated environmental 

 gradients are employed to test such hypotheses. Detection of 

 seabird affinities for water masses in high-latitude seas is often 

 complicated by the geographic adjacency of colonies (Wahl 

 et al.. 1989) and the foraging distances that limit birds 

 commuting between colonies and offshore foraging sites 

 (cf Schneider & Hunt, 1984). In this context, nonbreeding 



species such as the short-tailed shearwater may provide better 

 clues for determining factors that influence marine distributions 

 of seabirds in such environments. 



The Third Joint US-USSR Bering & Chukchi Seas Expedition 

 was organized at the 11th meeting of the US-USSR Joint Committee 

 on Environmental Protection in Moscow ( February 1988), the Soviet- 

 American Conference on the Ecology of the Bering Sea, and the plan 

 of the joint bilateral activity 02.07-2101 entitled "Comprehensive 

 Analysis of Marine Ecosystems and Ecological Programs of the 

 World Ocean." We appreciate the assistance of US Fish and Wildlife 

 Service personnel; Harold J. O'Connor, Patuxent Wildlife Research 

 Center, Steven G. Kohl. Office of International Affairs. Sharon Janis 

 and William Mattice of the Division of Realty, Regional Office, 

 Anchorage. Mr. Anthony Amos and Dr. Terry Whitledge of the 

 University of Texas Marine Science Institute provided technical 

 support and CTD data. Dr. Lawrence K. Coachman volunteered much 

 information on the oceanography of the Bering and Chukchi Seas 

 during the data gathering phase of the project. The Soviet delegation 

 was headed by Professor Alia V. Tsyban, Goskomgidromet and 

 USSR Academy of Sciences. Weather data were complied faithfully 

 and accurately by Irena Mataeva. Volodya Kalytyak assisted in data 

 gathering and provided much appreciated comradeship. Thanks are 

 also extended to the captain and crew of the RA' Akademik Kurotev 

 for providing a safe and friendly platform for observing birds and 

 mammals in the Bering and Chukchi Seas. Manuscript preparation 

 was supponed by The John D. and CatherineT.MacArthur Foundation, 

 The J. N. Pew, Jr. Charitable Trust and the Marine Policy Center 

 program in marine biodiversity and ocean conservation at Woods 

 Hole Oceanographic Institution. This is WHOI Contribution 

 No. 7324. 



10.2 Associations Between Seabirds and Water 

 Masses in the Northern Bering Sea 



AMY E. S. SCHAUER 



Institute of Marine Science. University of Alaska. Fairbanks. .Alaska. USA 



Introduction 



Seabirds are an important part of the high-latitude 

 ecosystems of the Bering Sea by virtue of the very large size of 

 their populations and the spatial and temporal concentration of 

 their numbers, particularly during the breeding season. Recent 

 estimates have shown that birds may consume a much greater 

 part of secondary production in the Bering Sea than previously 

 believed (Walsh & McRoy, 1986; McRoy et al., unpublished 

 report). Birds can also significantly contribute to recycling 

 carbon to an ecosystem (Portnoy, 1990). 



Over the past 30 years, it has become widely accepted that 

 seabirds have species-specific affinities for particular pelagic 

 habitats, and that these affinities are based on the factors in a 

 given habitat which, when compared with others (e.g., stratified 

 versus well-mixed waters, [Hunt et al.. 1990|), enhance the 

 foraging success of birds feeding there (Uspenski, 1958; Brown, 

 1980; Hunt ('/«/.. 1981). However, the mechanisms by which 

 birds find suitable pelagic habitats and how the characteristics 

 of the habitat promote foraging success are poorly understood 

 (Hunt et al.. 1990). In addition, little is yet known about the 

 scales at which birds use their marine environments (Hunt & 

 Schneider, 1987). 



388 



