Traditional monitoring strategies for marine ecosystems are expensive and difficult to undertake. An inexpensive and sensitive approach is to use seabirds as monitors of change in community structure and food webs. The student exchange program between the University of Alaska Fairbanks and the Institute for Biological Problems of the North in Magadan provided an opening for a study of seabirds on the coast of the Sea of Okhotsk. Data from seabird populations in this arctic sea will be combined with those for congeneric species in the Beaufort Sea and Gulf of Alaska.
Seabirds in general are very good samplers of a variety of forage fishes. Among the seabirds, guillemots (Cepphus spp.), the focus of this study, are important components of the nearshore community. The coastal ecosystem is distinct from other oceanic regions, and is receiving little attention from oceanographers. Monitoring elements of the breeding biology of nearshore foragers such as guillemots is a useful tool for tracking system-wide changes in ocean conditions and variability in food webs.
Spectacled Guillemots (Cepphus carbo ) were studied on Oomara Island, located 63 km across the water to the southeast of Magadan, Russia, in the Sea of Okhotsk. Oomara is small, just 500 m long, 200 m wide, and only 60 m high at its highest point. The island shelters a population of 600-800 Spectacled Guillemots, as well as Black-legged Kittiwakes, Thick-billed and Common Murres, Slaty-backed Gulls, Crested and Parakeet Auklets, Tufted and Horned Puffins, Pelagic Cormorants, and a pair of Steller's Sea Eagles.
Data on nesting success and chick growth rates of Spectacled Guillemots were gathered by visiting most nests every 1-2 days. Chicks were weighed, measured, and banded with a unique combination of 4 colored plastic leg bands. Rates of prey delivery to chicks and chick diets were determined by conducting 2-hour watches during daylight hours from a blind which overlooked 8 active nests. Colony attendance patterns were monitored by making counts every 30 minutes of all guillemots in a plot established around the blind. These counts were made for a 24-hour period once a week. Sea surface temperatures were measured daily at 2 locations.
Most studies of guillemots show competition within a nest, with a larger alpha chick growing at a faster rate than the smaller beta chick. Single chicks often grow at faster rates than paired chicks, presumably because parents are better able to provision them. On Oomara Island in 1994, single, first-hatched, and second-hatched Spectacled Guillemot chicks had similar nestling periods. First-hatched and second-hatched chicks had similar fledging weights. Single chicks had significantly lower fledging weights, but did not spend extra time in the nest to attain higher weights. These results indicate that, on Oomara Island in 1994, there was no additional cost to adults rearing 2 chicks instead of 1. Adults with broods of 2 were able to supply food to both chicks at optimal rates.
Food delivery rates did not increase with brood size, so perhaps forage fish are available to guillemots around Oomara in sufficient numbers to allow guillemots to select for size or nutritional characteristics. Furthermore, if Spectacled Guillemots at lower latitudes are able to rear only 1 chick per nest, perhaps Oomara Island is located in a particularly productive area, or perhaps 1994 was an atypical year in its high productivity. Answers to these questions will be sought through comparisons of guillemot breeding success in 1994 to time series data spanning the past decade on productivity of other seabirds nesting in the northern Sea of Okhotsk.
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