SEABIRDS

Black-legged Kittiwakes     Other seabird species     

Seabirds may serve as sensitive indicators of marine conditions that impact Steller sea lions because their diet overlaps that of sea lions and other apex predators in the Gulf of Alaska (Hobson et al. 1997) and because seabird reproductive parameters are both easily monitored and responsive to food availability (Cairns 1987). In particular, seabirds are useful indicators of relative abundance and demographics of intermediate trophic levels because they eat small, young-of-year fishes (Baird 1990; Hunt et al.1996) which are ecologically important links in the food web but difficult to quantify in trawl and hydro-acoustic surveys. Therefore, we use seabirds as bio-indicators to monitor the abundance and distribution of forage fishes and other trophic intermediates of the Gulf of Alaska food web. We focus research efforts on black-legged kittiwakes (Rissa tridactyla) because they are highly visible cliff nesters, tolerant of disturbance and handling and thus are easily monitored (Galbraith 1983).

Black-legged kittiwakes

1. Population trends
2. Reproductive performance
3. Nest-site attendance and Nestling growth

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Other Species

In addition, we document reproductive parameters and foraging areas of several other species of seabirds that breed within the Long Island Critical Habitat study area and occupy a variety of foraging niches. We monitor population trends and breeding performance of offshore divers (tufted puffins (Fratercula cirrhata) and common murres (Uria aalge)), surface feeders (glaucous-winged gulls (Larus glaucescens)), and nearshore divers (pigeon guillemots (Cepphus columba), pelagic cormorants (Phalacrocorax pelagicus), and red-faced cormorants (P.urile).

We also determine nestling diets and growth rates of tufted puffins, glaucous-winged gulls, and pigeon guillemots.

Population indices are determined from counts of adults and nests on established census plots for cliff-nesting kittiwakes, murres, and cormorants, and from whole-colony counts of adults for ground-nesting glaucous-winged gulls. Population indices and productivity measures for burrow-nesting tufted puffins are determined from counts of active burrows on established strip transects.

Standard monitoring techniques are used to document reproductive parameters of cliff-nesting species. Every 3-5 days during the breeding season, we visit 64 defined productivity plots (approx. 1600 nests) to determine clutch size, the timing of egg laying and hatching, timing of breeding failure, and the proportion of successful breeders at egg, chick and fledging stages. Chick growth rates are determined from periodic weights of nestlings (every 3 - 5 days). We statistically compare population indices and reproductive parameters among years using repeated measures ANOVAs.

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We incorporate seabirds into a regional food web model of apex predators by determining the total quantity and species composition of prey consumed by the three most abundant seabirds that breed within Chiniak Bay and the general vicinity of the LICH area. Specifically we determine seasonal abundance, diets and foraging areas of tufted puffins, black-legged kittiwakes, and glaucous-winged gulls. Abundance and foraging areas of these three species are determined from ship transect data and, for black-legged kittiwakes, foraging areas of active breeders are determined from locations of radio-tagged individuals. Seasonal diets are determined from food samples obtained from adults and nestlings when handled or may be supplemented with collections of adult birds where necessary. We compute total biomass of prey consumed by seabirds in the Chiniak Bay region using our data on bird abundance, diets, and productivity estimates but using published values for the daily energetic requirements of adults and nestlings of each species (Furness 1978; Gabrielsen et al.1987; Birt-Friesen et al.1989). In FY02, we also gathered seabirds killed incidentally in the Kodiak salmon setnet fishery and sampled by NMFS Marine Mammal Observers for morphometric and diet data.

tufted puffins
common murres
glaucous-winged gulls
pigeon guillemots
pelagic cormorants
red-faced cormorants

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