Alaska Science Center
Food Web Linkages in the Aleutian Archipelago
Linking the Food Webs of the Aleutian Archipelago
Seabird and marine mammal distributions in the Aleutian Archipelago are largely driven by prey availability and ocean climate cycles. Prey resources, including small-schooling fish and zooplankton, sustain 10 million breeding seabirds in the Gulf of Alaska/Aleutian Island region, and larger schooling fishes are consumed by nearly 30,000 adult Steller sea lions. Prey species are often transitory and patchy and so sampling must be conducted over broad spatial and temporal scales.
Why we did it:
Our knowledge of the occurrence and relative abundance of forage resources in the Aleutian Islands is limited because surveying the large area is expensive and logistically difficult. Abundance estimates are often difficult to make due to the patchiness of schooling fish and invertebrates. We wanted to find a logistically plausible way to sample prey and also quantify ocean climate conditions by opportunistically sampling from an established research platform. Ultimately we hope to gain a better understanding of ecological relationships between marine predators, prey resources, and marine habitat by using a cost-effective method with potential for long-term monitoring.
How We Did It:
We used the U.S. Fish and Wildlife Service M/V Tiglax, a vessel that routinely travels throughout the Alaska Maritime National Wildlife Refuge along the Alaska Peninsula and Aleutian Archipelago. During two cruises, we recorded acoustic backscatter and measured sea surface temperature and salinity using haul mounted equipment. We characterized pelagic forage species by deploying midwater trawls, and sampled nearshore forage species using a beach seine. At each trawl station we also sampled plankton and collected oceanographic data using a conductivity-temperature-depth water profiler.
What We Discovered:
We documented over 24 species of pelagic fishes and 30 species of nearshore fishes throughout the study area. Walleye pollock (Theragra chalcogramma), Pacific sand lance (Ammodytes hexapterus) and spawning capelin (Mallotus villosus) dominated the pelagic catch, and young of the year Gadids, Pacific sand lance and pink salmon (Oncorhynchus gorbuscha) dominated the nearshore catch. We detected a longitudinal gradient of physical oceanography that suggests cooler, more saline, and nutrient rich conditions in the west (i.e., central Aleutians) compared to the east (Alaska Peninsula). We found that automated data collection using equipment that is permanently installed on the vessel is an efficient and cost-effective way to sample the marine environment during travel of the Tiglax. We found that collection of opportunistic station data (CTD, plankton tows, beach seines) was moderately efficient, while trawling was least efficient of all sampling procedures. However, great efficiency in spatial sampling was achieved because transit time and cost were borne by the refuge during normal operations. We conclude that this research platform has enormous potential for monitoring key ecosystem components in the Gulf of Alaska and Aleutian Archipelago on seasonal, annual and decadal time-scales.