Oceanography and ecology of the Aleutian Archipelago: spatial and temporal variation

Abstract

This compilation of new information and summaries of earlier work emphasizes variability within marine waters of the Aleutian Archipelago. From the Alaska Peninsula to Near Strait, net flow through the passes is northward, with four passes (Amukta, Amchitka, Buldir, and Near Strait) contributing most of the flow. East of Samalga Pass (169°W), waters derived from the Alaska Coastal Current predominate, whereas west of Samalga Pass, waters of the Alaskan Stream predominate. The pattern of storm tracks creates a climatological (interannual and long term) transition zone in weather features (e.g. surface air temperature) near 170°W. The marine ecosystem of the Aleutian Archipelago also has a strong discontinuity at Samalga Pass, where cold‐water corals, zooplankton, fish, marine mammals and foraging seabirds show a step change in species composition. Diets of ground fish, Steller sea lions (Eumetopias jubatus) and some seabirds also change there. Lower growth rates of some fish species and stable isotope data indicate that productivity declines westward along the archipelago. The available data demonstrate considerable ecosystem variability over time scales of decades to millennia. Abrupt changes in composition of fish communities at several of the major passes suggest that Samalga Pass may mark only one of several ecological divisions of Aleutian waters. This spatial and temporal heterogeneity provides an important context within which to view recent declines in populations of Steller sea lions and other species, and has important implications for the management of regional marine resources. We conclude that the marine waters of the Aleutian Archipelago are divided into at least two different ecological regions, with potential for a concomitant separation of some fishery resources.

Fine-scale population genetic structure in Alaskan Pacific halibut (Hippoglossus stenolepis)

“…Water from the oceanic western boundary current, the Alaska Stream, flows through several deep passes between the islands in the central and western Aleutian Archipelago Bailey et al 2008). Many local eddies and gyres surround these islands Hunt and Stabeno 2005;Stabeno et al 2005). Oceanic conditions have been shown to be important transport mechanisms for micronutrients (Stabeno et al 2002Mordy et al 2005) and zooplankton in this area (Coyle et al 1998;Coyle 2005), potentially contributing to larval retention mechanisms.…”

“…Several other passes are known to carry currents between the Gulf of Alaska and the Bering Sea (Stabeno et al 1999(Stabeno et al , 2004Hunt and Stabeno 2005;Ladd et al 2005). This exchange of currents greatly influences the marine environment for marine birds and mammals, fish stocks and shellfish in the eastern Aleutian Archipelago and the southeast Bering Sea .…”

Cribrimorph and OtherCauloramphusSpecies (Bryozoa: Cheilostomata) from the Northwestern Pacific

“…This region has long been isolated from Asia by Near Strait and from mainland Alaska by distance (Gates et al, 1954;Thorson and Hamilton, 1986); the Aleutian passes comprise putative dispersal barriers for deep benthic animals (Dick, 2008); and there is (and has long been) considerable variation in environment along the archipelago (Hunt and Stabeno, 2005). We interpret the two geographically separate, morphologically distinct populations of C. ascofer in the western Aleutians as incipient species, and as evidence of ongoing allopatric speciation.…”

Unexpectedly High Diversity of Monoporella (Bryozoa: Cheilostomata) in the Aleutian Islands, Alaska: Taxonomy and Distribution of Six New Species

“…On the basis of island sizes, width and depth of intervening passes, and extent of surrounding shelf, the Aleutian Islands are considered to comprise the eastern Aleutians (as far west as Samalga Pass), central Aleutians (Samalga Pass to Amchitka Pass), and western Aleutians (westward from Amchitka Pass) (reviewed by Hunt and Stabeno, 2005). From 20 July-2 August 2004, I examined the catches from 63 otter-trawl tows made in the western Aleutian Islands (Fig.…”

“…Even along the archipelago, there are potential barriers. For example, there are three passes ≥430 m in depth between Aleutian island groups (Lindroth, 1963;Hunt and Stabeno, 2005) that might restrict larval dispersal, depending on the depth range of a species. Amchitka Pass, the boundary between the central and Western Aleutians, is both moderately broad (95 km) and exceptionally deep (1,155 m).…”