Marine environment of the eastern and central Aleutian Islands

Abstract

To examine the marine habitat of the endangered western stock of the Steller's sea lion (Eumetopias jubatus), two interdisciplinary research cruises (June 2001 and May to June 2002) measured water properties in the eastern and central Aleutian Passes. Unimak, Akutan, Amukta, and Seguam Passes were sampled in both years, and three additional passes (Umnak, Samalga, and Tanaga) were sampled in 2002. In the North Pacific (and to a lesser extent in the Bering Sea), a strong front in water properties was observed near Samalga Pass in June of both years, with significantly warmer, fresher, and more nitrate‐poor water east of Samalga Pass than west of the pass. These water properties reflect differences in source waters (Alaska Coastal Current versus Alaskan Stream), mixing depth, and Bering Sea influence. Strong cross‐Aleutian gradients were also observed with warmer, fresher water on the North Pacific side of the archipelago. The nutrient content of the waters flowing through the passes, combined with the effects of mixing within the passes, influences the transport of nutrients into the Bering Sea. As water moves away from the strong mixing of the passes and becomes more stratified, phytoplankton can take advantage of the enhanced nutrient concentrations. Thus, the northern side of the Aleutian Islands (especially in the lee of the islands) appears to be more productive. Combined with evidence of coincident changes in many ecosystem parameters near Samalga Pass, it is hypothesized that Samalga Pass forms a physical and biogeographic boundary between the eastern and central Aleutian marine ecosystems.

Highly Discordant Nuclear and Mitochondrial DNA Diversities in Atka Mackerel

“…A portion of the ACC DISCORDANT DNA DIVERSITIES IN ATKA MACKEREL filters through passes in the Aleutian Islands and drives the eastward-flowing Aleutian North Slope Current and the northwestern Bering Slope Current along the broad, shallow continental shelf in the southeastern Bering Sea (Stabeno et al 2001). While some of these currents may facilitate larval retention, especially in nearshore areas with complex circulation features (Ladd et al 2005), larvae entrained in offshore currents are potentially transported along the Aleutian Islands archipelago and into the Bering Sea. Ichthyoplankton surveys have documented Atka mackerel larvae in the Bering Sea (Matarese et al 2003); these fish were probably spawned in the major nesting areas along the Aleutian Islands, reinforcing the notion that the extent of larval dispersal via fast-moving current systems in both the Gulf of Alaska and the Aleutian Islands archipelago is sufficient to create the broad-scale genetic homogeneity of allozyme and microsatellite loci observed in these regions.…”

Estimating movement and abundance of Atka mackerel (Pleurogrammus monopterygius) with tag–release–recapture data

“…This creates a variety of microhabitats, each with its own degree of current exposure and blend of physical properties (e.g. mixing, prey abundance, temperature; Ladd et al, 2005). Atka mackerel seem to be well adapted to take advantage of the most favorable microhabitats such as high-relief rocky reefs with strong currents in the depth range between 100 and 200 m, resulting in their patchy distributions.…”

Islands of Inquiry: Colonisation, seafaring and the archaeology of maritime landscapes (TA29) : Colonisation, seafaring and the archaeology of maritime landscapes

“…At the height of the Neoglacial -with sea ice pressing down from the north virtually every spring -very large numbers of ringed seal were available for hunting at the edge of the ice, as were bearded seals and the occasional walrus (as reflected by the faunal component at Amaknak Bridge in Table 1). Extensive sea ice to the east of Unalaska (along the Bristol Bay coast of the Alaska Peninsula and Unimak Island, Figure 1) would have blocked one of the main passages into the Bering Sea used by modern cetaceans (Moore et al 2002;Ladd et al 2005;Sheldon et al 2005;Sinclair et al 2005;Zerbini et al 2006), forcing them to enter the Bering Sea west of Unalaska, where an eastward migration route would take all animals directly past the site location.…”

“…At the height of the Neoglacial -with sea ice pressing down from the north virtually every spring -very large numbers of ringed seal were available for hunting at the edge of the ice, as were bearded seals and the occasional walrus (as reflected by the faunal component at Amaknak Bridge in Table 1). Extensive sea ice to the east of Unalaska (along the Bristol Bay coast of the Alaska Peninsula and Unimak Island, Figure 1) would have blocked one of the main passages into the Bering Sea used by modern cetaceans (Moore et al 2002;Ladd et al 2005;Sheldon et al 2005;Sinclair et al 2005;Zerbini et al 2006), forcing them to enter the Bering Sea west of Unalaska, where an eastward migration route would take all animals directly past the site location.Today, spring migrating whales in the northern portion of the Bering Sea travel in the narrow strip of open water that lies between the shore and wind-driven sea ice, where they are far easier to hunt than autumn whales in relatively ice-free open water: modern Bering Strait whalers still find that spring whaling is the most successful (Bogoslovskaya 2003;Braham 2003;Jolles 2003). Along this moving edge of offshore sea ice, relatively large numbers of seals are also available during the spring and early summer (Nelson 1969).…”