Home About us Contact
|
Home About us Contact | ||
|
|
||
Aleutian Islands (aleutian + island)
Selected AbstractsSpatial and temporal variability of the Aleutian climateFISHERIES OCEANOGRAPHY, Issue 2005SERGEI N. RODIONOV Abstract The objective of this paper is to highlight those characteristics of climate variability that may pertain to the climate hypothesis regarding the long-term population decline of Steller sea lions (Eumetopias jubatus). The seasonal changes in surface air temperature (SAT) across the Aleutian Islands are relatively uniform, from 5 to 10°C in summer to near freezing temperatures in winter. The interannual and interdecadal variations in SAT, however, are substantially different for the eastern and western Aleutians, with the transition found at about 170°W. The eastern Aleutians experienced a regime shift toward a warmer climate in 1977, simultaneously with the basin-wide shift in the Pacific Decadal Oscillation (PDO). In contrast, the western Aleutians show a steady decline in winter SATs that started in the 1950s. This cooling trend was accompanied by a trend toward more variable SAT, both on the inter- and intra-annual time scale. During 1986,2002, the variance of winter SATs more than doubled compared to 1965,1985. At the same time in Southeast Alaska, the SAT variance diminished by half. Much of the increase in the intra-seasonal variability for the western Aleutians is associated with a warming trend in November and a cooling trend in January. As a result, the rate of seasonal cooling from November to January has doubled since the late 1950s. We hypothesize that this trend in SAT variability may have increased the environmental stress on the western stock of Steller sea lions and hence contributed to its decline. [source] Seabird distribution, abundance and diets in the eastern and central Aleutian IslandsFISHERIES OCEANOGRAPHY, Issue 2005J. JAHNCKE Abstract We examined the hypothesis that seabird distribution, abundance and diets differ among the eastern and central Aleutian Islands in response to distinct marine environments and energy pathways in each region. Research cruises were conducted in June 2001 and May,June 2002. We determined the distribution, abundance, diet and prey consumption of seabirds, and related these to zooplankton abundance and water masses that possess different physical properties. We found that distribution, abundance and diets of seabirds could be partitioned into two regions that correspond to marine environments determined by the extent of the Alaska Coastal Current along the eastern and central Aleutian Islands. Short-tailed shearwaters (Puffinus tenuirostris) were the most abundant seabird in the coastal waters of the eastern Aleutian Islands, and northern fulmars (Fulmarus glacialis) were the most abundant seabird in the oceanic waters of the central Aleutian Islands. Seabird communities in the central and eastern Aleutian Islands were likely associated with different food webs. In the central Aleutian Islands, short-tailed shearwaters and northern fulmars consumed shelf-break species of euphausiids (Thyssanoesa longipes) and oceanic copepods (Neocalanus cristatus), respectively; in the eastern Aleutian Islands, both short-tailed shearwaters and northern fulmars consumed shelf species of euphausiids (T. inermis). Carbon transport to seabirds was highest in Unimak and Akutan Passes where shearwaters removed large quantities of shelf euphausiids, followed by Samalga and Seguam Passes where northern fulmars removed large amounts of oceanic copepods. [source] Hydrographic features and seabird foraging in Aleutian PassesFISHERIES OCEANOGRAPHY, Issue 2005CAROL LADD Abstract Strong tidal currents crossing over the abrupt topography of the Aleutian Passes result in regions with high horizontal property gradients. These frontal regions vary with the tidal cycle and form the boundary between vertically mixed and stratified regions. Concentrations of seabirds were associated with convergence zones in the mixed water (MW) and with the front between North Pacific (NP) water and MW. Species that were foraging by picking at prey from the surface were associated with surface convergences that appeared to be associated with Langmuir circulation cells or tidal features (all fulmar aggregations) in the central passes (Samalga, Seguam). In contrast, subsurface foraging puffins and small alcids were mostly observed in areas of turbulent, well-mixed water near the shallow regions of the passes. Short-tailed shearwater flocks that were plunge-diving for prey were associated with the front between the NP water and MW in the passes. On our transects, we observed no significant aggregations of seabirds associated with Bering Sea water or NP water away from the frontal zones. The interaction of strong currents with bathymetric features results in zones of vertical advection, mixing, and surface convergences that make island passes attractive foraging regions for seabirds. Deep passes lacking these features, such as many of the passes in the western Aleutian Archipelago, are not as likely to facilitate trophic transfer to top predators as shallow passes, such as those found in the eastern Aleutian Islands. [source] The decline of Steller sea lions Eumetopias jubatus in Alaska: a review of the nutritional stress hypothesisMAMMAL REVIEW, Issue 1 2003A. W. TRITES ABSTRACT 1.,The decline of Steller sea lions Eumetopias jubatus in the Gulf of Alaska and Aleutian Islands between the late 1970s and 1990s may have been related to reduced availability of suitable prey. Many studies have shown that pinnipeds and other mammals suffering from nutritional stress typically exhibit reduced body size, reduced productivity, high mortality of pups and juveniles, altered blood chemistry and specific behavioural modifications. 2.,Morphometric measurements of Steller sea lions through the 1970s and 1980s in Alaska indicate reduced body size. Reduced numbers of pups born and an apparent increase in juvenile mortality rates also appear to be nutritionally based. Blood chemistry analyses have further shown that Steller sea lions in the Gulf of Alaska and Aleutian Islands area exhibited signs of an acute phase reaction, or immune reaction, in response to unidentified physical and/or environmental stress. Behavioural studies during the 1990s have not noted any changes that are indicative of an overall shortage in the quantity of prey available to lactating female sea lions. 3.,The data collected in Alaska are consistent with the hypothesis that Steller sea lions in the declining regions were nutritionally compromised because of the relative quality of prey available to them (chronic nutritional stress), rather than because of the overall quantity of fish per se (acute nutritional stress). This is further supported by captive studies that indicate the overall quality of prey that has been available to Steller sea lions in the declining population could compromise the health of Steller sea lions and hinder their recovery. [source] Sperm whale depredation of sablefish longline gear in the northeast Pacific OceanMARINE MAMMAL SCIENCE, Issue 1 2008Michael F. Sigler Abstract Interactions between marine mammals and fisheries include competition for prey (catch), marine mammal entanglement in fishing gear, and catch removal off fishing gear (depredation). We estimated the magnitude of sperm whale depredation on a major North Pacific longline fishery (sablefish) using data collected during annual longline surveys. Sperm whale depredation occurs while the longline gear is off-bottom during retrieval. Sperm whales were observed on 16% of longline survey sampling days, mostly (95% of sightings) over the continental slope. Sightings were most common in the central and eastern Gulf of Alaska (98% of sightings), occasional in the western Gulf of Alaska and Aleutian Islands, and absent in the Bering Sea. Longline survey catches were commonly preyed upon when sperm whales were present (65% of sightings), as evidenced by damaged fish. Neither sperm whale presence (P= 0.71) nor depredation rate (P= 0.78) increased significantly from 1998 to 2004. Longline survey catch rates were about 2% less at locations where depredation was observed, but the effect was not significant (P= 0.34). Estimated sperm whale depredation was <1% of the annual sablefish longline fishery catch off Alaska during 1998 to 2004. [source] Biology and taxonomy of encrusting alcyoniid soft corals in the northeastern Pacific Ocean with descriptions of two new genera (Cnidaria, Anthozoa, Octocorallia)INVERTEBRATE BIOLOGY, Issue 2 2003Catherine S. McFadden Abstract. In this paper we summarize current knowledge of the distribution, ecology, and reproductive biology of 4 encrusting species in the soft coral family Alcyoniidae, with descriptions of 2 new genera and 2 new species. The new genus Discophyton is erected for Alcyonium rudyi, a species common in the lower intertidal of exposed rocky headlands from Vancouver Island, British Columbia, Canada south to Point Lobos, California, USA. Discophyton rudyi n. gen. & n. comb. propagates extensively by clonal fission, giving rise to characteristic aggregations of small, regularly spaced, disc-shaped colonies. We describe 2 new species and place them in a new genus, Thrombophyton. Thrombophyton coronatum n. gen. & n. sp. forms irregularly shaped, membranous colonies on rock surfaces; it occurs subtidally along the southern California coast from the Palos Verdes Peninsula to San Diego and on the California Islands. Thrombophyton trachydermum n. gen. & n. sp. has a similar, membranous growth form; it occurs both intertidally and subtidally on Vancouver Island, British Columbia, Canada, and in the San Juan Archipelago, Washington, and intertidally in central California, USA. Alcyonium pacificum, reported for the first time from North American waters, occurs in subtidal kelp beds around the Aleutian islands of Attu and Adak; its mushroom-shaped colonies are raised above the substrate on a short stalk. D. rudyi, T. trachydermum, and A. pacificum are all gonochores that reproduce in late summer; in contrast, T. coronatum appears to reproduce in the spring. D. rudyi and T. coronatum brood larvae internally to a late planula stage. A key to species is presented for all shallow-water soft corals known to occur in the northeastern Pacific Ocean. [source] | ||||||||||