Western Aleutian Research Articles

First Records of the Whiteblotched Skate (Bathyraja maculata) in the Eastern Gulf of Alaska

The Whiteblotched Skate (Bathyraja maculata) is an elasmobranch species of the family Rajidae that was first described in 1977 from 21 specimens collected throughout the Bering Sea (Ishiyama and Ishihara 1977). Bathyraja maculata is distinctive, with a dorsal surface that varies from gray to dark brown and is punctuated with white to yellow blotches of various sizes. The ventral surface is white to light gray and often blotchy, darkening at the margins of the disc and on the uniformly dark tail, which has broad lateral folds. Nuchal and tail thorns are present and strongly developed, but middorsal, orbital, and scapular thorns are absent. The snout is short and flexible, and the interobital space is flat and wide (Ishiyama and Ishihara 1977; Mecklenburg and others 2002). Female B. maculata reach a maximum total length (TL) of 147 cm (Stevenson and others 2007), with males reported to a maximum size of 132 cm TL (JW Orr, National Marine Fisheries Service (NMFS), Alaska Fisheries Science Center (AFSC), Seattle, WA, pers. comm.). Bathyraja maculata ranges from the northern Sea of Japan and Sea of Okhotsk throughout the Bering Sea and Aleutian Islands (Mecklenburg and others 2002) at depths of 73 m (Fedorov 2000) to 1193 m (Stevenson and others 2007). Its easternmost record in the Aleutian Islands is off Umnak Island (53°24'N, 168041'W; Mecklenburg and others 2002). Bathyraja maculata has been commonly taken in trawl surveys of the western Bering Sea continental slope (Orlov 1998; Dolganov 1999), eastern Bering Sea continental slope (Hoff and Britt 2003, 2005) and Aleutian Islands (Zenger 2004). It also frequently occurs in shallower, continental shelf waters (ca. 100 to 200 m) of the western Bering Sea (Orlov 1998; Fedorov 2000) and Aleutian Islands (Zenger 2004), but appears to be scarce on the broad, eastern Bering Sea continental shelf (Lauth and Acuna 2007a, 2007b). Previous records of B. maculata from the Gulf of Alaska are few and restricted to the Gulf's western margin, where it has been reported at 3 locations during NMFS-AFSC bottom trawl surveys (Stevenson and others 2007, 2008; Fig. 1). The easternmost of these records represents a specimen collected approximately 163 km southwest of Kodiak Island (56°04.8'N, 156034.2'W, 191 m depth) during the summer of 1999 (DE Stevenson, NMFS-AFSC, Seattle, WA, pers. comm.). However, 3 B. maculata were recently collected from the Alexander Archipelago, southeastern Alaska, and are presented here. These records considerably extend the known distribution of B. maculata and suggest that it may be more widespread in the Gulf of Alaska than previously indicated. The Alaska Department of Fish and Game (ADFG) conducts annual longline surveys in Clarence Strait, including US waters of Dixon Entrance and Chatham Strait of the Alexander Archipelago, to assess the condition of Sablefish (Anoplopoma fimbria) stocks in these areas. Gear used during ADFG surveys consists of longlines containing forty-five 13/0 Mustad circle hooks per line, fastened at 2-m intervals and baited with squid. Twenty-five contiguous lines are deployed at established locations of 366 m depth, and gear is fished for 3 to 11 h prior to retrieval. All fishes caught during these surveys, including skates, are enumerated. Typically, only Longnose Skates (Raja rhina) are identified to species, but during the 2006 lower Clarence Strait survey, conducted from 17 to 22 May, skates of all species were distinguished. In addition, photos were taken of WINTER 2008 193

Harbor seal population decline in the Aleutian Archipelago

AbstractPopulations of Steller sea lions, northern fur seals, and northern sea otters declined substantially during recent decades in the Bering Sea and Aleutian Islands region, yet the population status of harbor seals has not been assessed adequately. We determined that counts obtained during skiff‐based surveys conducted in 1977–1982 represent the earliest estimate of harbor seal abundance throughout the Aleutian Islands. By comparing counts from 106 islands surveyed in 1977–1982 (8,601 seals) with counts from the same islands during a 1999 aerial survey (2,859 seals), we observed a 67% decline over the ∼20‐yr period. Regionally, the largest decline of 86% was in the western Aleutians (n= 7 islands), followed by 66% in the central Aleutians (n= 64 islands), and 45% in the eastern Aleutians (n= 35 islands). Harbor seal counts decreased at the majority of islands in each region, the number of islands with >100 seals decreased ∼70%, and the number of islands with no seals counted increased ∼80%, indicating that harbor seal abundance throughout the Aleutian Islands was substantially lower in the late 1990s than in the 1970s and 1980s.

Environmental contaminants in bald eagle eggs from the Aleutian archipelago

We collected 136 fresh and unhatched eggs from bald eagle (Haliaeetus leucocephalus) nests and assessed productivity on eight islands in the Aleutian archipelago, 2000 to 2002. Egg contents were analyzed for a broad spectrum of organochlorine (OC) contaminants, mercury (Hg), and stable isotopes of carbon (delta13C) and nitrogen (delta15N). Concentrations of polychlorinated biphenyls (SigmaPCBs), p,p'-dichlorodiphenyldichloroethylene (DDE), and Hg in bald eagle eggs were elevated throughout the archipelago, but the patterns of distribution differed among the various contaminants. Total PCBs were highest in areas of past military activities on Adak and Amchitka Islands, indicating local point sources of these compounds. Concentrations of DDE and Hg were higher on Amchitka Island, which was subjected to much military activity during World War II and the middle of the 20th century. Concentrations of SigmaPCBs also were elevated on islands with little history of military activity (e.g., Amlia, Tanaga, Buldir), suggesting non-point sources of PCBs in addition to point sources. Concentrations of DDE and Hg were highest in eagle eggs from the most western Aleutian Islands (e.g., Buldir, Kiska) and decreased eastward along the Aleutian chain. This east-to-west increase suggested a Eurasian source of contamination, possibly through global transport and atmospheric distillation and/or from migratory seabirds. Eggshell thickness and productivity of bald eagles were normal and indicative of healthy populations because concentrations of most contaminants were below threshold levels for effects on reproduction. Contrary to our predictions, contaminant concentrations were not correlated with stable isotopes of carbon (delta13C) or nitrogen (delta15N) in eggs. These latter findings indicate that contaminant concentrations were influenced more by point sources and geographic location than trophic status of eagles among the different islands.

Mercury levels and potential risk from subsistence foods from the Aleutians

Considerable attention has been devoted to contaminants (mainly PCBs and mercury) in subsistence foods (particularly fish) from various parts of the world. However, relatively little attention has been devoted to examining mercury levels in a full range of subsistence foods from a particular region. While managers and scientists compute risk based on site-specific data on contaminant levels and consumption rates, a first step in making risk decisions by subsistence peoples is knowledge about the relative levels of mercury in the foods they eat. This study examined levels of mercury in subsistence foods (edible components) from several islands in the western Aleutians of Alaska, including algae (4 species), invertebrates (9 species), fish (15 species) and birds (5 species). Samples were gathered by both subsistence hunters/fishers and by scientists using the same equipment. Another objective was to determine if there were differences in mercury levels in subsistence foods gathered from different Aleutian islands. We tested the null hypotheses that there were no interspecific and interisland differences in mercury levels. Because of variation in distribution and the nature of subsistence hunting and fishing, not all organisms were collected from each of the islands. There were significant and important differences in mercury levels among species, but the locational differences were rather small. There was an order of magnitude difference between algae/some invertebrates and fish/birds. Even within fish, there were significant differences. The highest mean mercury levels were in flathead sole (Hippoglossoides elassodon, 0.277 ppm), yellow irish lord (Hemilepidotus jardani, 0.281 ppm), great sculpin (Myoxocephalus polyacanthocephalus, 0.366 ppm), glaucous-winged gull (Larus glaucescens, 0.329 ppm) and its eggs (0.364 ppm), and pigeon guillemot (Cepphus columba, 0.494 ppm). Mercury levels increased with increasing weight of the organisms for limpets (Tectura scutum), and for 11 of the 15 fish species examined. Nine of the 15 fish species had some samples over the 0.3 ppm level, and 7 of 15 fish had some samples over 0.5 ppm. For birds, 95% of the pigeon guillemot muscle samples were above the 0.3 ppm, and 43% were above 0.5 ppm. While health professionals may argue about the risk and benefits of eating fish, and of eating alternative protein sources, the public should be provided with enough information for them to make informed decisions. This is particularly true for subsistence people who consume large quantities of self-caught foods, particularly for sensitive sub-populations, such as pregnant women. We argue that rather than giving people blanket statements about the health benefits or risks from eating fish, information on mean and maximum mercury levels should also be provided on a wide range of subsistence foods, allowing informed decisions, especially by those most at risk.

Demographic independence along ecosystem boundaries in Steller sea lions revealed by mtDNA analysis: implications for management of an endangered species

Previous genetic studies indicate Steller sea lions ( Eumetopias jubatus (Schreber, 1776)) comprise three phylogeographically distinct populations. However, differences in population trends and ecology and the limited extent of recorded dispersal suggest structure may be present at smaller scales. We examined sequence variation within a longer segment (531 bp) of the mtDNA control region in greater numbers (n = 1654) of sea lions from across Alaska than earlier investigations to investigate fine-scale dispersal patterns in Steller sea lions. We detected high levels of haplotypic diversity (h = 0.934) and confirmed phylogeographic differentiation between southeastern and western Alaska (Φst= 0.23, P < 0.0001), but also found significant differentiation at regional and local scales. Rookeries in the Gulf of Alaska, eastern Bering Sea, and eastern Aleutians were distinct from rookeries in the central and western Aleutians (Fst= 0.021, P < 0.0001; Φst= 0.017, P < 0.0001). The location of this split coincides with an oceanographic divergence between continental shelf and ocean basin waters and with differences in sea lion foraging ecology and population trends. A number of rookeries were also significantly differentiated from nearby rookeries (Fst= 0.02–0.025, P < 0.05), signifying substantial female-mediated philopatry, in some cases, at local scales. These findings have important implications for understanding the ecology of Steller sea lions in relation to marine ecosystems and the causes of population declines, and they provide guidance for management, including the identification of management stocks.

Developing a Health and Safety Plan for Hazardous Field Work in Remote Areas

Developing health and safety plans (HASPs) is a common feature of occupational safety and health for many workplaces. Formal HASPs are a requirement for hazardous waste work, requiring the anticipation and identification of hazards and embodying the training, equipping, and evaluation of workers. Aside from OSHA, there are relatively few manuals or examples and virtually no papers that provide practical guidance in what a HASP should cover or how to create and implement one. Moreover, existing guidance refers to spatially circumscribed worksites. This article details development of a HASP to cover field researchers and ship personnel conducting scientific research in a remote area of the world (Amchitka Island in the western Aleutians), hundreds of kilometers from the nearest emergency room. It required characterizing the kinds of work to be performed and anticipating the hazards that could be encountered. It illustrates the meshing of a general HASP with a ship safety plan, a dive safety plan, and specialized topics, including stop-work authority, rock climbing, firearms, vehicle safety, and communication strategy. Remote area operations are a growing challenge facing the profession. An expedition of this sort requires extensive planning and experienced safety personnel and cannot rely on luck to ensure the safe return of participants.

Ecosystem models show combined effects of fishing, predation, competition, and ocean productivity on Steller sea lions (Eumetopias jubatus) in Alaska

Steller sea lions (Eumetopias jubatus) increased in the eastern portion of their range while declining in the Gulf of Alaska and Aleutian Islands from the late 1970s to late 1990s. We constructed ecosystem models of the central and western Aleutians and of southeast Alaska to simultaneously evaluate four hypotheses explaining sea lion dynamics: killer whale (Orcinus orca) predation, ocean productivity, fisheries, and competition with other species. Comparisons of model predictions with historical time series data indicate that all four factors likely contributed to the trends observed in sea lion numbers in both ecosystems. Changes in ocean productivity conveyed by the Pacific Decadal Oscillation influenced the abundance trajectory of several species. Fishing could have affected the ecosystem structure by influencing the abundance of Atka mackerel (Pleurogrammus monopterygius) in the Aleutians and Pacific herring (Clupea pallasii) in southeast Alaska. Pacific halibut (Hippoglossus stenolepis) in the Aleutians and arrowtooth flounder (Atheresthes stomias) in southeast Alaska appear to impede sea lion population growth through competitive interactions. Predation by killer whales was important when sea lions were less abundant in the 1990s in the Aleutians and in the 1960s in Southeast Alaska, but appear to have little effect when sea lion numbers were high.

Submarine hydrothermal activity and mineralization on the Kurile and western Aleutian island arcs, N.W. Pacific

The Kurile Arc consists of at least 100 submarine volcanoes and 5 submarine caldera located mainly in the rear arc. The arc is seismically very active, particularly in the south, and is characterized by extensive volcanism and hydrothermal activity. At least one subaerial volcano on the arc (Medvezhy located on Iturup island) has an extremely shallow magma chamber and is intensely active. Three types of submarine hydrothermal deposit were recovered from this area, hydrothermal manganese crusts, nontronite and hydrothermal manganese crusts overlain by hydrogenous manganese oxides. In addition, submarine hydrothermal Fe oxyhydroxides enriched in P were sampled from the submerged caldera of Kraternaya Bight in the central part of the arc. These deposits appear to be analagous to deposits from Santorini caldera on the Aegean Arc. Piip submarine volcano located in the western Aleutian Arc is characterized by two shallow summit craters. Both intermediate-temperature (anhydrite, gypsum, barite, amorphous silica, pyrite, calcite and aragonite) and low-temperature (nontronite, Fe oxyhydroxides, hisingerite and ferromanganese crusts) hydrothermal minerals were recovered from this seamount together with bacterial mats and giant clams. The maximum measured temperature of the hydrothermal fluids was 133 °C, although the actual temperature may have reached 250 °C. Both the Kurile and Aleutian Arcs have the potential to host major submarine hydrothermal systems. Detailed exploration of these poorly studied areas using modern geophysical, geochemical and sampling techniques is therefore strongly recommended.

The use of biota sampling for environmental contaminant analysis for characterization of benthic communities in the Aleutians

It is increasingly clear that the public, native tribes, and governmental agencies are interested in assessing the well-being of natural resources and ecosystems. This may take the form of understanding species presence, monitoring population status and trends, measuring behavior, or quantifying physiology, biological stresses, or chemical/radiological exposure through biomarkers. Often there is a separation between understanding the biological aspects of species well-being and assessing exposure to contaminants. In this paper we examine the applicability of using scuba sampling aimed primarily at specimen collection for radionuclide analysis to assess species presence/absence and to compare among sampling sites and depths. We were especially interested in whether dive transects could provide information on species presence and potential exposure to environmental contaminants. In June/July 2004 we sampled at 49 depth stations along 19 transects at Amchitka and Kiska Islands in the western Aleutian Islands in the Northern Pacific/Bering Sea region. Amchitka Island, a former World War II U.S. Navy base, was the site of three underground nuclear test shots from 1965 to 1971. Four to six transects were established at three Amchitka sites and two Kiska Sites, and 2 to 4 stations were sampled on each transect. Bottom conditions, weather and currents prevented a complete sampling of all stations. There were interspecific differences in the percent of stations where biota were found and collected, in their occurrence near the three test shots on Amchitka, and in the depth where they were found. There were no significant differences between Amchitka and Kiska Island in the percent of stations where species were found. These data suggest that information gathered incidentally to the collection of specimens for chemical/radiological analysis can prove useful for understanding the presence of benthic organisms along particular transects, at given depths, and at different geographical locations. This information also provides a baseline for the range of organisms that could be exposed to future physical or chemical/radiological stressors. The data are useful for developing future biomonitoring plans to assess biological well-being and chemical/radiological exposure only if they are published and available to the public, public policy makers, and managers. Just as it is critical to select endpoints and bioindicators that are of interest for assessing both human and ecological health, specimens should be collected using a protocol that is useful for both chemical/radiological analysis and biological information.

Predictable hotspots and foraging habitat of the endangered short-tailed albatross (Phoebastria albatrus) in the North Pacific: Implications for conservation

The short-tailed albatross (Phoebastria albatrus) is a rare and endangered seabird that ranges widely over the northern North Pacific. Populations are slowly recovering but birds face several threats at sea, in particular the incidental capture of birds in long-line fisheries. Conservation efforts are hampered by a lack of information about the at-sea distribution of this species, especially knowledge of where it may predictably co-occur with long-line fishing effort. During 18 years of transiting the Aleutian Islands Unit of the Alaska Maritime National Wildlife Refuge on a research vessel, we observed short-tailed albatross on 65 occasions. They were consistently observed near Ingenstrem Rocks (Buldir Pass) in the western Aleutians and near Seguam Pass in the central Aleutians. Based on the oceanographic characteristics of the locations where we saw most of the birds, we hypothesized that short-tailed albatross “hotspots” were located where tidal currents and steep bottom topography generate strong vertical mixing along the Aleutian Archipelago. As a test of this hypothesis, we analyzed a database containing 1432 opportunistic observations of 2463 short-tailed albatross at sea in the North Pacific. These data showed that short-tailed albatross were closely associated with shelf-edge habitats throughout the northern Gulf of Alaska and Bering Sea. In addition to Ingenstrem Rocks and Seguam Pass, important hotspots for short-tailed albatross in the Aleutians included Near Strait, Samalga Pass, and the shelf-edge south of Umnak/Unalaska islands. In the Bering Sea, hotspots were located along margins of Zhemchug, St. Matthews and Pervenets canyons. Because these short-tailed albatross hotspots are predictable, they are also protectable by regulation of threatening activities at local spatial scales.

Population genetic structure and conservation of marbled murrelets (Brachyramphus marmoratus)

Marbled murrelets (Brachyramphus marmoratus) are coastal seabirds that nest from California to the Aleutian Islands. They are declining and considered threatened in several regions. We compared variation in the mitochondrial control region, four nuclear introns and three microsatellite loci among194 murrelets from throughout their range except Washington and Oregon. Significant population genetic structure was found: nine private control region haplotypes and three private intron alleles occurred at high frequency in the Aleutians and California; global estimates of FST or ΦST and most pairwise estimates involving the Aleutians and/or California were significant; and marked isolation-by-distance was found. Given the available samples, murrelets appear to comprise five genetic management units: (1) western Aleutian Islands, (2) central Aleutian Islands, (3) mainland Alaska and British Columbia, (4) northern California, and (5) central California.

PROJECTING THE TREND OF STELLER SEA LION POPULATIONS IN WESTERN ALASKA

This paper attempts to project the trends of Steller sea lion (Eumetopias jubatus) populations in six subdivisions of the western Alaska population. The overall Western Alaska population has declined dramatically since the 1970s. Trends in half of the areas appear to have leveled-off and possibly to be on the increase. Bootstrapping has been used to provide confidence intervals on predictions for the 2004 counts. For the three areas in which we expect increases, the 95% confidence intervals on predictions were: Eastern Gulf (2,430–3,740), Central Gulf (3,260–3,660) and Central Aleutians (5,160–6,580). The Western Gulf counts have been somewhat erratic, with a gradual rate of decrease (about 2% per year) and wide confidence limits on a linear prediction (logarithmic scale) of 2,690–3,240. Trends in the Eastern Aleutians have been even more erratic, so that about all that can be inferred is that the population may be roughly stabilized. Only the Western Aleutians appear to be rapidly declining at about 10% per year, with a 95% confidence interval on a linear trend of 610–1,100. The predictions were made before the 2004 counts and are in reasonable accord with the 2004 counts. Age structure changes do not appeat to provide a viable explanation for the changing trends.

Spatial and temporal variability of the Aleutian climate

AbstractThe 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.

Distribution patterns and population trends of breeding seabirds in the Aleutian Islands

AbstractThe 1800‐km‐long Aleutian Archipelago is a breeding area for more than 10 million seabirds of 26 species. We evaluated the distribution of breeding colonies of 24 common breeding species in relationship to ocean passes of two sizes, availability of nesting habitat and the distribution of introduced predatory mammals. Further, we evaluated population trends and reproductive rates to amplify information about distribution. We compared distributions and demographic parameters based on proposed differences in marine habitats in the eastern, central and western Aleutians. Samalga Pass did not appear to be a break point for breeding seabird distribution as is suggested for oceanographic characteristics and other species groups by papers in this volume. Factors affecting distribution varied with foraging and nesting strategies of various species groups. The three largest breeding aggregations of seabirds in the Aleutians (Buldir, Chagulak and Kiska) all have relatively high species diversity and are located next to large passes. However, when other predictors were considered, proximity to medium or large passes was important mainly for surface‐feeding piscivores. The extent of nesting habitat apparently does not limit the distribution of surface‐ or burrow‐nesting species (including planktivores and piscivores). Instead, the distribution of these species probably has been shaped by introduced mammals. Nesting habitat for ledge‐ and crevice‐nesting species is more limited than for surface and burrow nesters but is still fairly widespread. Ledge‐ and crevice‐nesting species are less susceptible to fox predation than are surface and burrow nesters. These species may have been reduced by predation but were not extirpated.

The palaeoenvironment of humans and marine birds of the Aleutian Islands: three millennia of change

AbstractA unique window into the biological history of the Aleutian Islands is provided by the zooarchaeology of early human sites. We focus on the palaeoavifauna hunted by early Aleuts who inhabited Amchitka and Buldir islands (central Aleutians), and Shemya Island (western Aleutians) from c. 3500 yr ago to the present. Most of the seabird species recovered from these early sites varied widely in distribution and abundance through time and space. Pelagic procellariids such as short‐tailed albatrosses and short‐tailed shearwaters were present and abundant at most sites and at most times. During periods of increased temperatures and precipitation (e.g. 650–1100 yr bp), nearshore foragers such as cormorants and parakeet auklets increased in abundance, but during periods of cooling (e.g. 1800–2100 yr bp), piscivorous birds feeding offshore, such as murres and kittiwakes, predominated. Over three millennia, we found that marine bird populations were negatively correlated with temperature and positively correlated with precipitation. We detected hunter‐related depletions of populations breeding in accessible colonies at small scales of space and time, but we did not observe widespread or long‐term effects. We conclude that local oceanography and regional changes in prey bases caused by environmental and climate change in the past had a significant impact on the distribution and abundance of Aleutian marine birds.

Hydrographic features and seabird foraging in Aleutian Passes

AbstractStrong 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.

A bumblebee new to the New World: Bombus distinguendus (Hymenoptera: Apidae)

AbstractBombus (Subterraneobombus) distinguendus Morawitz, 1869 is recorded from Attu Island, in the western Aleutian archipelago, and is recognised as a species new to both the Alaskan and the New World faunal lists. Colour variation and food plants are described and a key to females of Nearctic Subterraneobombus species is provided.

Slab portal beneath the western Aleutians

Tomographic images of the distribution of shear-wave speed beneath the northwestern Pacific delineate the configuration of the subducted oceanic lithosphere beneath the western Aleutian arc. At ;100 km depth, a fast shear-wave speed anomaly is beneath the Aleutian arc everywhere east of 1738E. Between 1648E and 1738E, however, seismic velocities at this depth are slow relative to the surrounding mantle. The lateral termination of the fast shear-wave speed anomaly at depth coincides with a gap in deep seismicity beneath the Aleutians. The absence of these two distinctive traits of subducting slabs leads us to conclude that this segment of the Aleutian arc overlies a very large window in the otherwise continuous lithospheric slab that we term a ‘‘slab portal.’’ This portal is likely to facilitate the production of distinctive volcanic rocks (adakites or high-Mg# andesites) by partially melting the adjacent edges of the slab. The Miocene age of most adakites in the westernmost Aleutians where no slab is present may indicate that the portal formed relatively recently. The chemistry of western Aleutian adakites approximates that of typical continental crust, so their genesis and subsequent lateral transport toward Kamchatka is a plausible mechanism for new continent formation.

Two Genetically Distinct Forms of Rougheye Rockfish Are Different Species

AbstractThe variation in mitochondrial DNA (mtDNA) and at eight microsatellite loci was analyzed in 700 rougheye rockfish Sebastes aleutianus sampled along the Pacific Rim from the Oregon coast to the western Aleutian Islands and Bering Sea. The program STRUCTURE was used to analyze the microsatellite genotypes and determine that the samples probably came from two genetically distinct sources (type I and type II) by minimizing the strong Hardy−Weinberg and gametic disequilibria observed in the total sample. The two types had nearly fixed differences at one microsatellite locus (μSma 6), which corresponded to divergent mtDNA haplotype clusters. We conclude that these two types are distinct species. The ranges of the two types overlapped but were not coincident; in some areas, one or the other predominated. For example, most of the Aleutian Island samples were type I fish. Although both types were caught in the same hauls in some regions, often one or the other species was predominant in a haul. The differences in distributions suggest a historic vicariant or ecological basis for their divergence. No phenotypic characteristics have been confirmed that can be used to distinguish the two species visually. Rougheye rockfish have high commercial value and their incidental catch has the potential to greatly affect larger fisheries. The discovery of cryptic speciation in a commercially important species underscores our need to learn more about the distribution and biology of these and other groundfish species.

Behaviour of high field strength elements in subduction zones: constraints from Kamchatka–Aleutian arc lavas

Models explaining the characteristic depletion of High Field Strength Elements (HFSE) relative to elements of similar compatibility in subduction zone magmas invoke either (1) the presence of HFSE-rich minerals in the subduction regime or (2) a selectively lower mobility of HFSE during subduction metasomatism of the mantle. In order to investigate the properties of HFSE in subduction regimes closer, we performed high precision measurements of Nb/Ta, Zr/Hf, and Lu/Hf ratios together with 176Hf/ 177Hf analyses on arc rocks from Kamchatka and the western Aleutians. The volcanic rocks of the Kamchatka region comprise compositional end members for both fluid and slab melt controlled mantle regimes, thus enabling systematic studies on the HFSE mobility at different conditions in the subarc mantle. Hf–Nd isotope and systematic Zr/Hf and Lu/Hf covariations illustrate that Zr–Hf and Lu are immobile in fluid-dominated regimes. Hf–Nd isotope compositions furthermore indicate the presence of “Indian” type depleted mantle beneath Kamchatka, as previously shown for the Mariana and Izu–Bonin arcs. In addition to a depleted mantle component, Hf–Nd isotope compositions enable identification of a more enriched mantle wedge component in the back-arc (Sredinny Ridge) that most likely consists of mantle lithosphere. The ratios of Nb/Ta and Zr/Hf are decoupled in rocks from fluid-dominated sources, indicating that Nb and Ta can be enriched in the mantle by subduction fluids to a small extent. In contrast to the fluid-dominated regime in Central Kamchatka, the budget of HFSE and Lu in rocks from the Northern Kamchatka Depression and in adakitic rocks from the western Aleutians is significantly affected by slab melts that originate from subducted oceanic crust. Compositions of the rocks with the highest slab melt components in their source (Sr/Y>30) provide no evidence that either Nb/Ta or Zr/Hf ratios are fractionated at a globally significant scale during melting of subducted oceanic crust. Subduction processes are therefore an unlikely candidate to explain the terrestrial Nb–Ta paradox (i.e., the subchondritic Nb/Ta ratios in all accessible terrestrial silicate reservoirs).