Eastern Aleutian Research Articles

Shorter Migration Distance and Breeding Latitude Correlate With Earlier Egg-Laying Across the Northeastern Pacific Ocean Range of the Rhinoceros Auklet (Cerorhinca monocerata).

Models of migratory behavior predict trade-offs between fitness costs and benefits with respect to migration distance. Shorter migration distances may confer a fitness benefit by facilitating earlier breeding, however this is rarely investigated. We tested this hypothesis using a large-scale geolocation (GLS) dataset from 109 rhinoceros auklets (Cerorhinca monocerata), a differentially migrating seabird, that was tagged at 12 breeding colonies along the Pacific Coast of North America, spanning southern California to the eastern Aleutian Islands, Alaska. Using GLS-based position estimates, we determined the geographic centroid of the pelagic areas occupied by birds in winter (1 January-28 February) and then calculated the distance between their wintering centroids and colony of origin. We then used GLS light-intensity and salt-water immersion (wet/dry) data to determine each individual's date of egg-laying the following spring. Rhinoceros auklets were very widely distributed across the northeastern Pacific Ocean in winter. Among all individuals, the distance between winter centroids and breeding colonies ranged from < 100 to > 2500 km, being greater among individuals originating from colonies at higher latitudes. As predicted, migration distance and colony latitude were positively related to lay date: after accounting for colony-level differences in phenology, individuals that migrated shorter distances tended to lay their eggs earlier, a pattern that emerged across all populations. Our study links the migration distance of rhinoceros auklets to a fitness-related outcome, underscoring the selective pressure that migration exerts on subsequent breeding activity.

Mechanical Essence of Double-Arc Formation Along the Eastern Aleutian Subduction Zone

The free-air gravity anomaly along the Aleutian subduction zone exhibits a single set of negative and positive trench-parallel belts in the western region, whereas it exhibits doubled negative–positive trench-parallel belts in the eastern region. The eastern inner–western positive gravitational belt corresponds to the topographic chain of the Alaska Peninsula and the Aleutian Islands. However, the eastern outer positive gravitational belt does not coincide with the chain of the topographic outer-arc highs. In this study, we determined the across-trench profiles of the plate interface geometry for the western and eastern Aleutian subduction zones on the basis of the hypocentre distribution. The surface uplift rates computed from the dislocation-based two-dimensional subduction model for the Aleutian plate interface profiles adequately reproduced the western single-arc and eastern double-arc characteristics. The essential factors of the double-arc formation are a low subduction dip angle and a bimodal plate interface curvature distribution within the elastic lithosphere. The double-arc highs of the computed uplift rates more closely coincided with the gravitational highs than the current topographic highs. This implies that tectonic events in the past caused the topographic activity shift towards the continental shelf edge and the subsequent topographic readjustment under the current tectonic state.

Multilayer anisotropy along the Alaska-Aleutians Subduction zone

SUMMARY Increasing evidence from seismic methods shows that anisotropy within subduction zones should consist of multiple layers. To test this, we calculate and model shear wave splitting across the Alaska-Aleutians Subduction Zone (AASZ), where previous studies have argued for separate layers of anisotropy in the subslab, slab and mantle wedge. We present an updated teleseismic splitting catalogue along the span of the AASZ, which has many broad-band seismometers recently upgraded to three components. Splitting observations are sparse in the Western Aleutians, and fast directions are oriented generally trench parallel. There are significantly more splitting measurements further east along the AASZ. We identify six regions in the Central and Eastern Aleutians, Alaskan Peninsula and Cook Inlet with a high density of splits suitable for multilayered anisotropy analyses. These regions were tested for multilayer anisotropy, and for five of the six regions we favour multiple layers over a single layer of anisotropy. We find that the optimal setup for our models is one with a dipping middle layer oriented parallel to palaeospreading. A prominent feature of our modelling is that fast directions above and below the dipping layer are generally oriented parallel to the strike of the slab. Additionally, we lay out a framework for robust and statistically reliable multilayer shear wave splitting modelling.

Mysticete whale abundance and observations of prey associations on the central Bering Sea shelf

Visual surveys for cetaceans were conducted along transect lines in the central Bering Sea in association with a groundfish stock assessment survey from 5 July to 5 August 1999. There were 125 sightings of single or groups of mysticete whales during 6,043km of survey effort. Fin whales were most common (60% of all sightings), with distribution clustered along the outer continental shelf break near the 200m isobath. In addition, there were 27 sightings of minke whales and 17 sightings of humpback whales. Minke whales were primarily found along the upper slope in water 100-200m deep, while humpbacks clustered along the eastern Aleutian Islands and near the USA/Russian Convention Line southwest of St. Lawrence Island. Abundance estimates for fin, humpback and minke whales were: 4,951 (95% CI = 2,833-8,653); 1,175 (95% CI = 197-7,009) and 936 (95% CI = 473-1,852), respectively. These three species were the only ones for which sufficient on-effort sightings were available to estimate abundance. Sei whales, a gray whale and a pair of northern right whales were also seen. Although right whales have been seen in this area before, some behavioural details are provided here because observations of these whales remain rare.

Two New Species of Snailfishes (Cottiformes: Liparidae) from the Aleutian Islands, Alaska, and a Redescription of the Closely Related Careproctus candidus

Two new species of snailfishes are described from the Aleutian Islands. Both are similar to Careproctus candidus, described originally from four specimens, here redescribed on the basis of 67 specimens in addition to the types. All three species are allocated to the Careproctus subgenus Temnocora. Careproctus candidus is distinguished from all other species of Careproctus by the combination of an anterior dorsal-fin lobe formed by a distinct notch, pupil a horizontal slit, and variegated reddish coloration. It is redescribed to note the presence of prickles, a variable pectoral-girdle morphology, and variable exsertions of the fin rays of the dorsal-fin lobe. Careproctus klisi, new species, is distinguished by having an anterior dorsal fin uniquely of five to seven short anterior dorsal-fin rays nearly equal in length preceding distinctly longer succeeding rays, pupil a horizontal slit, a variegated reddish coloration, and a relatively deep body. Careproctus bromius, new species, is distinguished by having low vertebral and median-fin ray counts, pupil a horizontal slit, a variegated light brown and pale coloration, and in lacking an anterior dorsal-fin lobe. Careproctus candidus ranges across the Aleutian Islands from Attu Island to the northern Gulf of Alaska at depths from 88 to 432 m. Careproctus klisi, new species, is found in the central and western Aleutian Islands from off Buldir Island in the west to Amlia Island in the east at depths from 134 to 180 m. Careproctus bromius, new species, is found in the central and eastern Aleutian Islands from Amchitka Pass to off Akutan Island at depths from 80 to 232 m.

New insight into migration patterns of western North Pacific humpback whales between the Babuyan Islands, Philippines and the Commander Islands, Russia

The population structure of humpback whales (Megaptera novaeangliae) in the North Pacific has received significant attention in recent years through the collaborative Structure of Populations, Levels of Abundance, and Status of Humpback whales in the North Pacific (SPLASH) study. However, the analysis of humpback whales in the western North Pacific Asian population was limited in the SPLASH study, due to small sample size. Much of the Asian population summers off Kamchatka, Russia and spends the winters in breeding grounds in Okinawa and Ogasawara, Japan and the Babuyan Islands in the northern Philippines. Prior studies grouped the Commander Islands feeding ground in Russia, with the eastern Aleutian Islands as part of the central humpback whale stock. This paper uses additional years of photo-ID data from both the Philippines (160 whales from 2000–12) and the Commander Islands (531 whales from 2008–10) to establish a previously unreported migratory connection by matching four animals between the two sites. The new migratory linkage found in the present study suggests that a small portion of humpback whales hypothesised to be migrating to a ‘missing’ breeding ground in the central North Pacific are actually migrating to the Philippines. However, additional studies on a wider geographical scale are required.

Fasting durations of Steller sea lion pups vary among subpopulations-evidence from two plasma metabolites.

Geographic differences in population growth trends are well-documented in Steller sea lions (Eumetopias jubatus), a species of North Pacific pinniped listed under the U.S. Endangered Species Act in 1990 following a marked decline in population abundance that began during the 1970s. As population growth is intrinsically linked to pup production and survival, examining factors related to pup physiological condition provides useful information to management authorities regarding potential drivers of regional differences. During dam foraging trips, pups predictably transition among three fasting phases, distinguished by the changes in the predominant metabolic byproduct. We used standardized ranges of two plasma metabolites (blood urea nitrogen and β-hydroxybutyrate) to assign pups to fasting categories (n = 1528, 1990-2016, 12 subpopulations): Recently Fed-Phase I (digestion/assimilation-expected hepatic/muscle glycogen usage), Phase II (expected lipid utilization), transitioning between Phases II-III (expected lipid utilization with increased protein reliance), or Phase III (expected protein catabolism). As anticipated, the majority of pups were classified as Recently Fed-Phase I (overall mean proportion = 0.72) and few pups as Phase III (overall mean proportion = 0.04). By further comparing pups in Short (Recently Fed-Phase II) and Long (all other pups) duration fasts, we identified three subpopulations with significantly (P < 0.03) greater proportions of pups dependent upon endogenous sources of energy for extended periods, during a life stage of somatic growth and development: the 1) central (0.27 ± 0.09) and 2) western (0.36 ± 0.13) Aleutian Island (declining population trend) and 3) southern Southeast Alaska (0.32 ± 0.06; increasing population trend) subpopulations had greater Long fast proportions than the eastern Aleutian Islands (0.10 ± 0.05; stabilized population). Due to contrasting population growth trends among these highlighted subpopulations over the past 50+ years, both density-independent and density-dependent factors likely influence the dam foraging trip duration, contributing to longer fasting durations for pups at some rookeries.

Birds of The Shumagin Islands, Alaska

We studied birds in the Shumagin Islands in 18 of the 37 years from 1970 to 2006 and synthesized all available information on birds of this area. A total of 126 forms of 125 species, including hypothetical species, has been recorded in the Shumagins, of which aquatic birds constitute 67% and terrestrial birds 33%. Overall, 52% of all forms breed, probably breed, or formerly bred; of these, aquatic birds represent 57% and terrestrial birds 43%. The avifauna is heavily weighted toward Nearctic (39% of all forms) and Beringian (32%) forms, followed by Holarctic (21%), Palearctic (6%), and Oceanian (2%) forms; breeding taxa are even more heavily weighted toward Beringian (46%) and Nearctic (40%) forms. The Shumagins have few breeding waterfowl, other freshwater birds, and shorebirds and are not on important flyways for any of these groups, despite lying near important spring and fall staging areas on the nearby Alaska Peninsula. The seabird and terrestrial avifaunas are diverse and similar to those in nearby areas, especially the eastern Aleutians. Populations of several seabird species in the Shumagins have declined substantially over the last 40 years. Two terrestrial species, the Pacific Wren (Troglodytes pacificus) and Pine Grosbeak (Pinicola enucleator), have expanded their breeding ranges into this area, and breeding distributions of some terrestrial birds in the outer Shumagins appear to be changing. Changes in range or breeding status have been caused, at least in part, by predation by introduced foxes, overgrazing by introduced cattle degrading already limited habitat, and the introduction of ground squirrels.

Length-based approaches to estimating natural mortality using tagging and fisheries data: The example of the eastern Aleutian Islands, Alaska golden king crab (Lithodes aequispinus)

We evaluated natural mortality (M yr−1) estimation reliability for eastern Aleutian Islands male golden king crab (Lithodes aequispinus), an exploited stock, by comparing an integrated length-based assessment model approach and a likelihood method using tag release-recapture data. We used 1997, 2003, and 2006 tag release-recapture data to estimate the size transition matrix, M, fishing mortality, total selectivity, and retained selectivity and compared M likelihood profiles between both methods. Furthermore, we conducted simulations with varying initial survival and tag reporting rates to show that M estimation reliability declines as these rates decline. Restricted time-at-large, full initial survival, and complete reporting assumptions produce an M estimate closer to that of the integrated length-based assessment method. Because the reliability of the M estimate is sensitive to changes in these assumptions, future efforts should focus on maximizing the number of tagged crab (and hence recaptures), evaluating initial tag-induced mortality, and optimizing tagged crab recapture reporting rates. The reliance of fishery-dependent data and high tag reporting rates highlights the importance for maintaining a positive cooperation with fishers for efforts towards sustainable management.

Genetic variation in sea otters (Enhydra lutris) from the North Pacific with relevance to the threatened Southwest Alaska Distinct Population Segment

AbstractFor the sea otter (Enhydra lutris), genetic population structure is an area of research that has not received significant attention, especially in Southwest Alaska where that distinct population segment has been listed as threatened since 2005 pursuant to the U.S. Endangered Species Act. In this study, 501 samples from 14 locations from Prince William Sound, Alaska to the Commander Islands in Russia were analyzed for variation at 13 microsatellite loci. Our results indicate a high degree of genetic divergence among the 14 locations (FST = 0.120) with gene flow conforming to the isolation by distance (IBD) model (r2 = 0.491, p &lt; .05). The 14 sampling locations formed six geographic associations in clustering and ordination analyses that likely correspond to remnant population lineages: (1) Southcentral Alaska, (2) Kodiak and North Alaska Peninsula, (3) South Alaska Peninsula and Bristol Bay, (4) Eastern Aleutian, (5) Western Aleutian, and (6) the Commander Islands. Except for South Alaska Peninsula and Bristol Bay, these clusters closely agree with previously defined stock and management unit boundaries. Our results reveal significant genetic population structure and are generally congruent with current management strategies for the threatened Southwest Alaska distinct population segment.

A hierarchical distance sampling model to estimate spatially explicit sea otter density

AbstractWildlife managers often rely on analyses conducted prior to the widespread adoption of hierarchical models which can lead to questions about the accuracy of previous inferences. Hierarchical models allow observed data to be partitioned into factors that influenced the collection of the data such as detectability of animals (i.e., observation processes) and factors that influence the ecology of a population such as features that affect the distribution of animals (i.e., ecological processes). Population surveys for sea otters in the Aleutian Islands, Alaska, have historically been conducted by conflating the observation and ecological processes potentially leading to inaccurate population estimates. Based on boat and plane‐based sea otter survey data collected in 2017, we sought to overcome many problems of previous sea otter surveys in southwestern Alaska. We developed a spatially explicit hierarchical distance sampling model to estimate the abundance of sea otters in the Eastern Aleutians Management Unit while explicitly accounting for factors that affect the ability to detect sea otters during surveys (i.e., group size, ocean conditions). We also sought to account for the environmental factors leading to the non‐uniform distribution of sea otter groups by identifying relationships between otter group abundance and environmental attributes (i.e., ocean depth, presence of kelp, underwater substrate). Detection of sea otter groups was related to group size, and ocean conditions (e.g., ocean swell size). After accounting for detection, we estimated a mean population size of 8593 individual sea otters (95% CI: 7450–9984) which is considerably higher than previous estimates, although comparisons are difficult given divergent methodologies. Sea otter group density was negatively related to ocean depth and the presence of rock and gravel as underwater substrates. Conversely, sea otter group density was positively related to the presence of kelp and mud as an underwater substrate. Our hierarchical distance sampling model accounted for the observation process which allowed better estimates of the environmental attributes affecting otter abundance. Our research can serve as a template for other study systems requiring spatially explicit density estimates from a distance sampling framework and can help provide a new baseline for managers to gauge future population changes in sea otters.

Comparing non-breeding distribution and behavior of red-legged kittiwakes from two geographically distant colonies.

Knowledge of non-breeding distributions is a crucial component to seabird conservation, as conditions during the non-breeding period can play an important role in regulating seabird populations. Specifically, if seabirds from different colonies share the same wintering grounds, conditions in that shared region could have a widespread impact on multiple breeding populations. Red-legged kittiwakes (Rissa brevirostris) are endemic to the Bering Sea and may be especially susceptible to effects of climate change due to a restricted breeding range, small population size, and specialized diet. To examine whether red-legged kittiwakes from different breeding colonies overlapped in winter distribution and activity patterns, we used geolocation loggers to simultaneously track individuals from the two largest red-legged kittiwake breeding colonies in Alaska (separated by over 1000 km) during two consecutive non-breeding periods. We found that non-breeding activity patterns were generally similar between birds originating from the two colonies, but birds employed different migratory strategies during the early winter. Kittiwakes from Buldir Island in the western Aleutian Islands left the colony in September and immediately headed west, spending October through December around the Sea of Okhotsk and the Kuril Islands. In contrast, birds from St. George Island in the Pribilof Islands remained in the eastern Bering Sea or around the eastern Aleutian Islands for a couple months before traveling farther west. During late winter however, from January through March, birds from both colonies converged south of Kamchatka and east of the Kuril Islands over the Kuril-Kamchatka Trench and in the Western Subarctic Gyre before returning to their respective colonies in the spring. This late winter overlap in distributions along the Kuril-Kamchatka Trench suggests the region is a winter hotspot for red-legged kittiwakes and highlights the importance of this region for the global kittiwake population.

Development of harvest control rules for hard-to-age crab stocks: the example of the golden king crab (Lithodes aequispinus) in the eastern Aleutian Islands in Alaska: suppl. fig. 1

Development of harvest control rules for hard-to-age crab stocks: the example of the golden king crab (Lithodes aequispinus) in the eastern Aleutian Islands in Alaska: suppl. fig. 1

Development of harvest control rules for hard-to-age crab stocks: the example of the golden king crab (Lithodes aequispinus) in the eastern Aleutian Islands in Alaska: suppl. materials

Development of harvest control rules for hard-to-age crab stocks: the example of the golden king crab (Lithodes aequispinus) in the eastern Aleutian Islands in Alaska: suppl. materials

Development of harvest control rules for hard-to-age crab stocks: the example of the golden king crab (Lithodes aequispinus) in the eastern Aleutian Islands in Alaska: suppl. fig. 3

Development of harvest control rules for hard-to-age crab stocks: the example of the golden king crab (Lithodes aequispinus) in the eastern Aleutian Islands in Alaska: suppl. fig. 3

Development of harvest control rules for hard-to-age crab stocks: the example of the golden king crab (Lithodes aequispinus) in the eastern Aleutian Islands in Alaska: suppl. fig. 5

Development of harvest control rules for hard-to-age crab stocks: the example of the golden king crab (Lithodes aequispinus) in the eastern Aleutian Islands in Alaska: suppl. fig. 5

Development of harvest control rules for hard-to-age crab stocks: the example of the golden king crab (Lithodes aequispinus) in the eastern Aleutian Islands in Alaska: suppl. fig. 4

Development of harvest control rules for hard-to-age crab stocks: the example of the golden king crab (Lithodes aequispinus) in the eastern Aleutian Islands in Alaska: suppl. fig. 4

Development of harvest control rules for hard-to-age crab stocks: the example of the golden king crab (Lithodes aequispinus) in the eastern Aleutian Islands in Alaska: suppl. tables

Development of harvest control rules for hard-to-age crab stocks: the example of the golden king crab (Lithodes aequispinus) in the eastern Aleutian Islands in Alaska: suppl. tables

Development of harvest control rules for hard-to-age crab stocks: the example of the golden king crab (Lithodes aequispinus) in the eastern Aleutian Islands in Alaska: suppl. fig. 2

Development of harvest control rules for hard-to-age crab stocks: the example of the golden king crab (Lithodes aequispinus) in the eastern Aleutian Islands in Alaska: suppl. fig. 2

Development of harvest control rules for hard-to-age crab stocks: the example of the golden king crab (Lithodes aequispinus) in the eastern Aleutian Islands in Alaska: suppl. fig. 6

Development of harvest control rules for hard-to-age crab stocks: the example of the golden king crab (Lithodes aequispinus) in the eastern Aleutian Islands in Alaska: suppl. fig. 6