We used seabird surveys and concurrent oceanographic observations in the Northern Gulf of Alaska during spring 1998-2019 to evaluate how seabirds responded to temperature variability, including a protracted marine heatwave, in a highly heterogeneous ecosystem. We examined temporally changing distributions of seabirds along the Seward Line, a 220 km transect across the shelf and slope, and evaluated relationships between water-mass properties and seabird abundance. Environmental factors associated with abundance include depth, water-column temperature and salinity, and surface-current velocities. Environmental responses of alcids and gulls contrasted with those of procellariiform (tubenose) seabirds, and their trajectories suggest a possible shift in community composition under future climate warming. Changes in seabird distribution and abundance associated with a shift from cold to warm conditions were especially pronounced over the middle- and outer-shelf domains, which are transitional between coastal and oceanic water masses. The abundance of tubenoses increased during and after the heatwave, whereas alcids and gulls shifted inshore, exhibited reproductive failures, and experienced mass mortalities due to starvation. Tubenoses appear well-adapted to periods of lower productivity during warming events because of their flight efficiency, allowing them to search widely to locate prey patches. In contrast, alcids, which forage by diving and have energetically expensive flight, appear sensitive to such conditions.

Introduction Seabirds are abundant, conspicuous members of marine ecosystems worldwide. Synthesis of distribution data compiled over time is required to address regional management issues and understand ecosystem change. Major challenges when estimating seabird densities at sea arise from variability in dispersion of the birds, sampling effort over time and space, and differences in bird detection rates associated with survey vessel type. Methods Using a novel approach for modeling seabirds at sea, we applied joint dynamic species distribution models (JDSDM) with a vector-autoregressive spatiotemporal framework to survey data collected over nearly five decades and archived in the North Pacific Pelagic Seabird Database. We produced monthly gridded density predictions and abundance estimates for 8 species groups (77% of all birds observed) within Cook Inlet, Alaska. JDSDMs included habitat covariates to inform density predictions in unsampled areas and accounted for changes in observed densities due to differing survey methods and decadal-scale variation in ocean conditions. Results The best fit model provided a high level of explanatory power (86% of deviance explained). Abundance estimates were reasonably precise, and consistent with limited historical studies. Modeled densities identified seasonal variability in abundance with peak numbers of all species groups in July or August. Seabirds were largely absent from the study region in either fall (e.g., murrelets) or spring (e.g., puffins) months, or both periods (shearwaters). Discussion Our results indicated that pelagic shearwaters (Ardenna spp.) and tufted puffin (Fratercula cirrhata) have declined over the past four decades and these taxa warrant further investigation into underlying mechanisms explaining these trends. JDSDMs provide a useful tool to estimate seabird distribution and seasonal trends that will facilitate risk assessments and planning in areas affected by human activities such as oil and gas development, shipping, and offshore wind and renewable energy.

Some of the longest and most comprehensive marine ecosystem monitoring programs were established in the Gulf of Alaska following the environmental disaster of the Exxon Valdez oil spill over 30 years ago. These monitoring programs have been successful in assessing recovery from oil spill impacts, and their continuation decades later has now provided an unparalleled assessment of ecosystem responses to another newly emerging global threat, marine heatwaves. The 2014–2016 northeast Pacific marine heatwave (PMH) in the Gulf of Alaska was the longest lasting heatwave globally over the past decade, with some cooling, but also continued warm conditions through 2019. Our analysis of 187 time series from primary production to commercial fisheries and nearshore intertidal to offshore oceanic domains demonstrate abrupt changes across trophic levels, with many responses persisting up to at least 5 years after the onset of the heatwave. Furthermore, our suite of metrics showed novel community-level groupings relative to at least a decade prior to the heatwave. Given anticipated increases in marine heatwaves under current climate projections, it remains uncertain when or if the Gulf of Alaska ecosystem will return to a pre-PMH state.

Common and thick–billed murres are among the most numerous and widespread seabirds in the northern hemisphere though they appear to be especially susceptible to mass die–off events. During the spring and summer of 2018, the Bering Sea experienced warmer than average sea temperatures following a winter of unprecedented, near complete lack of sea ice. To determine if breeding murres were negatively affected by these warm sea temperatures, surveys at most of the major murre breeding colonies in the eastern Bering and eastern Chukchi seas were conducted during the 2018 breeding season. Nearly all colonies surveyed experienced near-complete reproductive failure. Concurrently, above average levels of murre mortality were observed, primarily at St. Lawrence Island and in the Bering Strait region. The timing of this mortality is somewhat unusual and concerning as it occurred during the breeding season. Based on surveys at sea, overall murre abundance offshore was generally lower in 2018 compared to recent years (2012–2017), particularly in the northern Bering Sea, yet mean density for thick–billed murres increased in the Chukchi Sea. Reproductive failure is rare at monitored murre colonies within the study area and the widespread reproductive failures observed in 2018 were unprecedented over four decades of monitoring, but consistent with the reproductive failure of murres documented in the Gulf of Alaska and southeastern Bering Sea following a large murre die–off in 2015–2016. The combination of large–scale reproductive failure, evidence of elevated levels of mortality, and low abundance of birds offshore suggest that murres experienced severe distress in the Bering and Chukchi sea region during the summer of 2018.

In the northern Bering Sea and eastern Chukchi Sea, 2017-2019 were record-breaking years for warm ocean temperatures and lack of sea ice. The region supports millions of seabirds that could be affected by shifts in prey distribution and availability caused by changing environmental drivers. However, seabirds are highly mobile and often flexible in diet, and might alter their foraging distributions accordingly. To determine if there was evidence of long-term changes in abundance of seabirds, or if seabirds used the offshore habitat differently during recent warm years, we compared species richness, community composition, and distribution and abundance of selected species and Total seabirds (all species combined) between two periods, 2007-2016 and 2017-2019. We also evaluated annual changes in abundance during 2007-2019. We used 79,426 km of transects from vessel-based surveys conducted July through September. Total seabird density for the entire study area increased by -20% during 2017-2019, but changes were not consistent across the study area, nor among species, and species richness declined except for a slight increase in the northern Chukchi Sea. Total seabird density declined most in the northern Bering Sea (-27%), although it increased in the Chirikov Basin by 73%. During 2017-2019, abundance of piscivorous murres (Uria spp.) decreased everywhere, whereas planktivorous Aethia auklet density increased by 70% in Chirikov Basin; auklets apparently abandoned their post-breeding migration to the Chukchi Sea. Short-tailed shearwaters (Ardenna tenuirostris) expanded farther into the northern Chukchi Sea, with nearly twice the density of the previous decade. We identified five seabird community types, three of which (all dominated by an alcid species) contracted spatially in the later period, and shifted south or near colonies. In contrast, a short-tailed shearwater dominated community expanded northward, and a community defined by low seabird density expanded throughout the eastern portion of both the northern Bering and Chukchi seas, suggesting higher-density communities had shifted westward. The variable responses among species correspond to documented changes in the environment as well as their natural history.

An array of eight Distributed Biological Observatory (DBO) sites serve as long-term monitoring areas for three geographic regions: the northern Bering, eastern Chukchi, and Beaufort seas. The locations of the DBO sites were largely determined based on abundance and diversity of benthic invertebrates. It is not clear how well these fixed sampling sites can detect changes in processes and populations that operate over spatial scales that are 1-3 orders of magnitude greater than the areas sampled by the DBO sites. In this paper, we examine whether the DBO array provides a reasonable method by which to describe and monitor the distribution and community composition of seabirds in the eastern Pacific Arctic, and if it captures areas of high seabird abundance. We used vessel-based survey data totaling similar to 115,860 km of transects within the study area from July-October 2007-2015. We compared species richness, diversity, abundance, and community composition of seabirds among DBO sites and to the broader geographic regions. In general, the avifauna of DBO sites were representative of their respective surrounding region, although sampling effort in the Beaufort was limited. Species richness (totaling 63 species) was highest in the Bering region and lowest in the Beaufort region. Species diversity indices were similar among DBO sites and regions, except for exceptionally low diversity in the two easternmost DBO sites of the Beaufort region. Total seabird abundance was highest in and near Bering Strait, and dropped abruptly northward and eastward of Point Barrow. We used K-means cluster analysis to identify six community types across the entire study area, with five community types identified as having at least one numerically dominant species, and one community type defined by very low densities of a variety of species. Several community types were associated with major current systems (e.g. Anadyr Current, Alaska Coastal Current), and for two community types, breeding colony locations were also influential. Short-tailed shearwaters were the most abundant species in five of the eight DBO sites, and they were the numerically dominant species in a community that was represented from DBO 1 through DBO 6. Overall, variance in abundance was much greater by DBO site (or region) than by year for total birds and for seven of eleven taxa. Taxa with greater interannual variance than spatial variance were shearwaters and phalaropes (among regions), and murrelets (among DBO sites), all of which are late summer migrants to the study area, and glaucous gulls, a circumpolar species. The consistency in species' abundance by site indicates that DBO sites will be useful for monitoring seabirds in each region. As an array, the DBO sites captured major hotspots of seabird abundance as well as the seabird communities, except for the fulmar-dominated community in the outer Bering Shelf. However, all DBO sites will need to be surveyed to capture the full range of seabird communities in this study area. The Beaufort DBO sites require more survey coverage than currently achieved to fully evaluate their effectiveness to monitor changes in seabirds for that region.

Research and monitoring activities over the 28 years since the T/V Exxon Valdez ran aground and spilled oil into Prince William Sound, Alaska have led to an improved understanding of how wildlife populations were damaged, as well as the mechanisms and timelines of recovery. A key finding was that for some species, such as harlequin ducks and sea otters, chronic oil spill effects persisted for at least two decades and were a larger influence on population dynamics over the long term than acute effects of the spill. These data also offer insights into population variation resulting from factors other than the oil spill. For example, while many seabirds experienced direct and indirect effects of the spill, population trajectories of some piscivorous birds, including pigeon guillemots and marbled murrelets, were linked to long-term environmental changes independent of spill effects. Another species, killer whales, suffered population declines due to acute spill effects that have not been resolved despite lack of chronic direct effects, representing a novel pathway of long-term injury. The observed variation in mechanisms and timelines of recovery is linked to species specific life history and natural history traits, and thus may be useful for predicting population recovery for other species following other spills.

Over recent decades, marine ecosystems of Prince William Sound (PWS), Alaska, have experienced concurrent effects of natural and anthropogenic perturbations, including variability in the climate system of the northeastern Pacific Ocean. We documented spatial and temporal patterns of variability in the summer marine bird community in relation to habitat and climate variability using boat-based surveys of marine birds conducted during the period 1989–2012. We hypothesized that a major factor structuring marine bird communities in PWS would be proximity to the shoreline, which is theorized to relate to aspects of food web structure. We also hypothesized that shifts in physical ecosystem drivers differentially affected nearshore-benthic and pelagic components of PWS food webs. We evaluated support for our hypotheses using an approach centered on community-level patterns of spatial and temporal variability. We found that an environmental gradient related to water depth and distance from shore was the dominant factor spatially structuring the marine bird community. Responses of marine birds to this onshore-offshore environmental gradient were related to dietary specialization, and separated marine bird taxa by prey type. The primary form of temporal variability over the study period was monotonic increases or decreases in abundance for 11 of 18 evaluated genera of marine birds; 8 genera had declined, whereas 3 had increased. The greatest declines occurred in genera associated with habitats that were deeper and farther from shore. Furthermore, most of the genera that declined primarily fed on pelagic prey resources, such as forage fish and mesozooplankton, and few were directly affected by the 1989 Exxon Valdez oil spill. Our observations of synchronous declines are indicative of a shift in pelagic components of PWS food webs. This pattern was correlated with climate variability at time-scales of several years to a decade.

Ecological theory predicts that co-existing, morphologically similar species will partition prey resources when faced with resource limitations. We investigated local movements, foraging dive behavior, and foraging habitat selection by breeding adults of 2 closely related cormorant species, double-crested cormorants Phalacrocorax auritus and Brandt's cormorants P. penicillatus. These species nest sympatrically at East Sand Island in the Columbia River estuary at the border of Oregon and Washington states, USA. Breeding individuals of each species were tracked using GPS tags with integrated temperature and depth data-loggers. The overall foraging areas and core foraging areas (defined as the 95% and 50% kernel density estimates of dive locations, respectively) of double-crested cormorants were much larger and covered a broader range of riverine, mixed-estuarine, and nearshore marine habitats. Brandt's cormorant foraging areas were less expansive, were exclusively marine, and mostly overlapped with double-crested cormorant foraging areas. Within these areas of overlap, Brandt's cormorants tended to dive deeper (median depth = 6.48 m) than double-crested cormorants (median depth = 2.67 m), and selected dive locations where the water was deeper. Brandt's cormorants also utilized a deeper, more benthic portion of the water column than did double-crested cormorants. Nevertheless, the substantial overlap in foraging habitat between the 2 cormorant species in the Columbia River estuary, particularly for Brandt's cormorants, suggests that superabundant prey resources allow these 2 large and productive cormorant colonies to coexist on a single island near the mouth of the Columbia River.