Gulf Of Alaska Research Articles

Better Regional Ocean Observing Through Cross-National Cooperation: A Case Study From the Northeast Pacific

The ocean knows no political borders. Ocean processes like summertime, wind-driven upwelling stretch thousands of kilometers along the Northeast Pacific (NEP) coast. This upwelling drives marine ecosystem productivity and is modulated by weather systems and seasonal to interdecadal ocean-atmosphere variability. Major ocean currents in the NEP transport water properties like heat, fresh water, nutrients, dissolved oxygen, pCO2 and pH close to shore. The eastward North Pacific Current bifurcates offshore in the NEP, delivering open-ocean signals south into the California Current and north into the Gulf of Alaska. There are a large and growing number of NEP ocean observing elements operated by government agencies, Native American Tribes, First Nations groups, not-for-profit organizations, and private entities. Observing elements include moored and mobile platforms, shipboard repeat cruises, and land-based and estuarine stations. A wide range of multidisciplinary ocean sensors are deployed to track, for example, upwelling, downwelling, ocean productivity, harmful algal blooms, ocean acidification and hypoxia, seismic activity and tsunami wave propagation. Data delivery to shore and observatory control are done through satellite and cell phone communication, and via seafloor cables. Remote sensing from satellites and land-based coastal radar provide broader spatial coverage. Numerical circulation and biogeochemical modeling complement ocean observing efforts. Models span from the deep ocean into the inland Salish Sea and estuaries. NEP ocean observing systems are used to understand regional processes and, together with numerical models, to provide ocean forecasts. By sharing data, experiences and lessons learned, the regional ocean observatory is better than the sum of its parts.

The utility of length, age, liver condition, and body condition for predicting maturity and fecundity of female sablefish

The objectives of this study were to determine if relative body condition and relative liver size (hepatosomatic index, HSI) could be utilized to predict maturity 6–8 months prior to spawning, when samples are readily available, and if these condition measures were related to fecundity. Female sablefish were sampled on four survey legs during a summer longline survey in July and August 2015 and during a winter survey in December 2015, which is 1–3 months prior to the spawning season in the Gulf of Alaska. The relative body condition and HSI of fish increased throughout the summer survey, reaching measurements similar to those observed during the winter. There were significant differences between immature and mature fish HSI and relative body condition and these differences increased throughout the summer, making these factors useful for predicting maturity on the last legs of the survey. On these later legs, models that utilized relative body condition and HSI, as well as length and age, to predict whether a fish was immature or would spawn produced maturity curves that best matched models based on histological maturity classifications. However, models without HSI may be the best choice for future work because liver weight is not regularly collected on annual surveys and on the last leg of the survey the addition of HSI to predicitive models did not improve maturity-at-age curves. Utilizing the winter data set, which is the time period when fecundity could be enumerated, fecundity was significantly related to relative condition and HSI. Increasing or decreasing these measures of condition by one standard deviation in a model of fecundity, which also included length, resulted in an estimated decrease in fecundity of 32% or an increase of 47% for an average size fish (78 cm). These results show the importance of incorporating fish condition into measures of population productivity.

Diel vertical migration of sablefish (Anoplopoma fimbria)

AbstractTo investigate their diel vertical migration (DVM), 599 sablefish (Anoplopoma fimbria) were implanted with electronic archival tags in the Gulf of Alaska, Aleutian Islands, and the eastern Bering Sea. Of these tags, 98 were recovered with usable depth data (7,852,773 recordings representing 81,233 days) that we used to identify DVM and to classify DVM into one of two types: normal DVM (rise from the bottom during nighttime) and reverse DVM (rise from the bottom during daytime). The results of our study highlight three important attributes of DVM for sablefish. First, all tagged sablefish carried out DVM, although the occurrence was intermittent (26% of the days with usable data) and most commonly for short durations (10 days or less). Second, bottom depth for normal DVM was about 78 m shallower than for reverse DVM. Third, normal DVM occurred most often in fall and least often in spring, whereas this high/low pattern was shifted about 3 months later for reverse DVM; reverse DVM occurred most often in winter and least often in summer. Normal DVM likely occurred to increase foraging opportunity (e.g., nightly shift to match depth of prey). Reverse DVM more commonly occurred during winter and may represent an increase in foraging by sablefish during the daytime to compensate for decreased pelagic resources. The default foraging strategy for sablefish may be benthic because of the uncertainty of vertically migrating to a location where the occurrence of prey is not guaranteed; sablefish may invoke DVM when the non‐DVM foraging benefit is reduced.

Planetary and synoptic-scale dynamic control of extreme cold wave patterns over the United States

The roles of planetary and synoptic-scale waves in extreme cold wave (ECW) events over the southeastern (SE) and northwestern (NW) United States (US) are studied using a spherical harmonic decomposition in conjunction with piecewise tendency diagnosis (PTD). Planetary waves and synoptic waves jointly work together to initiate ECW events. Notably, the planetary waves not only provide a direct contribution to circulation field enacting ECW events but also alter the background circulation field in such a manner that promotes synoptic waves growth via increases in regional barotropic deformation. The SE-ECW events, concurrent with the Northern Hemisphere annular mode (NAM) negative phase, feature high latitude intensification and subsequent southeastward movement of cold surface air temperature (SAT) anomalies. The planetary-scale pattern provides a sizable contribution to the total wave pattern on both sea level pressure (SLP) and upper level. Moreover, the negative NAM planetary anomaly acts to displace the jet equatorward and thereby increases the barotropic deformation of the synoptic-scale anomaly over southeastern US. PTD confirms that the planetary-scale barotropic deformation plays a key role in deepening the negative height anomaly with a secondary contribution from baroclinic growth. In contrast, NW-ECW events feature a regional SAT cold anomaly that intensified in situ in association with a quasi-stationary positive SLP anomaly with a substantial planetary-scale wave component. The upper level circulation is characterized by a pronounced anomalous ridge over the Gulf of Alaska and a northeast-southwest tilted negative height anomaly to its east. The negative height anomaly axis is orthogonal to the planetary-scale dilatation, result in a stronger planetary barotropic deformation of the incipient negative height anomaly.

Response of early winter haze in the North China Plain to autumn Beaufort sea ice

Abstract. Recently, early winter haze pollution in the North China Plain has been serious and disastrous, dramatically damaging human health and the social economy. In this study, we emphasized the close connection between the number of haze days in early winter in the North China Plain and the September–October sea ice in the west of the Beaufort Sea (R=0.51) via both observational analyses and numerical experiments. Due to efficient radiative cooling, the responses of atmospheric circulations partially manifested as reductions of surface wind speed over the Beaufort Sea and Gulf of Alaska, resulting in a warmer sea surface in the subsequent November. The sea surface temperature anomalies over the Bering Sea and Gulf of Alaska acted as a bridge. The warmer sea surface efficiently heated the above air and led to suitable atmospheric backgrounds to enhance the potential of haze weather (e.g., a weaker East Asian jet stream and a Rossby wave-like train propagated from North China and the Sea of Japan, through the Bering Sea and Gulf of Alaska, to the Cordillera Mountains). Near the surface, the weakening sea level pressure gradient stimulated anomalous southerlies over the coastal area of China and brought about a calm and moist environment for haze formation. The thermal inversion was also enhanced to restrict the downward transportation of clear and dry upper air. Thus, the horizontal and vertical dispersion were both limited, and the fine particles were apt to accumulate and cause haze pollution.

In hot water.

Five years ago, a marine heat wave began to wash across Pacific ecosystems. Researchers fear it is a preview of the oceans' future.

Estimation of sea state from Sentinel-1 Synthetic aperture radar imagery for maritime situation awareness

ABSTRACTA new empirical algorithm CWAVE_S1-IW for estimation of significant wave height Hs including swell and wind sea from C-band satellite-borne Synthetic Aperture Radar (SAR) data has been developed for Sentinel-1 (S1) Interferometric Wide Swatrh Mode (IW) imagery. The algorithm was implemented into the Sea Sate Processor (SSP) for fully automatic processing for near real time (NRT) services and allow the estimation of wave fields of thousands of kilometres in the flight direction and 250 km swath from S1 IW scenes consisting of a sequence of individual images.The priority of CWAVE_S1-IW development was an automatic, fast and robust raster processing independent of wave patterns, applicable even when only clutter is visible in the SAR images. The algorithm is based on the spectral analysis of subscenes in wavenumber space. The empirical function allows direct Hs estimation from image spectra without first converting them into wave spectra and uses integrated image spectra parameters as well as estimated local wind information. A texture analysis based on Grey Level Co-occurrence Matrices (GLCM) is also applied. In this way, also the parameters of short waves can be estimated, which are not visible in S1 IW images and are only represented by clutter.The algorithm was tuned worldwide using in-situ collocated measurements of 92 buoys with more than 2500 acquisitions. The validated SSP allows automatic processing of worldwide S1 IW images in VV or HH polarization, including Atlantic storms, cyclones, and huge storms in the Gulf of Alaska with a root-mean-square (RMSE) error of 80 cm for Hs. For the closed seas like the North Sea, Baltic Seas and Black Sea the accuracy is higher with an RMSE = 55 cm. The algorithm is integrated into a demonstration service, used for further validation at the DLR ground station in Neustrelitz. The NRT processing has been tested by supporting a research ship cruise in the Antarctic Sea.

Extreme reduction in nutritional value of a key forage fish during the Pacific marine heatwave of 2014-2016

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 613:171-182 (2019) - DOI: https://doi.org/10.3354/meps12891 Extreme reduction in nutritional value of a key forage fish during the Pacific marine heatwave of 2014-2016 Vanessa R. von Biela1,*, Mayumi L. Arimitsu2, John F. Piatt1, Brielle Heflin2, Sarah K. Schoen1, Jannelle L. Trowbridge1,3, Chelsea M. Clawson1,4 1US Geological Survey, Alaska Science Center, 4210 University Drive, Anchorage, Alaska 99508, USA 2US Geological Survey, Alaska Science Center, 250 Egan Dr., Juneau, Alaska 99801, USA 3University of Alaska Anchorage, Alaska Native Science & Engineering Program, 3211 Providence Drive, Anchorage, Alaska 99508, USA 4Alaska Sea Grant Marine Advisory Program, 1007 W 3rd Avenue, Suite 100, Anchorage, Alaska 99501, USA *Corresponding author: vvonbiela@usgs.gov ABSTRACT: Pacific sand lance Ammodytes personatus are a key forage fish in the North Pacific for many species of salmon, groundfish, seabirds, and marine mammals and have historically been important to predators in relatively warm years. However, extreme declines in the nutritional value of sand lance in Prince William Sound, Alaska, USA, during 2012-2016 indicate that energy transfer from lower trophic levels to predators via sand lance may have been disrupted during the North Pacific marine heatwave in 2015 and 2016. Nutritional value (length, energy density, and whole-body energy) was measured in age-0 and age-1 sand lance collected during July in cool (2012-2013) and increasingly warm (2014-2016) years. The value of age-0 fish was relatively stable, with only minor differences among years for length and whole-body energy. By contrast, the value of age-1 fish significantly declined in 2015, and by 2016 they were 38% shorter and 13% lower in energy density compared to cooler years. This contributed to significant declines in whole-body energy of 44% in 2015 and 89% in 2016 compared to cooler years (2012-2014). The 2015 sand lance cohort experienced little growth or lipid accumulation from July 2015 at age-0 to July 2016 at age-1. This effective disruption of energy flow through pelagic food webs probably contributed to population declines and/or breeding failures observed among several predators in the Gulf of Alaska and suggests that tipping points were reached during the heatwave. KEY WORDS: Pacific sand lance · Ammodytes personatus · ‘The Blob’ · Gulf of Alaska · Body condition · Energy density Full text in pdf format PreviousNextCite this article as: von Biela VR, Arimitsu ML, Piatt JF, Heflin B, Schoen SK Trowbridge JL, Clawson CM (2019) Extreme reduction in nutritional value of a key forage fish during the Pacific marine heatwave of 2014-2016. Mar Ecol Prog Ser 613:171-182. https://doi.org/10.3354/meps12891 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 613. Online publication date: March 21, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

Trends in the Alaskan Bottom-Trawl Fishery from 1993 to 2015: A GIS-based Spatiotemporal Analysis

Using fishery-dependent observer data from National Marine Fisheries (NMFS) provides insight into the location and intensity of bottom-trawl fishing effort, and allows those areas most exposed to fishing pressure to be identified. In this study, the spatial and temporal extent of Alaskan bottom-trawl fishing effort in the Bering Sea, Aleutian Islands and Gulf of Alaska between 1993 and 2015 is explored within a space-time cube in ArcGIS Pro. The variables analysed were number of hauls per area and total catch per area. Statistical techniques were used to examine spatiotemporal clustering within the data. Results indicate that fishing was significantly clustered over space and time. A three-dimensional hotspot analysis shows which areas were most intensely fished and illustrates the trends over the relatively long study period. The data were then compared with sea ice concentration to determine the effect of changing climate on fishing activity. Sea ice had a limited effect on the spatial patterns of fishing effort, but certain areas in the Bering Sea exhibited increased fishing effort in years with less sea ice.

Assessing the potential for competition between Pacific Halibut (Hippoglossus stenolepis) and Arrowtooth Flounder (Atheresthes stomias) in the Gulf of Alaska

Pacific Halibut (Hippoglossus stenolepis) support culturally and economically important fisheries in the Gulf of Alaska, though recent decreases in mean size-at-age have substantially reduced fishery yields, generating concerns among stakeholders and resource managers. Among the prevailing hypotheses for reduced size-at-age is intensified competition with Arrowtooth Flounder (Atheresthes stomias), a groundfish predator that exhibited nearly five-fold increases in biomass between the 1960s and mid-2010s. To assess the potential for competition between Pacific Halibut and Arrowtooth Flounder, we evaluated their degree of spatiotemporal and dietary overlap in the Gulf of Alaska using bottom trawl survey and food habits data provided by the Alaska Fisheries Science Center (NOAA; 1990 to 2017). We restricted analyses to fish measuring 30 to 69 cm fork length and used a delta modeling approach to quantify species-specific presence-absence and catch-per-unit-effort as a function of survey year, tow location, depth, and bottom temperature. We then calculated an index of spatial overlap across a uniform grid by multiplying standardized predictions of species’ abundance. Dietary overlap was calculated across the same uniform grid using Schoener’s similarity index. Finally, we assessed the relationship between spatial and dietary overlap as a measure of resource partitioning. We found increases in spatial overlap, moving from east to west in the Gulf of Alaska (eastern: 0.13 ± 0.20; central: 0.21 ± 0.11; western: 0.31 ± 0.13 SD). Dietary overlap was low throughout the study area (0.13 ± 0.20 SD). There was no correlation between spatial and dietary overlap, suggesting an absence of resource partitioning along the niche dimensions examined. This finding provides little indication that competition with Arrowtooth Flounder was responsible for changes in Pacific Halibut alHHsize-at-age in the Gulf of Alaska; however, it does not rule out competitive interactions that may have affected resource use prior to standardized data collection or at different spatiotemporal scales.

A Comparison of Methods for Classifying Female Sablefish Maturity and Skip Spawning Outside the Spawning Season

AbstractOvarian development in Sablefish Anoplopoma fimbria was classified using three methods for samples collected during July and August in the Gulf of Alaska, approximately 6–8 months prior to spawning. Although not an ideal time for predicting future spawning, this is when survey platforms, such as longline and trawl vessels, are available annually. The three maturity classification methods included (1) macroscopic classification at sea by trained scientists but with these personnel varying throughout the survey period, (2) macroscopic classification after the survey from photographs by a single, highly trained scientist (standardized macroscopic), and (3) a microscopic evaluation of ovarian structures from histological slides. Based on certain oocyte development characteristics, the second half of August was identified as the time period when maturity could be the most accurately classified in the Gulf of Alaska. Age and length at maturity were estimated to be earlier or smaller, respectively, on some portions of the survey, when macroscopic at‐sea methods were used as opposed to standardized macroscopic or microscopic methods. Skip spawning was documented throughout the survey but at a lower rate than was reported in other studies (2% versus 6% and 21%), indicating that the rate of skip spawning is likely variable. The results demonstrate that accurate maturity classifications may be determined from collections during nonpreferable months when histology or the standardized macroscopic method is used. Identifying skip spawning is likely reliant on microscopic analysis, and so a combination of the standardized macroscopic method along with limited histological sampling, to identify skip spawning rates or to classify maturity when there is uncertainty at sea, may be the most time‐ and cost‐effective option for species similar to Sablefish that skip spawn.

Effects of climate and demography on reproductive phenology of a harvested marine fish population

Shifts in phenology are a well-documented ecological response to changes in climate, which may or may not be adaptive for a species depending on the climate sensitivity of other ecosystem processes. Furthermore, phenology may be affected by factors in addition to climate, which may accentuate or dampen climate-driven phenological responses. In this study, we investigate how climate and population demographic structure jointly affect spawning phenology of a fish species of major commercial importance: walleye pollock (Gadus chalcogrammus). We use 32years of data from ichthyoplankton surveys to reconstruct timing of pollock reproduction in the Gulf of Alaska and find that the mean date of spawning has varied by over 3weeks throughout the last >3 decades. Climate clearly drives variation in spawn timing, with warmer temperatures leading to an earlier and more protracted spawning period, consistent with expectations of advanced spring phenology under warming. However, the effects of temperature were nonlinear, such that additional warming above a threshold value had no additional effect on phenology. Population demographics were equally as important as temperature: An older and more age-diverse spawning stock tended to spawn earlier and over a longer duration than a younger stock. Our models suggest that demographic shifts associated with sustainable harvest rates could shift the mean spawning date 7days later and shorten the spawning season by 9days relative to an unfished population, independent of thermal conditions. Projections under climate change suggest that spawn timing will become more stable for walleye pollock in the future, but it is unknown what the consequences of this stabilization will be for the synchrony of first-feeding larvae with production of zooplankton prey in spring. With ongoing warming in the world's oceans, knowledge of the mechanisms underlying reproductive phenology can improve our ability to monitor and manage species under changing climate conditions.

Non-stationary climate-salmon relationships in the Gulf of Alaska.

Studies of climate effects on ecology often account for non-stationarity in individual physical and biological variables, but rarely allow for non-stationary relationships among variables. Here, we show that non-stationary relationships among physical and biological variables are central to understanding climate effects on salmon (Onchorynchus spp.) in the Gulf of Alaska during 1965-2012. The relative importance of two leading patterns in North Pacific climate, the Pacific Decadal Oscillation (PDO) and North Pacific Gyre Oscillation (NPGO), changed around 1988/1989 as reflected by changing correlations with leading axes of sea surface temperature variability. Simultaneously, relationships between the PDO and Gulf of Alaska environmental variables weakened, and long-standing temperature-salmon and PDO-salmon covariance declined to zero. We propose a mechanistic explanation for changing climate-salmon relationships in terms of non-stationary atmosphere-ocean interactions coinciding with changing PDO-NPGO relative importance. We also show that regression models assuming stationary climate-salmon relationships are inappropriate over the multidecadal time scale we consider. Relaxing assumptions of stationary relationships markedly improved modelling of climate effects on salmon catches and productivity. Attempts to understand the implications of changing climate patterns in other ecosystems might also be aided by the application of models that allow associations among environmental and biological variables to change over time.

Evaluating Pacific cod migratory behavior and site fidelity in a fjord environment using acoustic telemetry

Pacific cod (Gadus macrocephalus) inhabiting Prince William Sound (PWS) may constitute a localized population separate from Gulf of Alaska (GOA) populations; however, connectivity between these regions has not been previously explored. To address this knowledge gap, we investigated Pacific cod migratory behavior and site fidelity using passive acoustic telemetry techniques. Acoustic-tagged Pacific cod (n = 111) were monitored by Ocean Tracking Network acoustic arrays located at the straits and passages connecting PWS with the GOA and arrays deployed in two PWS fjords. Few Pacific cod tagged in PWS moved to the PWS–GOA boundary (1.8%), indicating that demographic connectivity with the GOA was low. Furthermore, 77% of tagged cod spent at least 90% of the time they were known to be alive within small (less than 30 km2) fjords. Cod were present at monitored fjords every month of the study, though some cod migrated away from the fjords during the summer and returned the following winter (11% in 2015 and 5% in 2016). Using continuous-time multistate Markov models, we determined that movement behavior was related to fish length. Larger fish tended to emigrate from monitored fjords more often and undergo longer duration migrations.

Notes on two Alaskan Volutopsiinae (Gastropoda: Buccinidae) with corrected type localities

Pyrulofusus harpa (Mörch, 1857) and Volutopsius castaneus (Mörch, 1857) were described from Sitka, Alaska, however no specimens of either species have been found at Sitka, nor indeed anywhere in the eastern Gulf of Alaska. It seems more likely that the types of both species came from Kodiak, where both species are frequently found. The type localities for both species are herein corrected.

Evidence of meltwater pulses into the North Pacific over the last 20 ka due to the decay of Kamchatka Glaciers and Cordilleran Ice Sheet

Abstract Glaciers, one of basic elements of climate system, play a crucial role in shaping global climate and regional environment. Combined with the published δ18O of Neogloboquadrina pachyderma (sin) (Nps), the data in this study show the impact of glacier decay on surface hydrography. Light peaks in δ18O Nps of one sediment core retrieved from the NW Pacific, after ice volume correction for water oxygen isotopic composition (δ18O Npsgwc), are referred to correspond to the melting-pulse events during the decay of Kamchatka glaciers. These events are synchronous with the sub-millennial scale warming in the Northern Hemisphere during the Greenland Interstadial 1. On the other hand, the influence of the Kamchatka Glacier decay on surface hydrography is limited to the adjoined area of the Kamchatka River Estuary. In contrast, the δ18O Npsgwc data from the North Pacific show that the effect of Cordilleran Ice Sheet (CIS) decay are remarkable in the Gulf of Alaska, the NE Pacific and the Bering Sea. Specifically, the CIS melting water results in a stronger surface stratification and thus the salinity and density decrease in the surface water of NE Pacific and the eastern Bering Sea. Moreover, this process causes an expansion of the oxygen minimum zone by limiting the ventilation down to intermediate depths, and acts also to give an explanation for the coeval formation of laminated sediments. Here, our data indicate the main role of the CIS melting water in controlling the North Pacific surface and intermediate hydrographic conditions by changing vertical ocean stratification.

Temperature-dependent growth and consumption of young-of-the-year sablefish Anoplopoma fimbria: Too hot, too cold or just right?

Sablefish Anoplopoma fimbria are a highly valued, economically important groundfish in Alaska; however, estimated stock biomass has been in steady decline since the early 1990s, likely as a result of poor recruitment. Among several factors found to impact recruitment strength, ocean temperature often has been to affect early-life condition. Despite the importance of early-life condition in predicting cohort success, few studies have examined the thermal response of young-of-the-year (YOY) sablefish in regards to growth and development, and those focus on only a narrow size range. In this study, we measured the effects of temperature on growth and consumption rates of YOY sablefish (218–289 mm TL) in laboratory trials with fish held over 5 temperature treatments (5 °C, 8 °C, 12 °C, 16 °C and 20 °C) and maintained on ad libitum ration for 3 weeks. We compared growth, consumption, and body condition of fish between treatments. Specific growth rate (SGR; % wet weight gain (g) d−1) was used to derive a temperature-dependent growth model, and consumption rates were used to calculate species-specific parameters for the consumption function of a Wisconsin-type bioenergetics model. Daily growth in length varied from 0.13 mm d−1 to 1.74 mm d−1 and SGR ranged from 0.52 to 2.31. SGR peaked at 15.4 °C, remained high at 12 °C and 16 °C, and steadily declined as temperatures shifted outside this range. Residuals of length-weight regressions were positive at 12 °C and 16 °C, and negative at 5 °C, 8 °C, and 20 °C. Consumption rose sharply with temperature, peaking at 17.6 °C. The narrow thermal range facilitating higher than average condition and optimal SGR indicates that YOY sablefish growth and development may be dramatically influenced by relatively small shifts in water temperatures. Further, when compared to similar studies of smaller-sized sablefish, we observed a shift with size in thermal performance, with larger fish performing better at colder temperatures compared to smaller fish. The shift in thermal performance with size is an important consideration for understanding the result of environmental perturbation on recruitment. While traditional recruitment models rely heavily on information from a single life-stage, resource use and physiological requirements often change with development. Given the widespread occurrence of anomalous thermal events in the Gulf of Alaska, a life-stage specific understanding of the effects of varying temperatures is crucial.

Larval fish assemblages in the eastern and western Gulf of Alaska: Patterns, drivers, and implications for connectivity

As stewardship goals in marine environments expand to encompass ecosystem dynamics, our comprehension of ecological structure must incorporate complex interactions among ecosystem components to define linkages and spatial boundaries for management. For example, the Gulf of Alaska (GOA) is currently considered a single Large Marine Ecosystem (LME), yet the GOA spans a large geographic domain, suggesting that ecosystem linkages may vary depending upon population, community, or process-based assessments. We used six years of larval fish assemblage data (2010–2015), co-collected oceanographic data, satellite-tracked drifters, adult fish trawl surveys, and an individual-based biophysical model to determine the processes that structure larval fish assemblages in the GOA focusing on 1) the local physical environment, 2) seasonality, 3) oceanographically-driven connectivity, and 4) adult fish distributions. Larval assemblages occurred along an eastern to western longitudinal gradient with regionally distinct assemblages in the spring and to a lesser degree in the summer. Assemblage patterns were largely driven by regional spring spawning events and only minimally influenced by temperature, salinity, and bottom depth over the continental shelf. Assemblage analyses and modeled particle trajectories suggest that longitudinal gradients in larval assemblages across the LME are influenced by the prevailing currents that promote connectivity despite variability in species-specific life-history characteristics such as spawning location and pelagic larval duration. Divergences in eastern and western GOA assemblages during the spring, and similarities in the summer, were consistent across most study years, but there were shifts in larval assemblages in the western GOA and not the eastern GOA during 2013 and 2015. Such geographic decoupling of assemblages in recent years highlights the potential for differential regional responses to environmental change across the GOA. Patterns in larval fish assemblages underscore the complex processes that structure pelagic ecosystems and suggest that assemblages diverged along a longitudinal gradient resulting in distinct communities in the eastern and western GOA. We propose that the influence of environmental or climatic variability on regional larval assemblages and life-history traits such as pelagic larval duration and phenology may alter future ecosystem linkages in rapidly changing environments.

Preliminary observations of the skeletal development in pre-flexion larvae of sablefish Anoplopoma fimbria

Sablefish Anoplopoma fimbria support a lucrative fishery in the Gulf of Alaska, but their numbers have been declining despite a regulated fishery. Recruitment in A. fimbria is poorly understood due to its unusual early life history relative to many other deep-water fishes. Developmental patterns can identify critical periods during ontogeny that influence foraging and swimming abilities among individual larvae. External development in A. fimbria has been described, but the data presented here are the first examination of the skeletal development of A. fimbria during the transition to first feeding.

A full life history synthesis of Arrowtooth Flounder ecology in the Gulf of Alaska: Exposure and sensitivity to potential ecosystem change

In recent decades, Arrowtooth Flounder (Atheresthes stomias) has been the most abundant groundfish in the Gulf of Alaska and an apex predator with trophic links to many pelagic and benthic species. Its abundance and trophic status implies that a small change in survival may result in substantial uncertainty in the ecosystem, with potentially large effects across multiple species. A synthesis of Arrowtooth Flounder ecology in the Gulf of Alaska was undertaken to determine exposure to the environment during different life history stages, and to develop hypotheses regarding population response to environmental forcing. Historical data sets were used to identify mechanisms of interaction with the pelagic environment during the egg and larval phase, assess habitat utilization and trophic interactions from early settlement through adult life, and evaluate sensitivity and potential response of the population to climate-induced variability in the Gulf of Alaska ecosystem. Modeling approaches include Individual-Based Modeling of the planktonic drift phase from spawning to settlement, Generalized Additive Modeling to examine the effects of location, bottom temperature, and depth on the distribution and density of different size categories of fish, and Habitat Suitability Modeling which integrates presence-absence and environmental data to develop predictive maps of suitable habitat for early juveniles, late juveniles, and adults. A strategy of high endurance characterizes the early ontogeny phase. Spawning and hatching occur during winter in deep water where predation risk is relatively low, and cold temperatures along with intrinsically low metabolic rates ensure extended availability of yolk reserves, lowering the risk of larval starvation in a food-poor environment. Larval duration and drift is protracted, contributing to widespread delivery of larvae to coastal, continental shelf and slope waters throughout the Gulf of Alaska, as well as expected transportation into the Bering Sea through the Aleutian Island Passes. Connectivity between spawning and settlement areas is less directed and juveniles are more ubiquitous across depths than previously understood. Juvenile and adult Arrowtooth Flounder are habitat and prey generalists, with some ontogenetic shifts apparent. Based on this comprehensive ecological synthesis, a preliminary climate-related vulnerability assessment indicates low risk, high resilience overall for this species in the Gulf of Alaska. However, some stage-specific sensitivity is hypothesized primarily relating to the potential for exacerbated temporal mis-match between early larvae and suitable zooplankton prey with increased temperatures. Density-dependent effects during the juvenile to adult stage may constrain further increases in Arrowtooth Flounder biomass in the Gulf of Alaska. This comprehensive ecological approach to assessing environmental sensitivities across life history stages for a commercially and ecologically important fish species has substantial merit for furthering the ecosystem approach to fisheries management, especially in marine ecosystems where there are robust sampling programs across trophic levels.