• Policy And Market Analysis Of World Dogfish Fisheries And An Evaluation Of The Feasibility Of A Dogfish Fishery In Waters Of Alaska, Usa

      Gasper, Jason R.; Kruse, Gordon; Greenberg, Joshua; Fong, Quentin; Miller, Marc (2011)
      Spiny dogfish is a valuable commodity on the world market and has a global capture distribution. There are three chapters evaluating dogfish markets and fisheries in this dissertation; Chapter 2 evaluates the spatial distribution of dogfish in the Gulf of Alaska; Chapter 3 provides an overview of world markets and evaluates conditions that have led to a decline in dogfish product demand in Europe; and Chapter 4 uses the information from the previous 2 chapters to provide and policy and market overview of dogfish fisheries in Alaska. Results from this study provide a comprehensive world overview of the modern dogfish fisheries and market segmentation using an evaluation of trade and price statistics. These results indicate that the dogfish market is adulterated, supplied by both sustainable and non-sustainable dogfish sources. Media attention resulting from overfishing has reduced demand for dogfish products in Europe due to the adulterated market. Overcoming the loss of market share will require eco-labeling to inform consumers about sustainable dogfish stocks. The impact of eco-labeling in Asian countries is less clear due to unknown inter-Asian market channels for fins and meat and little information on consumer attitudes towards labels. Alaska products could leverage either Asian or European consumers, but a profitable fishery will likely require regulatory changes and improved stock assessment to allow a directed fishery. In addition, pending regulatory changes, establishing robust market channels between Alaska and Europe will likely require some form of eco-labeling; especially given current eco-labeling efforts in Canada and the Atlantic US.
    • Population biology and ecology of the North Pacific giant octopus in the eastern Bering Sea

      Brewer, Reid; Norcross, Brenda L.; Seitz, Andrew C.; Blanchard, Arny L.; Ormseth, Olav A.; Tamone, Sherry L. (2016-08)
      The North Pacific giant octopus (Enteroctopus dofleini) is an important member of pan-Pacific coastal ecosystems and represents a large incidental catch in Alaska; however little is known about the biology and ecology of this species, which hinders management. To improve our understanding of E. dofleini biology, I conducted a multiyear tagging study in a 25 km2 study area in the eastern Bering Sea (EBS). I used Visible Implant Elastomers to determine growth and movement patterns for E. dofleini and sacrificed octopus were examined to determine seasonal and sex-specific reproductive characteristics. Using tagging data and Cormack-Jolly-Seber models, I estimated survival and study-area abundance for E. dofleini and expanded the abundance estimates to neighboring areas where most of the incidental catch of octopus occurs. In this three-year study, a total of 1,714 E. dofleini were tagged and 246 were recaptured. In autumn when temperatures were warmest, E. dofleini had higher growth rates, moved more and both sexes were predominantly mature when compared to colder winter months. Size also played a role in E. dofleini ecology, with smaller octopus growing faster than larger octopus and larger, mature octopus moving more than smaller, immature octopus. The abundance estimate for octopus in the study area was 3,180 octopus or 127 octopus per km2, and annual survival was 3.33%. Using 20 years of data from the federal groundfish observer program, I estimated that the biomass for E. dofleini in the area where most of the incident catch occurs was 20,697 mt of octopus, an order of magnitude larger than the current biomass estimate for the entire EBS. Though the study area and the scale of the mark-recapture effort were limited, the survival and abundance estimates are from the same area where most of the octopus are in incidentally captured and represent an important first step in enhancing octopus management. However, the large estimates of biomass suggest the current management is too conservative and the estimates of survival suggest that management estimates of mortality are too low.
    • Population dynamics of Pacific herring and humpback whales, Sitka Sound, Alaska 1981-2011

      Liddle, Joseph B.; Quinn, Terrance II; Hillgruber, Nicola; Adkison, Milo; Straley, Janice (2015-08)
      Humpback whales are a major predator in Sitka Sound, possibly consuming as much as a half-ton of Pacific herring per day. These large migratory baleen whales congregate in Sitka Sound to feed on schools of Pacific herring which spawn in April. In recent decades humpback whale abundance has increased tremendously in Sitka Sound after recovering from near extinction due to commercial whaling. In order to assess the long-term impact on herring by humpback whales, I estimated humpback whale abundance from 1981 to 2011. To do so I developed a Bayesian mark-recapture method for small sample sizes. I also modified a multi-strata Hilborn model to account for sporadic availability of whales in Sitka Sound. The multi-million dollar sac roe fishery in Sitka Sound is managed by the Alaska Department of Fish and Game (ADF&G) with an Age-Structured Assessment model (ASA). I modified the standard ASA model by including the humpback whale abundance estimates as a covariate for herring natural mortality. I found that there is no significant effect of humpback whales on herring mortality. In fact, both Pacific herring and humpback whale abundance have increased together, reaching their maximum values in 2011. This suggests that some other factor, perhaps better marine survival for both species, is driving their upwards trend.
    • Population dynamics of steller sea lions, Eumetopias jubatus, in the Eastern Gulf of Alaska

      Maniscalco, John Michael; Springer, Alan M.; Iverson, Sara J.; Horstmann, Larissa-A.; Hollmien, Tuula E.; Adkison, Milo D. (2015-05)
      Steller sea lions (Eumetopias jubatus) were listed as endangered following a collapse of the western population beginning in the late 1970s. Low juvenile survival and reduced reproductive rates (natality) have been implicated as important factors in the decline. I conducted separate mark-recapture analyses to estimate juvenile survival and natality in an area of the western population where Steller sea lions have begun to show signs of recovery since the early 2000s. I then used these vital-rate estimates in a population matrix to estimate the strength of the recovery and assess which rates pose the greatest threats to recovery. First year survival was estimated at 80% for both males and females, but second-year survival dropped to a low of 40.6% for males and 64.2 % for females that were weaned at age 1. In contrast, survival was greatly improved (88.2%) for males and females that continued to suckle between ages 1 and 2. Cumulative survival to age 4 was double (35.7%) that estimated during the population decline. Natality was also higher in recent years (70%) than during the height of the decline in the 1980s (55%). The mean rate of population growth, based on matrix modeling of vital rates estimated in this study, was 4.1% per year between 2003 and 2013. By projecting these trends into the future, I estimated that the population in the study area may be fully recovered within 14 years, if density independent growth is to be expected in the near future. If density dependent factors come into play, the population will need another 37 years to fully recover. As would be expected from a long-lived, K-selected species, population growth rate was most sensitive to variation in adult survival, less sensitive to juvenile survival, and least sensitivity to natality. The findings of this study have important implications for Steller sea lion population management and suggest research priorities should be shifted from an emphasis on natality to an emphasis on survival rates and causes of mortality.
    • Population genetic structure of Alaskan Pacific ocean perch (Sebastes alutus)

      Palof, Katie J.; Gharrett, Anthony J.; Heifetz, Jonathan; Hillgruber, Nicola (2008-05)
      Knowledge of the population structure of a species is essential for its effective management and sustained production. Although Pacific ocean perch (Sebastes alutus, POP) is an important species both economically and ecologically, little is known about its population structure and life history in Alaskan waters. The objectives of this study were to describe the population structure of POP in terms of the numbers and geographic scale oflocal populations, their connectivity, and the compatibility of that structure with current management. Fourteen micro satellite loci were used to characterize the population structure genetically in eleven geographically distinct collections from sites along the continental shelf from the Queen Charlotte Islands to the Bering Sea. In spite of the many opportunities for most life stages to disperse, there was strong geographically related genetic structure (Fst =0.0123, p <10⁻⁵). Adults appear to belong to neighborhoods that exchange genetic information at relatively small spatial scales (14 to 90 km). Although this suggests limited movement, connectivity is evidenced by the isolation-by-distance relationship, the apparent northwestward movement of gene flow in the Gulf of Alaska (GOA), and the break in geneflow in the central GOA. The observed population structure has a finer geographic scale than management areas, which suggests that current fisheries management should be revisited.
    • Population genetics and mating structure of blue king crab (Paralithodes platypus)

      Stoutamore, Jennifer L.; Tallmon, David; Eckert, Ginny; Gharrett, Anthony (2014-05)
      Blue king crab (Paralithodes platypus Brandt, 1850) has been an economically important species in Alaska since the 1970s, but its abundance has decreased substantially since the mid-1980s. Despite Fishery closures, abundances have not rebounded to previous levels. This failure has highlighted the dearth of information on the species and the need for research into genetic population structure and reproductive biology in order to better inform management efforts. Blue king crab tissue and hemolymph samples were collected from eight geographically distinct locations in Southeast Alaska, the Bering Sea, and Russia (n = 770). Allele frequencies at 10 polymorphic microsatellite loci were compared among collection locations. Moderate genetic differences were detected among all locations (overall Fst = 0.027, SE = 0.005). Heterogeneity was detected among temporal samples collected at the Pribilof Islands and St. Matthew Island. Comparisons suggested allele frequencies within each location had changed over time. Mating structure was examined by genotyping 20 progeny from each of 44 blue king crab broods collected from 3 different locations in the Bering Sea. All evidence supported single paternity for this species. This study suggests that Alaskan blue king crab stocks be managed at the population level, monitored for temporal genetic changes, and that potential future enhancement activities incorporate the single paternity mating system into determinations of broodstock composition and number.
    • Population Genetics And Mixed Stock Analysis Of Chum Salmon (Oncorhynchus Keta) With Molecular Genetics

      Garvin, Michael R.; Gharrett, A. J.; Kruse, Gordon; Pella, Jerome; Tallman, David (2012)
      Chum salmon (Oncorhynchus keta) are important for subsistence and commercial harvest in Alaska. Variability of returns to western Alaskan drainages that caused economic hardship for stakeholders has led to speculation about reasons, which may include both anthropogenic and environmental causes in the marine environment. Mixed stock analysis (MSA) compares genetic information from an individual caught at sea to a reference baseline of genotypes to assign it to its population of origin. Application of genetic baselines requires several complex steps that can introduce bias. The bias may reduce the accuracy of MSA and result in overly-optimistic evaluations of baselines. Moreover, some applications that minimize bias cannot use informative haploid mitochondrial variation. Costs of baseline development are species-specific and difficult to predict. Finally, because populations of western Alaskan chum salmon demonstrate weak genetic divergence, samples from mixtures cannot be accurately assigned to a population of origin. The chapters of this thesis address three challenges. The first chapter describes technical aspects of genetic marker development. The second chapter describes a method to evaluate the precision and accuracy of a genetic baseline that accepts any type of data and reduces bias that may have been introduced during baseline development. This chapter also includes a method that places a cost on baseline development by predicting the number of markers needed to achieve a given accuracy. The final chapter explores the reasons for the weak genetic structure of western Alaskan chum salmon populations. The results of those analyses and both geological and archaeological data suggest that recent environmental and geological processes may be involved. The methods and analyses in this thesis can be applied to any species and may be particularly useful for other western Alaskan species.
    • Population Structure And Behavior Of Pacific Halibut

      Seitz, Andrew C.; Norcross, Brenda (2006)
      Pacific halibut (Hippoglossus stenolepis) is not managed on regional scales with separate population dynamics, but rather as a single, fully mixed population extending from California through the Bering Sea. However, some of the evidence from which this paradigm was established is questionable and I hypothesize that there are separate spawning populations of Pacific halibut in three regions, the Gulf of Alaska, Bering Sea and Aleutian Islands, because these regions are geographically separated by land masses and/or deep water passes that may prevent movement by adults. Pop-up Archival Transmitting (PAT) tags were attached to Pacific halibut in each region to examine their movement and behavior. First, geolocation by ambient light was able to discern basin-scale movements of demersal fishes in high latitudes and therefore this technique provided a feasible method for providing scientific inference on large-scale population structure in Pacific halibut. Second, because seasonally low ambient light levels and inhabitation of deep water (>200 m) restricted geolocation by light during winter, an alternative method, a minimum distance dispersal model, was developed for identifying migration pathways of demersal fish in the Gulf of Alaska based on daily maximum depth. Third, the PAT tags provided no evidence that Pacific halibut in the southeastern Bering Sea and Aleutian Islands moved among regions during the mid-winter spawning season, supporting my hypothesis of separate populations. Fourth, geographic landforms and discontinuities in the continental shelf appeared to limit the interchange of Pacific halibut among areas and possibly delineate the boundaries of potential populations in the Gulf of Alaska and eastern Bering Sea, with apparent smaller, localized populations along the Aleutian Islands. This possible population structure may be reinforced by regional behavioral variation in response to the environment. Future research should be directed at quantifying the exchange of individual fish among regions for possible local area management plans that more accurately reflect population structure.
    • Predicting Distributions of Estuarine Associated Fish and Invertebrates in Southeast Alaska

      Miller, Katharine Bollinger; Norcross, Brenda; Iken, Katrin; Weingartner, Tom; Mundy, Phillip; Huettmann, Falk (2013-05)
      Estuaries in Southeast Alaska provide habitat for juveniles and adults of several commercial fish and invertebrate species; however, because of the area's size and challenging environment, very little is known about the spatial structure and distribution of estuarine species in relation to the biotic and abiotic environment. This study uses advanced machine learning algorithms (random forest and multivariate random forest) and landscape and seascape-scale environmental variables to develop predictive models of species occurrence and community composition within Southeast Alaskanestuaries. Species data were obtained from trawl and seine sampling in 49 estuaries throughout the study area. Environmental data were compiled and extracted from existing spatial datasets. Individual models for species occurrence were validated using independent data from seine surveys in 88 estuaries. Prediction accuracy for individual species models ranged from 94% to 63%, with 76% of the fish species models and 72% of the invertebrate models having a predictive accuracy of 70% or better. The models elucidated complex species-habitat relationships that can be used to identify habitat protection priorities and to guide future research. The multivariate models demonstrated that community composition was strongly related to regional patterns of precipitation and tidal energy, as well as to local abundance of intertidal habitat and vegetation. The models provide insight into how changes in species abundance are influenced by both environmental variation and the co-occurrence of other species. Taxonomic diversity in the region was high (74%) and functional diversity was relatively low (23%). Functional diversity was not linearly correlated to species richness, indicating that the number of species in the estuary was not a good predictor of functional diversity or redundancy. Functional redundancy differed across estuary clusters, suggesting that some estuaries have a greater potential for loss of functional diversity with species removal than others.
    • Prey selectivity and diet overlap in juvenile pink, chum and sockeye salmon in the Gulf of Alaska and Prince William Sound, Alaska

      Blikshteyn, Mikhail A. (2005-12)
      Pink, chum and sockeye salmon are the three most commercially important Pacific salmon. As juveniles, they co-occur in coastal waters of Alaska. To assess the potential for competition among juveniles of these species, I examined their diets in Prince William Sound and in nearby continental shelf waters in the summer and fall of 2001 and quantified surface zooplankton at the same sampling stations. I estimated diet diversity, diet overlap and prey selectivity of the three species. A large proportion of gelatinous prey, especially larvaceans, characterized juvenile chum salmon diet. A pteropod, Limacina sp., was an important prey for juvenile pink and sockeye salmon. Juvenile pink and sockeye salmon diets consisted of a wider variety of prey than those of chum salmon; they also had a higher prey overlap with each other than with chum salmon. The three species showed similar trends in selectivity in Prince William Sound and in shelf waters. These results suggest that there is a higher probability of competition between juvenile pink and sockeye salmon than between either juvenile pink or sockeye salmon and chum salmon.
    • Primary production and nutrient dynamics of the southeastern Bering Sea shelf

      Rho, TaeKeun (2004-05)
      Understanding the relationships between the distributions of organisms and oceanographic conditions was one of the major goals of the Southeastern Bering Sea Carrying Capacity (SEBSCC) study. As a part of SEBSCC, this study focused on the response of nutrients and primary production to the variations of physical conditions, the general distribution of primary production, and the dynamics of phytoplankton growth, and nutrient utilization over the middle shelf and shelf break regions. The concentration of nutrients and primary productivity were measured over the shelf during 1997-1999. Shipboard nutrient and iron addition experiments were conducted over the middle shelf and shelf break region of the southeastern Bering Sea shelf during 2000-2001. The variations in physical conditions strongly affected the distribution of nutrients in the surface euphotic layer as well as in the deep layer. The offshore transport of the middle shelf water at mid-depth over the outer shelf may playa very important role in the export of materials, including regenerated iron, from the middle shelf to the shelf break. There were large seasonal and spatial variations in the development of the spring phytoplankton bloom due to the strength of upwelling and the slope of the front at the shelf break. However, annual primary production, estimated by combining carbon uptake data of the PROBES study and this study, were similar over the inner (133 g C m⁻² y⁻¹), middle (144 g C m⁻² y⁻¹) and outer (138 g C m⁻² y⁻¹) shelves and the shelfbreak (143 g C m⁻² y⁻¹). Nutrient addition studies showed that nitrogen availability was essential to continuous phytoplankton growth during summer, and that the interaction between ammonium and nitrate may play an important role in the dynamics of nutrient utilization. The iron addition study suggested that lack of iron did not affect the growth of phytoplankton over the middle shelf, but slightly suppressed growth at the outside edge of the shelf break region.
    • Processes controlling radon-222 and radium-226 on the southeastern Bering Sea shelf

      Glover, David M. (1985-12)
      An investigation was made into the use of radon-222 and radium-226 as tracers of air-sea gas exchange, water column mixing and sediment-water exchange on the southeastern Bering Sea shelf. Further more, a two-dimensional model was developed to unity these three processes into a coherent picture of radon-222 flux out of the sediments, through the water column and into the atmosphere. The best time period to average wind speeds when regressing them against gas transfer coefficients was found to be 3.3 days by a linear regression optimization, approximately the synoptic time scale of storms in the southeastern Bering Sea. A statistically significant relationship between averaged wind speed and transfer coefficients was found at the 80% confidence level. Gas transfer coefficients were found to tie obscured in shallow waters by radon flux from the sediments. Two-dimensional mixing in these continental shelf waters rendered the traditional one-dimensional vertical mixing model of excess radon-222 unable to obtain reliable vertical eddy ditfusivities. Exchange across the sediment-water interface was calculated from the deficiency of radon-222 measured in sediment cores, the standing crop of excess radon-222 in the overlying water column and the radon-222 production rate of sediment surface grab samples. The flux of radon-222 out of the sediments was found to increase in the onshore direction. Biological irrigation appears to be the primary exchange mechanism between the sediment and water column s on this shelf. Distributions in the water column show fine structure reported previously as well as biological removal of radium-226. A chi-square hypersurface search found the optimal horizontal and vertical eddy diffusivities that explained the two-dimensional distribution of radon-222 provided from a kriging estimation exercise on the data measured in this study. This model was essentially a hybrid of a least squares surface fit and a numerical integration of the governing differential equation of radon-222. When considered as a two-dimensional system in the cross-shelf direction, the rates of gas exchange, water column mixing and sediment-water exchange agree with each other to an acceptable degree.
    • Processes Controlling Radon-222 And Radium-226 On The Southeastern Bering Sea Shelf (Chemical Oceanography, Two-Dimensional Model, Continental, Gas-Exchange, Sediment Flux)

      Glover, David Mark (1985)
      An investigation was made into the use of ('222)Rn and ('226)Ra as tracers of air-sea gas exchange, water column mixing and sediment-water exchange on the southeastern Bering Sea shelf. Furthermore, a two-dimensional model was developed to unify these three processes into a coherent picture of ('222)Rn flux out of the sediments, through the water column and into the atmosphere. The best time period to average wind speeds when regressing them against gas transfer coefficients was found to be 3.3 days by a linear regression optimization, approximately the synoptic time scale of storms in the southeastern Bering Sea. A statistically significant relationship between averaged wind speed and transfer coefficients was found at the 80% confidence level. Gas transfer coefficients were found to be obscured in shallow waters by radon flux from the sediments. Two-dimensional mixing in these continental shelf waters rendered the traditional one-dimensional vertical mixing model of excess ('222)Rn unable to obtain reliable vertical eddy diffusivities. Exchange across the sediment-water interface was calculated from the deficiency of ('222)Rn measured in sediment cores, the standing crop of excess ('222)Rn in the overlying water column and the ('222)Rn production rate of sediment surface grab samples. The flux of radon out of the sediments was found to increase in the onshore direction. Biological irrigation appears to be the primary exchange mechanism between the sediment and water columns on this shelf. Distributions in the water column show finestructure reported previously as well as biological removal of ('226)Ra. A (chi)('2) hypersurface search found the optimal horizontal and vertical eddy diffusivities that explained the two-dimensional distribution of ('222)Rn provided from a kriging estimation exercise on the data measured in this study. This model was essentially a hybrid of a least squares surface fit and a numerical integration of the governing differential equation of ('222)Rn. When considered as a two-dimensional system in the cross-shelf direction, the rates of gas exchange, water column mixing and sediment-water exchange agree with each other to an acceptable degree.
    • A protocol for assessing the impacts of urbanization on coho salmon with application to Chester Creek, Anchorage, Alaska

      Whitman, Matthew S. (2002-08)
      Coho salmon (Oncorhynchus kisutch) abundance has declined in many urban streams. The causes of these declines can be hard to identify because urban impacts on stream ecology are complex and can vary between watersheds. This makes it difficult to develop appropriate and effective strategies for stream rehabilitation or mitigation aimed at increasing coho productivity. To improve this situation I developed a habitat quality assessment protocol for urban coho salmon to help identify significant habitat degradation as a prelude to restoration planning. To evaluate the protocol I used it to assess coho habitat quality in Chester Creek, Anchorage, Alaska, an urban stream that once supported a large population of coho salmon but now only supports a remnant population. I compared habitat characteristics from one non-urban and two urban study reaches to 'healthy' standard guidelines. This application of the protocol showed that the most significant adverse effects of urbanization on coho salmon habitat in urbanized reaches were increased flood intensity, barriers to adult and juvenile migration, reduced physical habitat complexity, siltation of spawning gravels, stressful water quality conditions, and stocking of potential predators and competitors. These results provide useful information for prioritizing rehabilitation and mitigation efforts in Chester Creek.
    • Quantifying fisher responses to environmental and regulatory dynamics in marine systems

      Watson, Jordan T.; Mueter, Franz; Haynie, Alan C.; Sigler, Michael F.; Sullivan, Patrick J. (2017-12)
      Commercial fisheries are part of an inherently complicated cycle. As fishers have adopted new technologies and larger vessels to compete for resources, fisheries managers have adapted regulatory structures to sustain stocks and to mitigate unintended impacts of fishing (e.g., bycatch). Meanwhile, the ecosystems that are targeted by fishers are affected by a changing climate, which in turn forces fishers to further adapt, and subsequently, will require regulations to be updated. From the management side, one of the great limitations for understanding how changes in fishery environments or regulations impact fishers has been a lack of sufficient data for resolving their behaviors. In some fisheries, observer programs have provided sufficient data for monitoring the dynamics of fishing fleets, but these programs are expensive and often do not cover every trip or vessel. In the last two decades however, vessel monitoring systems (VMS) have begun to provide vessel location data at regular intervals such that fishing effort and behavioral decisions can be resolved across time and space for many fisheries. I demonstrate the utility of such data by examining the responses of two disparate fishing fleets to environmental and regulatory changes. This study was one of "big data" and required the development of nuanced approaches to process and model millions of records from multiple datasets. I thus present the work in three components: (1) How can we extract the information that we need? I present a detailed characterization of the types of data and an algorithm used to derive relevant behavioral aspects of fishing, like the duration and distances traveled during fishing trips; (2) How do fishers' spatial behaviors in the Bering Sea pollock fishery change in response to environmental variability; and (3) How were fisher behaviors and economic performances affected by a series of regulatory changes in the Gulf of Mexico grouper-tilefish longline fishery? I found a high degree of heterogeneity among vessel behaviors within the pollock fishery, underscoring the role that markets and processor-level decisions play in facilitating fisher responses to environmental change. In the Gulf of Mexico, my VMS-based approach estimated unobserved fishing effort with a high degree of accuracy and confirmed that the regulatory shift (e.g., the longline endorsement program and catch share program) yielded the intended impacts of reducing effort and improving both the economic performance and the overall harvest efficiency for the fleet. Overall, this work provides broadly applicable approaches for testing hypotheses regarding the dynamics of spatial behaviors in response to regulatory and environmental changes in a diversity of fisheries around the world.
    • Quantity and quality of freshwater rearing habitat in relation to juvenile Pacific salmon abundance in the Kulukak River, Alaska

      Coleman, Jesse M.; Sutton, Trent; Zimmerman, Christian; Adkison, Milo (2012-12)
      Monitoring of freshwater habitat and its influence on stream-rearing fish is essential for recognizing and mitigating the impacts of human- and climate-induced changes. For the purposes of developing a monitoring program in the U.S. Fish and Wildlife Service Togiak National Wildlife Refuge, densities and habitat relationships of juvenile coho salmon Oncorhynchus kisutch and sockeye salmon O. nerka were estimated in two tributaries of the Kulukak River, Alaska, in July 2010. Multiple-pass depletion electrofishing was used to estimate density in a random sample of habitat units belonging to one of four categorical habitat classes. Regression methods were also used to quantify the physical habitat associations of juvenile coho and sockeye salmon density in the study areas. Densities of juvenile coho and sockeye salmon ranged from 0.22 fish-m⁻² in West Fork riffles and 0.05 fish·m⁻² East Fork riffles to 2.22 fish M⁻² and 1.32 fish-m⁻² in East Fork eddy drop zones (EDZ), respectively. The largest proportions of freshwater habitat were comprised of run (71 %) and EDZ habitats (44%) in the East Fork and West Fork, respectively. Regression coefficients for coho and sockeye salmon densities were positive with respect to proportional areas of in-stream overhanging vegetation (0.78 and 0.74, respectively), large wood (0.99 and 0.97, respectively), and undercut banks (0.99 and 0.02, respectively). Conversely, coho and sockeye salmon density was negatively related to depth ( -1.45 and -0.52, respectively) and velocity ( -2.45 and -1.67, respectively). Although substrate size was negatively related to sockeye salmon density ( -0.40), this variable had a weak positive relationship with coho salmon density (0.08). These findings suggest that EDZ habitats are important for juvenile coho and sockeye salmon during summer rearing and in-stream cover is an essential component of these rearing habitats.
    • Quikscat measurements of the wind field over the Bering and Chukchi Seas

      Mull, Jeremy M.; Johnson, Mark; Weingartner, Tom; Simmons, Harper (2008-12)
      The purpose of this study is to investigate the dynamic wind field and resulting ocean circulation patterns in the Bering and Chukchi Seas. This region forms an important link in global ocean circulation as Bering Strait is a major conduit for water flowing into the Arctic Ocean. The Arctic has been identified as an area sensitive to climate change; thus it is vital to understand how water and energy flow through this region. We first quantify the differences between the winds measured in this region by the Quik Scatterometer (QuikSCAT) and those modeled by the National Centers for Environmental Prediction (NCEP). Although the data sets are well correlated, we find significant discrepancies between these data sets and use linear regressions to correct the NCEP data. The magnitudes of the NCEP wind components are greater than the magnitudes of the QuikSCAT wind components. This creates directional differences between the two data sets at low wind speeds and NCEP speeds that are greater than QuikSCAT speeds at high wind speeds. We next challenge the assumption that the wind field is spatially uniform over the Bering and Chukchi shelves. We produce mean monthly maps of the wind field, surface Ekman transport, and wind variance based upon the 12-hourly QuikSCAT data from July 1999 – May 2007. These maps reveal that the winds are spatially and temporally dynamic in this region. There are several areas and times in which surface Ekman transport is onshore or offshore near the coasts and may engender coastal downwelling and upwelling, respectively. There are also several instances when surface Ekman convergence and divergence may lead to Ekman pumping and suction. We use the entire NCEP record (January 1948 – May 2007) to examine patterns of surface Ekman transport across the shelf break. There was a significant increase in the amount of onshelf surface Ekman transport that coincided with the regime shift that occurred in the Bering Sea in the mid-1970s. We attempt to correlate the time series of surface Ekman cross-shelf transport with several climate indices but find only very weak correlations. The annual surface Ekman freshwater fluxes across the shelf break are iii calculated and found to be very small compared to the total annual freshwater fluxes calculated by Aagaard et al. (2006) and Kinney et al. (2008). To resolve the dominant modes of wind variability we compute hourly, monthly, and annual Complex Empirical Orthogonal Functions (CEOFs) with the QuikSCAT and NCEP data sets. The first modes in each analysis account for more than 60% of the variance. Different aspects of the mode amplitude time series are cross-correlated with climate and indices to produce small but significant correlation coefficients. Finally we calculate Ekman pumping and suction at four locations in the Bering Sea during the spring and summer months of seven years (2000 – 2006). We identify regions and times when Ekman pumping and suction were particularly strong, and perform several runs of a one-dimensional Price-Weller-Pinkel (PWP) vertical mixing model with the QuikSCAT winds, the QuikSCAT winds and a wind-stress-curl term, and the NCEP winds. The results suggest that Ekman suction might facilitate subsequent vertical mixing while Ekman pumping might inhibit subsequent vertical mixing when the winds are generally weak and wind-stress-curl is moderate or strong. The temporal resolution of the QuikSCAT data set is too low to resolve inertial motions at high latitudes. The NCEP data set has higher temporal resolution and is adequate for running the model within this region. We propose interpolating the hourly NWS data collected at St. Paul Island (station PASN) to the QuikSCAT grid using the complex amplitudes and phases from the complex cross-correlations between the two data sets to produce a data set of high temporal and spatial resolution. This would enable researchers to accurately resolve inertial motions and compute wind-stress-curl.