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• 21. [Article] Maximizing economic yield from a plankton feeding fish population on high latitudes

  Abstract only.

  Citation × Citation Citation Abstract Copy Title: Maximizing economic yield from a plankton feeding fish population on high latitudes Author: Eide, Arne, Flaaten, Ola, Henriksen, Edgar Abstract only. Title: Maximizing economic yield from a plankton feeding fish population on high latitudes Author: Eide, Arne, Flaaten, Ola, Henriksen, Edgar Abstract only. Close

• 22. [Article] Tev (total Economic Value) Analysis of A Marine Environment in Norway

  The push for ecosystem based management has opened up not only for including more of the natural systems when managing fish resources, but also a broader perspective on the human systems, and the diverse ...

  Citation × Citation Citation Abstract Copy Title: Tev (total Economic Value) Analysis of A Marine Environment in Norway Author: Kahui, Viktoria, Armstrong, Claire, Aanesen, Margrethe The push for ecosystem based management has opened up not only for including more of the natural systems when managing fish resources, but also a broader perspective on the human systems, and the diverse activities in the sea. This is reflected for instance in the EU Maritime Policy where fisheries is just one of many activities that marine management must take into account. Research into valuation of natural resources has shown that non-use values may be substantial in the marine environment; These are e.g. existence values, such as the existence of rare species and benthic components such as corals, and option values with regard to potential future applications, e.g. in marine bioprospecting. In addition, indirect use values, such as habitat values, recreational values and nutrient cycling often far exceed the direct use values, which are typically the value of the fisheries, aquaculture and marine tourism. Applying and critiquing the Total Economic Value (TEV) set up, we have estimated marine direct use values, including fisheries and aquaculture, indirect use values and non-use values in Nordland county in Norway, specifically connected to the Lofoten-Vesterålen marine area. Lofoten-Vesterålen is the most important spawning ground for commercial fish resources such as cod and herring, and it is also a very popular tourist destination. Yet when studying some of the other values that the marine environment supplies, these traditional values are not necessarily the most important. Title: Tev (total Economic Value) Analysis of A Marine Environment in Norway Author: Kahui, Viktoria, Armstrong, Claire, Aanesen, Margrethe The push for ecosystem based management has opened up not only for including more of the natural systems when managing fish resources, but also a broader perspective on the human systems, and the diverse activities in the sea. This is reflected for instance in the EU Maritime Policy where fisheries is just one of many activities that marine management must take into account. Research into valuation of natural resources has shown that non-use values may be substantial in the marine environment; These are e.g. existence values, such as the existence of rare species and benthic components such as corals, and option values with regard to potential future applications, e.g. in marine bioprospecting. In addition, indirect use values, such as habitat values, recreational values and nutrient cycling often far exceed the direct use values, which are typically the value of the fisheries, aquaculture and marine tourism. Applying and critiquing the Total Economic Value (TEV) set up, we have estimated marine direct use values, including fisheries and aquaculture, indirect use values and non-use values in Nordland county in Norway, specifically connected to the Lofoten-Vesterålen marine area. Lofoten-Vesterålen is the most important spawning ground for commercial fish resources such as cod and herring, and it is also a very popular tourist destination. Yet when studying some of the other values that the marine environment supplies, these traditional values are not necessarily the most important. Close

• 23. [Article] Natal source contributions of Pacific cod (Gadus macrocephalus) recruits in the southeastern Bering Sea

  Effective and sustainable fisheries management not only depends on identifying and defining stocks (fundamental unit of management), but also on having knowledge of factors influencing the abundance, distribution ...

  Citation × Citation Citation Abstract Copy Title: Natal source contributions of Pacific cod (Gadus macrocephalus) recruits in the southeastern Bering Sea Author: DiMaria, Ruth A. Effective and sustainable fisheries management not only depends on identifying and defining stocks (fundamental unit of management), but also on having knowledge of factors influencing the abundance, distribution and connectivity of stocks. Population structure of Pacific cod (Gadus macrocephalus) in the southeastern Bering Sea (EBS) remains unresolved although genetic data indicate isolation-by-distance throughout the species range across the North Pacific Ocean. Pacific cod are fished on their spawning grounds, therefore, it is important to evaluate whether particular spawning sources are more critical than others in sustaining the productivity of fished populations. Chemical analysis of otoliths can provide information on mixing among groups of fish on ecological time scales and at finer spatial scales than genetic analyses. Therefore, I completed laboratory and field research on the otolith elemental composition of larval and juvenile cod to: (1) investigate temperature and growth-rate effects on otolith elemental incorporation to aid interpretations of field data; (2) evaluate the potential to detect larval exchange between the Gulf of Alaska (GOA) and the EBS; (3) quantify spatial scales at which there was significant variation in otolith elemental composition; and (4) quantify the number of larval sources (chemically distinct groups) contributing to juvenile recruits in the EBS. In the laboratory study, I observed higher rates of incorporation at lower temperatures for both Sr and Ba but similar ranges of Mg incorporation at 2°C, 6°C and 8°C. There was no significant effect of somatic growth or otolith precipitation rate on elemental incorporation detected, indicating that variation in individual growth rates should not confound interpretations of field data. In two years of field collections (2006 & 2008), otolith elemental signatures (Mg:Ca, Mn:Ca, Zn:Ca, Sr:Ca, and Ba:Ca) differed between larvae collected in the EBS and GOA, and over 70% of the larvae were correctly classified to source. Furthermore, I examined the chemical signatures of the otolith edge (representing approximately the last 10 d of life) for juveniles collected at six locations throughout the EBS. Seventy-nine and 71% of the juveniles were correctly classified to their collection location in 2006 and 2008, respectively. These results demonstrate that there is sufficient spatial variation in otolith composition to examine spatial structure in Pacific cod within the EBS and to identify GOA larval contribution to the EBS population. Finally, larval source signatures, represented by otolith core chemistry, of juveniles collected throughout the EBS were classified into chemically distinct groups using hierarchical cluster analysis. In both years we identified two dominant sources representing 56% and 30% of the cohort in 2006, and 53% and 40% in 2008. Most collection sites contained a mixture of larval sources although one or two sites per year were comprised of a single source. These chemically unique sources likely represent different spawning locations with distinct environmental characteristics, although the exact locations are unknown. These sources potentially represent contributions from known spawning areas, which include the Alaskan Peninsula, Aleutian Islands, and Pribilof Islands. Our results highlight the potential of otolith chemical analyses to identify source contributions of Pacific cod in the EBS but larval collections throughout the spawning season are needed to provide additional detail on the spatial distribution of those sources. Title: Natal source contributions of Pacific cod (Gadus macrocephalus) recruits in the southeastern Bering Sea Author: DiMaria, Ruth A. Effective and sustainable fisheries management not only depends on identifying and defining stocks (fundamental unit of management), but also on having knowledge of factors influencing the abundance, distribution and connectivity of stocks. Population structure of Pacific cod (Gadus macrocephalus) in the southeastern Bering Sea (EBS) remains unresolved although genetic data indicate isolation-by-distance throughout the species range across the North Pacific Ocean. Pacific cod are fished on their spawning grounds, therefore, it is important to evaluate whether particular spawning sources are more critical than others in sustaining the productivity of fished populations. Chemical analysis of otoliths can provide information on mixing among groups of fish on ecological time scales and at finer spatial scales than genetic analyses. Therefore, I completed laboratory and field research on the otolith elemental composition of larval and juvenile cod to: (1) investigate temperature and growth-rate effects on otolith elemental incorporation to aid interpretations of field data; (2) evaluate the potential to detect larval exchange between the Gulf of Alaska (GOA) and the EBS; (3) quantify spatial scales at which there was significant variation in otolith elemental composition; and (4) quantify the number of larval sources (chemically distinct groups) contributing to juvenile recruits in the EBS. In the laboratory study, I observed higher rates of incorporation at lower temperatures for both Sr and Ba but similar ranges of Mg incorporation at 2°C, 6°C and 8°C. There was no significant effect of somatic growth or otolith precipitation rate on elemental incorporation detected, indicating that variation in individual growth rates should not confound interpretations of field data. In two years of field collections (2006 & 2008), otolith elemental signatures (Mg:Ca, Mn:Ca, Zn:Ca, Sr:Ca, and Ba:Ca) differed between larvae collected in the EBS and GOA, and over 70% of the larvae were correctly classified to source. Furthermore, I examined the chemical signatures of the otolith edge (representing approximately the last 10 d of life) for juveniles collected at six locations throughout the EBS. Seventy-nine and 71% of the juveniles were correctly classified to their collection location in 2006 and 2008, respectively. These results demonstrate that there is sufficient spatial variation in otolith composition to examine spatial structure in Pacific cod within the EBS and to identify GOA larval contribution to the EBS population. Finally, larval source signatures, represented by otolith core chemistry, of juveniles collected throughout the EBS were classified into chemically distinct groups using hierarchical cluster analysis. In both years we identified two dominant sources representing 56% and 30% of the cohort in 2006, and 53% and 40% in 2008. Most collection sites contained a mixture of larval sources although one or two sites per year were comprised of a single source. These chemically unique sources likely represent different spawning locations with distinct environmental characteristics, although the exact locations are unknown. These sources potentially represent contributions from known spawning areas, which include the Alaskan Peninsula, Aleutian Islands, and Pribilof Islands. Our results highlight the potential of otolith chemical analyses to identify source contributions of Pacific cod in the EBS but larval collections throughout the spawning season are needed to provide additional detail on the spatial distribution of those sources. Close

• 24. [Article] Effects of Current Hatchery Practices on Salmon Odor Recognition and Responses

  Salmon hatcheries have been utilized throughout the Pacific Northwest for many decades to mitigate losses, supplement natural spawning populations, and to provide tribal, sport and commercial fishing opportunities. ...

  Citation × Citation Citation Abstract Copy Title: Effects of Current Hatchery Practices on Salmon Odor Recognition and Responses Author: Lemanski, Joseph R. Salmon hatcheries have been utilized throughout the Pacific Northwest for many decades to mitigate losses, supplement natural spawning populations, and to provide tribal, sport and commercial fishing opportunities. Currently, there is substantial debate on their efficacy and the potential threats hatchery-reared salmonids pose to natural populations. These concerns have lead to a large body of scientific investigation. The potential impacts hatchery-reared salmon may have on natural spawning populations can take many forms, such as competition, predation, and genetic introgression. Many of these issues arise from straying of hatchery-reared salmon from target return locations into areas where naturally spawning populations of salmon occur. In my thesis, I considered two questions related to hatchery practices and straying of hatchery-reared salmon. First, I addressed whether exposure to unfamiliar conspecifics during incubation (embryonic development) affects the population recognition responses of emergent steelhead (Oncorhynchus mykiss). I then examined whether dissolved free amino acids (DFAAs, chemicals believed to be important for natal stream identification in salmonids) are significantly altered as water sourced from a river passes through a salmon hatchery. The results of my first study suggested that newly emergent steelhead showed no preference for water conditioned by either familiar (fish from the same population) or unfamiliar (fish from geographically separate population) populations. These results suggest that exposure to unfamiliar or unrelated population specific odors during incubation in a hatchery may not have any significant effects on population recognition responses. The data from my second study suggested that both hatchery and river water DFAA profiles are very similar. I hypothesize that straying observed in hatchery-reared salmon may be due in part to a lack of a unique, distinguishable odor profile that hatchery-reared salmon might use to differentiate between target return locations and other potential spawning grounds. Title: Effects of Current Hatchery Practices on Salmon Odor Recognition and Responses Author: Lemanski, Joseph R. Salmon hatcheries have been utilized throughout the Pacific Northwest for many decades to mitigate losses, supplement natural spawning populations, and to provide tribal, sport and commercial fishing opportunities. Currently, there is substantial debate on their efficacy and the potential threats hatchery-reared salmonids pose to natural populations. These concerns have lead to a large body of scientific investigation. The potential impacts hatchery-reared salmon may have on natural spawning populations can take many forms, such as competition, predation, and genetic introgression. Many of these issues arise from straying of hatchery-reared salmon from target return locations into areas where naturally spawning populations of salmon occur. In my thesis, I considered two questions related to hatchery practices and straying of hatchery-reared salmon. First, I addressed whether exposure to unfamiliar conspecifics during incubation (embryonic development) affects the population recognition responses of emergent steelhead (Oncorhynchus mykiss). I then examined whether dissolved free amino acids (DFAAs, chemicals believed to be important for natal stream identification in salmonids) are significantly altered as water sourced from a river passes through a salmon hatchery. The results of my first study suggested that newly emergent steelhead showed no preference for water conditioned by either familiar (fish from the same population) or unfamiliar (fish from geographically separate population) populations. These results suggest that exposure to unfamiliar or unrelated population specific odors during incubation in a hatchery may not have any significant effects on population recognition responses. The data from my second study suggested that both hatchery and river water DFAA profiles are very similar. I hypothesize that straying observed in hatchery-reared salmon may be due in part to a lack of a unique, distinguishable odor profile that hatchery-reared salmon might use to differentiate between target return locations and other potential spawning grounds. Close

• 25. [Article] Systematics, variation, distribution, and biology of lampreys of the genus Lampetra in Oregon

  Based on the number of velar tentacles and the form of longitudinal lingual laminae found in Lampetra (Entosphenus) t. tridentata and its closely related forms, the taxon Entosphenus should not be considered ...

  Citation × Citation Citation Abstract Copy Title: Systematics, variation, distribution, and biology of lampreys of the genus Lampetra in Oregon Author: Kan, Ting Tien Based on the number of velar tentacles and the form of longitudinal lingual laminae found in Lampetra (Entosphenus) t. tridentata and its closely related forms, the taxon Entosphenus should not be considered as a genus as commonly adopted, but, along with the taxa Lethenteron and Lampetra, should be regarded as a subgenus of the genus Lampetra. The genus Lampetra is distinct for various reasons, including particularly the character that no cusps are present in the area distal to the lateral circumorals. Six nominal species, belonging to the subgenera Entosphenus and Lampetra, have been known to occur in four of the seven major drainage systems of Oregon. The anadromous L. (E.) t.tridentata, is widespread in the Columbia River and Coastal drainage systems, occurring in most streams with access to the ocean regardless of distance to the ocean, as long as suitable spawning grounds and ammocoete habitats are present. Morphometrics and dentitional features vary little over its geographical range. The number of trunk myomeres and the adult body size vary appreciably so that two categories of regional forms, coastal and inland, may be recognized. The coastal forms are generally smaller and have fewer trunk myomeres compared to those of the larger inland forms. The spawning migration begins from the late spring to late summer for the coastal forms but may occur much earlier for the inland forms. The adult body size appears to be positively correlated with absolute fecundity, but is negatively correlated with relative fecundity. Duration of the larval period is from four to six years. Metamorphosis usually takes place in the fall. Macrophthalmia are known to enter the ocean over a long period, those descending coastal streams enter salt water in the late fall and early winter, whereas the peak of emigration from inland streams is in the early spring. Duration of its marine parasitic phase appears to be from 20 to 40 months. The small landlocked L. (E.) t. kawiaga n. subsp., found only in the Klamath and Goose Lake drainage systems in southern Oregon and northern California, differs from t. tridentata in body size and various meristic and morphometric characters. Its lacustrine parasitic phase is about 12 months long. L. (E.) lethophaga, the nonparasitic derivative of tridentata, occurs in the Klamath and probably also the Goose Lake drainage system. It is characterized by an extension of the larval phase and by a greatly reduced post-larval period. The presumably extinct L. (E. ) minima, a parasitic derivative of tridentata, found formerly only in Miller Lake, Oregon, possessed a number of characters that were concomitants of dwarfism, the distinctive feature of the species. Relationships and evolution among the subgenus Entosphenus were discussed. Distributional records of L. ayresii and L. richardsoni of the subgenus Lampetra in Oregon were given. Evidence indicates that a complex of clinal races, including L. pacifica Vladykov, 1973, may exist in the latter species. Title: Systematics, variation, distribution, and biology of lampreys of the genus Lampetra in Oregon Author: Kan, Ting Tien Based on the number of velar tentacles and the form of longitudinal lingual laminae found in Lampetra (Entosphenus) t. tridentata and its closely related forms, the taxon Entosphenus should not be considered as a genus as commonly adopted, but, along with the taxa Lethenteron and Lampetra, should be regarded as a subgenus of the genus Lampetra. The genus Lampetra is distinct for various reasons, including particularly the character that no cusps are present in the area distal to the lateral circumorals. Six nominal species, belonging to the subgenera Entosphenus and Lampetra, have been known to occur in four of the seven major drainage systems of Oregon. The anadromous L. (E.) t.tridentata, is widespread in the Columbia River and Coastal drainage systems, occurring in most streams with access to the ocean regardless of distance to the ocean, as long as suitable spawning grounds and ammocoete habitats are present. Morphometrics and dentitional features vary little over its geographical range. The number of trunk myomeres and the adult body size vary appreciably so that two categories of regional forms, coastal and inland, may be recognized. The coastal forms are generally smaller and have fewer trunk myomeres compared to those of the larger inland forms. The spawning migration begins from the late spring to late summer for the coastal forms but may occur much earlier for the inland forms. The adult body size appears to be positively correlated with absolute fecundity, but is negatively correlated with relative fecundity. Duration of the larval period is from four to six years. Metamorphosis usually takes place in the fall. Macrophthalmia are known to enter the ocean over a long period, those descending coastal streams enter salt water in the late fall and early winter, whereas the peak of emigration from inland streams is in the early spring. Duration of its marine parasitic phase appears to be from 20 to 40 months. The small landlocked L. (E.) t. kawiaga n. subsp., found only in the Klamath and Goose Lake drainage systems in southern Oregon and northern California, differs from t. tridentata in body size and various meristic and morphometric characters. Its lacustrine parasitic phase is about 12 months long. L. (E.) lethophaga, the nonparasitic derivative of tridentata, occurs in the Klamath and probably also the Goose Lake drainage system. It is characterized by an extension of the larval phase and by a greatly reduced post-larval period. The presumably extinct L. (E. ) minima, a parasitic derivative of tridentata, found formerly only in Miller Lake, Oregon, possessed a number of characters that were concomitants of dwarfism, the distinctive feature of the species. Relationships and evolution among the subgenus Entosphenus were discussed. Distributional records of L. ayresii and L. richardsoni of the subgenus Lampetra in Oregon were given. Evidence indicates that a complex of clinal races, including L. pacifica Vladykov, 1973, may exist in the latter species. Close

• 26. [Article] Tuberculosis in Pacific salmon and steelhead trout

  Tuberculosis in salmonoid fishes was first observed in the 1952 run of fall chinook salmon (Oncorhynchus tshawytscha) returning to the Bonneville Hatchery of the Oregon Fish Commission. In the studies ...

  Citation × Citation Citation Abstract Copy Title: Tuberculosis in Pacific salmon and steelhead trout Author: Ordal, Erling Josef, 1906-, Oregon. Fish Commission, Wood, James W. Tuberculosis in salmonoid fishes was first observed in the 1952 run of fall chinook salmon (Oncorhynchus tshawytscha) returning to the Bonneville Hatchery of the Oregon Fish Commission. In the studies reported here, tuberculosis was found not only in adult spring chinook but in silver salmon (0. kisutch), blueback salmon (0. nerka), and in anadromous and resident strains of rainbow trout (Salmo gairdnerii). Advanced tuberculosis was found in salmonoid fishes held in fresh water for two years or longer, as well as in adults returning from the sea. Lesions were most frequently observed in the liver, and varied in size from small miliary tubercles to huge necrotic areas, filled with characteristic acid-fast bacilli. The typical bacilli were found in stained smears from the kidney, heart, musculature, brain, intestines, pyloric caeca, and roe of infected fish. The disease was originally observed in sexually-underdeveloped fish, and there is indication that it interferes with sexual maturation. It was found that tuberculosis in marked salmon known to be of hatchery origin was extremely high - in some cases 100 percent. Tuberculosis was absent in the small number of silver and chum salmon examined which were known to be the progeny from natural spawning. It is suggested that dissemination of the disease may be due to fish-cultural practices such as the feeding of untreated carcasses and the viscera from tuberculous fish. Since acid-fast bacilli were found in the roe of some fish, it is also suggested that the disease may be transmitted to healthy eggs during the process of fertilization. Tuberculous adult spring chinook were found less capable of surviving to maturity after they reached the spawning grounds than were non-infected fish. It is likely that tuberculosis also influences the ability of salmon to survive during earlier stages of their life history. The incidence of tuberculosis in adult spring chinook entering the Dexter holding ponds on the Middle Fork of the Willamette River in 1955 and 1956 was 8.7 and 6.1 percent, respectively. The increase in incidence to 58.8 percent in 1957 is attributed to the increased dependency of the run on artificial propagation necessitated by the construction of Lookout Point Dam. Among chinook caught in the Columbia River gill-net fishery in. February and in May 1956, 12.3 and 10.5 percent, respectively, of those examined were tuberculous. Although these are spring chinook, it is believed that hatchery reared fall chinook also entered the catch, especially during May, and may have contributed to the number of tuberculous fish taken. Title: Tuberculosis in Pacific salmon and steelhead trout Author: Ordal, Erling Josef, 1906-, Oregon. Fish Commission, Wood, James W. Tuberculosis in salmonoid fishes was first observed in the 1952 run of fall chinook salmon (Oncorhynchus tshawytscha) returning to the Bonneville Hatchery of the Oregon Fish Commission. In the studies reported here, tuberculosis was found not only in adult spring chinook but in silver salmon (0. kisutch), blueback salmon (0. nerka), and in anadromous and resident strains of rainbow trout (Salmo gairdnerii). Advanced tuberculosis was found in salmonoid fishes held in fresh water for two years or longer, as well as in adults returning from the sea. Lesions were most frequently observed in the liver, and varied in size from small miliary tubercles to huge necrotic areas, filled with characteristic acid-fast bacilli. The typical bacilli were found in stained smears from the kidney, heart, musculature, brain, intestines, pyloric caeca, and roe of infected fish. The disease was originally observed in sexually-underdeveloped fish, and there is indication that it interferes with sexual maturation. It was found that tuberculosis in marked salmon known to be of hatchery origin was extremely high - in some cases 100 percent. Tuberculosis was absent in the small number of silver and chum salmon examined which were known to be the progeny from natural spawning. It is suggested that dissemination of the disease may be due to fish-cultural practices such as the feeding of untreated carcasses and the viscera from tuberculous fish. Since acid-fast bacilli were found in the roe of some fish, it is also suggested that the disease may be transmitted to healthy eggs during the process of fertilization. Tuberculous adult spring chinook were found less capable of surviving to maturity after they reached the spawning grounds than were non-infected fish. It is likely that tuberculosis also influences the ability of salmon to survive during earlier stages of their life history. The incidence of tuberculosis in adult spring chinook entering the Dexter holding ponds on the Middle Fork of the Willamette River in 1955 and 1956 was 8.7 and 6.1 percent, respectively. The increase in incidence to 58.8 percent in 1957 is attributed to the increased dependency of the run on artificial propagation necessitated by the construction of Lookout Point Dam. Among chinook caught in the Columbia River gill-net fishery in. February and in May 1956, 12.3 and 10.5 percent, respectively, of those examined were tuberculous. Although these are spring chinook, it is believed that hatchery reared fall chinook also entered the catch, especially during May, and may have contributed to the number of tuberculous fish taken. Close

• 27. [Article] Migration, movement, and habitat use of humpback whitefish (Coregonus pidschian) in the Copper River Delta, Alaska

  Research conducted on humpback whitefish Coregonus pidschian in the Copper River Delta, Alaska has revealed a complex life history involving seasonal migrations and the occupation of a variety of freshwater ...

  Citation × Citation Citation Abstract Copy Title: Migration, movement, and habitat use of humpback whitefish (Coregonus pidschian) in the Copper River Delta, Alaska Author: Neilson, Brian J. Research conducted on humpback whitefish Coregonus pidschian in the Copper River Delta, Alaska has revealed a complex life history involving seasonal migrations and the occupation of a variety of freshwater and marine habitats including lacustrine, riverine, estuarine, and marine. Forty-five whitefish were tagged with radio transmitters in 2006 and 2007, and another 29 whitefish were tagged with acoustic tags in 2008. In addition, otolith chemistry was used to evaluate marine habitat use of humpback whitefish sampled from McKinley Lake in the Copper River Delta, Alaska. Movements and migration of tagged fish were tracked using biotelemetry techniques from boats, airplanes, and fixed receiver stations throughout the spring, summer, and fall. Sagittal otoliths were extracted from 20 humpback whitefish and a chemical analysis was performed to evaluate levels of Sr:Ca. Biotelemetry and sampling results revealed seasonal migrations where humpback whitefish migrated into McKinley Lake in mid to late spring and left the lake by late summer and early fall. Fish migrated to the Copper River in the fall by traveling down Alaganik Slough and then to the Copper River by traveling through Pete Dahl Cutoff Slough or the Gulf of Alaska. Fish travel up the Copper River presumably to their spawning grounds. Nine tagged fish returned to McKinley Lake in 2007 and four tagged fish in 2008, indicating some fidelity to the summer feeding site. Otolith chemistry detected marine migrations in 45% of the samples. Three migratory behaviors were observed, while some individuals inhabited only freshwater environments, some individuals made single migrations to marine habitats, and other individuals made multiple migrations to marine habitats. Age of whitefish ranged from 2 to 9 years. Analysis of small-scale movement of humpback whitefish in McKinley Lake found movement rates to be significantly higher at dusk compared to night in one sampling period. However, diel movement activity in all other diel periods did not significantly differ, suggesting arrhythmic diel movement. A large portion of the lake was occupied at any given time, but not all areas were used equally. Activity levels, measured by change in zones, were variable between dates and indicated that fish often moved between detection zones. An increase in activity was observed in individuals 48 h prior to migration from the lake. This study provides the first documentation of migration, movement, and habitat use of humpback whitefish in the Copper River Delta, Alaska. Results of this study will help inform management of humpback whitefish in order to sustain populations into the future. This information should be considered in land use and species management planning in the Copper River basin including fish passage and harvest regulations. Title: Migration, movement, and habitat use of humpback whitefish (Coregonus pidschian) in the Copper River Delta, Alaska Author: Neilson, Brian J. Research conducted on humpback whitefish Coregonus pidschian in the Copper River Delta, Alaska has revealed a complex life history involving seasonal migrations and the occupation of a variety of freshwater and marine habitats including lacustrine, riverine, estuarine, and marine. Forty-five whitefish were tagged with radio transmitters in 2006 and 2007, and another 29 whitefish were tagged with acoustic tags in 2008. In addition, otolith chemistry was used to evaluate marine habitat use of humpback whitefish sampled from McKinley Lake in the Copper River Delta, Alaska. Movements and migration of tagged fish were tracked using biotelemetry techniques from boats, airplanes, and fixed receiver stations throughout the spring, summer, and fall. Sagittal otoliths were extracted from 20 humpback whitefish and a chemical analysis was performed to evaluate levels of Sr:Ca. Biotelemetry and sampling results revealed seasonal migrations where humpback whitefish migrated into McKinley Lake in mid to late spring and left the lake by late summer and early fall. Fish migrated to the Copper River in the fall by traveling down Alaganik Slough and then to the Copper River by traveling through Pete Dahl Cutoff Slough or the Gulf of Alaska. Fish travel up the Copper River presumably to their spawning grounds. Nine tagged fish returned to McKinley Lake in 2007 and four tagged fish in 2008, indicating some fidelity to the summer feeding site. Otolith chemistry detected marine migrations in 45% of the samples. Three migratory behaviors were observed, while some individuals inhabited only freshwater environments, some individuals made single migrations to marine habitats, and other individuals made multiple migrations to marine habitats. Age of whitefish ranged from 2 to 9 years. Analysis of small-scale movement of humpback whitefish in McKinley Lake found movement rates to be significantly higher at dusk compared to night in one sampling period. However, diel movement activity in all other diel periods did not significantly differ, suggesting arrhythmic diel movement. A large portion of the lake was occupied at any given time, but not all areas were used equally. Activity levels, measured by change in zones, were variable between dates and indicated that fish often moved between detection zones. An increase in activity was observed in individuals 48 h prior to migration from the lake. This study provides the first documentation of migration, movement, and habitat use of humpback whitefish in the Copper River Delta, Alaska. Results of this study will help inform management of humpback whitefish in order to sustain populations into the future. This information should be considered in land use and species management planning in the Copper River basin including fish passage and harvest regulations. Close

• 28. [Article] Monitoring river restoration using fiber optic temperature measurements in a modeling framework

  The Middle Fork of the John Day River (MFJD) in Northeastern Oregon contains important spawning grounds for spring Chinook and summer steelhead of the Columbia River Basin. In the summer of 2008 phase ...

  Citation × Citation Citation Abstract Copy Title: Monitoring river restoration using fiber optic temperature measurements in a modeling framework Author: Huff, Julie A. The Middle Fork of the John Day River (MFJD) in Northeastern Oregon contains important spawning grounds for spring Chinook and summer steelhead of the Columbia River Basin. In the summer of 2008 phase one of a river restoration project was completed which included the addition of engineered log jams (ELJs) and scour pools. The restoration focuses on increasing habitat diversity and decreasing peak summer temperatures which, perhaps, had been degraded due to anthropogenic activities such as dredge mining, cattle grazing, channelization and deforestation. This study utilized Distributed Temperature Sensing (DTS) technology to measure the temperature the MFJD study site before and after restoration during the summer of 2008. The temperature data along with other physical and climatic data were modeled using a physically based stream temperature model which incorporated groundwater inflows and an average depth of hyporheic exchange over the entire study reach. The root mean square errors for the pre- and post-restoration model are 0.57°C and 0.47°C, respectively. An average depth of the thermal mass associated with hyporheic exchange was calculated within the model to be 11m for pre- restoration and 1.6m for post-restoration. It is unclear as to whether the hyporheic exchange increased due to restoration or is an artifact of high flows during the pre-restoration period. A statistical analysis was completed on the longitudinal temperature profiles of the MFJD to identify lengths of the river whose temperatures are different upstream and downstream. Groundwater inflow was defined as locations with cooler day time and night time temperatures than the surroundings whereas hyporheic discharge was defined as locations with cooler day time temperatures but warmer night time temperature than the surroundings. Statistically significant locations were highlighted for both pre- and post-restoration and equated to an average decrease in local temperature of 0.08°C pre-restoration and 1.18°C post-restoration. This equates to 0.004 m³/s and 0.012 m³/s of groundwater inflow for pre- and post-restoration, respectively. Again, these differences could be artifacts of high flows during pre-restoration and cannot conclusively be linked to the restoration efforts. However, the largest groundwater inflow (0.004 m³/s) can be associated with one ELJ structure and its corresponding scour pool. Title: Monitoring river restoration using fiber optic temperature measurements in a modeling framework Author: Huff, Julie A. The Middle Fork of the John Day River (MFJD) in Northeastern Oregon contains important spawning grounds for spring Chinook and summer steelhead of the Columbia River Basin. In the summer of 2008 phase one of a river restoration project was completed which included the addition of engineered log jams (ELJs) and scour pools. The restoration focuses on increasing habitat diversity and decreasing peak summer temperatures which, perhaps, had been degraded due to anthropogenic activities such as dredge mining, cattle grazing, channelization and deforestation. This study utilized Distributed Temperature Sensing (DTS) technology to measure the temperature the MFJD study site before and after restoration during the summer of 2008. The temperature data along with other physical and climatic data were modeled using a physically based stream temperature model which incorporated groundwater inflows and an average depth of hyporheic exchange over the entire study reach. The root mean square errors for the pre- and post-restoration model are 0.57°C and 0.47°C, respectively. An average depth of the thermal mass associated with hyporheic exchange was calculated within the model to be 11m for pre- restoration and 1.6m for post-restoration. It is unclear as to whether the hyporheic exchange increased due to restoration or is an artifact of high flows during the pre-restoration period. A statistical analysis was completed on the longitudinal temperature profiles of the MFJD to identify lengths of the river whose temperatures are different upstream and downstream. Groundwater inflow was defined as locations with cooler day time and night time temperatures than the surroundings whereas hyporheic discharge was defined as locations with cooler day time temperatures but warmer night time temperature than the surroundings. Statistically significant locations were highlighted for both pre- and post-restoration and equated to an average decrease in local temperature of 0.08°C pre-restoration and 1.18°C post-restoration. This equates to 0.004 m³/s and 0.012 m³/s of groundwater inflow for pre- and post-restoration, respectively. Again, these differences could be artifacts of high flows during pre-restoration and cannot conclusively be linked to the restoration efforts. However, the largest groundwater inflow (0.004 m³/s) can be associated with one ELJ structure and its corresponding scour pool. Close

• 29. [Article] The physiology ecology and run diversity of adult Pacific lamprey, Entosphenus tridentatus, during the freshwater spawning migration

  Pacific lamprey, Entosphenus tridentatus, have shown recent and rapid declines in abundance. These anadromous fish return to streams where they mature, spawn and die. It has been inferred that Pacific ...

  Citation × Citation Citation Abstract Copy Title: The physiology ecology and run diversity of adult Pacific lamprey, Entosphenus tridentatus, during the freshwater spawning migration Author: Clemens, Benjamin Jacob, 1976- Pacific lamprey, Entosphenus tridentatus, have shown recent and rapid declines in abundance. These anadromous fish return to streams where they mature, spawn and die. It has been inferred that Pacific lamprey enter freshwater and reside for ~ 1 year before spawning. This long exposure to the freshwater environment may affect the plasticity of the maturation process and the migration timing of Pacific lamprey. Diversity in run times and body size has been observed for Pacific lamprey, yet it is unknown if this diversity is induced by the freshwater environment or if it is genetic. My first goal was to describe the maturation and migration characteristics of adult Pacific lamprey during their freshwater migration. My second goal was to use these data to make an estimation of the run diversity in Pacific lamprey. I conducted three complementary studies, in the laboratory and the field, to achieve these goals. I held immature adult lamprey (non-ripe fish that had ceased parasitic feeding in the ocean and had returned to freshwater) in the laboratory at temperatures that mimicked what these fish would experience in the wild, during the summer (mean: 21.8 °C), and another group of lamprey at cooler temperature (mean: 13.6 °C) to compare maturation timing and characteristics. The warm water group of lamprey showed significantly greater proportional decreases in body mass following temperature exposure than fish in the cooler water. All fish exposed to the warm water matured the following spring (8-10 months later) whereas only about half of the fish from the cool water exposure matured. To understand the migration distances and timing of adult Pacific lamprey, I tracked radio-tagged fish throughout the Willamette Basin above Willamette Falls, Oregon, by airplane and recorded their location. Fish migrated primarily during the spring to early summer period before stopping during the remainder of summer, when peak river temperatures (≥ 20°C) occurred. These fish tended to remain stationary through the fall and winter. However, at least a few fish continued to migrate upstream after September. I monitored maturation characteristics of adult Pacific lamprey, over time at Willamette Falls, Oregon and compared these fish with recent migrants collected from the Pacific Ocean as they entered freshwater. The results suggest a unimodal spawn timing between April and June, at water temperatures < 20 °C. Between July and mid-September, as water temperatures peaked at ~ 25 °C, relatively immature fish for both sexes prevailed. Warm summer temperatures coincided with an increase and prevalence of testicular atrophy in males, and I also observed a large die-off of lamprey during this time. The immature fish had maturation stages and phenotypic characteristics similar to recent migrants collected at the mouth of the Klamath River, suggesting that the immature fish at Willamette Falls would spawn the following year, and spawners in any given year may have been recent migrants during the previous year. However there is a temporal overlap in the spring of immature and mature fish, and I found evidence from gonad histology of maturing fish as they entered the river from the ocean, suggesting that a cohort is comprised of recent migrants that spawn within several weeks of entering freshwater, and another cohort is comprised of recent migrants that mature and spawn at least 1 year later. I hypothesize that the recent migrants that would likely spawn shortly after entering freshwater are akin to a winter or "ocean maturing" steelhead, Oncorhynchus mykiss, that optimizes feeding and growth in the open ocean for a few years before entering freshwater to spawn low in the river system shortly afterwards. Alternatively, these lamprey may be similar to coastal cutthroat trout, O. clarki clarki, that feed and grow in the coastal areas of the ocean for a few months before entering freshwater to spawn. There could be other less apparent explanations as well. I also hypothesize that the lamprey that would likely spawn within ~ 1 year of entering freshwater are akin to a "stream maturing" steelhead that foregoes feeding and growth opportunities, enters freshwater during the summer – fall, and accesses spawning grounds to spawn at temperatures that promote evolutionary fitness via successful spawning the following spring. Based on the results of my research, I hypothesize that warm summer temperatures (> 20 °C) can act as a strong selection factor against stream maturing Pacific lamprey in two ways. First, these temperatures may expedite their maturation, while at the same time slowing their migration. If these hypotheses are true, then I predict an uncoupling of spawn timing with optimal habitat characteristics, that would promote fitness, in the upper watershed. Second, summer temperatures may cause gonad atrophy and death prior to spawning. This scenario may select for ocean maturing Pacific lamprey. Title: The physiology ecology and run diversity of adult Pacific lamprey, Entosphenus tridentatus, during the freshwater spawning migration Author: Clemens, Benjamin Jacob, 1976- Pacific lamprey, Entosphenus tridentatus, have shown recent and rapid declines in abundance. These anadromous fish return to streams where they mature, spawn and die. It has been inferred that Pacific lamprey enter freshwater and reside for ~ 1 year before spawning. This long exposure to the freshwater environment may affect the plasticity of the maturation process and the migration timing of Pacific lamprey. Diversity in run times and body size has been observed for Pacific lamprey, yet it is unknown if this diversity is induced by the freshwater environment or if it is genetic. My first goal was to describe the maturation and migration characteristics of adult Pacific lamprey during their freshwater migration. My second goal was to use these data to make an estimation of the run diversity in Pacific lamprey. I conducted three complementary studies, in the laboratory and the field, to achieve these goals. I held immature adult lamprey (non-ripe fish that had ceased parasitic feeding in the ocean and had returned to freshwater) in the laboratory at temperatures that mimicked what these fish would experience in the wild, during the summer (mean: 21.8 °C), and another group of lamprey at cooler temperature (mean: 13.6 °C) to compare maturation timing and characteristics. The warm water group of lamprey showed significantly greater proportional decreases in body mass following temperature exposure than fish in the cooler water. All fish exposed to the warm water matured the following spring (8-10 months later) whereas only about half of the fish from the cool water exposure matured. To understand the migration distances and timing of adult Pacific lamprey, I tracked radio-tagged fish throughout the Willamette Basin above Willamette Falls, Oregon, by airplane and recorded their location. Fish migrated primarily during the spring to early summer period before stopping during the remainder of summer, when peak river temperatures (≥ 20°C) occurred. These fish tended to remain stationary through the fall and winter. However, at least a few fish continued to migrate upstream after September. I monitored maturation characteristics of adult Pacific lamprey, over time at Willamette Falls, Oregon and compared these fish with recent migrants collected from the Pacific Ocean as they entered freshwater. The results suggest a unimodal spawn timing between April and June, at water temperatures < 20 °C. Between July and mid-September, as water temperatures peaked at ~ 25 °C, relatively immature fish for both sexes prevailed. Warm summer temperatures coincided with an increase and prevalence of testicular atrophy in males, and I also observed a large die-off of lamprey during this time. The immature fish had maturation stages and phenotypic characteristics similar to recent migrants collected at the mouth of the Klamath River, suggesting that the immature fish at Willamette Falls would spawn the following year, and spawners in any given year may have been recent migrants during the previous year. However there is a temporal overlap in the spring of immature and mature fish, and I found evidence from gonad histology of maturing fish as they entered the river from the ocean, suggesting that a cohort is comprised of recent migrants that spawn within several weeks of entering freshwater, and another cohort is comprised of recent migrants that mature and spawn at least 1 year later. I hypothesize that the recent migrants that would likely spawn shortly after entering freshwater are akin to a winter or "ocean maturing" steelhead, Oncorhynchus mykiss, that optimizes feeding and growth in the open ocean for a few years before entering freshwater to spawn low in the river system shortly afterwards. Alternatively, these lamprey may be similar to coastal cutthroat trout, O. clarki clarki, that feed and grow in the coastal areas of the ocean for a few months before entering freshwater to spawn. There could be other less apparent explanations as well. I also hypothesize that the lamprey that would likely spawn within ~ 1 year of entering freshwater are akin to a "stream maturing" steelhead that foregoes feeding and growth opportunities, enters freshwater during the summer – fall, and accesses spawning grounds to spawn at temperatures that promote evolutionary fitness via successful spawning the following spring. Based on the results of my research, I hypothesize that warm summer temperatures (> 20 °C) can act as a strong selection factor against stream maturing Pacific lamprey in two ways. First, these temperatures may expedite their maturation, while at the same time slowing their migration. If these hypotheses are true, then I predict an uncoupling of spawn timing with optimal habitat characteristics, that would promote fitness, in the upper watershed. Second, summer temperatures may cause gonad atrophy and death prior to spawning. This scenario may select for ocean maturing Pacific lamprey. Close

• 30. [Article] Distribution, Abundance, and Settlement of Slope-spawning Flatfish during Early Life Stages in the Eastern Bering Sea

  Changes in environmental conditions in marine ecosystems could directly or indirectly influence distribution, abundance, settlement, and size at settlement of flatfish. Understanding species-specific and ...

  Citation × Citation Citation Abstract Copy Title: Distribution, Abundance, and Settlement of Slope-spawning Flatfish during Early Life Stages in the Eastern Bering Sea Author: Sohn, Dongwha Changes in environmental conditions in marine ecosystems could directly or indirectly influence distribution, abundance, settlement, and size at settlement of flatfish. Understanding species-specific and age-specific responses to environmental variability is important for managing commercially important flatfish stocks. Slope-spawning flatfish whose offspring rely on extensive drift from the slope (spawning) to the shelf (settlement) and which require specific habitat for settlement could be especially vulnerable to environmental variability. Arrowtooth flounder (ATF; Atheresthes stomias), Greenland halibut (GH; Reinhardtius hippoglossoides), and Pacific halibut (PH; Hippoglossus stenolepis) are commercially and ecologically important slope-spawning flatfish species in the eastern Bering Sea (EBS), which has experienced fluctuating warm and cold periods since 2000. Although the three species share many attributes, their population trajectories have fluctuated differently. This difference could result from contrasting responses to environmental variability during early life history. To understand how physical variability of the Bering Sea can differentially affect flatfish ecology from pre-settlement to post-settlement phases, I used a combination of field data, biophysical modeling, and statistical modeling to characterize early life stage attributes (chapter 2), settlement success (chapter 3), and size, abundance, and distribution at settlement (age-0) and age-1 (chapter 4). Based on historical ichthyoplankton survey data for GH and PH, I found that there were species-specific differences in the spatial distribution (vertically and horizontally) and juvenile nursery areas between the two species during early life stages in the EBS. Specifically, I found that PH larvae abruptly move to shallower water as they grow, and cross onto the shelf earlier than GH. This ontogenetic movement has the benefit of allowing PH larvae to take advantage of on-shelf transport to reach their settlement locations. However, an early transition from the slope to the shelf may not equally benefit GH, whose settlement locations are further from the spawning ground. Using a bio-physical modeling approach parameterized on the field data summarized in chapter 2, I found that species-specific variability of early life attributes causes interannual and species-specific variability of GH and PH settlement success in the EBS. GH settlement increased with increasing along-shelf (northwestward) flow whereas PH settlement decreased. GH that spawned in November and December were highly successful at settling while PH settlement was most successful when they spawned in January and February. Furthermore, GH settlement is affected by temperature dependence of pelagic larval duration, but not PH, indicating a strong resilience of PH to temperature induced variations in development and dispersal duration. Using otolith microstructure analysis, I found that variations in size at settlement for ATF are significantly correlated with latitude of sampling location. For GH, their size at settlement is associated with bottom water temperature and sea ice extent. Especially, sea ice coverage has a strong negative correlation with on-shelf winds, which drive along-shelf Ekman transport to southeast impacting dispersal pathways and duration. Size at settlement for ATF increased with increasing latitude of sampling location, which could be impacted by currents. For GH, size at settlement decreased with decreasing bottom water temperature and increasing sea ice extent. Also, my results showed that settlement habitat increases for GH in cold years whereas that of ATF increases in warm years. The bottom temperature of age-0 habitat for both ATF and GH affected on their age-1 abundance; GH age-1 abundance increased with decreasing bottom temperature of age-0 habitat, but no clear directionality was found for ATF. The findings from this study have implications for understanding settlement success and recruitment of slope-spawning flatfish in the EBS. In most cold years when along-shelf flow is generally strong, the level of larval supply of GH to their settlement areas is higher than in warm years. Size at settlement for GH decreased in cold years. The larger amount of suitable habitat for settlement and post-settlement stages could result in lower competition and less predation in comparison to warm years. In support of this hypothesis, I found greater age-1 abundance in cold years, indicating size at settlement in GH may not be critical compared to suitability of habitat features and larval supply to settlement grounds. On the other hand, in cold years with strong along-shelf transport to northwest, PH (or ATF), which settle in the southern part of the EBS, have lower numbers of successful settlers. Size at settlement for ATF increased in cold years, and I assumed that size at settlement for PH may have similar patterns. The amount of suitable habitat after settlement would be smaller, resulting in lower recruitment due to increased competition for limited resources. By studying how physical factors and their variability influence these three flatfish during early life stages, this study provides valuable insight into the response of flatfish stocks to past and future climate changes in the eastern Bering Sea – a system that is especially vulnerable to warming. Title: Distribution, Abundance, and Settlement of Slope-spawning Flatfish during Early Life Stages in the Eastern Bering Sea Author: Sohn, Dongwha Changes in environmental conditions in marine ecosystems could directly or indirectly influence distribution, abundance, settlement, and size at settlement of flatfish. Understanding species-specific and age-specific responses to environmental variability is important for managing commercially important flatfish stocks. Slope-spawning flatfish whose offspring rely on extensive drift from the slope (spawning) to the shelf (settlement) and which require specific habitat for settlement could be especially vulnerable to environmental variability. Arrowtooth flounder (ATF; Atheresthes stomias), Greenland halibut (GH; Reinhardtius hippoglossoides), and Pacific halibut (PH; Hippoglossus stenolepis) are commercially and ecologically important slope-spawning flatfish species in the eastern Bering Sea (EBS), which has experienced fluctuating warm and cold periods since 2000. Although the three species share many attributes, their population trajectories have fluctuated differently. This difference could result from contrasting responses to environmental variability during early life history. To understand how physical variability of the Bering Sea can differentially affect flatfish ecology from pre-settlement to post-settlement phases, I used a combination of field data, biophysical modeling, and statistical modeling to characterize early life stage attributes (chapter 2), settlement success (chapter 3), and size, abundance, and distribution at settlement (age-0) and age-1 (chapter 4). Based on historical ichthyoplankton survey data for GH and PH, I found that there were species-specific differences in the spatial distribution (vertically and horizontally) and juvenile nursery areas between the two species during early life stages in the EBS. Specifically, I found that PH larvae abruptly move to shallower water as they grow, and cross onto the shelf earlier than GH. This ontogenetic movement has the benefit of allowing PH larvae to take advantage of on-shelf transport to reach their settlement locations. However, an early transition from the slope to the shelf may not equally benefit GH, whose settlement locations are further from the spawning ground. Using a bio-physical modeling approach parameterized on the field data summarized in chapter 2, I found that species-specific variability of early life attributes causes interannual and species-specific variability of GH and PH settlement success in the EBS. GH settlement increased with increasing along-shelf (northwestward) flow whereas PH settlement decreased. GH that spawned in November and December were highly successful at settling while PH settlement was most successful when they spawned in January and February. Furthermore, GH settlement is affected by temperature dependence of pelagic larval duration, but not PH, indicating a strong resilience of PH to temperature induced variations in development and dispersal duration. Using otolith microstructure analysis, I found that variations in size at settlement for ATF are significantly correlated with latitude of sampling location. For GH, their size at settlement is associated with bottom water temperature and sea ice extent. Especially, sea ice coverage has a strong negative correlation with on-shelf winds, which drive along-shelf Ekman transport to southeast impacting dispersal pathways and duration. Size at settlement for ATF increased with increasing latitude of sampling location, which could be impacted by currents. For GH, size at settlement decreased with decreasing bottom water temperature and increasing sea ice extent. Also, my results showed that settlement habitat increases for GH in cold years whereas that of ATF increases in warm years. The bottom temperature of age-0 habitat for both ATF and GH affected on their age-1 abundance; GH age-1 abundance increased with decreasing bottom temperature of age-0 habitat, but no clear directionality was found for ATF. The findings from this study have implications for understanding settlement success and recruitment of slope-spawning flatfish in the EBS. In most cold years when along-shelf flow is generally strong, the level of larval supply of GH to their settlement areas is higher than in warm years. Size at settlement for GH decreased in cold years. The larger amount of suitable habitat for settlement and post-settlement stages could result in lower competition and less predation in comparison to warm years. In support of this hypothesis, I found greater age-1 abundance in cold years, indicating size at settlement in GH may not be critical compared to suitability of habitat features and larval supply to settlement grounds. On the other hand, in cold years with strong along-shelf transport to northwest, PH (or ATF), which settle in the southern part of the EBS, have lower numbers of successful settlers. Size at settlement for ATF increased in cold years, and I assumed that size at settlement for PH may have similar patterns. The amount of suitable habitat after settlement would be smaller, resulting in lower recruitment due to increased competition for limited resources. By studying how physical factors and their variability influence these three flatfish during early life stages, this study provides valuable insight into the response of flatfish stocks to past and future climate changes in the eastern Bering Sea – a system that is especially vulnerable to warming. Close