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Chinook salmon ( Oncorhynchus tshawytscha ) populations have experienced widespread declines in abundance and abrupt shifts toward younger and smaller adults returning to spawn in rivers. The causal agents underpinning these shifts are largely unknown. Here we investigate the potential role of late-stage marine mortality, defined as occurring after the first winter at sea, in driving this species’ changing age structure. Simulations using a stage-based life cycle model that included additional mortality during after the first winter at sea better reflected observed changes in the age structure of a well-studied and representative population of Chinook salmon from the Yukon River drainage, compared with a model estimating environmentally-driven variation in age-specific survival alone. Although the specific agents of late-stage mortality are not known, our finding is consistent with work reporting predation by salmon sharks ( Lamna ditropis ) and marine mammals including killer whales ( Orcinus orca ). Taken as a whole, this work suggests that Pacific salmon mortality after the first winter at sea is likely to be higher than previously thought and highlights the need to investigate selective sources of mortality, such as predation, as major contributors to rapidly changing age structure of spawning adult Chinook salmon.

Polar cod (Boreogadus saida) is a key forage fish in the Arctic marine ecosystem and provides an energetic link between lower and upper trophic levels. Despite its ecological importance, spatially explicit studies synthesizing polar cod distributions across research efforts have not previously been conducted in its Pacific range. We used spatial generalized additive models to map the distribution of polar cod by size class and relative to environmental variables. We compiled demersal trawl data from 21 cruises conducted during 2004–2017 in the Chukchi and Beaufort seas, and investigated size-specific patterns in distribution to infer movement ecology of polar cod as it develops from juvenile to adult life stages. High abundances of juvenile polar cod (≤ 70 mm) in the northeastern Chukchi Sea and western Beaufort Sea were separated from another region of high abundance in the eastern Beaufort Sea, near the US and Canadian border, suggesting possible population structure in the Pacific Arctic. Relating environmental correlates to polar cod abundance demonstrated that temperature and salinity were related to juvenile distribution patterns, while depth was the primary correlate of adult distribution. A comparison of seasonal 2017 abundances of polar cod in the southern Chukchi Sea found low demersal abundance in the spring when compared to the summer. Seasonal differences in polar cod abundance suggest that polar cod migration may follow a classical ‘migration triangle’ route between nursery grounds as juveniles, feeding grounds as subadults, and spawning grounds as adults, in relation to ice cover and seasonal production in the Chukchi Sea.

A diversified energy portfolio may include marine energy in the form of current energy converters (CECs) such as tidal or in-river turbines. New technology development in the research stage typically requires monitoring for environmental effects. A significant environmental effect of concern for CECs is the risk of moving parts (e.g., turbine blades) colliding with animals such as fishes. CECs are installed in energetic locations in which it is difficult to operate sensors to fulfill monitoring requirements for informing collision risk. Collecting data (i.e., about blade strikes or near-misses) that inform interactions of fishes with CECs is usually attempted using active acoustic sensors or video cameras (VCs). Limitations of low-light conditions or water turbidity that preclude effective use of VCs are overcome by using high-resolution multibeam echosounders (or acoustic cameras (ACs)). We used an AC at two sites to test its ability to detect artificial and real fish targets and determine if strike, near-miss, and near-field behavior could be observed. Interactions with fish and artificial targets with turbines have been documented but strike confirmation with an AC is novel. The first site was in a tidal estuary with a 25 kW turbine and water clarity sufficient to allow VC data to be collected concurrently with AC data showing turbine blade strike on tethered artificial fish targets. The second site was a turbid, debris-laden river with a 5 kW turbine where only AC data were collected due to high water turbidity. Data collection at the second site coincided with downstream Pacific salmon (Oncorhynchus spp.) smolt migration. Physical fish capture downstream of the turbine was performed with an incline plane trap (IPT) to provide context for the AC observations, by comparing fish catches. Discrimination between debris and fishes in the AC data was not possible, because active movement of fishes was not discernable. Nineteen fishes were released upstream of the turbine to provide known times of possible fish/turbine interactions, but detection was difficult to confirm in the AC data. ACs have been used extensively in past studies to count large migratory fish such as Pacific salmon, but their application for small fish targets has been limited. The results from these two field campaigns demonstrate the ability of ACs to detect targets in turbid water and observe blade strikes, as well as their limitations such as the difficulty of distinguishing small fishes from debris in a high-energy turbid river. Recommendations are presented for future applications associated with CEC device testing.

Background Although steelhead ( Oncorhynchus mykiss ) is a culturally and recreational important species throughout North America, less is known about its ocean than its freshwater ecology. To provide insights into migratory routes and habitats occupied by steelhead in the North Pacific Ocean, we attached pop-up satellite archival tags (PSATs) to female steelhead kelts from three watersheds on the east coast of Prince of Wales Island, in southern southeast Alaska. Results PSATs successfully recorded extensive westward post-spawning migrations of nine female kelts across the Gulf of Alaska to areas near the Alaska Peninsula and Aleutian Islands. From the months of June to October, tagged steelhead occasionally dived to 10–20 m, but spent approximately 90% of their time in surface waters (< 4.5 m). During this same time period, 90% of all tag-recorded temperatures were between 8.7 and 12.8°C. Conclusion These results corroborate past research on other North American steelhead populations, demonstrating that steelhead kelts predominantly occupy surface waters with sea-surface temperatures of 5–15 °C while transiting to and occupying purported feeding grounds in the western Gulf of Alaska and Aleutian Islands. Taken together, these results suggest that steelhead kelts originating from rivers throughout this species’ North American range occupy similar habitats in the North Pacific Ocean. While we only studied the ocean ecology of a limited number of steelhead kelts from southern Southeast Alaska, our results are pertinent for other populations throughout the northern west coast of North America, and provide better understanding of this species’ ocean ecology.

Polar cod ( Boreogadus saida ) is an important link between top predators and lower trophic levels in high-latitude marine ecosystems. Previous findings describe differences in its diet throughout the western Arctic; however, the causes of this variation are not well known. This study examined the diets of juvenile polar cod collected via demersal trawling methods over three summers in the northeastern Chukchi Sea (2010–2012) and one summer in the western Beaufort Sea (2011) to determine the amount of variability explained by biological, spatial, and interannual factors. Prey were identified, measured for length, and aggregated by percent mean weight into taxonomically coarse prey categories for analysis. Within seas, variation in juvenile polar cod diet composition was significantly related to body size, latitude, longitude, depth, and interannual (Chukchi Sea only) factors. Canonical correspondence analysis indicated body size was the most important factor contributing to the total variance in juvenile polar cod diet in the Chukchi and Beaufort Seas. Body size-based diet differences between the Chukchi and Beaufort Seas were evaluated using non-metric multidimensional scaling. This method revealed that similar-sized polar cod consumed similar-sized prey in both seas, but their diets were more benthically influenced in the Chukchi Sea and more pelagically influenced in the Beaufort Sea. Juvenile polar cod diet compositions vary by body size and region of inhabitance throughout their distribution. Here, we show that body size was the primary factor explaining variation in the summer diet of juvenile polar cod within the Chukchi and Beaufort Seas.

Background The salmon shark ( Lamna ditropis ) is a widely distributed apex predator in the North Pacific Ocean. Many salmon sharks from the eastern North Pacific, specifically Prince William Sound, Alaska, have been satellite tagged and tracked, but due to the sexual segregation present in salmon sharks, most of these tagged sharks were female. Consequently, little information exists regarding the migration patterns of male salmon sharks. To better understand the migration and distribution of this species, information on the male component of the population as well as from sharks outside of Prince William Sound, Alaska, is needed. In this study, we deployed satellite transmitters on two mature male salmon sharks caught in the Bering Sea. Results The two mature male salmon sharks tagged in the Bering Sea exhibited distinct migration patterns. The first male, tagged in August 2017, traveled to southern California where it remained from January to April after which it traveled north along the United States’ coast and returned to the Bering Sea in August 2018. The second male, tagged in September 2019, remained in the North Pacific between 38° N and 50° N before returning to the Bering Sea in July of year one and as of its last known location in year two. The straight-line distance traveled by the 2017 and 2019 sharks during their 12 and 22 months at liberty was 18,775 km and 27,100 km, respectively. Conclusions Before this study, our understanding of salmon shark migration was limited to female salmon sharks satellite tagged in the eastern North Pacific. The 2017 male salmon shark undertook a similar, but longer, north–south migration as tagged female sharks whereas the 2019 shark showed little overlap with previously tagged females. The different migration patterns between the two male sharks suggest distinct areas exist for foraging across the North Pacific. The return of both sharks to the Bering Sea suggests some fidelity to the region. Continued tagging efforts are necessary to understand the population structure of salmon sharks in the North Pacific. This tagging study highlights the importance of opportunistic efforts for obtaining information on species and sex with limited distribution data.

Background Pacific halibut support high-value commercial and sport fisheries in the north Pacific Ocean, making survival of Pacific halibut bycatch in trawl fisheries an important management concern. We present a method for characterizing activity and inferring survival of Pacific halibut based on accelerometer data from Pop-up Satellite Archival Tags (PSATs). A PSAT attached to a fish with a dart and tether floats freely above the fish in a vertical orientation when the fish is stationary, but switches to a more horizontal orientation when towed behind an active fish. We hypothesized that characteristic changes in PSAT orientation associated with activity could be detected by accelerometers and summarized for transmission by PSATs to provide valuable information on fish activity. Results We developed procedures for inferring survival of Pacific halibut with accelerometer PSATs based on a progression of analysis steps that linked PSAT orientation, PSAT acceleration data, and Pacific halibut activity patterns. Relationships between PSAT orientation and Pacific halibut activity were confirmed by observations of PSAT orientation on Pacific halibut swimming in the laboratory and comparisons with depth data from tags on free-ranging Pacific halibut. We developed two metrics summarizing 1 Hz acceleration data for transmission to the Argos satellite network. The “knockdown” metric records abrupt changes in vertical acceleration, indicating both initiation of swimming bouts and sustained swimming behavior, and is robust to the effects of tidal currents. The “%tilt” metric records the amount of time the tag tilts past a vertical orientation threshold and captures the proportion of each time bin that the fish is active. These PSAT metrics revealed diel behavior and three activity modes present in free-ranging Pacific halibut that allowed inference of survival when compared to PSAT data from fish carcasses and weighted tags. Conclusions Accelerometer PSAT metrics developed in this study revealed Pacific halibut activity patterns, and thus survival, and may be extended to other fish species. Economical accelerometer PSATs can allow larger sample sizes that enhance bycatch survival studies while detecting fish activity in flat study areas. PSAT advantages over other survival estimation methods include providing outcomes for all specimens during exposure to natural conditions.

Animal telemetry is the science of elucidating the movements and behavior of animals in relation to their environment or habitat. Here, we focus on telemetry of aquatic species (marine mammals, sharks, fish, sea birds and turtles) and so are concerned with animal movements and behavior as they move through and above the world’s oceans, coastal rivers, estuaries and great lakes. Animal telemetry devices (“tags”) yield detailed data regarding animal responses to the coupled ocean–atmosphere and physical environment through which they are moving. Animal telemetry has matured and we describe a developing US Animal Telemetry Network (ATN) observing system that monitors aquatic life on a range of temporal and spatial scales that will yield both short- and long-term benefits, fill oceanographic observing and knowledge gaps and advance many of the U.S. National Ocean Policy Priority Objectives. ATN has the potential to create a huge impact for the ocean observing activities undertaken by the U.S. Integrated Ocean Observing System (IOOS) and become a model for establishing additional national-level telemetry networks worldwide. Background Telemetry can provide environmental, behavioral and physiological data in near-real time, or by use of archival tags in which the data are stored or later transmitted to satellites. Aquatic animal species tagged have ranged from 6-g salmon smolts to 150-ton whales. Detailed observations of animal movements and behavior in relation to critical habitats in their aquatic environment have significantly improved our understanding of ecosystem function and dynamics. These observations are critical for sustaining populations, conserving biodiversity and implementing ecosystem-based management through an increased understanding of ecosystem structures, functions, and processes, as well as their importance to ecosystem services and values. Sensors carried by tagged animals have come of age and deliver high-resolution physical oceanographic data at relatively low costs. Animals are particularly adept at helping scientists identify critical habitats, spawning locations, and important oceanographic features (e.g., fronts, eddies and upwelling areas). They also provide important insights into regions of the oceans that are difficult and expensive to monitor (e.g., offshore environments, Arctic). This paper focuses on how to integrate an operational ATN into U.S. IOOS. Results The development of U.S. IOOS initially focused on the acquisition and integration of physical and chemical oceanographic data. With this system now operational, U.S. IOOS is ready to add the acquisition of relevant biological observations, and to enhance the acquisition of physical and chemical oceanographic observations via ATN platforms. Conclusion A U.S. ATN observing system that monitors aquatic life on a range of temporal and spatial scales could yield both short- and long-term benefits, fill oceanographic observing and knowledge gaps, and advance many of the National Ocean Policy Priority Objectives. ATN has the potential to create a huge impact for the ocean observing activities undertaken by IOOS and become a model for establishing additional national-level telemetry networks worldwide.

Population declines and demographic changes of Chinook salmon (Oncorhynchus tshawytscha), have been documented throughout this species’ range, though information on natural and anthropogenic mechanisms related to these changes are not fully understood. To provide insights into marine behaviors and survival of Chinook salmon, 40 pop-up satellite archival tags (PSATs), that collected environmental data, were attached to large (69–100 cm FL) Chinook salmon caught in the marine waters of Cook Inlet, Alaska. PSATs provided evidence of predation on tagged Chinook salmon by ectothermic and unconfirmed predators, and provided valuable information about the migratory characteristics and occupied depths and temperatures of this species while occupying Cook Inlet and the Gulf of Alaska. The results from this study suggest that late-marine mortality of Chinook salmon of a variety of stock-origins by apex predators is more common in Cook Inlet than previously thought, and may be used to improve our understanding this species’ population dynamics. Furthermore, results from this study adds to the existing knowledge of marine habitat use by Chinook Salmon and may be useful in assessing the vulnerability and interactions between this species and anthropogenic activities.

Big skate Beringraja binoculata is the most frequently landed skate in the Gulf of Alaska portion of the Northeast Pacific Ocean, with recent stock assessment surveys showing relatively healthy skate stocks and continued interest from the commercial fishing industry to increase skate landings. Considered a data-poor species, there is a need for additional ecological information on big skates, including movement patterns and habitat use. We deployed pop-up satellite archival transmitting (PSAT) tags on 8 big skates in the Gulf of Alaska and set the tags to release 1 yr after deployment. The minimum distance traveled by big skates varied between 6 and 205 km, with 1 individual traveling at least 2100 km based on light geolocation data. Three individuals showed evidence of having made long-range movement and crossed at least 1 management boundary, and 3 remained relatively close to their tagging locations. Two tags did not report. The PSAT tags also extended the maximum documented depth of big skates to over 500 m and confirmed that they are thermally tolerant, occupying waters between 2 and 18°C. Because the total catch of big skate is divided into multiple areas and limited movement between areas is assumed, information from this study will aid in the development of appropriate spatial management plans for this species.