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.

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.

Throughout the northern extent of its range, Chinook salmon (Oncorhynchus tshawytscha) adult returns have been in decline for over a decade, leading to severe harvest restrictions on subsistence, commercial, and recreational fisheries. In addition to these overall declines in abundance, changes in size structure and age structure, including a proportional decrease of older age classes returning to spawn, suggest that late-stage marine mortality for this species may be more frequent than currently assumed. To examine this late-stage mortality hypothesis, we examined diagnostic evidence of predation on large (57–100 cm fork length) Chinook salmon (n = 33) from depth, temperature, and light records collected during recent satellite tagging research. Satellite tags provided evidence of predation on tagged Chinook salmon by salmon sharks (Lamna ditropis) (n = 14), marine mammals (n = 2), ectothermic fish(es) (n = 3), and unidentified predators (n = 5) in the Bering Sea and Gulf of Alaska. High mortality rates in this study suggest that fisheries scientists should consider that late-stage mortality by marine apex predators may be shaping this species’ abundance and demographics.

Chinook salmon are widely distributed in offshore waters of the North Pacific Ocean, and of great economical and subsistence importance; however, little is known about their oceanic ecology. To address this, we tagged 43 Chinook salmon Oncorhynchus tshawytscha (57–100 cm) with pop-up satellite archival tags (PSATs) in the eastern (October– December) and central Bering Sea (August) to provide insights into the oceanic movements, behavior, and thermal environment of this species. The tags retrieved data for up to 260 days and end locations of tagged Chinook salmon spanned from the central Bering Sea ( n = 6), eastern Bering Sea/Aleutian Islands ( n = 20), and the Gulf of Alaska (n = 6). While at liberty, Chinook salmon occupied depths ranging from 0 to 538 m and experienced a thermal environment ranging from −0.6 to 13.5 °C. Overall, mean depths of individual fish ranged from 4.5 to 127.9 m, while median depths ranged from 1.3 to 99.5 m. Although sample sizes were not even among months of the year, Chinook salmon occupied the shallowest and warmest water in May–September and the deepest and coolest water in December–March. Diel depth-specific diving behaviors of Chinook salmon were found in some tag records, but these behaviors appeared to be variable among individuals and plastic in nature within individuals. Results from this study provide insights into movement, diving behavior and the thermal environment of individual Chinook salmon which may have future application in understanding its ecology and developing strategies to further reduce incidental catch of this species.

Installation of hydrokinetic power-generating devices is currently being considered for the Yukon and Tanana rivers, two large and glacially turbid rivers in Alaska. We sampled downstream-migrating fish along the margins of both rivers, a middle island in the Yukon River, and mid-channel in the Tanana River in order to assess the temporal and spatial patterns of movement by resident and anadromous fishes and hence the potential for fish interactions with hydrokinetic devices. Results suggest that (1) river margins in the Yukon and Tanana rivers are primarily utilized by resident freshwater species, (2) the mid-channel is utilized by Pacific salmon Oncorhynchus spp. smolts, and (3) only Chum Salmon O. keta smolts utilize both river margin and mid-channel areas. Some species exhibited distinct peaks and trends in downstream migration timing, including Longnose Suckers Catostomus catostomus, whitefishes (Coregoninae), Arctic Grayling Thymallus arcticus, Lake Chub Couesius plumbeus, Chinook Salmon O. tshawytscha, Coho Salmon O. kisutch, and Chum Salmon. Due to their downstream migration behavior, Pacific salmon smolts out-migrating in May-July will have the greatest potential for interactions with hydrokinetic devices installed in mid-channel surface waters of the Yukon and Tanana rivers.

Atlantic halibut (Hippoglossus hippoglossus) in a Norwegian fjord were tagged with pop-up archival transmitting (PAT) tags to investigate whether they join offshore spawning events with halibut from other regions. All fish (n = 4) remained in the fjord throughout the spawning season, suggesting that they may be reproductively segregated from other stocks.

Hydrokinetic devices generate electricity by capturing kinetic energy from flowing water as it moves across or through a rotor, without impounding or diverting the water source. The Tanana River in Alaska, a turbid glacial system, has been selected as a pilot location to evaluate the effects of such a device on fish communities that are highly valued by subsistence, sport, and commercial users. The basic ecology and habitat use of fishes in turbid glacial systems are poorly understood; therefore it is necessary to study the species composition of the fish community and the spatial and temporal patterns of mainstem river use by these fishes to evaluate impacts of a hydrokinetic device. In this document, we provide an overview of existing knowledge of fish ecology in the Tanana River and impacts of hydrokinetic devices on fishes in other river systems. Seventeen fish species are known to inhabit the Tanana River and several may utilize the deepest and fastest section of the channel, the probable deployment location for the hydrokinetic device, as a seasonal migration corridor. Previous studies in clearwater river systems indicate that mortality and injury rates from turbine passage are low. However, the results from these studies may not apply to the Tanana River because of its distinctive physical properties. To rectify this shortcoming, a conceptual framework for a comprehensive fish ecology study is recommended to determine the impacts of hydrokinetic devices on fishes in turbid, glacial rivers.