Ecosystem-based fisheries management (EBFM) remains an aspirational goal for management throughout the world. One of the primary limitations of EBFM is the incorporation of basic lower trophic level information, particularly for zooplankton, despite the importance of zooplankton to fish. The generation of zooplankton abundance estimates requires significant time and expertise to generate. The rapid zooplankton assessment (RZA) is introduced as a tool whereby nontaxonomic experts may produce rapid zooplankton counts shipboard that can be applied to management in near real time. Zooplankton are rapidly counted shipboard and placed into three broad groups of zooplankton relevant to higher trophic levels: large copepods (> 2 mm), small copepods (< 2 mm), and euphausiids. A Bayesian, hierarchical linear regression modeling approach was used to validate the relationship between RZA abundances and laboratory-processed abundances to ensure the rapid method is a reliable indicator. Additional factors likely to impact the accuracy of the RZA abundance predictions were added to the initial regression model: RZA sorter, survey, season, and large marine ecosystem (Bering Sea, Chukchi/Beaufort Sea, and Gulf of Alaska). We tested models that included the random effect of sorter nested within survey, which improved fits for both large copepods (Bayes R-2 = 0.80) and euphausiids (Bayes R-2 = 0.84). These factors also improved the fit for small copepods when the fixed effect of season was also included (Bayes R-2 = 0.65). Additional RZA data were used to predict laboratory-processed abundances for each zooplankton category and the results were consistent with model training data: large copepods (Bayes R-2 = 0.80), small copepods (Bayes R-2 = 0.64), and euphausiids (Bayes R-2 = 0.88). The Bayesian models were therefore able to predict laboratory-processed abundances with an associated error when accounting for these fixed and random effects. To demonstrate the utility of zooplankton data in management, zooplankton time series from the Bering Sea shelf were shown to vary in relation to warm and cold conditions. This variability impacted commercially important fish, notably Walleye Pollock (Gadus chalcogrammus), and these time series were used by managers using a risk table approach. The RZA method provides a rapid zooplankton population estimation in near real time that can be applied to the management process quickly, thus helping to fill a gap in EBFM.

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Many fish species have moved poleward with ocean warming, and species distribution shifts can occur because of adult fish movement, or juveniles can recruit to new areas. In the Bering Sea, recent studies document a dramatic northward shift in the distribution of Gadus macrocephalus (Pacific cod in English and tikhookeanskaya treska in Russian) during a period of ocean warming, but it is unknown whether the current northward distribution shift continues into the Chukchi Sea. Here, we use catch data from multiple gear types to present larval, age-0, and older Pacific cod distributions from before (2010 and 2012) and during (2017, 2018, and 2019) recent Chukchi Sea warming events. We also report on the habitat, diet, and condition of age-0 Pacific cod, which were present in the eastern Chukchi Sea in recent warm years (2017 and 2019), but were absent in a cold year (2012). We hypothesize that age-0 recruitment to the eastern Chukchi Sea is associated with recent warm temperatures and increased northward transport through the Bering Strait in the spring. Age-0 fish were present in both benthic and pelagic habitats and diets reflected prey resources at these capture locations. Age-1 Pacific cod were observed in the western Chukchi Sea in 2018 and 2019, indicating possible overwinter survival of age-0 fish, although there was little evidence that they survive and/or remain in the Chukchi Sea to age-2. Observed low lipid accumulation in age-0 Pacific cod from the Chukchi Sea suggests juvenile overwinter mortality may be relatively high compared to more boreal regions (e.g. Gulf of Alaska). Adult Pacific cod were also observed in the Chukchi Sea during 2018 and 2019. Although densities in the western Chukchi Sea were very low compared to the Bering Sea, the adults are the first known (to us) records from the Chukchi Sea. The increased presence of multiple age-classes of Pacific cod in the Chukchi Sea suggests poleward shifts in both nursery areas and adult summer habitat beyond the Bering Sea, but the quantity and quality (e.g. summer productivity and overwintering potential) of these habitats will require continued surveys.

Ecosystem indicators track information about states and trends in ocean systems and are a valuable tool for ecosystem assessment and management. To ensure that indicators are used appropriately in both science and management contexts, it is important to understand the extent to which they represent broader spatial patterns. In the Northern California Current (NCC) off the Oregon and Washington state coasts in the USA, copepod metrics derived from data collected at a well-sampled station on the Newport Hydrographic (NH) Line ('NH05', five nmi offshore from Newport, OR, USA) are commonly used as indicators of the region's general ocean conditions. Using correlation analyses, we examined the utility of NH05 as a sentinel station (i.e. representative of a broader region) with respect to the abundance and biomass of warm-water and cold-water copepods in the NCC. Copepod correlations between NH05 and other locations in the NCC were higher for the warm-water copepods than the cold-water group, with correlations being slightly higher for abundance than biomass. Paracalanus parvus had the highest NH05 correlations among the warm-water copepod species, and Acartia longiremis had the highest NH05 correlations among the cold-water copepod species. We also broadened our analysis to evaluate other sampling sites as sentinel stations and found that some sites were equally or more representative of copepod dynamics in the NCC than NH05, though none of these sites tend to be sampled as often as NH05. This analysis emphasized that the warm-water copepods tend to be more similarly distributed in the NCC than the cold-water copepods, and thus their changes through time are better captured by most stations. In contrast, correlations among the cold-water copepods in the NCC vary by location and appear to be strongly related to depth, with the highest correlations at mid-shelf stations.

The North Pacific marine heatwave of 2014-2016 (nicknamed "The Blob") impacted marine ecosystems from California to Alaska, USA, with cascading effects on fisheries and fishing communities. We investigated the effects of this anomalous ocean warming on early life stages of walleye pollock (Gadus chalcogrammus) in the Gulf of Alaska. In spring of 2015, pollock larvae were caught at record low levels relative to a 30-year time series. Survival rates were low during the summer, and by late summer, numbers were further reduced, with very low abundances of juvenile (age-0) pollock. Our analyses suggested multiple mechanisms for this decline: (a) Low-saline conditions may have impacted egg buoyancy and survival; (b) population densities of zooplankton nauplii may have been too low to support first-feeding larvae; (c) body condition of age-0 pollock was poor and a bioenergetics model indicated that reduced quality of zooplankton prey, coupled with warmer temperatures, increased the ration required for positive growth by up to 19%, at a time when prey abundance was likely reduced. Thus, walleye pollock experienced a cascade of poor conditions for growth and survival through early life stages, resulting in the near disappearance of the 2015 year class in the population by the end of their first year. These impacts differ from previous warm years and emphasize the importance of looking beyond simple temperature-abundance relationships when predicting species responses to climate warming.

A survey-based time series (2001-2019) showed that age-0 walleye pollock (Gadus chalcogrammus) occurred in very high abundances in 2013 compared with other years; however, recruitment of the 2013 year class to age-1 was lower than average. Diet composition of age-0 fish was examined from the 2013 year class to assess the potential impact of the consumed prey on walleye pollock. High abundances of smaller age-0 fish were found at stations southwest of the Shumagin Islands compared with low abundances of larger fish found surrounding Kodiak Island. Fish in the southwest region showed a higher intake of low-quality food items such as pteropods and larvaceans compared with fish in the northwest region that had consumed mostly higher quality prey such as large copepods and euphausiids. Even though no significant differences were found in fish condition between regions overall, spatial differences in fish weight were found after accounting for sample day of year. Prey-specific Index of Relative Importance analysis showed southwest region fish had consumed a larger diversity of taxa, whereas fish from the rest of study area primarily consumed large copepods and euphausiids. These results suggest that high abundances of smaller pollock found in the southwestern part of the study region consumed a higher percentage of low-quality, lipid-poor prey taxa, which likely contributed to reduced overwinter survival and increased mortality.

AbstractBering Sea sea ice during winter 2017–2018 was the lowest ever recorded. Ecosystem effects of low ice have been observed in the southeastern Bering Sea, but never in the northern Bering Sea. Observations in both systems included weakened water column stratification, delayed spring bloom, and low abundances of large crustacean zooplankton. Summer Cold Pool presence was extremely limited. Young walleye pollock production and condition were similar to prior warm years, though catches of other pelagic forage fishes were low. Summer seabird die‐offs were observed in the northern Bering Sea, and to lesser extent in the southeastern Bering Sea, and reproductive success was poor at monitored colonies. Selected bottom‐up responses to lack of sea ice in the north were similar to those in the south, potentially providing environmental indicators to project ecosystem effects in a lesser studied system. Results offer a potential glimpse of the broader Bering Sea pelagic ecosystem under future low‐ice projections.

Yearling Chinook salmon Oncorhynchus tshawytscha were sampled off Washington and Oregon, USA, along with environmental factors, every June from 1998 to 2010. The abundance of yearling Chinook salmon varied over space with a high proportion of zero catches. Positive catches were more numerous north of the Columbia River, likely because most yearling Chinook salmon turn north after leaving the Columbia River. Using the latitude of the Columbia River mouth as a geographical border, the survey area was divided into 2 regions: north and south of the Colum- bia River. We hypothesized that (1) the spatial distribution pattern within each region was related to local environmental factors and (2) the difference between north and south was related to large- scale ocean processes. A constrained zero-inflated generalized additive model (COZIGAM) was applied to examine the non-linear relationships between juvenile salmon abundance and environ- mental factors. Results from the COZIGAM suggested that water temperature, chlorophyll a (chl a) concentration, copepod biomass and spatial factors were significantly correlated with the density of salmon in the northern region, and only chl a concentration was correlated significantly with year- ling Chinook density in the southern region. The difference between the abundances north and south of the Columbia River was significantly correlated with alongshore ocean currents, with weaker alongshore currents leading to greater difference between north and south. Results sug- gest that salmon distribution is determined not only by standard habitat parameters (local biotic and abiotic factors) but by ocean conditions such as the strength of alongshore coastal currents.

Yearling Chinook (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch) were sampled concurrently with physical variables (temperature, salinity, depth) and biological variables (chlorophyll a concentration and copepod abundance) along the Washington and Oregon coast in June 1998–2008. Copepod species were divided into four different groups based on their water-type affinities: cold neritic, subarctic oceanic, warm neritic, and warm oceanic. Generalized linear mixed models were used to quantify the relationship between the abundance of these four different copepod groups and the abundance of juvenile salmon. The relationships between juvenile salmon and different copepod groups were further validated using regression analysis of annual mean juvenile salmon abundance versus the mean abundance of the copepod groups. Yearling Chinook salmon abundance was negatively correlated with warm oceanic copepods, warm neritic copepods, and bottom depth, and positively correlated with cold neritic copepods, subarctic copepods, and chlorophyll a concentration. The selected habitat variables explained 67% of the variation in yearling Chinook abundance. Yearling coho salmon abundance was negatively correlated with warm oceanic copepods, warm neritic copepods, and bottom depth, and positively correlated with temperature. The selected habitat variables explained 40% of the variation in yearling coho abundance. Results suggest that copepod communities can be used to characterize spatio-temporal patterns of abundance of juvenile salmon, i.e., large-scale interannual variations in ocean conditions (warm versus cold years) and inshore-offshore (cross-shelf) gradients in the abundance of juvenile salmon can be characterized by differences in the abundance of copepod species with various water mass affinities.

An analysis was conducted of the strengths and limitations of acoustic methods to determine biomass and taxonomic distribution patterns over the Oregon continental shelf. Measurements of volume backscatter from two different acoustic instruments were compared with each other and with predicted volume backscatter calculated from a coincident net tow. Spatially and temporally coincident data were collected from a six-frequency bioacoustic system (Tracor Acoustic Profiling System (TAPS)) and from a 1 m 2 Multiple Opening Closing Net and Environmental Sensing System (MOCNESS). The combined net/acoustic tows were conducted over the Oregon continental shelf in August 2001, during both day and night. The TAPS was mounted on the upper frame of the MOCNESS and ensonified a volume of water directly in front of the net mouth. A four-frequency echosounder (Hydroacoustic Technologies Inc. (HTI)) with downward looking transducers was towed off the port side of the ship during the MOCNESS/TAPS tows. Fine-scale vertical distributions of zooplankton that were resolved acoustically were not apparent within the integrated depth strata of the individual MOCNESS net samples. The taxonomic and size composition of the zooplankton community had strong effects on volume backscatter (S V ), although the magnitude of S V was not linearly related to zooplankton biomass. Predicted S V calculated from scattering models and the contents of the MOCNESS nets agreed best (sometimes within 5 dB) with measured S V from the TAPS at 420 and 700 kHz and measured S V at 420 kHz from the HTI.

To determine the mechanisms that might explain retention and/or loss of plankton during the coastal upwelling season, one needs an understanding of the vertical migration behavior and ontogenetic changes in vertical distribution and data on direction and magnitude of currents at depths where the animals reside. In this paper we compare and contrast the cross‐shelf distributions of four copepod species, Calanus marshallae, Pseudocalanus mimus, Acartia longiremis, and Centropages abdomalis, and the euphausiid Euphausia pacifica, from sampling during the Coastal Ocean Advances in Shelf Transport (COAST) program. The COAST study region was off central Oregon (44°–45°N), ranged from the nearshore zone out to ∼1000 m isobath, and was a trapezoid 120 km in length and 40 km wide in the north by 100 km wide in the south. Plankton were sampled along three transects, in the north, middle, and southern portions of the study region. For the two most abundant copepods, C. marshallae and P. mimus, sampling with a Multiple Opening/Closing Net and Environmental Sampling System showed that naupliar and early copepodite stages were found within the warm phytoplankton‐rich upper 20 m of the water column but that copepodite stages C3 through adult were found at progressively deeper strata in the water column. Similarly, euphausiid larvae were most abundant within the upper 20 m, whereas juveniles and adults lived deeper in the water column. Diel vertical migration was observed only in the older developmental stages. Because older stages occupy different strata than younger stages, there is cross‐shelf displacement of zooplankton.

An analysis was conducted of the strengths and limitations of acoustic methods to determine biomass and taxonomic distribution patterns over the Oregon continental shelf. Measurements of volume backscatter from two different acoustic instruments were compared with each other and with predicted volume backscatter calculated from a coincident net tow. Spatially and temporally coincident data were collected from a six‐frequency bioacoustic system (Tracor Acoustic Profiling System (TAPS)) and from a 1 m2 Multiple Opening Closing Net and Environmental Sensing System (MOCNESS). The combined net/acoustic tows were conducted over the Oregon continental shelf in August 2001, during both day and night. The TAPS was mounted on the upper frame of the MOCNESS and ensonified a volume of water directly in front of the net mouth. A four‐frequency echosounder (Hydroacoustic Technologies Inc. (HTI)) with downward looking transducers was towed off the port side of the ship during the MOCNESS/TAPS tows. Fine‐scale vertical distributions of zooplankton that were resolved acoustically were not apparent within the integrated depth strata of the individual MOCNESS net samples. The taxonomic and size composition of the zooplankton community had strong effects on volume backscatter (SV), although the magnitude of SV was not linearly related to zooplankton biomass. Predicted SV calculated from scattering models and the contents of the MOCNESS nets agreed best (sometimes within 5 dB) with measured SV from the TAPS at 420 and 700 kHz and measured SV at 420 kHz from the HTI.