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Variation in the recruitment of salmon is often found to be correlated with marine climate indices, but mechanisms behind environment–recruitment relationships remain unclear and correlations often break down over time. We used an ecosystem modeling approach to explore bottom‐up and top‐down mechanisms linking a variable environment to salmon recruitment variations. Our ecosystem model incorporates a regional ocean circulation submodel for hydrodynamics, a nutrient‐phytoplankton‐zooplankton submodel for producing planktonic prey fields, and an individual‐based model (IBM) representing juvenile Chinook salmon (Oncorhynchus tshawytscha), combined with observations of foraging distributions and diet of a seabird predator. The salmon IBM consists of modules, including a juvenile salmon growth module based on temperature and salmon–prey availability, a behavior‐based movement module, and a juvenile salmon predation mortality module based on juvenile salmon size distribution and predator–prey interaction probability. Seabird–salmon interactions depend on spatial overlap and juvenile salmon size, whereby salmon that grow past the size range of the prey distribution of the predator will escape predation. We used a 21‐year historical simulation to explore interannual variability in juvenile Chinook salmon growth and predation‐mediated survival under a range of ocean conditions for sized‐based mortality scenarios. We based a series of increasingly complex predation scenarios on seabird observational data to explore variability in predation mortality on juvenile Chinook salmon. We initially included information about the predator spatial distribution, then added population size, and finally the predator's diet percentage made up of juvenile salmon. Model agreement improves with added predator complexity, especially during periods when predator abundance is high. Overall, our model found that when the fraction of juvenile salmon in seabird diet increased relative to alternate prey (e.g., Northern anchovy Engraulis mordax, and juvenile rockfish Sebastes spp.), there was a concomitant decrease in salmon cohort survival during their first year at sea. [ABSTRACT FROM AUTHOR]

Understanding environmental drivers of recruitment variability in marine fishes remains an important challenge in fish ecology and fisheries management. We developed a conceptual life‐history model for Pacific hake (Merluccius productus) along the west coast of the United States and Canada to generate stage‐specific and spatiotemporally‐specific hypotheses regarding the oceanographic and biological variables that likely influence their recruitment. Our model included seven life stages from pre‐spawning female conditioning through pelagic juvenile recruitment (age‐0 fish) for the coastal Pacific hake stock. Model‐estimated log recruitment deviations from the 2020 hake assessment were used as the dependent variable, with predictor variables drawn primarily from a regional ocean reanalysis for the California Current Ecosystem. Indices of prey and predator abundance were also included in our analysis, as were predictors of local‐ and basin‐scale climate. Five variables explained 59% of the recruitment variability not accounted for by the stock–recruitment relationship in the hake assessment. Recruitment deviations were negatively correlated with May–September eddy kinetic energy between 34.5° and 42.5°N, the North Pacific Current Bifurcation Index, and Pacific herring (Clupea pallasii) biomass during the spawner preconditioning stage, alongshore transport during the yolk‐sac larval stage, and the number of days between storm events during the first‐feeding larval stage. Other important predictors included upwelling strength during the preconditioning stage, the number of calm periods during the first‐feeding larval stage, and age‐1 hake predation on age‐0 pelagic juveniles. These findings suggest that multiple mechanisms affect Pacific hake survival across different life stages, leading to variability in population‐level recruitment. [ABSTRACT FROM AUTHOR]

Pacific chub mackerel (Scomber japonicus) is a relevant fishery resource shared among three countries in the northeastern Pacific. The spatiotemporal distribution of larvae has been related to the convergence of oceanographic mesoscale structures, which can generate considerable variability in the morphology of fish larvae. The main goal of this work was to describe the shape changes of larval S. japonicus and their relationship with oceanographic variability, through geometric morphometric analysis to assess the seasonal variability of 10 homologous landmarks distributed on the pre‐anal section of 331 larvae from off the western coast of the Baja California Peninsula (WCBCP), Mexico (2006–2008). The results showed two principal morphotypes in Pacific chub mackerel larvae: The first morphotype had a more hydrodynamic body (longer and shallower head), influenced by increased sea surface flow and colder sea surface temperatures mainly during spring, and the second morphotype had robust larvae (shorter and deeper head) under slower current flow and warmer sea surface temperatures during winter and summer. We concluded that changes in larval body shape are influenced mainly by sea surface flow and sea temperatures, probably associated with the ability to reach higher swimming speeds during feeding success. [ABSTRACT FROM AUTHOR]

Many fish species are shifting spatial distributions in response to climate change, but projecting these shifts and measuring their impact at fine scales are challenging. We present a simulation that projects change in fishery landings due to spatial distribution shifts, by combining regional ocean and biogeochemical models (forced by three earth system models, ESMs: GFDL‐ESM2M, HadGEM2‐ES, IPSL‐CM5A‐MR), correlative models for species distribution and port‐level landings, and a simulation framework which provides realistic values for species abundance and fishery conditions using an historical "reference period". We demonstrate this approach for the northern subpopulation of Pacific sardine, an iconic commercial species for the U.S. West Coast. We found a northward shift in sardine landings (based on the northern subpopulation's habitat suitability), with projected declines at southern ports (20%–50% decline by 2080) and an increase (up to 50%) or no change at northern ports, and this was consistent across the three ESMs. Total sardine landings were more uncertain, with HadGEM2 indicating a 20% decline from 2000 to 15 levels by 2070 (a rate of 170 mt/y), IPSL a 10% increase (115 mt/y), and GFDL an 15% increase by the year ~2050 followed by a sharp decrease. The ESMs also differed in their projected change to the timing of the fishing season and frequency of fishery closures. Our simulation also identified key constraints on future landings that can be targeted by more tactical assessment; these included the seasonality of quota allocation and the abundance of other species in the catch portfolio. [ABSTRACT FROM AUTHOR]

This paper investigates environmental drivers of U.S. West Coast petrale sole (Eopsetta jordani) recruitment as an initial step toward developing an environmental recruitment index that can inform the stock assessment in the absence of survey observations of age‐0 and age‐1 fish. First, a conceptual life history approach is used to generate life‐stage‐specific and spatio‐temporally specific mechanistic hypotheses regarding oceanographic variables that likely influence survival at each life stage. Seven life history stages are considered, from female spawner condition through benthic recruitment as observed in the Northwest Fisheries Science Center West Coast Groundfish Bottom Trawl Survey (age‐2 fish). The study area encompasses the region from 40 to 48°N in the California Current Ecosystem. Hypotheses are tested using output from a regional ocean reanalysis model outputs and model selection techniques. Four oceanographic variables explained 73% of the variation in recruitment not accounted for by estimates based exclusively on the spawning stock size. Recruitment deviations were (a) positively correlated with degree days during the female precondition period, (b) positively correlated with mixed‐layer depth during the egg stage, (c) negatively correlated with cross‐shelf transport during the larval stage, and (d) negatively correlated with cross‐shelf transport during the benthic juvenile stage. While multiple mechanisms likely affect petrale sole recruitment at different points during their life history, the strength of the relationship is promising for stock assessment and integrated ecosystem assessment applications. [ABSTRACT FROM AUTHOR]

We investigate the impact of oceanographic variability on Pacific bluefin tuna (Thunnus orientalis: PBF) distributions in the California Current system using remotely sensed environmental data, and fishery‐dependent data from multiple fisheries in a habitat‐modeling framework. We examined the effects of local oceanic conditions (sea surface temperature, surface chlorophyll, sea surface height, eddy kinetic energy), as well as large‐scale oceanographic phenomena, such as El Niño, on PBF availability to commercial and recreational fishing fleets. Results from generalized additive models showed that warmer temperatures of around 17–21°C with low surface chlorophyll concentrations (<0.5 mg/m3) increased probability of occurrence of PBF in the Commercial Passenger Fishing Vessel and purse seine fisheries. These associations were particularly evident during a recent marine heatwave (the "Blob"). In contrast, PBF were most likely to be encountered on drift gillnet gear in somewhat cooler waters (13–18°C), with moderate chlorophyll concentrations (0.5–1.0 mg/m3). This discrepancy was likely a result of differing spatiotemporal distribution of fishing effort among fleets, as well as the different vertical depths fished by each gear, demonstrating the importance of understanding selectivity when building correlative habitat models. In the future, monitoring and understanding environmentally driven changes in the availability of PBF to commercial and recreational fisheries can contribute to the implementation of ecosystem approaches to fishery management. [ABSTRACT FROM AUTHOR]

Recruitment varies substantially in small pelagic fish populations. Understanding of the mechanisms linking environment to recruitment is essential for the effective management of fisheries resources. In this study, we used a fully coupled end‐to‐end ecosystem model to study the effect of climate variability on sardine recruitment in the California Current System during 1965–2006. Ocean variability was represented by ROMS hydrodynamic and NEMURO biogeochemical models, and sardine population dynamics was simulated through a full life cycle individual‐based model. Model analysis was designed to elucidate how changes in abiotic and biotic conditions may impact the spawning habitats, early life stage survival, and ultimately recruitment of sardine. Our findings revealed the importance of spatial processes to shape early life stages dynamics. Shifts in spawning habitats were dictated by the spatial variations in temperature and the behavioral movement of adults. Additionally, the spatial match of eggs with warmer temperatures and larvae with their prey influenced their survival. The northward shifts in spawning locations and the accomplishment of good recruitment in warmer years agreed with existing knowledge. Egg production and survival during egg and yolk‐sac larval stages were key factors to drive the long‐term variations in recruitment. Finally, our analysis provided a quantitative assessment of climate impact on year‐to‐year variation in sardine recruitment by integrating multiple hypotheses. [ABSTRACT FROM AUTHOR]

Abstract: The California Current System (CCS) is an eastern boundary current system with strong biological productivity largely due to seasonal wind‐driven upwelling and transport of the California Current (CC). Two independent, yet complementary time series, CalCOFI ichthyoplankton surveys and sampling of southern California power plant cooling‐water intakes, have indicated that an assemblage of predominantly cool‐water affinity fishes spanning nearshore to oceanic environments in the southern CCS has declined dramatically from the 1970s to the 2000s. We examined potential oceanographic drivers behind this decline both within and north of the CalCOFI survey area in order to capture upstream processes as well. Empirical orthogonal function (EOF) analyses using output from a data‐assimilative regional ocean model revealed significant relationships between the fish time series and spatial patterns of upwelling, upper ocean heat content and eddy kinetic energy in the CCS. Correlation and linear regression analyses indicated that the declining trend in fish abundance was correlated with a suite of factors: reduced offshore and increased inshore upwelling; a long term warming trend combined with more recent interannual variability in ocean temperature; weaker eddy kinetic energy north of Point Conception (35°N), potentially indicating reduced transport of the California Current (CC); increased influence of the California Undercurrent (CUC); and a decline in zooplankton displacement volume across the southern CCS. Understanding how changes in oceanography affect fish populations will offer insights into managing fisheries in a changing climate. [ABSTRACT FROM AUTHOR]

Abstract: Oceanographic processes and ecological interactions can strongly influence recruitment success in marine fishes. Here, we develop an environmental index of sablefish recruitment with the goal of elucidating recruitment‐environment relationships and informing stock assessment. We start with a conceptual life‐history model for sablefish Anoplopoma fimbria on the US west coast to generate stage‐ and spatio‐temporally‐specific hypotheses regarding the oceanographic and biological variables likely influencing sablefish recruitment. Our model includes seven stages from pre‐spawn female condition through benthic recruitment (age‐0 fish) for the northern portion of the west coast U.S. sablefish stock (40°N–50°N). We then fit linear models and use model comparison to select predictors. We use residuals from the stock‐recruitment relationship in the 2015 sablefish assessment as the dependent variable (thus removing the effect of spawning stock biomass). Predictor variables were drawn primarily from ROMS model outputs for the California Current Ecosystem. We also include indices of prey and predator abundance and freshwater input. Five variables explained 57% of the variation in recruitment not accounted for by the stock‐recruitment relationship in the sablefish assessment. Recruitment deviations were positively correlated with (i) colder conditions during the spawner preconditioning period, (ii) warmer water temperatures during the egg stage, (iii) stronger cross‐shelf transport to near‐shore nursery habitats during the egg stage, (iv) stronger long‐shore transport to the north during the yolk‐sac stage, and (v) cold surface water temperatures during the larval stage. This result suggests that multiple mechanisms likely affect sablefish recruitment at different points in their life history. [ABSTRACT FROM AUTHOR]

Abstract: The preferential larval distributions of 22 fish species in the California Current System were identified in their temporal, spatial, and thermal domains using single parameter quotient analysis. This analysis allowed the characterization of their reproductive habitats based on ranges of preference, tolerance, and avoidance. In the temporal domain, the species’ preference intervals were wider than those previously reported, and all species showed preferences during two or more seasons of the year. In the spatial domain, the preferential distributions of the species were also wider, and some of them had different preferred zones from those described in previous works. Because one group of species was preferably distributed in coastal zones, and the other group was preferably distributed in oceanic zones, the biological production mechanisms sustaining these groups differ, namely, coastal upwelling and geostrophic fluxes of subarctic origin, respectively. In the thermal domain, the larval distribution preferences of 20 of 22 species have been determined for the first time, providing important information on their thermal tolerance window during the larval stage, a window that changes in width throughout each of the ontogenetic stages of fish. The distribution in each domain suggests association patterns between species, but additional studies are necessary to validate these patterns. [ABSTRACT FROM AUTHOR]

Effective ecosystem-based management requires a comprehensive understanding of the functional links in the system. In many marine systems, forage species constitute a critical link between primary production and upper trophic level marine predators. As top predators, seabirds can be indicators of the forage species they consume and the ocean processes that influence these populations. We analyzed the diet and breeding success for the years 1994, 2003, 2005, and 2007-2012 of the Brandt's cormorant ( Phalacrocorax penicillatus), a piscivorous diving seabird, breeding in central California, to evaluate the extent to which cormorant diet composition relates to prey availability, and how diet composition relates to breeding success and ocean conditions. Cormorant diet was primarily composed of young-of-the-year ( YOY) northern anchovy ( Engraulis mordax), YOY rockfish ( Sebastes spp.), and several species of small flatfish (order Pleuronectiformes). YOY rockfish consumption was positively related to their abundance as measured in a late spring pelagic midwater trawl survey. Northern anchovy appeared to be the most important prey as its consumption was positively related to cormorant breeding success. More northern anchovy were consumed in years where warm-water conditions prevailed in the fall season before cormorant breeding. Thus, warm ocean conditions in the fall appear to be an important contributing factor in producing a strong year-class of northern anchovy in central California and consequently a strong-year class of Brandt's cormorant on the Farallon Islands. [ABSTRACT FROM AUTHOR]

Extreme variability in abundance of California salmon populations is often ascribed to ocean conditions, yet relatively little is known about their marine life history. To investigate which ocean conditions influence their distribution and abundance, we surveyed juvenile Chinook salmon ( Oncorhynchus tshawytscha) within the California Current (central California [37°30′N) to Newport, Oregon (44°00′N]) for a 2-week period over three summers (2010-2012). At each station, we measured chlorophyll- a as an indicator of primary productivity, acoustic-based metrics of zooplankton density as an indicator of potential prey availability and physical characteristics such as bottom depth, temperature and salinity. We also measured fork lengths and collected genetic samples from each salmon that was caught. Genetic stock identification revealed that the majority of juvenile salmon were from the Central Valley and the Klamath Basin (91-98%). We constructed generalized logistic-linear negative binomial hurdle models and chose the best model(s) using Akaike's Information Criterion ( AIC) to determine which covariates influenced the salmon presence and, at locations where salmon were present, determined the variables that influenced their abundance. The probability of salmon presence was highest in shallower waters with a high chlorophyll- a concentration and close to an individual's natal river. Catch abundance was primarily influenced by year, mean fork length and proximity to natal rivers. At the scale of sampling stations, presence and abundance were not related to acoustic indices of zooplankton density. In the weeks to months after ocean entry, California's juvenile Chinook salmon population appears to be primarily constrained to coastal waters near natal river outlets. [ABSTRACT FROM AUTHOR]

Nearshore hypoxia along the coast of Oregon and Washington is a seasonal phenomenon that has generated concern among scientists studying this temperate upwelling ecosystem. These waters are affected by coastal upwelling-induced hypoxia mainly during late summer and fall, but the effects of low oxygen levels on fish and invertebrate communities, particularly during the early-life history stages, are poorly known. We investigated the effects of hypoxia and other variables on the species composition, density, vertical and horizontal distribution of fish larvae along the Oregon and Washington coasts during the summers of 2008, 2009 and 2010. Bottom-dissolved oxygen ( DO) values ranged from 0.49 to 4.79 mL L−1, but the overall water column DO values were only moderately hypoxic during the 3 yr of sampling compared with recent extreme years. In this study, DO was found to be an environmental parameter affecting the species composition, but other variables such as season, year and depth of capture were also important. Although the overall density of fish larvae increased with increasing bottom- DO values, the effect on individual species density was limited. Slender sole ( Lyopsetta exilis) and sand sole ( Psettichthys melanostictus) were the only species to have a weak trend of density with DO, but both showed negative relationships and neither relationship was significant. Our results indicate that larval fish spatial distribution was only moderately affected within the range of observed oxygen values, but low DO may be an important factor under intense hypoxic conditions. [ABSTRACT FROM AUTHOR]

Various ocean-climate models driven by increased greenhouse gases and higher temperatures predict a decline in oceanic dissolved oxygen ( DO) as a result of greater stratification, reduced ventilation below the thermocline, and decreased solubility at higher temperatures. Since spreading of low oxygen waters is underway and predicted to increase, understanding impacts on higher trophic levels is essential. Within the California Current System, shoaling of the oxygen minimum zone ( OMZ) is expected to produce complex changes. Onshore movement of the OMZ could lead to habitat compression for species with higher oxygen requirements while allowing expansion of species tolerant of low bottom DO. As part of annual groundfish surveys, we sampled catch across a range of conditions from the upper to the lower limit of the OMZ and shoreward across the continental shelf of the US west coast. DO ranged from 0.02 to 4.25 mL L−1 with 642 stations (of 1020 sampled) experiencing hypoxic conditions in 2008-2010. Catch and species richness exhibited significant and positive relationships with near-bottom oxygen concentration. The probability of occurrence was estimated for four species (spotted ratfish, petrale sole, greenstriped rockfish and Dover sole) using a binomial Generalized Additive Model. The models for each species included terms for position, day of the year, salinity, near-bottom temperature and the interaction term between depth and near-bottom DO. Spotted ratfish and petrale sole were sensitive to changes in near-bottom oxygen, while greenstriped rockfish and Dover sole show no changes in probability of occurrence in relation to changes in oxygen concentration. [ABSTRACT FROM AUTHOR]

We examined the dominant patterns of variability in the fish fauna of the southern California Current based on a principal component ( PC) analysis of the California Cooperative Oceanic Fisheries Investigations ichthyoplankton data set, 1951-2008. Eighty-six taxa were analyzed, including all ecologically dominant fish species, both exploited and unexploited. The first three PCs accounted for 20.5, 12.4 and 6.8% of the variance of the data, respectively (total: 39.7%). Each was dominated by taxa from particular adult or larval habitats. PC 1 predominantly represented the coherent response of 24 mesopelagic taxa from 10 families and was most highly correlated with long-term trends in midwater oxygen levels. PC 2 was dominated by six of the seven most abundant ichthyoplankton taxa in the region, predominantly California Current endemics including key pelagic species (northern anchovy, Pacific sardine and Pacific hake), rockfishes (genus Sebastes) and two midwater taxa. It was correlated primarily with sea surface temperature and exhibited a significant declining trend. PC 3 was dominated by coastal and reef-associated fishes with predominantly southerly affinities. It was positively correlated with sea surface temperature and sea level height, a proxy for diminished flow of the California Current. The taxa dominating PCs 2 and 3 mostly spatially co-occur as ichthyoplankton. These results suggest that fish assemblages in the California Current are predominantly influenced by environmental forcing of their ocean habitats as adults or larvae, or both. [ABSTRACT FROM AUTHOR]

We examined variability in growth rate during the larval stage of northern anchovy ( Engraulis mordax) in response to physical and biological environmental factors in 2005 and 2006. The onset of spring upwelling was anomalously delayed by 2-3 months until mid-July in 2005; in contrast, spring upwelling in 2006 began as a normal year in the northern California Current. Larval and early juvenile E. mordax were collected in August, September, and October off the coast of Oregon and Washington. Hatch dates ranged from May to September, with peaks in June and August in 2005 and a peak in July in 2006, based on the number of otolith daily increments. Back-calculated body length-at-age in the June 2005 hatch cohort was significantly smaller than in the August 2005 cohort, which had comparable growth to the July 2006 cohort. Standardized otolith daily increment widths as a proxy for seasonal variability in somatic growth rates in 2005 were negative until late July and then changed to positive with intensification of upwelling. The standardized increment width was a positive function of biomass of chlorophyll a concentration, and neritic cold-water and oceanic subarctic copepod species sampled biweekly off Newport, Oregon. Our results suggest that delayed upwelling in 2005 resulted in low food availability and, consequently, reduced E. mordax larval growth rate in early summer, but once upwelling began in July, high food availability enhanced larval growth rate to that typical of a normal upwelling year (e.g., 2006) in the northern California Current. [ABSTRACT FROM AUTHOR]

Seasonal and inter-annual variability in the abundance and biomass of copepodid stages of the sub-arctic oceanic copepod, Neocalanus plumchrus, was studied during the January–May growth season, using an 11-yr time series of zooplankton samples collected over the upper 100 m of the water column. Abundance and biomass peaks occur in March/April. Abundance and biomass of N. plumchrus were significantly negatively correlated with sea surface temperature and significantly positively correlated with sea surface chlorophyll a, salinity, and density above the pycnocline. The seasonal integrated abundance and biomass of N. plumchrus declined during the warm years (2003–05), and increased during the cold years (2006–08). The date when 50% of the population had passed through stage C5 was significantly negatively correlated with temperature – earlier in warm years and later in cold years. In 3 yr (2003, 2007 and 2008), a second cohort appeared in mid-May, as indicated by the presence of stages C1 and C2 in the samples. Unusually high abundances of N. plumchrus in the spring of 2007 and 2008 were associated with cool ocean temperatures and an early spring transition in the NCC ecosystem, suggesting that the NCC ecosystem has returned to a cold phase. We discuss the merits of a hypothesis that the N. plumchrus population observed off Oregon is a local population as opposed to one that is expatriated from the Gulf of Alaska. [ABSTRACT FROM AUTHOR]

Ecosystem-based management places a strong emphasis on habitat, but little work has been done to examine how water column properties may influence the distribution, abundances and structure of groundfish assemblages. We identified and described oceanographic habitats in the northern California Current based on temperature, salinity, chlorophyll- a and the inherent variability in these factors. We then examined the distribution and the abundance of groundfishes in relation to these oceanographic habitats and conditions with the long-term goal of improving science for ecosystem-based management of the groundfish fishery of the west coast of the USA. Five summertime oceanographic habitats with distinct physical and biological characteristics were identified in the northeast Pacific Ocean off the northwest Coast of the USA: Offshore Habitat, Upwelling Habitat, Highly Variable Upwelling Habitat, River Plume Habitat, and Highly Variable Habitat. Overall, the species composition differed among the five oceanographic habitats, with certain groundfish species being highly indicative of some habitats; however, the majority of the associations were weak due to overlap of species distributions in the nearshore oceanographic habitats. In contrast, groundfish species showed strong associations with individual oceanographic factors, primarily depth, surface chlorophyll- a, and bottom salinity and temperature. In addition, latitudinal variations in upwelling intensity, river discharge and productivity led to the identification of three regions where high chlorophyll- a concentrations were associated with large abundances of specific groundfish species. The combined oceanographic datasets and data products that we produced have the potential to be a powerful tool for improving our knowledge of the west coast ecosystem. [ABSTRACT FROM AUTHOR]

The distributions, concentrations, and community structure of pelagic larval fishes collected from the central and northern California Current in the northeast Pacific Ocean during May 2004, 2005, and 2006 were analyzed to investigate inter-annual, latitudinal, cross-shelf, and depth-stratified variability. The inter-annual climate-induced variability during the sampling period provided a unique opportunity to observe how larval fish communities adjust to rapidly changing environmental conditions. The 170 depth-stratified samples collected from three cruises yielded 14 819 fish larvae from 56 taxa representing 23 families. Dominant larval taxa were Engraulis mordax, Citharichthys spp., Sebastes spp., and Stenobrachius leucopsarus. Larval concentrations decreased significantly in 2006 from 2004 and 2005 levels following the anomalous oceanic conditions observed in 2005 and decreased water temperature in 2006. Larvae were generally found in higher concentrations at northern (>43°N) versus southern (<43°N) stations, with larval E. mordax and Citharichthys spp. found almost exclusively in the north during all sampled years. Inter-annual variability related to dynamic upwelling intensity was observed in cross-shelf larval distributions, although concentrations of S. leucopsarus larvae consistently increased in the offshore direction, while larval Sebastes spp. were generally found in highest concentrations at intermediate stations along the shelf. Multivariate analyses revealed that latitude, station depth, and sea-surface temperature were the most important factors explaining variability in larval concentrations. The present study shows that the ichthyoplankton community of the central and northern California Current changed dramatically in response to the variable environmental conditions of 2004–06. [ABSTRACT FROM AUTHOR]

We model age-specific growth rates of Chinook salmon ( Oncorhynchus tshawytscha) with two life-history behaviors from Alaska (i. Situk and ii.Taku Rivers), Puget Sound, Washington (iii., iv. Skagit River), and California (v. Smith River) relative to oceanic conditions in those regions. By analyzing over 20 yr of biological and physical data from the NE Pacific downwelling, upwelling, and transition zones, we are able to determine the factors affecting growth across much of the species’ range and between life-history behaviors. With scale increment data from returning fish, we use path analysis and partial least squares regression to quantify the relationships between growth and regional- and large-scale oceanic conditions (e.g., sea level height, sea surface temperature, upwelling). Alaskan fish with both ocean- and stream-type behaviors were fit best by the environmental data from the winter in Alaska waters. Specifically, coastal and gyre factors such as sea surface temperature, river flow, and Ekman pumping positively correlated to growth, indicating a productive and strong Alaska Current promoted growth. Growth of fish from California was fit by local factors such as increased upwelling, lower coastal sea surface temperature, and wind stresses during summer and spring, indicating a productive and strong California Current promoted growth. For Puget Sound, Washington, growth of fish that migrate to sea in their first year was generally negatively correlated to a strong California Current. Puget Sound fish that spend a year in freshwater before migrating to sea were modeled well with environmental data from their source region for the first 2 yr at sea and by data from Alaska waters in their third year at sea. Results suggest that conditions in which the transition zone is dominated by neither the Alaska nor California Currents are best for increased growth of Puget Sound fish. [ABSTRACT FROM AUTHOR]

We use trivariate kernel density estimation to define spawning habitat of northern anchovy ( Engraulis mordax) and Pacific sardine ( Sardinops sagax) in the California Current using satellite data and in situ egg samples from the Continuous Underway Fish Egg Sampler (CUFES) deployed during surveys in April by the California Cooperative Oceanic Fisheries Investigations (CalCOFI). Observed egg distributions were compared with monthly composite satellite sea surface temperature (SST) and surface chlorophyll a (chl a) data. Based on the preferred spawning habitat, as defined in SST and chl a space, the satellite data were used to predict potential spawning habitat along two areas of the west coast of North America. Data from the southern area (21.5 to 39°N) were compared to observations from the CUFES data for the period 1998–2005. Northern anchovy and Pacific sardine exhibited distinctly different spawning habitat distributions. A significant relationship was found between satellite-based spawning area and that measured during surveys for sardine. CUFES area estimated for sardine was similar in magnitude to that estimated from satellite data (∼60 000 km2). In contrast, spawning habitat of anchovy averaged between 1000 and 200 000 km2 for the period 1998–2005, for CUFES and satellite estimates, respectively. Interannual variability in the area (km2) and duration (months) of estimates of suitable habitat varied between species and between the northern (39 to 50.5°N) and southern portions of the California Current. Long-term monitoring of habitat variability using remote sensing data is possible in the southern portion of the California Current, and could be improved upon in the northern area with the addition of surveys better timed to describe relationships between observed and estimated spawning habitats. [ABSTRACT FROM AUTHOR]

As the eastward-flowing North Pacific Current approaches the North American continent it bifurcates into the southward-flowing California Current and the northward-flowing Alaska Current. This bifurcation occurs in the south-eastern Gulf of Alaska and can vary in position. Dynamic height data from Project Argo floats have recently enabled the creation of surface circulation maps which show the likely position of the bifurcation; during 2002 it was relatively far north at ∼53°N then, during early 2003, it moved southwards to a more normal position at ∼45°N. Two ship-of-opportunity transects collecting plankton samples with a Continuous Plankton Recorder across the Gulf of Alaska were sampled seasonally during 2002 and 2003. Their position was dependent on the commercial ship’s operations; however, most transects sampled across the bifurcation. We show that the oceanic plankton differed in community composition according to the current system they occurred in during spring and fall of 2002 and 2003, although winter populations were more mixed. Displacement of the plankton communities could have impacts on the plankton’s reproduction and development if they use cues such as day length, and also on foraging of higher trophic-level organisms that use particular regions of the ocean if the nutritional value of the communities is different. Although we identify some indicator taxa for the Alaska and California currents, functional differences in the plankton communities on either side of the bifurcation need to be better established to determine the impacts of bifurcation movement on the ecosystems of the north-east Pacific. [ABSTRACT FROM AUTHOR]

Seasonal assemblages of mesopelagic fish larvae and changes related with environmental factors (plankton biomass, sea surface temperature anomaly, upwelling, and the multivariate El Niño index) were investigated. From 1982 to 1987, 16 oceanographic cruises were carried out along the Pacific coast of Baja California Sur, Mexico. Larvae of 42 mesopelagic fish taxa were collected. Larval abundance was highly variable during the studied period, but summer months coincided with higher abundance (>200 larvae under 10 m2). Larval assemblages were dominated by three of the most common species of tropical ( Vinciguerria lucetia, Diogenichthys laternatus) and subtropical affinity ( Triphoturus mexicanus). A group of species of tropical affinity ( Diplophos proximus, Diaphus pacificus, Benthosema panamense) was useful for distinguishing the 1982–84 El Niño event, and an assemblage of larvae of temperate affinity ( Symbolophorus californiensis, Melamphaes lugubris, Bathylagus ochotensis, Leuroglossus stilbius, Protomyctophum crockeri) characterized ‘normal’ years (mid-1984 to mid-1987). [ABSTRACT FROM AUTHOR]

Interannual variability in the California Current System is analyzed through its effects on the temporal distribution of fauna, particularly southern-origin organisms moving north during warming events and south during cooling ones. In temperate waters north of 24°N latitude, northward movements of southern fauna occur at intervals of about 5 yr. This is different from El Niño events, whose frequency of occurrence is mostly centered in the 3-yr period but with considerable dispersion. Possible causes for northward displacement of fauna include relaxation of the California Current, intensification of the countercurrent, and the formation and persistence of mesoscale eddies among others. Strong events appear to be a consequence of the decadal variation peaks. [ABSTRACT FROM AUTHOR]

Time series of adult recruitment for natural runs of coho salmon from the Oregon coastal region (1970–94) and marine survival of hatchery-reared coho salmon from California to Washington (1960–94) are significantly correlated with a suite of meteorological and oceanographic variables related to the biological productivity of the local coastal region. These variables include strong upwelling, cool sea surface temperature (SST), strong wind mixing, a deep and weakly stratified mixed layer, and low coastal sea level, indicating strong transport of the California Current. Principal component analysis indicates that these variables work in concert to define the dominant modes of physical variability, which appear to regulate nutrient availability and biological productivity. Multiple regression analysis suggests that coho marine survival is significantly and independently related to the dominant modes acting over this region in the periods when the coho first enter the ocean and during the overwintering/spring period prior to their spawning migration. Linear relationships provided good fits to the data and were robust, capable of predicting randomly removed portions of the data set. [ABSTRACT FROM AUTHOR]

We examined the distribution of sardine larvae relative to environmental conditions with the purpose of identifying and characterizing habitat that encourages high larval growth and survival, based on the 1983–1998 surveys of the California Cooperative Oceanic Fisheries Investigations (CalCOFI). Long-term averages show that sardine ‘survivors’ (spatially aggregated larvae ≥ 18 days old) were most abundant offshore, whereas sardine egg density, chlorophyll biomass and zooplankton volume were greatest inshore. In contrast, mesoscale eddies, observed in remotely sensed sea surface temperature imagery, were found only in offshore regions. To further examine the link between eddies – which often result in locally elevated chlorophyll and zooplankton – and sardine survival, we compared the distribution of larvae and eddies survey by survey. Sardine survivors were most abundant offshore in only one-quarter of the research surveys, and when they were most abundant offshore they were associated with eddies. This indicates that the offshore eddy habitat produced exceptionally large numbers of survivors, as evidenced by the disproportionate effect on the long-term average. [ABSTRACT FROM AUTHOR]

A time series of mean weekly sea surface temperature (SST) images was used to investigate the relationship between fluctuations in the marine survival of hatchery-reared coho salmon and coastal ocean dynamics off the north-western United States (51° to 37°N) between 1985 and 1996, using univariate and nonlinear bivariate regression analysis. Ocean conditions were matched against survival for a number of different annual time frames according to the sum of negative or positive weekly SST anomalies. From the univariate analyses, the sum of negative anomalies from April to June, when the juvenile salmon first enter the ocean, was found to have an R2 of 0.88 against survival with 1991 excluded as an outlier. The bivariate multiple regressions used the sum of negative anomalies from April to June as the first independent variable. When the sums of positive anomalies from the following periods during the fishes’ second calendar year in the ocean were each used as the second independent variable, the R2 values were all greater than or equal to 0.92 (with no data points excluded): January to June, February to June, April to June, March to June. These results are discussed within the context of coastal ocean processes. It is concluded that the analysis of SST image time series might allow management to make reasonable forecasts of hatchery-reared coho salmon survival. [ABSTRACT FROM AUTHOR]