Understanding changes in the migratory and reproductive phenology of fish stocks in relation to climate change is critical for accurate ecosystem-based fisheries man- were the highest observed since annual collections first occurred in 1998, primarily due to increased abundances of Engraulis mordax (northern anchovy) and Sardinops sagax (Pacific sardine) larvae, which are normally summer spawning species in this region. Sardinops sagax and Merluccius productus (Pacific hake) exhibited an unprecedented early and northward spawning expansion during 2015-16. In addition, spawning duration was greatly increased for E. mordax, as the presence of larvae was observed throughout the majority of 2015-16, indicating prolonged and nearly continuous spawning of adults throughout the warm period. Larvae from all three of these species have never before been collected in the NCC as early in the year. In addition, other southern species were collected in the NCC during this period. This suggests that the spawning phenology and distribution of several ecologically and commercially important fish species dramatically and rapidly changed in response to the warming conditions occurring in 2014-2016, and could be an indication of future conditions under projected climate change. Changes in spawning timing and poleward migration of fish populations due to warmer ocean conditions or global climate change will negatively impact areas that were historically dependent on these fish, and change the food web structure of the areas that the fish move into with unforeseen consequences.

Although the California Current has undergone substantial environmental shifts in the past few decades, the summer of 2005 exhibited highly anomalous conditions relative to all previous recorded summers in terms of late initiation of upwelling and the resulting elevated surface temperatures and depressed productivity through July. The response of pelagic nekton to these anomalous conditions was widespread and included onshore and poleward displacement of taxa to new geographic areas, population changes within the normal range, and reduced productivity of early life stages based on larval and juvenile surveys. Some nekton exhibited anomalous distributions in 2004. Many ecologically important species were affected. The response of the nektonic community off California was greater than during El Niño conditions.

The community structure of pelagic zooplankton and micronekton may be a sensitive indicator of changes in environmental conditions within the California Current ecosystem. Substantial oceanographic changes in 2015 and 2016, due to the anomalously warm ocean conditions associated with a large-scale marine heatwave perturbation, resulted in onshore and northward advection of warmer and more stratified surface waters resulting in reduced upwelling. Here we quantify changes in the macrozooplankton and micronekton community composition and structure based on five highly contrasting ocean conditions. Data from fine-mesh pelagic trawl surveys conducted off Oregon and Washington during early summer of 2011 and 2013-2016 were examined for interannual changes in spatial distribution and abundance of fish and invertebrate taxa. Overall species diversity was highest in 2015 and lowest in 2011, but 2016 was similar to the other years, although the evenness was somewhat lower. The community of taxa in both 2015 and 2016 was significantly different from the previously sampled years. Crustacean plankton densities (especially Euphausiidae) were extremely low in both of these years, and the invertebrate composition became dominated mostly by gelatinous zooplankton. Fishes and cephalopods showed mixed trends overall, but some species such as age-0 Pacific hake were found in relatively high abundances mainly along the shelf break in 2015 and 2016. These results suggest dramatically different pelagic communities were present during the recent warm years with a greater contribution from offshore taxa, especially gelatinous taxa, during 2015 and 2016. The substantial reorganization of the pelagic community has the potential to lead to major alterations in trophic functioning in this normally productive ecosystem.

Spatial distributions of marine fauna are determined by complex interactions between environmental conditions and animal behaviors. As climate change leads to warmer, more acidic, and less oxygenated oceans, species are shifting away from their historical distribution ranges, and these trends are expected to continue into the future. Correlative Species Distribution Models (SDMs) can be used to project future habitat extent for marine species, with many different statistical methods available. However, it is vital to assess how different statistical methods behave under novel environmental conditions before using these models for management advice, and to consider whether future projections based on these techniques are biologically reasonable. In this study, we built SDMs for adults and larvae of two ecologically important pelagic fishes in the California Current System (CCS): Pacific sardine (Sardinops sagax) and northern anchovy (Engraulis mordax). We used five different SDM methods, ranging from simple [thermal niche model (TNM)] to complex (artificial neural networks). Our results show that some SDMs trained on data collected between 2003 and 2013 lost substantial predictive skill when applied to observations from more recent years, when ocean temperatures associated with a marine heatwave were outside the range of historical measurements. This decrease in skill was particularly apparent for adult sardine, which showed non-stationary relationships between catch locations and sea surface temperature (SST) through time. While sardine adults and larvae shifted their distributions markedly during the marine heatwave, anchovy largely maintained their historical spatiotemporal distributions. Our results suggest that correlative relationships between species and their environment can become unreliable during anomalous conditions. Understanding the underlying physiology of marine species is therefore

We examined ichthyoplankton sampled from 2 stations, 9 and 18 km offshore of Newport, Oregon, USA, over a decade of cruises every 2 wk from 1996 to 2005. The 10 most dominant taxa comprised approximately 87.3% of the total catch. Concentration of fish larvae was highest in January to March, whereas diversity peaked from March through May. Both overall diversity and density of larval fishes were relatively constant throughout the period of 1996 to 2003, with a dramatic decrease in these metrics since 2004, especially for winter-spawning (January−May) species. During cool years (1999−2002), the assemblage was dominated by northern or coastal taxa such as sand lance Ammodytes hexapterus, sanddabs Citharichthys spp., and smelts Osmeridae, whereas in warm years (2003−2005), southern or offshore taxa such as English sole Parophrys vetulus, northern anchovy Engraulis mordax, and rockfishes Sebastes spp. were more abundant. These changes were related to concurrent shifts in the zooplankton biomass and composition off Oregon during cold and warm environmental regimes. We have identified a small subset of fish whose larvae can be monitored as indicators of warm and cold phases in the northeast Pacific Ocean. KEY WORDS: Larval fish · Density · Diversity · Temporal variability · Upwelling ecosystem · California CurrentResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 366: 187-202, 2008 provide information on the relative effects of climate and fishing on marine fish populations (Hsieh et al. 2005).Ichthyoplankton collections were made from sampling every 2 wk along the Newport Hydrographic (NH) line off Newport, Oregon from 1996 to 2005. This period witnessed dramatic and perhaps unprecedented change in climate, ocean dynamics, and biological communities (Peterson & Schwing 2003, Hooff & Peterson 2006. The timing of these ichthyoplankton collections coincided with a wide variety of environmental conditions (e.g. warm and cool climate regimes, El Niño and La Niña events, and extended periods of positive and negative upwelling). This makes these data particularly suitable and valuable for evaluating changes in ichthyoplankton abundance relative to a fluctuating environment. The NH line was sampled intensively in the 1970s and 1980s (Richardson & Pearcy 1977, Mundy 1984, Boehlert et al. 1985, Brodeur et al. 1985, Doyle et al. 1993, 2002, so substantial historical data exists during different oceanographic regimes with which to compare our data.The purposes of this study are to: (1) identify and compare larval fish concentration and community structure from samples collected at 2 nearshore stations off the central Oregon coast to test for annual, seasonal, and monthly differences; (2) compare and contrast these findings to those of similar historical studies along the NH line; and (3) relate the larval communities to fluctuating marine environmental conditions observed in this dynamic upwelling region. We assessed trends in larval concentrations and diversity indices u...

The species composition, distribution and concentration of ichthyoplankton off the central Oregon coast in the NE Pacific Ocean were examined during 2000 and 2002 to investigate annual, seasonal, vertical, and cross-shelf variability. Larval concentrations were also analyzed in relation to water temperature and salinity. The 281 samples collected from 5 cruises along a historically sampled transect between April and September in each of the 2 study years yielded 4944 fish larvae comprising 72 taxa in 28 families. The dominant taxa collected were Engraulis mordax, Lyopsetta exilis, Sebastes spp., Stenobrachius leucopsarus and Tarletonbeania crenularis. ). Relatively few larvae were found at depths >100 m, while highest larval concentrations generally occurred from 0 to 50 m. However, L. exilis concentrations were highest from 50 to 100 m. Larval diversity and concentration were higher offshore (46 to 84 km) than in coastal areas (9 to 28 km). Highest concentrations were normally found at an intermediate station 65 km off the coast. Species designated as either coastal or offshore species by previous studies were predominantly found in their respective shelf regions. With the exception of L. exilis, larval concentrations were positively correlated with temperature and negatively correlated with salinity (p < 0.0001).

The California Current System (CCS) has experienced large fluctuations in environmental conditions in recent years that have dramatically affected the biological community. Here we synthesize remotely sensed, hydrographic, and biological survey data from throughout the CCS in 2019–2020 to evaluate how recent changes in environmental conditions have affected community dynamics at multiple trophic levels. A marine heatwave formed in the north Pacific in 2019 and reached the second greatest area ever recorded by the end of summer 2020. However, high atmospheric pressure in early 2020 drove relatively strong Ekman-driven coastal upwelling in the northern portion of the CCS and warm temperature anomalies remained far offshore. Upwelling and cooler temperatures in the northern CCS created relatively productive conditions in which the biomass of lipid-rich copepod species increased, adult krill size increased, and several seabird species experienced positive reproductive success. Despite these conditions, the composition of the fish community in the northern CCS remained a mixture of both warm- and cool-water-associated species. In the southern CCS, ocean temperatures remained above average for the seventh consecutive year. Abundances of juvenile fish species associated with productive conditions were relatively low, and the ichthyoplankton community was dominated by a mixture of oceanic warm-water and cosmopolitan species. Seabird species associated with warm water also occurred at greater densities than cool-water species in the southern CCS. The population of northern anchovy, which has been resurgent since 2017, continued to provide an important forage base for piscivorous fishes, offshore colonies of seabirds, and marine mammals throughout the CCS. Coastal upwelling in the north, and a longer-term trend in warming in the south, appeared to be controlling the community to a much greater extent than the marine heatwave itself.

The effects of climate warming on ecosystem dynamics are widespread throughout the world's oceans. In the Northeast Pacific, large‐scale climate patterns such as the El Niño/Southern Oscillation and Pacific Decadal Oscillation, and recently unprecedented warm ocean conditions from 2014 to 2016, referred to as a marine heatwave (MHW), resulted in large‐scale ecosystem changes. Larval fishes quickly respond to environmental variability and are sensitive indicators of ecosystem change. Categorizing ichthyoplankton dynamics across marine ecosystem in the Northeast Pacific can help elucidate the magnitude of assemblage shifts, and whether responses are synchronous or alternatively governed by local responses to regional oceanographic conditions. We analyzed time‐series data of ichthyoplankton abundances from four ecoregions in the Northeast Pacific ranging from subarctic to subtropical: the Gulf of Alaska (1981–2017), British Columbia (2001–2017), Oregon (1998–2017), and the southern California Current (1981–2017). We assessed the impact of the recent (2014–2016) MHW and how ichthyoplankton assemblages responded to past major climate perturbations since 1981 in these ecosystems. Our results indicate that the MHW caused widespread changes in the ichthyoplankton fauna along the coast of the Northeast Pacific Ocean, but impacts differed between marine ecosystems. For example, abundances for most dominant taxa were at all‐time lows since the beginning of sampling in the Gulf of Alaska and British Columbia, while in Oregon and the southern California Current species richness increased as did abundances of species associated with warmer waters. Lastly, species associated with cold waters also increased in abundances close to shore in southern California during the MHW, a pattern that was distinctly different from previous El Niño events. We also found several large‐scale, synchronized ichthyoplankton assemblage composition shifts during past major climate events. Current climate projections suggest that MHWs will become more intense and thus our findings can help project future changes in larval dynamics, allowing for improved ecosystem management decisions.