California Cooperative Oceanic Fisheries Investigations Research Articles

California Current temperatures adjacent to Southern California: 1949–2020

The southward flowing California Current, which lies adjacent to the California Pacific coastline as part of the North Pacific Ocean gyre circulation, is an important element in characterizing California's climate variability. This study improves and extends the historic record of California Current temperatures along the Southern California coastline for the last 71 years. The data come from long-term sea surface temperature measurements determined by the California Cooperative Oceanic Fisheries Investigations (CalCOFI) partners. The sea-surface temperature measurements come from a grid of 31 oceanic sampling sites within the core of the California Current off the Southern California coast. The sites have been sampled intermittently over the course of each year with ∼100 measurements/year on average. The Southern California Current temperatures in our grid have risen ∼2.5 °C since 1949.The California current temperatures are strongly correlated with the larger-scale North Pacific Ocean Pacific Decadal Oscillation (PDO) index and the North Pacific Gyre Oscillation (NGPO) index. All three show distinctive correlation with decadal (∼14-yr) California rainfall cyclicity.

Compound marine cold spells and hypoxic events in a nearshore upwelling system

Prolonged periods of extreme warm and cold seawater temperature anomalies, known as marine heatwaves (MHWs) and marine cold spells (MCSs), respectively, can have significant impacts on coastal marine ecosystems. Prior research has examined the co-occurrence of multiple extremes [low dissolved oxygen (DO) and/or low pH] during MHWs, with the impact of these compound events potentially exceeding that of a single stressor due to synergistic effects. However, we are not aware of any studies that have examined compound extreme events during MCSs, despite the ecosystem implications. Along Eastern Boundary Current Upwelling Systems (EBUS), strong-wind driven upwelling has led to reduced warming trends and persistence of MCSs, as well as an increased seasonal risk for coastal hypoxia via the cross-shelf advection of cold, low DO subthermocline waters. In this short communication, we investigated for the first time compound MCS-hypoxic events at a nearshore site in central California using several decades of nearshore water temperature data, short-term nearshore DO data, and several decades of DO data from the California Cooperative Oceanic Fisheries Investigations program. From 1988 to 2020, we identified 55 MCS events, with 50 events (∼90.9%) initiated during anomalously strong upwelling. Using long-term temperature-DO relationships, we identified 20 of the 55 MCS events (∼34.6%) as potential compound MCS-hypoxic events, with an average duration of 11.7 days. These compound events occurred almost exclusively during the major upwelling season (March to June) when there is a high propensity for the advection of cold, low DO subthermocline waters from the adjacent shelf into the nearshore. This work provides the first known investigation into the co-occurrence of MCS and hypoxic events in a nearshore upwelling system and provides a baseline for assessing future changes to these compound events in a changing climate, with important implications for ecosystem health in EBUS globally.

The California current system off Baja California Sur

Based on hydrographic data from two cruises (June 2010 and May 2012) off Baja California Sur, Mexico, historical in situ measurements from the World Ocean Database 2018, California Cooperative Oceanic Fisheries Investigations, and Investigaciones Mexicanas de la Corriente de California cruise programs, as well as satellite images and data from the Global Reanalysis, this study describes the California Current System off Baja California Sur. The California Current System is characterized by the interaction of four near-surface currents. Far from the coast, the California Current flows within the North Pacific Subtropical Gyre but does not reach the Pacific Tropical-Subtropical Convergence off Mexico. From December to June, an equatorward flow known as the Tropical Branch of California Current emerges along the coast. This flow intensifies from March to June and is closely related to the mass flux induced by coastal upwelling. In July, a new branch of the Tropical Branch of the California Current turns poleward along the Baja California Sur coast. This flow is often referred to as the California Surface Countercurrent because it flows in the opposite direction to the California Current. Additionally, the California Undercurrent is detected, influencing the water column from 100 to 900 m, with a maximum poleward flow between 200 m and 300 m, decreasing toward the surface. The California Undercurrent persists throughout the year over the continental slope, displaying a significant semiannual component around the Gulf of California entrance. The California Current System off Baja California Sur plays a crucial role in the formation of Transitional Waters within the Pacific Tropical-Subtropical Convergence off Mexico. The importance of equatorward flows by the Tropical Branch of California Current in ventilating the Oxygen Minimum Zone waters in the Central Pacific off Mexico is emphasized.

Evaluating robustness of harvest control rules to climate-driven variability in Pacific sardine recruitment

Climate-driven changes in ocean temperatures, currents, or plankton dynamics may disrupt pelagic forage fish recruitment. Being responsive to such impacts enables fisheries management to ensure continued sustainable harvest of forage species. We conducted a management strategy evaluation to assess the robustness of current and alternative Pacific sardine harvest control rules under a variety of recruitment scenarios representing potential projections of future climate conditions in the California Current. The current environmentally informed control rule modifies the harvest rate for the northern sardine subpopulation based on average sea surface temperatures measured during California Cooperative Oceanic Fisheries Investigations field cruises. This rule prioritizes catch at intermediate biomass levels but may increase variability in catch and closure frequency compared to alternative control rules, especially if recruitment is unrelated to ocean temperatures. Fishing at maximum sustainable yield and using dynamically estimated reference points reduced the frequency of biomass falling below 150 000 mt by up to 17%, while using survey index-based biomass estimates resulted in a 14% higher risk of delayed fishery closure during stock declines than when using assessment-based estimates.

A 37-year record of ocean acidification in the Southern California current

Long-term ocean time series have proven to be the most robust approach for direct observation of climate change processes such as Ocean Acidification. The California Cooperative Oceanic Fisheries Investigations (CalCOFI) program has collected quarterly samples for seawater inorganic carbon since 1983. The longest time series is at CalCOFI line 90 station 90 from 1984–present, with a gap from 2002 to 2008. Here we present the first analysis of this 37- year time series, the oldest in the Pacific. Station 90.90 exhibits an unambiguous acidification signal in agreement with the global surface ocean (decrease in pH of −0.0015 ± 0.0001 yr−1), with a distinct seasonal cycle driven by temperature and total dissolved inorganic carbon. This provides direct evidence that the unique carbon chemistry signature (compared to other long standing time series) results in a reduced uptake rate of carbon dioxide (CO2) due to proximity to a mid-latitude eastern boundary current upwelling zone. Comparison to an independent empirical model estimate and climatology at the same location reveals regional differences not captured in the existing models.

Interannual response of euphausiid community abundance during the anomalous warming period (2014–2016) in the Gulf of California

El Niño in the northeast Pacific and Gulf of California typically causes a decrease in euphausiid abundance (biomass), and modifies their latitudinal biogeographic distributions, but the effect of recent marine heat waves (or their combined effect with El Niño) are less understood. The interannual response of euphausiid community structure and abundance were investigated during the cold–warm transition period (June) of six years (2013–2019, except 2015) in the central Gulf of California, Mexico. Abundance in June 2013–2019 was compared with historical baseline for euphausiid abundance made in June 1957 from a California Cooperative Oceanic Fisheries Investigation cruise, just before El Niño 1957–1958. During 2014–2019 two anomalously warm events occurred: the marine heat wave of 2014 (MHW 2014) and El Niño 2015–2016 (May 2015–May 2016). We tested the hypothesis that the numerically dominant subtropical neritic species Nyctiphanes simplex and temperate oceanic Nematoscelis difficilis significantly decrease in abundance in response to the prolonged warming that occurred during 2014–2016 and that tropical euphausiid species could increase in relative abundance during this period. Ten euphausiid species were collected accounting for < 3% of total relative abundance of 34 zooplankton taxonomic groups collected during June 2013–2014, 2016, 2018 and between 7 and 22.4% during 2017 and 2019. N. simplex and Ne. difficilis accounted for > 80% of euphausiid total abundance during June 2013–2019, with considerably lower abundance during 2013, the MHW 2014, and El Niño 2015–2016 than in June 2017, 2018, and 2019. Mean euphausiid abundance in 2017 and 2019 was slightly higher than that recorded in June 1957. Tropical species increased their relative abundances during El Niño 2015–2016 event, but they were always < 15% of total euphausiid relative abundance during 2013–2019. We estimated that it took at least 3 years for the euphausiid species abundance in the gulf to slowly recover from the unfavorable conditions associated with MHW 2014, and El Niño 2015–2016 to attain highest mean abundance in 2019. Multi–variated ordination analyses showed that the prolonged warming and anomalously low Chl-a concentrations recorded in 2014–2016 negatively influenced euphausiid abundance, a proxy for euphausiid biomass available for pelagic predators in the Gulf of California.

Oxygen and irradiance constraints on visual habitat in a changing ocean: The luminoxyscape

Oxygen and irradiance constraints on visual habitat in a changing ocean: The luminoxyscape

Stable isotopes of nitrate record effects of the 2015–2016 El Niño and diatom iron limitation on nitrogen cycling in the eastern North Pacific Ocean

AbstractIn eastern boundary current systems, strong coastal upwelling brings deep, nutrient‐rich waters to the surface ocean, supporting a productive food web. The nitrate load in water masses that supply the region can be impacted by a variety of climate‐related processes that subsequently modulate primary productivity. In this study, two coastal upwelling regimes along central and southern California were sampled seasonally for nitrogen and oxygen stable isotopes of nitrate (i.e., nitrate isotopes) over several years (2010–2016) on 14 California Cooperative Oceanic Fisheries Investigations (CalCOFI) cruises. Seasonal, interannual, and spatial variations in euphotic zone nitrate isotopes were largely driven by the extent of nitrate utilization, sometimes linked to iron limitation of diatom productivity. Pronounced isotopic enrichment developed with the El Niño conditions in late 2015 and early 2016 which likely resulted from increased nitrate utilization linked to reduced nitrate supply to the euphotic zone. Differential enrichment of nitrogen and oxygen isotopes was observed in the surface ocean, suggesting that phytoplankton increased their reliance on locally nitrified (recycled) nitrate during warmer and more stratified periods. Overall, nitrate isotopes effectively differentiated important euphotic zone processes such as nitrate assimilation and nitrification, while archiving the influence of disparate controls such as iron limitation and climatic events through their effects on nitrate utilization and isotopic fractionation.

Fisheries Surveys Are Essential Ocean Observing Programs in a Time of Global Change: A Synthesis of Oceanographic and Ecological Data From U.S. West Coast Fisheries Surveys

As climate change and other anthropogenic impacts on marine ecosystems accelerate in the 21st century, there is an increasing need for sustained ocean time series. A robust and collaborative network of regional monitoring programs can detect early signs of unanticipated changes, provide a more holistic understanding of ecosystem responses, and prompt faster management actions. Fisheries-related surveys that collect fisheries-independent data (hereafter referred to as “fisheries surveys”) are a key pillar of sustainable fisheries management and are ubiquitous in the United States and other countries. From the perspective of ocean observing, fisheries surveys offer three key strengths: (1) they are sustained due to largely consistent funding support from federal and state public sector fisheries agencies, (2) they collect paired physical, chemical, and biological data, and (3) they have large and frequently overlapping spatial footprints that extend into the offshore region. Despite this, information about fisheries survey data collection can remain poorly known to the broader academic and ocean observing communities. During the 2019 CalCOFI Symposium, marking the 70th anniversary of the California Cooperative Oceanic Fisheries Investigations (CalCOFI), representatives from 21 ocean monitoring programs on the North American West Coast came together to share the status of their monitoring programs and examine opportunities to leverage efforts to support regional ecosystem management needs. To increase awareness about collected ocean observing data, we catalog these ongoing ocean time series programs and detail the activities of the nine major federal or state fisheries surveys on the U.S. West Coast. We then present three case studies showing how fisheries survey data contribute to the understanding of emergent ecosystem management challenges: marine heatwaves, ocean acidification, and contaminant spills. Moving forward, increased cross-survey analyses and cooperation can improve regional capacity to address emerging challenges. Fisheries surveys represent a foundational blueprint for ecosystem monitoring. As the international community moves toward a global strategy for ocean observing needs, fisheries survey programs should be included as data contributors.

An hypoxia-tolerant flatfish: consequences of sustained stress on the slender sole Lyopsetta exilis (Pleuronectidae) in the context of a changing ocean.

Slender sole Lyopsetta exilis is an abundant groundfish on the continental shelf and inner waters of British Columbia, Canada, where it reaches a maximum standard length of 44 cm. Benthic image surveys coupled with oxygen measurements in Saanich Inlet document a dense population in bottom conditions near anoxia (0.03 ml l−1 oxygen) where diel migrating zooplankton intersect the bottom; we confirm this species is a planktivore, which limits its depth range to the base of the migration layer. In a comparison with slender sole from a nearby well‐oxygenated habitat, several probable effects of living in severe hypoxia emerge: both sexes are significantly smaller in Saanich and the sex ratio is male‐skewed. Otoliths from the Saanich fish were difficult to read due to many checks, but both sexes were smaller at age with the largest female (20 cm) from the hypoxia zone registering 17 years. Hypoxia appears to have a direct consequence on growth despite good food supply in this productive basin. Hyperventilation, a low metabolic rate and a very low critical oxygen tension help this fish regulate oxygen uptake in severely hypoxic conditions; it will be particularly resilient as the incidence of hypoxia increases on the continental shelf. Data from small‐mesh bottom‐trawl surveys over four decades reveal an increase in mean annual catch per unit effort in southern regions of the province, including the outer shelf and the Strait of Georgia. The California Cooperative Oceanic Fisheries Investigations (CalCOFI) ichthyoplankton database records a general decline in fish larvae on the Oregon–California shelf since 1990, but slender sole larvae are increasing there, as they are in the Strait of Georgia. We project that the slender sole will gain relative benefits in the future warming, deoxygenated northeast Pacific Ocean.

Bridging From Monitoring to Solutions-Based Thinking: Lessons From CalCOFI for Understanding and Adapting to Marine Climate Change Impacts

Multidisciplinary, integrated ocean observing programs provide critical data for monitoring the effects of climate change on marine ecosystems. California Cooperative Oceanic Fisheries Investigations (CalCOFI) samples along the US West Coast and is one of the world’s longest-running and most comprehensive time series, with hydrographic and biological data collected since 1949. The pairing of ecological and physical measurements across this long time series informs our understanding of how the California Current marine ecosystem responds to climate variability. By providing a baseline to monitor change, the CalCOFI time series serves as a Keeling Curve for the California Current. However, challenges remain in connecting the data collected from long-term monitoring programs with the needs of stakeholders concerned with climate change adaptation (i.e. resource managers, policy makers, and the public), including for the fisheries and aquaculture sectors. We use the CalCOFI program as a case study to ask: how can long-term ocean observing programs inform ecosystem based management efforts and create data flows that meet the needs of stakeholders working on climate change adaptation? Addressing this question and identifying solutions requires working across sectors and recognizing stakeholder needs. Lessons learned from CalCOFI can inform other regional monitoring programs around the world, including those done at a smaller scale in developing countries.

Euphotic zone nitrification in the California Current Ecosystem

AbstractNitrification, the microbial conversion of ammonium to nitrite then to nitrate, occurs throughout the oceanic water column, yet the environmental factors influencing the production of nitrate in the euphotic zone (EZ) remain unclear. In this study, the natural abundances of N and O isotopes (δ15N and δ18O, respectively) in nitrate were used in an existing model framework to quantify nitrate contributed by EZ nitrification in the California Current Ecosystem (CCE) during two anomalously warm years. Model data estimated that between 6% and 36% of the EZ nitrate reservoirs were derived from the combined steps of nitrification within the EZ. The CCE data set found nitrification contributions to EZ nitrate to be positively correlated with nitrite concentrations () at the depth of the primary nitrite maximum (PNM). Building on this correlation, EZ nitrification in the southern California Current was estimated to contribute on average 20% ± 6% to EZ nitrate as inferred using the PNM of the long‐term California Cooperative Oceanic Fisheries Investigation (CalCOFI) survey record. A multiple linear regression analysis of the CalCOFI PNM time series identified two conditions that led to positive deviations in . Enhanced PNM , and potentially enhanced EZ nitrification, may be linked to (1) reduced phytoplankton competition for ammonium () and as interpreted from particulate organic carbon:chlorophyll ratios, and/or (2) to increased supply of (and then oxidation to ) from the degradation of organic nitrogen as interpreted from particulate organic nitrogen concentrations.

Annual and Interannual Variability in the California Current System: Comparison of an Ocean State Estimate with a Network of Underwater Gliders

AbstractA data-constrained state estimate of the southern California Current System (CCS) is presented and compared with withheld California Cooperative Oceanic Fisheries Investigations (CalCOFI) data and assimilated glider data over 2007–17. The objective of this comparison is to assess the ability of the California State Estimate (CASE) to reproduce the key physical features of the CCS mean state, annual cycles, and interannual variability along the three sections of the California Underwater Glider Network (CUGN). The assessment focuses on several oceanic metrics deemed most important for characterizing physical variability in the CCS: 50-m potential temperature, 80-m salinity, and 26 kg m−3 isopycnal depth and salinity. In the time mean, the CASE reproduces large-scale thermohaline and circulation structures, including observed temperature gradients, shoaling isopycnals, and the locations and magnitudes of the equatorward California Current and poleward California Undercurrent. With respect to the annual cycle, the CASE captures the phase and, to a lesser extent, the magnitude of upper-ocean warming and stratification from late summer to early fall and of isopycnal heave during springtime upwelling. The CASE also realistically captures near-surface diapycnal mixing during upwelling season and the semiannual cycle of the California Undercurrent. In terms of interannual variability, the most pronounced signals are the persistent warming and downwelling anomalies of 2014–16 and a positive isopycnal salinity anomaly that peaked with the 2015–16 El Niño.

SMAP and CalCOFI Observe Freshening during the 2014–2016 Northeast Pacific Warm Anomaly

Data from NASA’s Soil Moisture Active Passive Mission (SMAP) and from the California Cooperative Oceanic Fisheries Investigations (CalCOFI) were used to examine the freshening that occurred during 2015–2016 in the Southern California Current System. Overall, the freshening was found to be related to the 2014–2016 Northeast Pacific Warm Anomaly. The primary goal was to determine the feasibility of using SMAP data to observe the surface salinity signal associated with the warming and its coastal impact. As a first step, direct comparisons were done with salinity from the CalCOFI data at one-meter depth. During 2015, SMAP was saltier than CalCOFI by 0.5 Practical Salinity Units (PSU), but biases were reduced to &lt;0.1 PSU during 2016. South of 33°N, and nearer to the coast where upwelling dominates, SMAP was fresher in 2015 by almost 0.2 PSU. CalCOFI showed freshening of 0.1 PSU. North of 33°N, SMAP and CalCOFI saw significant freshening in 2016, SMAP by 0.4 PSU and CalCOFI by 0.2 PSU. Differences between SMAP and CalCOFI are consistent with the increased stratification in 2015 and changes in the mixed layer depth. SMAP observed freshening that reached the Baja California Coast.

Nonsinking Organic Matter Production in the California Current

AbstractProductive eastern boundary upwelling systems such as the California Current Ecosystem (CCE) are important regions for supporting both local and remote food webs. Several studies have reported on the temporal and spatial variability of primary production and gravitational export in the CCE. However, few studies have quantified the partitioning of net primary and new production into other reservoirs of detrital organic matter. This study tested the hypothesis that nonsinking detrital reservoirs are an exportable reservoir of new production in the CCE with samples collected by the California Cooperative Oceanic Fisheries Investigation survey between 2008 and 2010. Water column gradients in nitrate (NO3−) and total organic carbon (TOC; which excludes sinking particulate organic carbon) were used to estimate potential rates of new production (PNew) and TOC production (PTOC), respectively. The PTOC:PNew varied between 0.16 and 0.56 and often increased with indicators of enhanced autotrophic production. At times, surface stratification was also correlated with elevated PTOC:PNew. In the most productive, inshore region, PTOC exceeded previously reported sinking export rates, which identified TOC as a quantitatively significant repository of exportable carbon in the CCE. However the sum of PTOC and sinking export for these productive regions was less than both PNew and oxygen‐based estimates of net community production. These results imply that nonsinking reservoirs alone are not sufficient to explain observed imbalances between production and export for the most productive CCE regions.

Chlorophyll Dynamics Around the Southern Channel Islands

We determine spatial and temporal dynamics of chlorophyll for the Southern California Bight through analysis of 10 years of chlorophyll product derived from the Moderate Resolution Imaging Spectroradiometer on the Earth Observing System satellite Aqua (MODIS-AQUA). Concentrating on the Southern Channel Islands, we find an island mass effect associated with San Nicolas; that is, some chlorophyll originates near the island. This signal is most evident during the fall after the typical spring phytoplankton bloom subsides. In contrast, there is a relative dearth of chlorophyll around Santa Catalina Island, and its seasonal modulation corresponds to the spring bloom, implying that the dynamics are much simpler for this island. Previous studies of temperature in the inner Southern California Bight near Santa Catalina indicate that a simple one-dimensional model of temperature diffusion explains well the seasonal and depth temperature modulations found there. We couple the temperature-derived vertical diffusion coefficient with nitrate measurements from California Cooperative Oceanic Fisheries Investigations (CalCOFI) cruises to make a simple one-dimensional model relating chlorophyll, insolation, and nitrate for Santa Catalina.

Habitat-Based Density Models for Three Cetacean Species off Southern California Illustrate Pronounced Seasonal Differences

Managing marine species effectively requires spatially and temporally explicit knowledge of their density and distribution. Habitat-based density models, a type of species distribution model (SDM) that uses habitat covariates to estimate species density and distribution patterns, are increasingly used for marine management and conservation because they provide a tool for assessing potential impacts (e.g., from fishery bycatch, ship strikes, anthropogenic sound) over a variety of spatial and temporal scales. The abundance and distribution of many pelagic species exhibit substantial seasonal variability, highlighting the importance of predicting density specific to the season of interest. This is particularly true in dynamic regions like the California Current, where significant seasonal shifts in cetacean distribution have been documented at coarse scales. Finer scale (10 km) habitat-based density models were previously developed for many cetacean species occurring in this region, but most models were limited to summer/fall. The objectives of our study were two-fold: 1) develop spatially-explicit density estimates for winter/spring to support management applications, and 2) compare model-predicted density and distribution patterns to previously developed summer/fall model results in the context of species ecology. We used a well-established Generalized Additive Modeling framework to develop cetacean SDMs based on 20 California Cooperative Oceanic Fisheries Investigations (CalCOFI) shipboard surveys conducted during winter and spring between 2005 and 2015. Models were fit for short-beaked common dolphin (Delphinus delphis delphis), Dall’s porpoise (Phocoenoides dalli), and humpback whale (Megaptera novaeangliae). Model performance was evaluated based on a variety of established metrics, including the percentage of explained deviance, ratios of observed to predicted density, and visual inspection of predicted and observed distributions. Final models were used to produce spatial grids of average species density and spatially-explicit measures of uncertainty. Results provide the first fine scale (10 km) density predictions for these species during the cool seasons and reveal distribution patterns that are markedly different from summer/fall, thus providing novel insights into species ecology and quantitative data for the seasonal assessment of potential anthropogenic impacts.

A climatology of the California Current System from a network of underwater gliders

Autonomous underwater gliders offer the possibility of sustained observation of the coastal ocean. Since 2006 Spray underwater gliders in the California Underwater Glider Network (CUGN) have surveyed along California Cooperative Oceanic Fisheries Investigations (CalCOFI) lines 66.7, 80.0, and 90.0, constituting the world’s longest sustained glider network, to our knowledge. In this network, gliders dive between the surface and 500m, completing a cycle in 3h and covering 3km in that time. Sections extend 350–500km offshore and take 2–3weeks to occupy. Measured variables include pressure, temperature, salinity, and depth-average velocity. The CUGN has amassed over 10,000 glider-days, covering over 210,000km with over 95,000 dives. These data are used to produce a climatology whose products are for each variable a mean field, an annual cycle, and the anomaly from the annual cycle. The analysis includes a weighted least-squares fit to derive the mean and annual cycle, and an objective map to produce the anomaly. The final results are variables on rectangular grids in depth, distance offshore, and time. The mean fields are finely resolved sections across the main flows in the California Current System, including the poleward California Undercurrent and the equatorward California Current. The annual cycle shows a phase change from the surface to the thermocline, reflecting the effects of air/sea fluxes at the surface and upwelling in the thermocline. The interannual anomalies are examined with an emphasis on climate events of the last ten years including the 2009–2010 El Niño, the 2010–2011 La Niña, the warm anomaly of 2014–2015, and the 2015–2016 El Niño.

Ichthyoplankton sampling design to monitor marine fish populations and communities

The ability to assess, model, predict and manage the impacts of climate change and other anthropogenic stressors on marine ecosystems depends on having adequate ecological time series. Unfortunately the development of ecological time series considerably lags those for the physics and chemistry of the oceans. Ichthyoplankton time series are proposed here to fill this gap in ocean observations. Marine fish species spanning a wide range of families, habitats, feeding guilds, and trophic levels broadcast large numbers of their reproductive products into the open waters. For a limited period, the larvae generally reside in the upper 200m of the water column, where they may be quantitatively sampled with plankton nets. Larval abundance provides a relative index for adult spawning stock biomass, enabling diverse fish communities to be monitored quantitatively by relatively simple means. Recent analyses of the ichthyoplankton time series extending back to 1951 from the California Cooperative Oceanic Fisheries Investigations (CalCOFI) program indicate that non-commercial as well as commercially-exploited taxa have experienced dramatic change in recent decades. The CalCOFI data set is re-sampled here to show that a reduced sampling program—one based on a few stations along a single transect (cf >50 stations along 6 transects for CalCOFI) or one based on a shorter time series—can, within limits, obtain similar single-species and multivariate patterns of abundance. Ichthyoplankton survey programs may thus provide the basis for a global system of ocean ecological observations in addition to their primary use today for fisheries stock assessment.

Recent collapse of northern anchovy biomass off California

New estimates of abundance of northern anchovy (Engraulis mordax) are developed from California Cooperative Oceanic Fisheries Investigations (CalCOFI) data on egg and larval densities for the period 1951–2011. Previous estimates utilizing mean density over the CalCOFI area show a hyperstability bias because of the nearshore concentration of CalCOFI stations and the tendency of the anchovy population to contract into this area when abundances are low. New abundance estimates weight sample egg and larval densities to the local area represented by that sample, and then sum contributions to obtain total abundance. We develop total egg and larval abundance estimates for January and April, form a combined index, and calibrate it to the absolute biomass estimates produced by the Daily Egg Production Method in the early 1980s. Anchovy spawning biomass was very low, 10,000–20,000 Metric Tons (MT), in the early 1950s when CalCOFI sampling began. Abundance increased and fluctuated between 0.5 and 2 million metric tons from 1960 through 1990. After 1990, spawning biomass fluctuated around 200,000 tons, briefly increased during 2005–2006, then declined substantially over four years to below 20,000 tons from 2009 to 2011. CalCOFI ichthyoplankton data collected after 2011 are not yet available for analysis, but continuous underway egg sampling conducted during CalCOFI cruises indicates continued low abundance and very limited spawning through 2015 in both southern and central California. The recent collapse of anchovy abundance occurred in the absence of a significant fishery. Present annual catches of a few thousand tons are small by historical comparison, but the exploitation rate may now be relatively high given the low stock abundance. The decline in anchovy abundance coincides with recent die-offs and reproductive failures of anchovy-dependent predators in the ecosystem (e.g., sea lions and pelicans).