Pacific Sardine Sardinops Sagax Research Articles

Climate and fishing simultaneously impact small pelagic fish in the oceans around the southernmost tip of Africa

Climate and fisheries interact, often synergistically, and may challenge marine ecosystem functioning and, ultimately, seafood provision and human wellbeing that depend on them. Holistic and integrative approaches aiming at evaluating the spatial overlap between these major stressors are crucial for identifying marine regions and key fish species that require conservation priority to prevent possible future collapses. Based on highly resolved information on environmental conditions and fishing pressure from the Southern Benguela and the Agulhas Bank ecosystems off South Africa, we identified the main areas where small pelagic fish species (European anchovy Engraulis encrasicolus, Pacific sardine Sardinops sagax, and West Coast round herring Etrumeus whiteheadi) have been highly impacted in terms of unfavourable environmental conditions and fishing pressure over the period 1993-2018. We termed these areas cumulative “hotspots” of climate change and fishing impact. We also identified fishing grounds where environmental conditions are now more favourable for these pelagic fish species, terming these “bright spots” of climate change. Environmental conditions and fishing intensity show contrasting patterns between the Southern Benguela and the Agulhas Bank ecosystems, with the Southern Benguela region accumulating most of the cumulative hotspots and showing the most negative trends in CPUE (a proxy for local fish abundance). Contrastingly, bright spots, identified on the south coast but also south of Cape Town, showed more positive trends in CPUE, suggesting that they may support sustainable growth of the small pelagic fishery in the medium term. Focussing future fishing effort on these bright spots may serve to alleviate pressure on the doubly and highly impacted cumulative hotspots from the western side of the southernmost tip of Africa.

A Collaborative Aerial Survey of Coastal Pelagic Species in Nearshore California Waters

Pacific Sardine Sardinops sagax and Northern Anchovy Engraulis mordax are commercially important West Coast fish stocks managed within the Coastal Pelagic Species (CPS) complex by the Pacific Fishery Management Council and National Marine Fisheries Service. Before 2020, survey indices used in Pacific Sardine stock assessments did not explicitly account for nearshore biomass, which presumably had been relatively small compared to the total biomass of the population, but since 2015, has been a more substantial component of total biomass. During the recent Pacific Sardine stock decline, the California Department of Fish and Wildlife and the California Wetfish Producers Association collaborated on an aerial survey off California to estimate nearshore (within 3,600 m from shore) CPS biomass to inform assessments. This project has also involved federal fisheries biologists and Pacific Fishery Management Council advisory bodies and committees, representing a unique collaborative effort to improve data used in CPS fisheries management. We will discuss successes, issues, and challenges in implementing this nontraditional survey and how these data can continue to inform future stock assessments.

Spatio-temporal diet variability of the California sea lion Zalophus californianus in the southern California Current Ecosystem

Characterizing predator diets is essential to understanding food web dynamics. We investigated the dietary breadth and variation of the California sea lion (CSL) Zalophus californianus at 3 of the California Channel Islands from 1981-2015. Prey species were identified from hard parts and soft-tissue remains of pyrosomes recovered from fecal samples, revealing a diverse diet of fish and cephalopods. Percent frequency of occurrence and percent split-sample frequency of occurrence were used to describe long-term trends, correlations between prey taxa, diet diversity, and diet similarity. The most common of 142 prey taxa identified to species were market squid Doryteuthis opalescens, northern anchovy Engraulis mordax, shortbelly rockfish Sebastes jordani, jack mackerel Trachurus symmetricus, Pacific sardine Sardinops sagax, Pacific hake Merluccius productus, and Pacific mackerel Scomber japonicus. Dietary differences were observed between male and female sea lions, and between animals from different islands and seasons. Intra-island diets at 2 locations were more similar than inter-island diets. Important inter-annual and decadal changes in diet were identified. CSL diet shifted from an anchovy-based diet in the 1980s to a market squid based-diet in the 1990s and 2000s, with other prey taxa being consumed more frequently when consumption of those 2 main prey declined. Prey-switching likely provides flexibility needed in the dynamic California Current Ecosystem, and may allow CSLs to adapt to changes in food supply and availability driven by climate change.

Putting the Pacific marine heatwave into perspective: The response of larval fish off southern California to unprecedented warming in 2014-2016 relative to the previous 65 years.

The 2014-2016Northeast Pacific marine heatwave (MHW) induced the warmest 3-year period on record in the California Current Ecosystem. We tested whether larval fish assemblage structure, phenology, and diversity dynamics were comparable to past warming events from 1951 to 2013. First, we hypothesized, based on past observations of biological effect of warming, that mesopelagic species with southern distributions relative to southern California and Pacific sardine Sardinops sagax (a coastal pelagic species) would increase during the MHW while northern mesopelagics and northern anchovy Engraulis mordax (coastal pelagic) abundances would decline. Similar to past warming, southern mesopelagics increased and northern mesopelagics decreased. Unexpectedly, however, a common southern mesopelagic, Mexican lampfish Triphoturus mexicanus, was approximately three times more abundant than the previous annual high. Furthermore, whereas sardine abundance did not increase, larval anchovy abundance rose to near-record highs in summer 2016. Second, we hypothesized that fishes would spawn earlier during the MHW. Fishes did not spawn in an earlier season within a year, but five of six southern mesopelagic taxa spawned earlier than typical within winter and spring. Third, we predicted that species richness would increase moderately due to an influx of southern and exodus of northern species. Richness, however, was very high in all seasons and the highest ever during the summer as multiple species with primarily southern distributions were recorded spawning for the first time in southern California. The richness of northern species was also unexpectedly high during the MHW. Northern species likely persisted in the study area because in addition to the warm water, pockets of cold water were consistently present. If, as predicted, conditions similar to the MHW become more common as oceans warm, this unique and largely unexpected combination of fishes may reflect future biological conditions.

The complete mitochondrial genome of Sardinops sagax (Jenyns, 1842) (Clupeiformes: Clupeidae) and phylogenetic analyses of sardines

Pacific sardine Sardinops sagax (Jenyns, 1842), a sardine species that widely distributes in Pacific, is an important commercial species in many areas. In this study, we characterized the complete mitochondrial genome of S. sagax using next generation sequencing technology. The complete mitogenome of S. sagax was 16,883 base pairs (bp) in length and comprised 13 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes, 2 ribosomal RNA genes (rRNA), and one control region (D-loop). Phylogenetic analysis indicated that sardine species included three clades (I, II and III) and S. sagax clustered with Sardinops melanostictus.

Metabolic measurements and parameter estimations for bioenergetics modelling of Pacific Chub Mackerel Scomber japonicus

AbstractAs a crucial step in developing a bioenergetics model for Pacific Chub Mackerel Scomber japonicus (hereafter chub mackerel), parameters related to metabolism, the largest dissipation term in bioenergetics modelling, were estimated. Swimming energetics and metabolic data for nine chub mackerel were collected at 14°C, a low temperature within the typical thermal range of this species, using variable‐speed swim‐tunnel respirometry. These new data were combined with previous speed‐dependent metabolic data at 18 and 24°C and single‐speed (1 fork length per second: FL/s) metabolic data at 15 and 20°C to estimate respiration parameters for model development. Based on the combined data, the optimal swimming speed (the swimming speed with the minimum cost of transport, Uopt) was 42.5 cm/s (1.5–3.0 FL/s or 2.1 ± 0.4 FL/s) and showed no significant dependence on temperature or fish size. The daily mass‐specific oxygen consumption rate (R, g O2 g fish−1 day−1) was expressed as a function of fish mass (W), temperature (T) and swimming speed (U): R = 0.0103W−0.490 e(0.0457T) e(0.0235U). Compared to other small pelagic fishes such as Pacific Herring Clupea harengus pallasii, Pacific Sardine Sardinops sagax and various anchovy species, chub mackerel respiration showed a lower dependence on fish mass, temperature and swimming speed, suggesting a greater swimming ability and lower sensitivity to environmental temperature variation.

Length conversions and mass-length relationships of five forage-fish species in the California current ecosystem.

Length-measurement conversions and seasonal mass-length relationships (MLR) for Pacific herring Clupea pallasii, northern anchovy Engraulis mordax, Pacific sardine Sardinops sagax, Pacific mackerel Scomber japonicus and jack mackerel Trachurus symmetricus in the California Current are presented. The conversions between total (LT ), fork (LF ,) and standard lengths (LS ) should facilitate comparisons of data across disciplines and institutions. These equations resulted from an analysis of measurements spanning 14 years and the western seaboard of North America, from the north end of Vancouver Island to the USA-Mexico border. Major-axis regressions were used to calculate reciprocal length-measurement conversions (e.g., LT to LS and LS to LT ) and generalised linear models and ordinary least-squares models were used to create MLRs that account for seasonal variations. The MLR models indicated seasonal differences for all species except C. pallasii, for which there was no multi-season data. Discrepancies between these and published models were examined, along with the suitability and benefit of the various types of models used for length-measurement conversion and MLRs.

Establishing genome sizes of focal fishery and aquaculture species along Baja California, Mexico

Genome size—the total haploid content of nuclear DNA— is constant in all cells in individuals within a species, but differs among species. Consequently, the genome size is a quantifiable genetic signature that not only characterizes a species, but it can reflect chromatin modifications, which play fundamental roles in most biological processes that are involved in the manipulation and expression of DNA. This characteristic makes the genome size a crucial parameter for genetic research on endemic aquatic species and for genetic manipulations in aquaculture species. Technologies for genetic assessments and improvements applied to fishery and aquaculture species use genome size values as a means by which hybrids, polyploids, and sex can be identified, when sex chromosomes exist. The objectives of this study were to determine genome sizes of aquatic species with economic and biological importance along the Pacific coast of Mexico, as well as to identify the appropriate reference standards for use in this study. Blood, hemolymph or milt were collected from 10 species occurring along the coast of Baja California: Sablefish Anoplopoma fimbria, Black Snapper Lutjanus novemfasciatus, California Halibut Paralichthys californicus, Pacific Sardine Sardinops sagax, Flag Rockfish Sebastes rubrivinctus, Starry Rockfish Sebastes constellatus, Totoaba Totoaba macdonaldi, Whiteleg Shrimp Litopenaeus vannamei and two Yellowtail Seriola lalandi and S. dorsalis. Nuclear DNA was stained with propidium iodide solution and the genome size was determined by flow cytometry, with results ranging from 0.61 pg (1.22 pg/diploid cell) to 2.59 pg (5.18 pg/diploid cell), with the smallest value in Sablefish and the largest in the Whiteleg Shrimp. No significant differences were detected (P ≤ 0.05) among individuals of the same species; the likely reason behind any dissimilar DNA content values with those from the literature were differences in methodologies or variations in genetics. Red-ear Slider Turtle Trachemys scripta elegans 2.65 pg (5.30 pg/diploid cell) and Red Junglefowl Gallus gallus 1.27 pg (2.54 pg/diploid cell) were chosen as the standards for reference values. These results establish the basis for the Mexican National Aquatic Genetic Resources project supporting genetic improvements for aquaculture and conservation status parameters for fisheries species.

Performance of fish-habitat classifiers based on derived predictors from a coupled biophysical model

Abstract Fish habitat models based on remotely-sensed data may be limited by satellite coverage and availability. We compared the fit and predictive power of Random Forest habitat classifiers that were developed using predictors derived from a coupled biophysical model (i.e., modeled predictors) versus similar classifiers that used remotely-sensed satellite data for two data sets (eggs and adults) and four species that occur widely in the California Current system. When tested on independent data, classifiers of spawning habitat that used derived predictors (derived classifiers) had nearly identical accuracies (0–2% difference) to similar classifiers based on satellite data (satellite classifiers). Accuracies of derived classifiers of adult habitat were within −8% to +7% of comparable satellite classifiers. Accuracies of both types of classifiers on test data were much greater for Northern anchovy Engraulis mordax and Pacific hake Merluccius productus (0.75–0.97) than for jack mackerel Trachurus symmetricus and Pacific sardine Sardinops sagax (0.61–0.72), and generally were greater for classifiers of spawning habitat than for adult habitat. Specificity was very good for both types of classifiers, but sensitivity was poor, because classifiers identified potential habitat which was not fully occupied. Adults of all species used a broader range of habitat conditions during summer than during the spring spawning period. Derived classifiers have some advantages over satellite classifiers; they are not limited by cloud cover and they can make predictions in near real-time or the short-term future. However, there was no consistent improvement in the accuracy of derived predictors that included modeled zooplankton concentrations over comparable satellite classifiers that included reflectance/chlorophyll concentration.

Defining an ideal temperature range for the northern subpopulation of Pacific sardine, Sardinops sagax caeruleus

The aim of this study was to determine a physiologically “ideal” temperature range of Pacific sardine (Sardinops sagax caeruleus) from the northern stock by assessing the effects of cumulatively increasing or decreasing temperature on their stress physiology. Sardines collected off the coast of Southern California during late spring and late fall were exposed to cumulatively increasing or decreasing temperatures that reached +/− 8 °C from their acclimation temperature over a period of approximately one month. Blood plasma and tissue samples were collected at every 2 °C temperature change. Measurements included plasma cortisol, expression of heat shock proteins (Hsp70, Hsp90, HOP) in liver tissue, expression of an immune gene (IgM) in liver tissue, and Michaelis-Menton (Km) determinations of lactate dehydrogenase (LDH) and citrate synthase (CS) from white and red muscle tissue, respectively. Critical thermal minimum and maximum temperatures were also measured to identify the outer edges of their thermal tolerance. Feeding behavior ceased and plasma cortisol was elevated at the lowest temperature, while Hsp90 and Km pyr (LDH) values were elevated at the highest temperatures to which sardines were exposed. An additional finding was that Vmax of LDH increased with increasing condition factor, indicating the occurrence of metabolic scaling in Pacific sardine. Critical thermal minimums and maximums for sardines acclimated to 15 °C and 17 °C were 3.4 °C – 29.1 °C and 4.8 °C – 29.9 °C, respectively. This study indicates Pacific sardine from the northern stock have a physiologic ideal temperature range of 9 °C – 19 °C for 15 °C acclimated sardines and 11 °C – 21 °C for 17 °C acclimated sardines.

Changes in growth and maturation parameters of Pacific sardine Sardinops sagax collected off California during a period of stock recovery from 1994 to 2010.

Whether fluctuation in density influenced the growth and maturation variables of three aggregated cohorts (fish born during the 1986-1993, 1996-2003 and 2004-2008 periods) of Pacific sardine Sardinops sagax caeruleus collected off the Californian coast from 2004 to 2010 was investigated. Using a von Bertalanffy mixed-effects model with aggregated cohorts as covariates, estimated growth rate significantly covaried with aggregated cohorts. Growth rate (K) was modelled as a fixed effect and estimated to be 0.264 ± 0.015 (±s.e). Statistical contrasts among aggregated cohorts showed that the 1996-2003 cohorts had a significantly lower growth rate than the other two aggregated cohorts. The theoretical age at length zero (t0) and the standard length at infinity (L(S∞)) were modelled as random effects, and were estimated to be -2.885 ± 0.259 (±s.e) and 273.13 ± 6.533 mm (±s.e). The relation of ovary-free mass at length was significantly different among the three aggregated cohorts, with the allometric coefficient estimated to be 2.850 ± 0.013 (±s.e) for the S. sagax population. The age-at-length trajectory of S. sagax born between 1986 and 2008 showed strong density dependence effects on somatic growth rates. In contrast to the density-dependent nature of growth, the probability to be mature at-size or at-age was not significantly affected by aggregated cohort density. The size and the age-at-50% maturity were estimated to be 150.92 mm and 0.56 years, respectively. Stock migration, natural fluctuations in biomass and removal of older and larger S. sagax by fishing might have been interplaying factors controlling growth parameters during 1986-2010.

Transport patterns of Pacific sardine Sardinops sagax eggs and larvae in the California Current System

We simulated transport of Pacific sardine eggs captured offshore of California in spring of 2001–2012 using a regional ocean circulation model. Eggs were assumed to have developed into larvae within a few days and were modeled using five behavioral patterns: passive transport, diel vertical migration, diel vertical migration combined with swimming against the current, diel migration combined with migration toward shore, and diel migration combined with migration toward the best habitat. Simulated larvae with no swimming behavior were advected far offshore to poor habitat where they were unlikely to survive. Diel vertical migration resulted in less offshore transport because larvae were less affected by surface currents during the day. However, in half the years simulated nearly all juveniles were also located in poor habitat by late summer in this scenario. Swimming against the current combined with diel vertical migration resulted in similar transport patterns to the diel-vertical-migration scenario because currents dominated the transport of eggs and small larvae during the spring and early summer. Migration toward shore resulted in a large fraction of juveniles being located in appropriate habitat during late summer in all years. Migration toward the best habitat was the best strategy modeled. This strategy resulted in a slightly greater proportion of larvae being located in appropriate habitat at the end of summer than the swimming-toward-shore scenario, despite the fact that most larvae were located farther offshore. These results suggest that larval sardine might use directed horizontal swimming behavior to remain in suitable habitat conditions. A large fraction of larvae were transported south into Mexican waters by late summer in all five scenarios. Surveying juvenile sardines in fall near the border of the U.S. and Mexico may be an efficient means of estimating recruitment because the advection pattern of eggs and larvae to the south is opposite the adult migration pattern to the north. This pattern may cause juveniles to be spatially segregated from adults at the time they are being recruited.

Pilot California Spiny Lobster Postlarvae Sampling Program: Collector Selection

Lobster (infraorder Astacidea) is perhaps the most intensively studied shellfish around the world due to its economic importance (Phillips 2006). Fishery management tools almost universally include catch reporting, but fishery-dependent data such as this often fails to adequately inform managers about the true state of the population (Erisman et al. 2011). Increasingly, fishery-independent surveys are being relied upon to provide the robust information fishery managers require, such as the California Cooperative Oceanic Fisheries Investigation (CalCOFI). The CalCOFI program attempts to understand and predict variations in the Pacific Sardine (Sardinops sagax) fishery, among others, in California through quarterly sampling of fish larvae and other biological and hydrographic data. This focus on larval stages stems from Hjort’s seminal work in 1914, which hypothesized the recruitment and transition of larval forms into postlarval and juvenile life stages is a critical period in population dynamics (Houde 2008). In modern times, fishery management agencies expend significant effort towards cataloging and understanding recruitment levels and patterns which provide the foundation for most fishery management tools (e.g. stock assessments). Recruitment monitoring is at the core of many of global lobster fishery management programs (Cruz et al. 1995; Acosta et al. 1997; Cruz and Adriano 2001; Phillips et al. 2005; Phillips and Melville-Smith 2005; Phillips et al. 2006; Arteaga-Rios et al. 2007; Phillips et al. 2010). Recruitment monitoring of numerous lobster taxa globally have been well correlated with future catch-rate predictions, typically with a 4 to 5 year time lag (e.g. Gardner et al. 2002; Caputi and Brown 2011; Linnane et al. 2014). Long-term recruitment monitoring programs, such as that in Australia (Linnane et al. 2010), are vital in assessing future stock levels and setting the total allowable commercial catches. Like many lobster species, the California Spiny Lobster (Panulirus interruptus) is an economically important fishery species, supporting one of California’s most valuable fisheries with annual ex-vessel values exceeding $9 million (Porzio et al. 2012). However, unlike many of the world’s lobster fisheries, no California Spiny Lobster recruitment monitoring program exists. Recent attempts to address this data gap have been made using plankton collection (Koslow et al. 2012) and power plant entrapment records (Miller 2014). Plankton collections were unable to reliably predict recent landings while entrapment records were more successful, but both articles noted the likely effect of unknown recreational harvest levels impacting the analyses and final conclusions. While informative, neither existing program fulfills the need for targeted information on California Spiny Lobster recruitment in southern California. Furthermore, as southern California power plants shift away from once-throughcooling, lobster entrapment data may soon be unavailable, in which case no regular abundance estimates of California Spiny Lobster postlarvae will be available. Noting the clear need for lobster recruitment monitoring in California, a pilot program was initiated in Orange County, California with the hopes of establishing a model that Bull. Southern California Acad. Sci. 113(3), 2014, pp. 180–186 E Southern California Academy of Sciences, 2014

Spatial overlap between forage fishes and the large medusa Chrysaora fuscescens in the northern California Current region

As in many regions of the world, the shelf waters of the western United States have experienced large increases and high interannual variability in jellyfish populations in recent decades. The northern California Current (NCC) is a productive upwelling zone that is home to large populations of medusae, particularly during some years. Seasonal trawl surveys in the NCC over 13 yr have documented a substantial biomass of jellyfish consisting primarily of one species, the sea nettle Chrysaora fuscescens, with abundances generally peaking in late summer. Trophic overlap can be high in the NCC with planktivorous species such as Pacific sardines and herring that consume copepods and other zooplankton. In this study, we examine the spatial overlap and co-occurrence of C. fuscescens and Pacific herring Clupea pallasii, northern anchovy Engraulis mordax and Pacific sardine Sardinops sagax in the NCC using spatial analysis tools to determine the species that have the potential to be most affected by high jellyfish biomass and the geo- graphic areas in which these interactions are likely to occur. Significant spatial overlap of C. fuscescens with these pelagic fishes occurred during certain months and years, although the results were highly variable. There was an overall negative relationship between the abundance of C. fuscescens and the catch of the 3 forage fishes for both June and September. End-to-end food web models show that jellyfish have a greater potential to affect production of pelagic forage fishes than the reverse.

Feeding Habits Variability and Trophic Position of Dolphinfish in Waters South of the Baja California Peninsula, Mexico

AbstractUsing data from analyses of stomach contents and stable isotopes, we examined high‐resolution variations in the feeding habits and trophic position of Dolphinfish Coryphaena hippurus during 2005–2007. In total, 418 specimens were collected off the southern Baja California peninsula, Mexico. Based on analysis of stomach contents (% index of relative importance [%IRI]), Dolphinfish consumed mainly epipelagic prey, with the red crab Pleuroncodes planipes as the most abundant prey species. The diet was highly similar between sexes but differed between size‐classes: Dolphinfish smaller than 65 cm FL fed mainly on Pacific Sardine Sardinops sagax caeruleus (%IRI = 30), whereas those larger than 110 cm FL fed mainly on jumbo squid Dosidicus gigas (%IRI = 45) in addition to red crabs. Dietary differences between the smallest and largest specimens were mainly related to changes in morphology and spatial stratification by size (i.e., to avoid cannibalism). Trophic positions estimated by both methods indicated that the Dolphinfish is a secondary to tertiary carnivore with a high degree of trophic plasticity, and thus it plays different trophic roles within the area. Elevated variability in δ15N and Shannon–Wiener diversity index values on an annual scale revealed that Dolphinfish are opportunistic predators. Interannual diet variation related to the availability and abundance of prey species can be explained by changes in environmental conditions due to climate anomalies associated with El Niño–Southern Oscillation events. We highlight that the Dolphinfish is a good indicator of changes occurring in the food web structure of pelagic ecosystems. The observed variations in feeding habits and trophic position are critical to understanding the ecology and role of Dolphinfish in marine ecosystems by providing knowledge on feeding locations, seasonal prey utilization, and prey availability and allowing predictions of possible ecological responses to environmental change.

Changes in California Chinook salmon diet over the past 50 years: relevance to the recent population crash

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 498:249-261 (2014) - DOI: https://doi.org/10.3354/meps10608 Changes in California Chinook salmon diet over the past 50 years: relevance to the recent population crash Julie A. Thayer1,*, John C. Field2, William J. Sydeman1 1Farallon Institute for Advanced Ecosystem Research, 101 H Street, Suite Q, Petaluma, California 94952, USA 2NOAA/NMFS Southwest Fisheries Science Center, Fisheries Ecology Division, 110 Shaffer Road, Santa Cruz, California 95060, USA *Corresponding author: jthayer@faralloninstitute.org ABSTRACT: Salmon are affected by variation in ocean productivity; thus, improved understanding of mechanisms behind variability in ocean survival should help management of these ecologically and economically important populations. Based on a cooperative fisheries research program, we compared central California Chinook salmon Oncorhynchus tshawytscha adult food habits from spring and summer in the mid-2000s with historical records from 1955 and the 1980s. Diet diversity decreased through time, and was particularly low in May and June of the 2000s. Previously important prey, including juvenile rockfish Sebastes spp., krill Euphausiidae, Pacific herring Clupea pallesi and market squid Doryteuthis opalsecens, declined or disappeared from the diet, while Pacific sardine Sardinops sagax became very important prey in the 2000s; anchovy Engraulis mordax remained important throughout the study. Diet composition was correlated with regional mid-water trawls of prey abundance and also with local sea surface temperature (SST). Diet composition was related to the Sacramento Index of fall-run Chinook ocean abundance with a lag of 1 or 2 yr, and reflected the importance of prey availability during the second ocean year and smolt ocean-entry period, respectively. Spring is peak ocean entry for fall-run Chinook smolts, so declining prey diversity (specifically in May and June in the mid-2000s) may be related to recent population crashes. Seasonally, winter and fall diet data further demonstrated the significance of temporal variation in specific prey. This study highlights the importance of marine predator–prey interactions at an appropriate temporal resolution for understanding salmonid population dynamics. KEY WORDS: Chinook salmon · Diet diversity · Diet composition · Seasonal variation · Decadal variation · Prey availability · SST Full text in pdf format Supplementary material PreviousNextCite this article as: Thayer JA, Field JC, Sydeman WJ (2014) Changes in California Chinook salmon diet over the past 50 years: relevance to the recent population crash. Mar Ecol Prog Ser 498:249-261. https://doi.org/10.3354/meps10608 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 498. Online publication date: February 17, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Measurements of natural mortality for Pacific sardine (Sardinops sagax)

Abstract Zwolinski, J. P., and Demer, D. A. 2013. Measurements of natural mortality for Pacific sardine (Sardinops sagax). – ICES Journal of Marine Science, 70: . The northern stock of Pacific sardine (Sardinops sagax) in the California Current Ecosystem is periodically assessed to provide harvest guidelines for the United States and Canadian fisheries. The assessment model incorporates the estimates of abundance from acoustic-trawl method (ATM) and other surveys and many parameters including a constant value for the instantaneous natural mortality coefficient (M). Here, the ATM-estimated length-structured sardine abundances for 2006–2011 are combined to directly estimate M. The stock was dominated by the 2003, 2004, and 2005 year classes (2003–2005 cohort) from 2006 to 2010 and by the 2009 and 2010 year classes in 2011. Insignificant recruitments during 2006–2010 allowed the 2003–2005 cohort to be tracked and M to be estimated. The bootstrap distributions of estimated M encompass the assessment-assumed value of 0.4−year. The measurements suggest that M is high for a new cohort, declines during mid-life, then increases as the fish approach their longevity. The mean M for the entire period, 0.52, is 30% higher than the one currently assumed for the assessment, reflecting the steeper decline in the ATM-estimated biomass versus that in the assessment model.

Comparing body and otolith shape for stock discrimination of Pacific sardine, Sardinops sagax Jenyns, 1842

Stock discrimination in fishes is important for fisheries management. Morphometric analysis has been a viable approach when different structures (overall body, otoliths, and scales) are used. However, in cases where a single source of information may already differentiate among stocks, different conclusions may be obtained when using different sources of information. These have to be considered because they could lead to different management plans. Using geometric morphometrics, data was analyzed regarding the body and otolith shape of the Pacific sardine Sardinops sagax Jenyns, 1842 collected off the west coast of Baja California Peninsula, Mexico. Results confirm seasonal differences in body shape and otolith shape in stocks previously associated with sea surface temperature. Although both measures resulted in compatible conclusions, the shape of the body discriminated groups more appropriately; the data indicate that differential resolution could be thus obtained, depending on the source of the data. If possible, the application of more than one source of information is suggested in comparable cases because this would detect the extent of stock isolation with greater certainty.

Sampling selectivity in acoustic-trawl surveys of Pacific sardine (Sardinops sagax) biomass and length distribution†

Abstract Demer, D. A., Zwolinski, J. P., Cutter, G. R. Jr, Byers, K. A., Macewicz, B. J., and Hill, K. T. Sampling selectivity in acoustic-trawl surveys of Pacific sardine (Sardinops sagax) biomass and length distribution. – ICES Journal of Marine Science, 70: . To annually assess the northern stock of Pacific sardine (Sardinops sagax) in the California Current and set harvest quotas for the US fishery, managers have used an age-structured stock synthesis model fitted with results from acoustic-trawl (ATM), daily-egg-production, and aerial-photogrammetric survey methods, fishery landing and individual-length data, and many assumed or empirically derived parameters. In these assessments, sardine landed at ports spanning from Ensenada, México to Vancouver Island, Canada were assumed to be solely from the northern stock. It was also assumed that the ATM estimates of sardine biomass were negligibly biased for the sizes of fish sampled by the survey trawls (i.e., catchability q = 1 for sardine standard length (SL) values greater than ∼17 cm). Due to these catchability and length-selectivity assumptions, the ATM- and assessment-estimated abundances are mostly similar for larger sardine. However, the assessment estimates include large abundances of small sardine (SL values less than ∼15 cm) that are not represented in either the ATM-survey results or the fishery landings, and generally did not recruit to the migrating northern stock sampled by the ATM surveys. We considered four explanations for this disparity: (i) the ATM length-selectivity assumption is correct; (ii) the non-recruiting small fish may comprise a smaller portion of the stock than indicated by the assessments; (iii) during years of low recruitment success, those size classes may be virtually completely fished by the Ensenada and San Pedro fisheries; or (iv) they may belong to the southern sardine stock. This investigation emphasizes the previously identified importance of differentiating samples from the northern and southern stocks and surveying their entire domains.

Timing of forage fish seasonal appearance in the Columbia River plume and link to ocean conditions

This study described the phenology and patterns of variability of forage fish and meso- zooplankton populations near the Columbia River plume. Our objective was to identify the timing of the seasonal appearance of forage fish and to characterize the temporal patterns of abundance in relation to ocean conditions including zooplankton availability. Observations were collected at 2 sta- tions in 2008 and 2009 using 200 kHz bio-acoustic moorings, and with bi-weekly net sampling surveys conducted at nearby stations to measure total fish density and relative species composition. Acoustic time series results revealed that the seasonal timing of acoustic schools, representing the forage fishes northern anchovy Engraulis mordax, whitebait smelt Allosmerus elongatus, and Pacific sardine Sardinops sagax, occurred abruptly, with specific dates of appearance identified at each station in mid-May in both years. Both 2008 and 2009 represented very similar years for the timing and strength of wind-driven coastal upwelling. The timing of forage fish appearances in these years was linked with ocean temperature and salinity data collected at a nearby oceanographic buoy but was poorly correlated with mesozooplankton abundance, which was highly variable and fluctuating over a period of hours to days. Fluctuations in zooplankton and forage fish populations drive many trophic interactions, including juvenile salmon, seabirds, and large predators (e.g. adult salmon) that rely on the timing and abundances of these populations and have significant implications for eco- system based management.