Pacific Hake Research Articles

Interannual variability in the abundance and composition of spring larval fish assemblages in the Strait of Georgia (British Columbia, Canada) from 2007 to 2010

AbstractSpring larval fish assemblages in the Strait of Georgia (British Columbia, Canada) were characterized for the first time based on three spatially extensive field surveys in late‐April of 2007, 2009 and 2010, a period which spanned both warm and cold environmental conditions. The abundance, diversity and community structure of the assemblages were examined to investigate interannual variability, and responses to environmental fluctuations. A total of 49 taxa from 23 families were identified. The dominant taxa were Clupea pallasi, Gadus chalcogrammus, Merluccius productus, Leuroglossus schmidti, Lyopsetta exilis and Sebastes spp. Total larval abundance was much lower in 2009 (c. 32 per 1000 m3) than in 2007 and 2010 (c. 200 per 1000 m3). However, the mean size of individuals from several species was largest in 2009. Assemblage structure varied dramatically; from dominance by M. productus in 2007, to dominance by C. pallasi and G. chalcogrammus in 2009, followed by a shift to dominance by benthic species including Sebastes spp. and several flatfishes in 2010. Variability in assemblage structure among the three study years was primarily related to water temperature, whereas within‐year patterns were more closely associated with salinity and chlorophyll, both of which were affected by estuarine circulation. This study provides baseline information about the status of the larval fish community in the Strait of Georgia in recent years, and offers a better understanding of their short‐term dynamics and response to environmental fluctuations.

Image and chemical analyses of freezing-induced aggregates of fish natural actomyosin as affected by various phosphate compounds

Abstract The impact of various phosphate compounds [sodium tripolyphosphate (STPP), tetrasodium pyrophosphate (TSPP), STPP/TSPP, trisodium pyrophosphate (3SP), sodium hexametaphosphate (SHMP), and disodium phosphate anhydrous (DSPA)] on retarding freeze-induced protein denaturation and aggregation was evaluated. Using natural actomyosin (NAM) extracted from fresh Pacific whiting, the phosphate treatments were evaluated at various concentrations (0.1%, 0.3%, and 0.5%), with and without cryoprotectants (CP) (4% sorbitol and 5% sugar), after different freeze/thaw cycles (F/TC) (0, 3, and 9F/TC). Trimethylamine- N -oxide demethylase (TMAOase) activity, formaldehyde (FA) content, solubility, and turbidity were measured. The other NAM mixture containing the 0.5% STPP/TSPP, STPP, or TSPP along with CP showed low TMAOase activity, low FA production, high salt-soluble proteins solubility, and high turbidity. Among the phosphate treatments, STPP seemed to be the most effective compound in retarding both FA- and freeze-induced protein denaturation and aggregation. NAM without CP was more rapidly denatured and aggregated than NAM with CP as F/TC increased, resulting in a gradual increase in the degree of aggregation (DA). The DA, which was calculated based on graphical images, correlated with biochemical properties.

Collapse and recovery of forage fish populations prior to commercial exploitation

AbstractWe use a new, well‐calibrated 500 year paleorecord off southern California to determine collapse frequency, cross correlation, persistence, and return times of exploited forage fish populations. The paleorecord shows that “collapse” (defined as <10% of the mean peak biomass) is a normal state repeatedly experienced by northern anchovy, Pacific hake, and Pacific sardine which were collapsed 29–40% of the time, prior to commercial fishing exploitation. Mean (± SD) persistence of “fishable biomass” (defined as one third mean peak biomass from the paleorecord) was 19 ± 18, 15 ± 17, and 12 ± 7 years for anchovy, hake, and sardine. Mean return times to the same biomass was 8 years for anchovy but 22 years for sardine and hake. Further, we find that sardine and anchovy are positively correlated over 400 years, consistent with coherent declines of both species off California. Persistence and return times combined with positive sardine‐anchovy correlation indicate that on average 1–2 decades of fishable biomass will be followed by 1–2 decades of low forage. Forage populations are resilient on the 500 year time scale, but their collapse and recovery cycle (based on the paleorecord) are suited to alternating periods of high fishing mortality and periods of little or no fishing.

An investigation of the biological basis of recruitment, growth and adult survival rate variability of Pacific herring (Clupea pallasi) from British Columbia: a synthesis

AbstractI explored the biological basis of variation in recruitment (age 3 abundance), growth and age‐specific adult survival rate for the major populations [West Coast Vancouver Island (WCVI), Strait of Georgia, Central Coast, North Coast and Haida Gwaii] of Pacific herring (Clupea pallasi) that inhabit British Columbian waters. The analyses were based on a synthesis of time series of empirical observations of herring population characteristics (egg deposition, age‐specific abundance and size) and prey, competitor and predator biomass/abundance. Recruitment was not correlated among populations. Recruitment variability was explained for WCVI herring only, as a consequence of prey (the euphausiid Thysanoessa spinifera) biomass during August in each of the first 3 years of life, and the biomass of piscivorous Pacific hake (Merluccius productus) during the first year of life. Recruit mass and adult mass‐at‐age were correlated among populations and over ages within populations. Recruit mass was affected by T. spinifera biomass in August of the first and third years of life. Adult mass‐at‐age variability was determined mainly by size at the beginning of the growth season, but also by T. spinifera biomass in August. Age‐specific adult survival rates were not correlated among the five populations. Survival rates decreased with age; there were additional population‐specific effects of somatic mass and T. spinifera biomass in August. The analyses were repeated using physical oceanographic explanatory variables. Only recruit mass variation was explained significantly by physical oceanographic variables, and the biological‐based explanation of recruit mass variability accounted for more of the variation.

Preventing Soft Texture Fish Fillets through Brine Injection Technology

An exploratory study was conducted to determine if multineedle injection technology could deliver protease inhibitor ingredients into fish fillets at sufficient levels to inhibit protease activity. Pacific whiting is used as a model in this study. Fillet treatments (n=8/treatment) included noninjection (C), injection of base brine containing 3% salt and 3% sodium tripolyphosphate (B), injection of base brine and 3% egg white(BEW), and injection of base brine, 0.1% xanthan gum, and 3% dried potato extract(BPE). Xanthan gum was used as a suspension aid. Actual brine incorporation was12.2±0.5%. Cathepsin L activity was evaluated at pH 5.5 (optimal pH) and ultimate pH. Quality measures evaluated included CIE Lab color, shear force, and lipid oxidation. Fillets injected with BEWand BPEwere significantly lower in cathepsin L activity when measured at pH 5.5. BEWand BPEfillets were darker in appearance than B or C fillets. Untreated fillets (C) had higher variability in shear force value than treated fillets. There was no effect of treatment on lipid oxidation. Results suggested that injection technology can be utilized to incorporate protease inhibitor ingredients (3% EW or 3% PE) at levels sufficient to reduce cathepsin L activity in Pacific whiting fillets.

A Profitability Analysis of Catch Quotas for the Pacific Hake Fishery in the Gulf of California

AbstractFishing for Pacific Hake Merluccius productus in the Gulf of California is carried out by shrimp trawlers. When the shrimp fishing season ends, these boats shift to catching Pacific Hake and other finfish. The Pacific Hake fishery is relatively new and has the potential to grow as an industry. Therefore, there is interest in defining management plans to create a sustainable fishery. One option is an individual vessel quota system. This paper estimates the per‐vessel quota in the Pacific Hake fishery that achieves a break‐even operation and estimates the number of vessels that could enter the fishery to avoid overexploitation and overcapacity. Potential per‐vessel quotas were estimated based on the cash flow of a representative trawler and the estimate of total Pacific Hake biomass. The results indicate that individual catch quotas for Pacific Hake should be 90.4 or 100 metric tons to achieve a 30% or 45% increase, respectively, in net cash. Additionally, with total allowable catch values equivalent to 25% of the available biomass, the corresponding fleet size would be 74, 82, or 103 vessels based on different scenarios. Because the Pacific Hake fishery is under development, these approximations can be used during the planning stage to meet resource conservation and right‐of‐use standards.Received November 12, 2015; accepted August 16, 2016Published online December 20, 2016

Impacts of moderate hypoxia on fish and zooplankton prey distributions in a coastal fjord

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 560:57-72 (2016) - DOI: https://doi.org/10.3354/meps11910 Impacts of moderate hypoxia on fish and zooplankton prey distributions in a coastal fjord Mei Sato1,5,*, John K. Horne1, Sandra L. Parker-Stetter1,2, Timothy E. Essington1, Julie E. Keister3, Pamela E. Moriarty1, Lingbo Li3, Jan Newton4 1School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA 98195-5020, USA 2Fishery Resource Analysis and Monitoring Division, Northwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, 2725 Montlake Boulevard East, Seattle, WA 98112-2013, USA 3School of Oceanography, University of Washington, Seattle, WA 98195-7940, USA 4Applied Physics Laboratory, University of Washington, Seattle, WA 98105-6698, USA 5Present address: College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331-5503, USA *Corresponding author: msato@coas.oregonstate.edu ABSTRACT: Hypoxia can cause significant disturbances in aquatic ecosystems, but the impacts of moderately low dissolved oxygen (DO) where physiological tolerance levels vary among organisms and likely have consequences for key food web linkages are not well understood. We hypothesized that the greater sensitivity of fish to DO, compared with their zooplankton prey, would reduce spatial overlap between fish and zooplankton at moderately low DO (2-4 mg l-1). We used a combination of multifrequency acoustics and net samples to characterize distributions and abundances of zooplankton and pelagic fish in Hood Canal, Washington, a seasonally hypoxic fjord. We employed a sampling design that included both high and moderately low DO sites sampled prior to, during, and after the onset of seasonally low DO over 2 yr. Contrary to our hypothesis, we found that fish and their zooplankton prey did not change their horizontal or vertical distributions during periods and in locations with moderately low DO levels. Consequently, the vertical overlap between fish and zooplankton did not change with DO concentration. The apparent lack of response of fish to moderately low DO in our system may result from decreased metabolic oxygen demand due to cool temperatures, availability of prey in moderately low DO waters, increased predation risk at shallower depths, and/or phenotypic adaptations to chronic exposure. Stability in distributions of pelagic communities suggests resilience of trophic coupling to moderately low DO in Hood Canal. KEY WORDS: Hypoxia · Temperature · Hood Canal · Pacific herring · Pacific hake · Zooplankton Full text in pdf format PreviousNextCite this article as: Sato M, Horne JK, Parker-Stetter SL, Essington TE and others (2016) Impacts of moderate hypoxia on fish and zooplankton prey distributions in a coastal fjord. Mar Ecol Prog Ser 560:57-72. https://doi.org/10.3354/meps11910 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 560. Online publication date: November 24, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Extending Vulnerability Assessment to Include Life Stages Considerations.

Species are experiencing a suite of novel stressors from anthropogenic activities that have impacts at multiple scales. Vulnerability assessment is one tool to evaluate the likely impacts that these stressors pose to species so that high-vulnerability cases can be identified and prioritized for monitoring, protection, or mitigation. Commonly used semi-quantitative methods lack a framework to explicitly account for differences in exposure to stressors and organism responses across life stages. Here we propose a modification to commonly used spatial vulnerability assessment methods that includes such an approach, using ocean acidification in the California Current as an illustrative case study. Life stage considerations were included by assessing vulnerability of each life stage to ocean acidification and were used to estimate population vulnerability in two ways. We set population vulnerability equal to: (1) the maximum stage vulnerability and (2) a weighted mean across all stages, with weights calculated using Lefkovitch matrix models. Vulnerability was found to vary across life stages for the six species explored in this case study: two krill–Euphausia pacifica and Thysanoessa spinifera, pteropod–Limacina helicina, pink shrimp–Pandalus jordani, Dungeness crab–Metacarcinus magister and Pacific hake–Merluccius productus. The maximum vulnerability estimates ranged from larval to subadult and adult stages with no consistent stage having maximum vulnerability across species. Similarly, integrated vulnerability metrics varied greatly across species. A comparison showed that some species had vulnerabilities that were similar between the two metrics, while other species’ vulnerabilities varied substantially between the two metrics. These differences primarily resulted from cases where the most vulnerable stage had a low relative weight. We compare these methods and explore circumstances where each method may be appropriate.

Model-based estimates of effective sample size in stock assessment models using the Dirichlet-multinomial distribution

Theoretical considerations and applied examples suggest that stock assessments are highly sensitive to the weighting of different data sources whenever data sources conflict regarding parameter estimates. Previous iterative reweighting approaches to weighting compositional data are generally ad hoc, do not propagate uncertainty about data-weighting when calculating uncertainty intervals, and often are not re-adjusted when conducting sensitivity or retrospective analyses. We therefore incorporate the Dirichlet-multinomial distribution into Stock Synthesis, and propose it as a model-based method for estimating effective sample size. This distribution incorporates one additional parameter per fleet (with the option of mirroring its value among fleets), and we show that this parameter governs the ratio of nominal (“input”) and effective (“output”) sample size. We demonstrate this approach using data for Pacific hake, where the Dirichlet-multinomial distribution and an iterative reweighting approach previously developed by McAllister and Ianelli (1997) give similar results. We also use simulation testing to explore the estimation properties of this new estimator, and show that it provides approximately unbiased estimates of variance inflation when compositional samples capture clusters of individuals with similar ages/lengths. We conclude by recommending further research to develop computationally efficient estimators of effective sample size that are based on alternative, a priori consideration of sampling theory and population biology.

Meta-analysis in zooarchaeology expands perspectives on Indigenous fisheries of the Northwest Coast of North America

Fisheries are of fundamental importance to Indigenous peoples of the Pacific Northwest of North America today and in the past but few archaeological analyses have documented geographic patterning in fisheries across the entire region. This paper adopts meta-analysis methods and GIS-based spatial visualizations to survey the single largest compilation of fine-screened zooarchaeological fisheries data reported to date, including 513,605 fish remains identified at 222 sites from Oregon to southeast Alaska. These systematically collected zooarchaeological data indicate the most ubiquitous and proportionally abundant fish taxa over the late Holocene and reveal previously undocumented spatial patterning, indicating where certain fish taxa are consistently found in high relative proportions. Rather than seeking to evaluate chronological and/or evolutionary change, this study explores the environmental and cultural basis for assessing variability in Indigenous fisheries over millennial time scales. Specifically, we observe Pacific herring and the Pacific salmons to be the two most ubiquitous and proportionally abundant fish taxa across the Northwest Coast followed by flatfishes, sculpins, rockfishes, greenlings, dogfish, and a host of other poorly known taxa that represent consistent fishing effort. We document geographic patterning in the abundance and ubiquity of a range of fish including greater abundance of salmons in northern portions of the study area and outline trends that could represent biogeographic ranges for northern anchovy, Pacific hake, and pollock, among others. We conclude that examining patterning in the ubiquity and rank-order abundance represented by archaeological fisheries data offers significant potential for linking regionally distinct cultural practices noted in the 18th and 19th centuries to much longer human and ecological histories over the Holocene.

White fish authentication by COIBar-RFLP: Toward a common strategy for the rapid identification of species in convenience seafood

The global trade and the increased demand for seafood products have encouraged the common practice of replacement of valuable species with species of lower value worldwide. The species of the genus Merluccius are often subject to fraudulent substitution due to their high commercial interest. The present investigation of labeling accuracy on 54 samples taken from 20 convenience seafood products collected from Southern Italy markets, allowed the identification of four species through DNA barcoding: Gadus chalcogrammus, Merluccius merluccius, Merluccius productus and Merluccius paradoxus. Mislabeling was observed in seven of 20 (35%) products (frozen breaded steaks and fish fingers), six of which (30%) were labeled as hake (M. merluccius). To reduce analysis time of fish species authentication, a COIBar-RFLP, using DNA barcoding in combination with PCR-RFLP methods, was performed for species discrimination. The restriction enzyme HinfI yielded differential digestion patterns suitable for unveiling inconsistencies between product labels and genetic species identification. The COIBar-RFLP represents an effective tool for fish authentication in convenience seafood and responds to the emerging interest in molecular identification technologies that reduce processing time and eliminate the need for lab-based DNA sequencing.

Model‐based inference for estimating shifts in species distribution, area occupied and centre of gravity

Summary Changing climate is already impacting the spatial distribution of many taxa, including bees, plants, birds, butterflies and fishes. A common goal is to detect range shifts in response to climate change, including changes in the centre of the population's distribution (the centre of gravity, COG), population boundaries and area occupied. Conventional estimators, such as the abundance‐weighted average (AWA) estimator for COG, confound range shifts with changes in the spatial distribution of available survey data and may be biased when the distribution of survey data shifts over time. AWA also does not estimate the standard error of COG in individual years and cannot incorporate data from multiple survey designs. To explicitly account for changes in the spatial distribution of survey effort, we propose an alternative species distribution function (SDF) estimator. The SDF approach involves calculating distribution metrics, including COG, population boundary and area occupied, directly from the predicted species distribution or density function. We illustrate the SDF approach using a spatiotemporal model that is available as an r package. Using simulated data, we confirm that the SDF substantially decreases bias in COG estimates relative to the AWA estimator. We then illustrate the method by analysing data from two data sets spanning 1977–2013 for 18 marine fishes along the U.S. West Coast. In our case study, the SDF estimator shows significant northward shifts for six of 18 species (with southward shifts for only 2), where two species (darkblotched and greenstriped rockfishes) have both a northward shift and a decreased area occupied. Pelagic species (e.g. Pacific hake and spiny dogfish) have more variable distribution than bottom‐associated species. We also find substantial differences between AWA and SDF estimates of COG that are likely caused by shifts in sampling distribution (which affect the AWA but not the SDF estimator). We caution that common estimators for range shift can yield inappropriate inference whenever sampling designs have shifted over time. We conclude by suggesting further improvements in model‐based approaches to analysing climate impacts, including methods addressing the impact of local and regional temperature changes on species distribution.

Application of acoustic technologies to study the temporal and spatial distributions of the Pacific hake (Merluccius productus) in the California Current System

Advances in acoustics technologies offer a remote and non-invasive sensing means to conduct fisheries acoustic surveys. Over the past two decades, joint US and Canada acoustic and trawl surveys on Pacific hake (Merluccius productus), one of the most important commercial fisheries off the West Coasts of the United States and Canada, have been conducted at the intervals of one to three years within the California Current System (CCS). In this presentation, the temporal and spatial distributions of Pacific hake resulting from these surveys spanning a period of nearly two decades will be presented. Challenges in converting the measured acoustic quantities to biological quantities, such as abundance and biomass, will be addressed, including uncertainties associated with mixed species, environmental parameters, and properties in fish morphology and anatomy. Issues related to transitions from single-species to ecosystem-based acoustic surveys will also be discussed.

Techniques for improving estimates of maturity ogives in groundfish using double-reads and measurement error models

The reproductive output of a population depends upon physiological factors, including maturation rates and fecundity -at-size and -at-age, as well as the rate at which post-maturation females fail to spawn (i.e. skipped spawning). These rates are increasingly included in stock assessment models, and are thought to change over time due to harvest and environmental factors. Thus, it is important to accurately estimate maturation and skipped spawning rates while also including information on imprecision. For this task, we developed a new double-read and measurement-error modeling protocol for estimating maturity that is based on the use of multiple histological reads of ovaries to account for reader error caused by poorly prepared slides, nuclear smear, and early yolk development. Application to three U.S. West Coast groundfishes (Pacific hake Merluccius productus, darkblotched rockfish Sebastes crameri, and canary rockfish Sebastes pinniger) indicates that reader uncertainty is strongly predictive of reader error rates. Results also show differences in rates of skipped spawning among species, which should be further investigated. We recommend that future maturity studies record reader certainty, use models that incorporate covariates into the analysis, and conduct an initial double reader analysis. If readers exhibit little variation, then double reads may not be necessary. In addition, slide quality should also be recorded, so that future studies do not confuse this with reader imprecision. This improved protocol will assist in estimating life history, as well as environmental, and anthropogenic effects on maturity.

Cestodes of the blue shark, Prionace glauca (Linnaeus 1758),(Carcharhiniformes: Carcharhinidae), off the west coast of Baja California Sur, Mexico.

The cestode species recovered from the spiral intestines of 27 blue sharks (Prionace glauca) (Linnaeus, 1758) are reported from the western coast of Baja California Sur (BCS). The sampling was undertaken on a monthly basis from January 2003 to January 2004. The helminthological examination indicated the presence of four species of cestodes: Platybothrium auriculatum Yamaguti, 1952; Prosobothrium japonicum Yamaguti, 1934; Anthobothrium caseyi (Yamaguti, 1934) Ruhnke & Caira, 2009; and Paraorygmatobothrium prionacis (Yamaguti, 1934) Ruhnke, 1994. Of all the 27 sharks examined, 88.8% were infected with at least one cestode species. The most frequent species was P. auriculatum infecting 85% of the spiral intestines examined. In contrast the species with the highest mean intensity was P. prionacis (80.4 200). The species richness of cestodes in P. glauca is very similar in other regions of the world despite its wide distribution; however, this richness is low compared with other species of sharks within the same family. The feeding and host-specific are important factors that influence the parameters of infection of cestodes in this shark. On the west coast of BCS, Prionace glauca feeds mainly on red crab Pleuroncodes planipes Stimpson, 1860; squids Gonatus californiensis Young, 1972, Ancistrocheirus lesueurii (D'Orbigny, 1842), Haliphron atlanticus Steenstrup, 1861, and low proportion of fish teleosts as Merluccius productus (Ayres, 1855), Sardinops sp. Hubbs, 1929 and Scomber japonicus Houttuyn, 1872. We speculate that these prey could be involved as the second intermediate hosts of these cestodes, as in other members of these genera, although the life cycles of none are known.

Effects of Sustainable Diets containing Fish-Trim Waste, on Growth Performance of Juvenile Sablefish (Anopoploma fimbria)

A feeding trial was conducted to investigate the use of alternative fish feeds produced from fish-trim waste in high plant protein diets for juvenile sablefish (Anopoploma fimbria). Fish meal in the control diet (CD) was replaced in the experimental diets by low molecular weight hydrolysate (LMWH) protein derived from Pacific whiting (Merluccius productus) processing waste, or by Atlantic salmon (Salmo salar) processing trim (ST), which was incorporated into the feed with an experimental heated ball mill. The feeding trial was conducted in an indoor recirculating seawater system and each feed was randomly assigned to triplicate groups of 50 fish (average initial body weight of 57.5 g). The results showed that compared to the control diet, the diets containing LMWH or ST significantly increased feed consumption and fish weight gain. The ST group showed a significantly higher weight gain than the LMWH group. The ST feed, but not the LMWH feed, had a significantly lower feed conversion ratio than the CD feed. The ST feed increased lipid retention efficiency and lipid content in whole body tissue. These results demonstrate that salmon fish trim waste and enzyme hydrolyzed whiting trim in high plant protein diets can increase the performance in sablefish.

A comparison of spring larval fish assemblages in the Strait of Georgia (British Columbia, Canada) between the early 1980s and late 2000s

The concentration and composition of the larval fish assemblage in the Strait of Georgia (British Columbia, Canada) has changed between the early 1980s (1980 and 1981) and the late 2000s (2007, 2009 and 2010). During both periods, the spring larval fish assemblages were dominated by pelagic species: Clupea pallasi (Pacific herring), Merluccius productus (Pacific hake), Leuroglossus schmidti (northern smoothtongue) and Theragra chalcogramma (walleye Pollock). The average concentration of Merluccius productus, Theragra chalcogramma, Leuroglossus schmidti, and Sebastes spp. declined between the early 1980s and the late 2000s; in contrast, the absolute concentration and proportion of Pleuronectidae and several demersal fish taxa increased in the spring larval assemblage. Examination of the associations between larval fish assemblages and environmental fluctuations suggests that large-scale climate processes are potential contributors to variations in overall larval concentrations of the dominant taxa and assemblage composition in the Strait of Georgia.

Microsatellite DNA analysis of Pacific hake Merluccius productus population structure in the Salish Sea

AbstractThis study presents the first microsatellite DNA study of population structure of Pacific hake, Merluccius productus (also known as Pacific whiting) within the Salish Sea, which has been identified as a distinct population segment under the US Endangered Species Act and is currently listed as a federal Species of Concern. In contrast, a separate coastal stock component of Pacific hake represents the most abundant commercial groundfish species on the US West Coast. We surveyed variation at 10 microsatellite DNA loci in a total of 655 individuals from three Salish Sea locations (Port Susan (PTS) and Dabob Bay in Washington and south-central Strait of Georgia (SOG) in British Columbia), three coastal locations (two off southern California and one in the Gulf of Alaska), and the Northern Gulf of California (GOC), México. No significant differences were detected among temporal samples from both PTS and SOG locations. Multilocus measures of population subdivision between coastal and Salish Sea populations (all pairwise FST ≥ 0.03) and between PTS and SOG populations (FST ≥ 0.01) suggest a moderate degree of demographic isolation among these spawning populations. No significant genetic differences were found among the three coastal Pacific hake samples; however, Pacific hake from the GOC were significantly differentiated from both coastal (FST > 0.05) and Salish Sea (FST ≥ 0.03) Pacific hake. Correlations between genetic and geographic distance showed that Pacific hake display a very strong isolation by distance signal, both over the whole study area (∼4500 km; r2 = 0.94) and within the Salish Sea (∼280 km; r2 = 0.72). This study suggests that PTS and SOG populations are to some extent demographically isolated from each other.

Acoustic classification of coexisting taxa in a coastal ecosystem

Classifying coexisting taxa in a coastal ecosystem remains an analytic challenge due to the difficulty in verifying species compositions within backscatter data. Multifrequency measurements (38, 70, 120, 200kHz) were combined with midwater trawls and zooplankton MultiNet tows in Hood Canal, WA, to classify backscatter dominated by single fish species (Pacific Herring, Pacific Hake) or major zooplankton taxa (euphausiids, copepods). Backscatter was categorized into aggregations, single targets, and layers based on morphology. Aggregations and single targets were identified in raw volume backscattering strength (Sv), while layers were classified using differences in mean volume backscattering strength (ΔMVBSi-j=MVBSi – MVBSj, where i and j denote frequency in kHz). Based on a subset of trawl-validated in situ acoustic measurements, backscatter with −16dB < ΔMVBS200-38≤2dB were classified as fish, and 2dB<ΔMVBS200-38<30dB as zooplankton. Backscatter identified as fish were further classified to hake when ΔMVBS120-38<−4.8dB, and herring when ΔMVBS120-38≥−4.8dB. The classification method was evaluated using a second set of trawl-validated acoustic data, resulting in classification accuracy of fish or zooplankton ranging from 95% to 100%. At the species level, misclassifications of herring and hake were both ∼13%. Removal of aggregations and single targets before calculating ΔMVBS values minimized the possibility of mixed species backscatter within layers. This classification technique provides an approach to separate coexisting aggregations of dominant taxa which are common in mid- and low-latitude coastal ecosystems.

Forage species in predator diets: Synthesis of data from the California Current

Characterization of the diets of upper-trophic pelagic predators that consume forage species is a key ingredient in the development of ecosystem-based fishery management plans, conservation of marine predators, and ecological and economic modeling of trophic interactions. Here we present the California Current Predator Diet Database (CCPDD) for the California Current region of the Pacific Ocean over the past century, assimilating over 190 published records of predator food habits for over 100 predator species and 32 categories of forage taxa (species or groups of similar species). Literature searches targeted all predators that consumed forage species: seabirds, cetaceans, pinnipeds, bony and cartilaginous fishes, and a predatory invertebrate. Diet data were compiled into a relational database. Analysis of the CCPDD highlighted differences in predator diet data availability based on geography, time period and predator taxonomy, as well as prominent prey categories. The top 5 forage taxa with the most predators included juvenile rockfish, northern anchovy, euphausiid krill, Pacific herring and market squid. Predator species with abundant data included Pacific hake, common murre, and California sea lion. Most diet data were collected during the summer; the lack of winter data will restrict future use of the CCPDD to understand seasonal patterns in predator diet unless more such data become available. Increased synthesis of historical information can provide new resources to understand patterns in the role of forage species in predator diet. Increased publication and/or accessibility of long-term datasets and data-sharing will further foster the synthesis of information intended to inform the management, conservation and understanding of marine food webs.