Pacific Hake Merluccius Productus Research Articles

Population genomics of coastal Pacific Hake

AbstractObjectiveUnderstanding the genetic structure of harvested fishery species is crucial for accurate stock assessments and effective management strategies. There have been several rangewide population genetic analyses of Pacific Hake Merluccius productus; however, a thorough focus on the heavily harvested coastal stock off the west coast of North America is missing. Recent observations of spatial–temporal variability in life history and migratory patterns of the coastal population have brought into question whether this variation may be related to genetic differentiation.MethodsHere, we used restriction site‐associated DNA sequencing markers to thoroughly assess the potential for spatial–temporal genetic differentiation in the coastal stock of Pacific Hake. We sampled during different seasons from British Columbia down to the U.S.–Mexico border over multiple years on what traditionally have been thought to constitute spawning and feeding grounds, resulting in the most comprehensive assessment of coastal Pacific Hake population structure to date.ResultGenerally, our results suggest very weak to no structure among coastal spatial–temporal sites and corroborate previous findings of strong differentiation between coastal and Salish Sea populations. The lack of structure among coastal sites is likely due to significant amounts of gene flow in this highly migratory population.ConclusionThese findings align with the ongoing management strategy for coastal Pacific Hake, which is based on an annual stock assessment that considers the coastal stock homogenous and distinct from the Salish Sea population. The understanding that management units indeed match genetic populations provides managers with additional confidence in existing management strategy.

Pacific Lamprey and Western River Lamprey marine ecology: Insight from new ocean collections

AbstractObjectiveLittle is known about the marine ecology of anadromous Pacific Lamprey Entosphenus tridentatus and Western River Lamprey Lampetra ayresii. This information is needed to determine how marine life regulates adult abundances and to identify management actions that may benefit declining populations.MethodsTo address this deficit, we compiled historic data, collected lamprey from marine stock assessment surveys and commercial fisheries, and documented fish with Pacific Lamprey wounds.ResultPacific Lamprey were most commonly caught by midwater trawls targeting Pacific Hake Merluccius productus along the continental shelf break from northern California to northern Washington. Pacific Lamprey ranged in size from 115 mm total length (TL) and 2.9 g to 714 mm TL and 655 g (n = 1912) and were expected to represent multiple ocean ages. The vast majority (93%) of Pacific Lamprey were small (≤300 mm TL) and thus were likely in their first year in marine waters. Growth for small Pacific Lamprey was estimated as 0.37 mm/day and 0.13 g/day over the summer. Gut fullness for Pacific Lamprey was high (5.5% of body weight [BW]), but it was highly variable for larger individuals (range = 0–55% BW). Our results suggest that there is a positive relationship between calendar day and lamprey length and condition factor in most years, while the effect of latitude varies by life stage. We documented Pacific Lamprey wounds on 240 individual fish representing 16 species, of which six species are newly identified as lamprey hosts. We had comparably few records for Western River Lamprey (n = 72; mean length = 285.5 mm TL), which were primarily found in surface waters on the continental shelf from northern California to southern British Columbia.ConclusionOur results have implications for both fisheries and conservation management, including development of best practices for lamprey caught by net fisheries and the use of new marine information to inform conservation actions.

Reconstructing trophic position over the past century for five Puget Sound fish species

The comparison of historical and modern food web dynamics allows ecologists to test whether the trophic connectivity we observe today is ‘normal’ in its historical context. Fish densities and abundances have changed across time, making it likely that fish trophic interactions and their trophic positions have also changed. Historical trophic data of marine fishes can now be extracted from the tissues of fluid-preserved specimens held in natural history collections via compound-specific stable isotope analysis of amino acids (CSIA-AA) of nitrogen. We conducted CSIA-AA to quantify trophic position change over the past century in 5 ecologically important fishes of Puget Sound, Washington, USA: Pacific hake Merluccius productus, walleye pollock Gadus chalcogrammus, copper rockfish Sebastes caurinus, English sole Parophrys vetulus, and Pacific herring Clupea pallasii, and examined the canonical trophic (glutamic acid) and source (phenylalanine) amino acids. For all fishes except copper rockfish, trophic position, glutamic acid, and phenylalanine values remained similar across time. For copper rockfish, glutamic acid but not phenylalanine values increased over time, indicating an increase in this species’ trophic position. The observed increase in copper rockfish trophic position may be a function of diet switching and declining prey quality rather than a consequence of rockfish consuming higher trophic level prey. This study leverages more than 100 yr of trophic data of fishes representing various feeding guilds and demonstrates that some fish species may be more trophically resilient to major environmental change than expected. Efforts should be made to identify and conserve the trophic interactions of species experiencing change.

Trophoscapes of predatory fish reveal biogeographic structuring of spatial dietary overlap and inform fisheries bycatch patterns

Trophic interactions are proximate drivers of ecosystem function, including predator-prey dynamics, and their spatio-temporal variability may reflect ecosystem shifts and changes in trophic transfer. We investigated biogeographic structuring of trophic interactions by analyzing multi-decadal time series of diet for Pacific hake Merluccius productus and Chinook salmon Oncorhynchus tshawytscha from a large marine ecosystem. We compared our predictions for spatio-temporal variability of hake and salmon trophoscapes (i.e. spatially explicit predictions of trophic relationships) to inform ecosystem dynamics and fishery bycatch patterns. We have 3 inter-related findings pertaining to the spatial coherence of the trophoscapes and the potential consequences to juvenile and sub-adult (i.e. after the first year at sea but prior to maturation) salmon when sharing foraging areas with Pacific hake. First, the spatial scale of Pacific hake diet represents coastwide variability, and the spatial variability of Chinook salmon diets differs across regions and demonstrates a broad diet. Second, the expectation for increased diet and spatial overlap of Pacific hake and Chinook salmon during low productivity periods (e.g. periods with low krill biomass, suboptimal upwelling) can inform fishery management challenges. In this regard, we explore the role of shared foraging habitats on increased predation, and consequentially reduced recruitment, by Pacific hake on juvenile salmon during sub-optimal upwelling conditions. Third, we show that above-average bycatch of sub-adult Chinook salmon was associated with later spring transition, potentially as a result of both Pacific hake and salmon sharing foraging areas and prey species on the shelf and shelf break.

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.

Spatio-temporal patterns in juvenile habitat for 13 groundfishes in the California Current Ecosystem.

Identifying juvenile habitats is critical for understanding a species’ ecology and for focusing spatial fishery management by defining references like essential fish habitat (EFH). Here, we used vector autoregressive spatio-temporal models (VAST) to delineate spatial and temporal patterns in juvenile density for 13 commercially important species of groundfishes off the US west coast. In particular, we identified hotspots with high juvenile density. Three qualitative patterns of distribution and abundance emerged. First, Dover sole Microstomus pacificus, Pacific grenadier Coryphaenoides acrolepis, shortspine thornyhead Sebastolobus alascanus, and splitnose rockfish Sebastes diploproa had distinct, spatially-limited hotspots that were spatially consistent through time. Next, Pacific hake Merluccius productus and darkblotched rockfish Sebastes crameri had distinct, spatially limited hotspots, but the location of these hotspots varied through time. Finally, arrowtooth flounder Atheresthes stomias, English sole Parophrys vetulus, sablefish Anoplopoma fimbria, Pacific grenadier Coryphaenoides acrolepis, lingcod Ophiodon elongatus, longspine thornyhead Sebastolobus altivelis, petrale sole Eopsetta jordani, and Pacific sanddab Citharichthys sordidus had large hotspots that spanned a broad latitudinal range. These habitats represent potential, if not likely, nursery areas, the location of which will inform spatial management.

Effects on the bycatch of eulachon and juvenile groundfish by altering the level of artificial illumination along an ocean shrimp trawl fishing line

Abstract We examined how catches of ocean shrimp (Pandalus jordani), eulachon (Thaleichthys pacificus), and juvenile groundfish could be affected by altering the level of artificial illumination along the fishing line of an ocean shrimp trawl. In the ocean shrimp trawl fishery, catches of eulachon are of special concern, as the species’ southern Distinct Population Segment is listed as “threatened” under the US Endangered Species Act. Using a double-rigged trawl vessel, with one trawl illuminated and the other unilluminated, we compared the catch efficiencies for ocean shrimp, eulachon, and juvenile groundfish between an unilluminated trawl and trawls illuminated with 5, 10, and 20 LED fishing lights along their fishing line. The addition of artificial illumination along the trawl fishing line significantly affected the average catch efficiency for eulachon, rockfish (Sebastes spp.), and flatfish, with the three LED configurations each catching significantly fewer individuals than the unilluminated trawl without impacting ocean shrimp catches. For Pacific hake (Merluccius productus), the ten LED-configured trawl caught significantly more fish than the unilluminated trawl. For the five and 20 LED configurations, mean Pacific hake catches did not differ from the unilluminated trawl. This study contributes new data on how artificial illumination can affect eulachon catches (and other fish) and contribute to their conservation.

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.

Role of oceanography in shaping the genetic structure in the North Pacific hake Merluccius productus.

Determining the relative influence of biotic and abiotic factors on genetic connectivity among populations remains a major challenge in evolutionary biology and in the management and conservation of species. North Pacific hake (Merluccius productus) inhabits upwelling regions in the California Current ecosystem from the Gulf of California to the Gulf of Alaska. In this study, we examined mitochondrial DNA (mtDNA) and microsatellite variation to estimate levels of genetic differentiation of M. productus in relation to the role of oceanographic features as potential barriers to gene flow. Samples were obtained from nine sites spanning a large part of the geographic range of the species, from Puget Sound, Washington to Costa Rica. The microsatellite results revealed three genetically discrete populations: one spanning the eastern Pacific coast, and two apparently resident populations circumscribed to the Puget Sound and the northern Gulf of California (FST = 0.032, p = 0.036). Cytochrome b sequence data indicated that isolation between the Puget Sound and northern Gulf of California populations from the coastal Pacific were recent phenomena (18.5 kyr for Puget Sound and 40 kyr for the northern Gulf of California). Oceanographic data obtained from the Gulf of California support the hypothesis that permanent fronts within the region, and strong gradients at the entrance to the Gulf of California act as barriers to gene flow. A seascape genetics approach found significant genetic–environment associations, where the daytime sea surface temperature and chlorophyll concentrations were the best predictive variables for the observed genetic differentiation. Considering the potential causes of genetic isolation among the three populations, e.g. spawning areas in different latitudes associated with upwelling processes, oceanographic barriers, asymmetric migration and specialized diet, oceanographic barriers appear to be a likely mechanism restricting gene flow.

Morphological and molecular characterisation of Aporocotyle margolisi Smith, 1967 (Digenea: Aporocotylidae) from the North Pacific hake Merluccius productus (Ayres) (Gadiformes: Merlucciidae) off Oregon, USA.

Aporocotylid blood flukes conspecific with Aporocotyle margolisi Smith, 1967 were collected from the bulbus arteriosus of the North Pacific hake Merluccius productus (Ayres). This study revisits the morphology of A. margolisi, including drawings, measurements and scanning electron microscopy images, and provides for the first time molecular data for the large subunit of the ribosomal RNA (28S rDNA) and the mitochondrial cytochrome c oxidase subunit 1 (cox1) genes for this species. A 28S rDNA phylogenetic study of A. margolisi, and all available Aporocotyle spp., was also performed. The distribution range of A. margolisi is extended to the Pacific coast of the USA. We provide a morphological comparison of Aporocotyle spp. from the Pacific coast in North America as well as other Aporocotyle spp. infecting hake. Comparisons with the original description revealed that the new specimens of A. margolisi were considerably larger with respect to all morphological features, except for shorter spines. Molecular results showed a close relationship between A. margolisi and A. argentinensis Smith, 1969 from the Argentine hake Merluccius hubbsi Marini. The phylogenetic relationships of Aporocotyle spp. point to a possible co-speciation of hakes species and these blood fluke parasites.

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

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.

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.

Relationships between the Abundance of Pacific Lamprey in the Columbia River and Their Common Hosts in the Marine Environment

AbstractThe returns of Pacific Lamprey Entosphenus tridentatus to the Columbia River over the past decade have declined significantly compared with the peak returns of the 1950s and 1960s, with no quantifiable mechanisms identified. To determine if the abundance of documented host species in the marine environment is related to adult returns of Pacific Lamprey, we examined stock assessment data, commercial fishery statistics, and counts of adult fish at Bonneville Dam between 1997 and 2010. Significant positive correlations were observed between lamprey returns and abundance indices of Pacific Hake Merluccius productus, Walleye Pollock Theragra chalcogramma, Pacific Cod Gadus macrocephalus, Chinook Salmon Oncorhynchus tshawytscha, and Pacific Herring Clupea pallasii throughout the U.S. Pacific Northwest. Commercial landings of these species in Washington and Oregon were also significantly and strongly correlated to lamprey returns, with the exception of Walleye Pollock. Several of these fisheries have demonstrated significant reductions in mean landings since the 1950s and 1960s, and adult lamprey returns have declined proportionally. We further examined large‐scale and regional indices of oceanic productivity as a potential underlying mechanism. Multiple regression techniques indicated that host abundance was the principal factor in predicting lamprey returns, though inclusion of oceanic conditions increased the precision of the model. These results represent the first established relationship to recent trends of Pacific Lamprey returns to the Columbia River and indicate that spawning escapement is primarily a function of conditions experienced during the predatory phase of the life cycle. We hypothesize that Pacific Lamprey abundance in the Columbia River is cyclical in nature, but limited by availability of several host species over a potentially vast geographic range. Biologists and resource managers should reassess the relatively overlooked marine ecology of Pacific Lamprey.

Pacific hake (Merluccius productusAyres, 1855) hydrolysates as feed attractants for juvenile Chinook salmon (Oncorhynchus tshawytschaWalbaum, 1792)

Soybean meal (SBM) inclusion in salmonid diets can lower feed cost, but dramatically reduces growth and feed utilization, and increases mortality in juvenile chinook salmon Oncorhynchus tshawytscha, due to diminished diet palatability and/or other adverse physiological effects exerted by antinutritional factors in SBM. The objective of this study was to investigate whether commercial Antarctic krill meal Euphausia superba or hydrolysates enzymatically produced from Pacific hake Merluccius productus could reverse the negative palatability effects of SBM inclusion in juvenile chinook salmon diets. Diets without SBM or with SBM and no added feed attractant were used as positive and negative control diets respectively. Incorporation of 2% krill meal or Alcalase®-produced hydrolysates into SBM-containing diets (20% of dry matter by isonitrogenous replacement of fishmeal) significantly (P < 0.05) increased feed intake, feed utilization, fish weight gain and thermal growth coefficient during a 5-week trial. Nevertheless, the negative effects on fish performance incurred by dietary inclusion of 20% SBM could not be fully reversed, indicating that most of those effects were likely unrelated to palatability. This study demonstrates the potential for using Pacific hake hydrolysates as a dietary feed attractant for salmonid diets, and supports the need for further research to optimize its application for ideal fish performance.

Recent Increase in Nybelinia surmenicola Prevalence and Intensity in Pacific Hake (Merluccius productus) Off the United States West Coast

A larval marine cestode was found in 82.0% of 834 Pacific hake (Merluccius productus) stomachs collected from 341 trawl stations along the United States west coast during the summers of 2008 and 2009. Morphology and DNA sequencing was used to identify the cestode as Nybelinia surmenicola. In an examination of 131 Pacific hake stomachs collected from the same region in 1999, N. surmenicola prevalence was 35.1%. The results from a general linear model suggested that their prevalence is influenced by year and latitude, Pacific hake size, and sex. Mean intensity of N. surmenicola in 2008-2009 was 20.22 (±1.13 SE) and was positively related to Pacific hake length and the latitude of collection. Year-1 Pacific hake (<27 cm length) had significantly lower prevalence and intensity of N. surmenicola compared to older and larger fish. Pacific hake collected south of Point Conception, California (32.5 to 35°N) had lower prevalence and intensity of N. surmenicola compared to those collected in northern latitudes (35.1 to 48.4°N). Higher N. surmenicola prevalence in Pacific hake in recent years suggests food-web fluctuations in the northern California current ecosystem caused by changes in ocean transport of zooplankton or pelagic fish distributions and warrants future monitoring as a metric for ecosystem change.

Isotopic Correlation (δ18O versus δ13C) of Otoliths in Identification of Groundfish Stocks

AbstractThe management of many marine fish stocks suffers from a lack of genetic data or insignificant genetic differentiations, particularly for the commercially important groundfish along the U.S. Pacific coast. In this study, we investigated a large number of otoliths of various groundfish species from the coasts of Washington and Oregon and analyzed them for stable oxygen (18O/16O, or δ18O) and carbon isotope ratios (13C/12C, or δ13C). The isotopic results and correlation of δ18O versus δ13C of Pacific hake Merluccius productus, sablefish Anoplopoma fimbria, Pacific halibut Hippoglossus stenolepis, and Pacific cod Gadus macrocephalus indicated that most of the groundfish we examined had two or more spawning stocks or subpopulations; the only tested species that might belong to a single coastwide stock was yelloweye rockfish Sebastes ruberrimus. Compared with genetic methods of stock identification, the isotopic signatures of otoliths have distinct advantages in determining (1) a time series to separate the different life stages of marine fish and (2) the oceanographic and environmental conditions to which fish are exposed. Thus, stable isotopic signatures in otoliths appear to be an alternative for marine fish stocks when there is little genetic differentiation between populations or no genetic data are available.

Interannual distribution of Pacific hake Merluccius productus larvae in the southern part of the California Current

The interannual distribution of early life stages of Pacific hake Merluccius productus, within the southern part of the California Current (32-23 degrees N) from 1951 to 2001, was examined to describe the relationship between spawning habitat and environmental conditions. Mean annual abundance was affected by different factors along the west coast of the Baja California Peninsula. In the northern areas (Ensenada and Punta Baja), reduced abundance of larvae coincided with the El Niño and a North Pacific Ocean climatic regime shift, but in the southern areas (San Ignacio to Bahía Magdalena), the drastic reductions suggested a fishery effect for large adults of the coastal migratory population, starting in 1966. Two spawning stocks, coastal and dwarf, were evident in comparisons of latitudinal differences in occurrence of early stages and differences in temperature preferences that seemed to break at Punta Eugenia.

Trophic and fishery interactions between Pacific hake and rockfish: effect on rockfish population rebuilding times

Several species of overfished Pacific rockfish (genus Sebastes) are incidentally caught in the fishery targeting Pacific hake Merluccius productus. Juvenile rockfish also comprise a small amount of Pacific hake diets. We used 2-species, age-structured models to estimate how prey selectivity by Pacific hake, life history and population structure of rockfish, spatiotemporal overlap, and fishery closures might affect the time required to rebuild overfished rockfish populations to 40% of unfished spawning stock biomass. As prey selectivity increased, rebuilding time increased moderately for widow rockfish S. entomelas and darkblotched rockfish S. crameri, and more sharply for canary rockfish S. pinniger. Darkblotched rockfish were the least sensitive to Pacific hake predatory selectivity, which was likely related to their rarity in Pacific hake diets, not their stochastic reproductive success. Spatiotemporal overlap between rockfish and Pacific hake also increased rebuilding times, primarily because of higher rockfish bycatch, not predation. Early fishery closures and Pacific hake predation had an interactive effect that prolonged widow and canary rockfish rebuilding times, partly as a function of model assumptions and partly because fishery closures led to increased predation on juvenile rockfish. Because an ecosystem-based approach to fisheries management involves considering the influence of ecological factors on fish populations, models that examine interactions between depleted species and predatory species are essential. In this case, it appears that overfished rockfish rebuilding times can be significantly affected by the dynamics of a key predator, but also that the predatory effect can be mitigated by effective bycatch control.