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Morales C.E.,Center for Oceanographic Research in the Eastern South Pacific | Morales C.E.,University of Concepcion | Loreto Torreblanca M.,Center for Oceanographic Research in the Eastern South Pacific | Hormazabal S.,UdeC | And 3 more authors.
Progress in Oceanography

In the Humboldt Current System, the region off central-southern Chile has relatively high eddy kinetic energy, generating an extensive coastal transition zone (∼600 km offshore) in which coastally derived eddies are recurrent features. This energy might promote strong exchanges of water, biogeochemical properties, and plankton between the coastal upwelling band and the adjacent oceanic zone. In this study, the mesoscale structure of epipelagic copepod assemblages and its relationship to environmental variability and the eddy field in the coastal transition zone and oceanic areas off Concepción (34-39°S, 73-84°W) were investigated. Zooplankton samples were collected during cruises of opportunity carried out during the 2006 coastal upwelling season and the oceanographic conditions were derived from satellite data on sea surface height, temperature, and chlorophyll a. The use of cluster analyses and indicator species revealed two main copepod assemblages: (i) species with a mainly coastal distribution, the maximum in total abundance being found nearshore and (ii) species with a mainly oceanic distribution (beyond ∼500 km from the coast), where a secondary maximum was observed. Both types of assemblages, however, included species widely distributed in the coastal transition zone. An ordination analysis identified sea surface temperature and chlorophyll a as the main factors affecting the distribution of most species and the clustering of stations resembled the distribution of these variables. Some of the large calanoid species that are common in shelf waters were more abundant within nearshore eddies rich in chlorophyll a and other cyclonic eddies far offshore; however, the eddy field alone did not explain the copepod mesoscale distribution. Altogether, the wide distribution of shelf/slope copepod species in this region suggests that physical and biological mechanisms might be acting to extend the productive area of the coastal upwelling zone. © 2009 Elsevier Ltd. All rights reserved. Source

Parada C.,University of Concepcion | Parada C.,Institute Investigacion Pesquera INPESCA | Armstrong D.A.,University of Washington | Ernst B.,University of Concepcion | And 2 more authors.
Bulletin of Marine Science

Landings of the snow crab Chionoecetes opilio (J. C. Fabricius, 1788), which supports a lucrative fishery in the eastern Bering Sea (EBS), dropped to historical lows by 2000, and the geographic range of reproductive females contracted to the northwest. Resilience of the mature female range through larval advection may be hampered because hatching now occurs downstream. These changes have been punctuated by four pulses of recruitment, with a remarkably regular period of 6-7 yrs. Major pulses of the fishery, during the 1990s, were sustained by recruitment pulses that originated in regions of the northwest section of the EBS shelf beyond the reach of the fishery. Here we present, for the first time, a conceptual model of snow-crab spatial dynamics that integrates empirical information with new results from modeling of circulation and larval transport. The geographic region of interest, defined by means of biophysical modeling and tracking ontogenetic migrations, consists of the middle and outer domains of the EBS shelf, bounded by the 50-and 200-m isobaths. Connectivity analysis highlights the significance of subsystems in the southeast and northwest sections of the EBS's middle domain. Predicted settlement regions match historical regions of abundance of immature crabs and are consistent with observed fields of suitable near-bottom temperature. Our study, together with others, highlights the significance of climate change for the fate of important highlatitude fisheries. © 2010 Rosenstiel School of Marine and Atmospheric Science of the University of Miami. Source

Ospina-alvarez A.,CSIC - Institute of Marine Sciences | Palomera I.,CSIC - Institute of Marine Sciences | Parada C.,Institute Investigacion Pesquera INPESCA
Fisheries Research

Small pelagic fish populations exhibit reproductive strategies resulting from past natural selection pressure, by which certain traits become more or less common in a population, allowing them to adapt and become better suited to certain habitats. One such adaptation is the buoyancy of eggs, which is observed as density changes during development. This is an important issue in fisheries and modeling science, as it affects the vertical distribution of eggs and, therefore, egg transport. Recently, individual-based models for anchovies in the Mediterranean have focused on developing adequate biological algorithms to simulate realistic spatial variations of eggs and larvae. Some models that include movements of particles according to Stokes' law also assume a constant value of egg density during egg development. However, field observations show differences in the vertical distribution of eggs when egg density during development is considered. We address the problem of egg density and its vertical distribution within a biological context. In Mediterranean waters, the incubation time for anchovy eggs during peak spawning is approximately 48-70. h; during these first hours, egg density has an influence on the horizontal and vertical trajectories of eggs, as well as their routes and hatching zones. In this study, we introduce an algorithm describing the egg density of European anchovy eggs throughout development. Egg density measurements were carried out in a density gradient column (DGC). We fitted a polynomial model that estimated egg density, as a function of time from fertilization and that was dependent on temperature. Simulations to study the vertical transport of eggs in the Mediterranean were carried out using ICHTHYOP/MARS3D. The vertical distribution of pelagic eggs was determined by a set of interacting biological and physical parameters related to eggs (density, diameter) and ambient seawater (density, viscosity, turbulence), respectively. The egg buoyancy model introduced here was validated and will provide insight for the design of anchovy egg surveys, as the vertical position of the eggs in the water column during development can be inferred by the hydrographic structure of seawater. © 2011 Elsevier B.V. Source

Ospina-Alvarez A.,CSIC - Institute of Marine Sciences | Parada C.,Institute Investigacion Pesquera INPESCA | Palomera I.,CSIC - Institute of Marine Sciences
Ecological Modelling

Recruitment of European anchovy has been traditionally thought to largely depend on the passive transport and dispersion of eggs and larvae from spawning to nursery areas. Knowledge of the factors influencing the vertical distribution of fish early stages, and consequently influencing the transport, is a crucial issue in fisheries science. The aim of this study is to assess the relevance of diel vertical migration (DVM) as a mechanism involved in the transport of European anchovy larvae toward nursery areas taking into account age/stage-dependent vertical migration (i.e., the maximum migration). We developed a simplified vertical migration sub-model for anchovy larvae included in an Individual-based (IBM) hydrodynamic coupled model. Two types of simulation experiments were conducted: (1) 'Pure' Lagrangian (passive) transport experiments and (2) biological behavior transport experiments with a realistic scheme for egg-buoyancy, larval growth, and DVM scheme. We detected high variability in the trajectory and final position of larvae with 14. mm length between the passive and biological behavior experiments. The particles were less clustered in the passive transport experiment. In the biological experiment the particles were aggregated depending on the mesoscale oceanographic structures, evidencing a transport associated to filaments and meanders. The formation of schools was facilitated by the transport in filaments and larvae transported within filaments generally avoided the nucleus of the eddies and the central part of the North Current. Moreover, our results suggest that there is interconnectivity between all the anchovy sub-populations in the NW Mediterranean and that the Gulf of Lions and the shelf waters surrounding the Ebro River Delta are the most important areas for anchovy reproduction in this region. Additionally, we detected that the pre-recruitment is higher in those years when the larvae retention is favored. We underline that bottlenecks in larval transport modeling are related to the scarcity of knowledge in developmental biology and behavior of anchovy larvae and emergent mechanistic processes. © 2012 Elsevier B.V. Source

Parada C.,Institute Investigacion Pesquera INPESCA | Parada C.,University of Concepcion | Colas F.,University of California at Los Angeles | Colas F.,University Pierre and Marie Curie | And 2 more authors.
Progress in Oceanography

An individual-based model (IBM) of anchoveta (Engraulis ringens) larvae was coupled to a climatological hydrodynamic (Regional Oceanic Modeling System, ROMS) model for central-southern Chile to answer the question as to whether or not across- and alongshore transport off central-southern Chile enhances retention in the spawning areas during the winter and summer reproductive periods, using model-based pre-recruitment indices (simulated transport success to nursery areas). The hydrodynamic model validation showed that ROMS captures the mean Seas Surface Temperature and Eddie Kinetic Energy observed in satellite-based data over the entire region. The IBM was used to simulate the transport of eggs and larvae from spawning zones in central Chile (Constitución, Dichato, Gulf of Arauco and Lebu-Corral) to historical nursery areas (HRZ, region between 35°S and 37°S). Model results corroborated HRZ as the most successful pre-recruitment zone (particles originated in the Dichato and Gulf of Arauco spawning areas), as well as identifying Lebu-Corral as a zone of high retention with a high associated pre-recruitment index (particles originated in the Lebu-Corral spawning zone). The highest pre-recruitment values were mainly found in winter. The Constitución and Dichato spawning zones displayed a typical summer upwelling velocity pattern, while the Gulf of Arauco in summertime showed strong offshore and alongshore velocity components. The Lebu-Corral region in winter presented important near-surface cross-shore transport towards the coast (associated with downwelling events), this might be one of the major mechanisms leading to high retention levels and a high pre-recruitment index for Lebu-Corral spawning zone. The limitations of the modeling approach are discussed and put into perspective for future work. © 2011 Elsevier Ltd. Source

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