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Early life history dynamics of European anchovy in the Western Mediterranean: an Individual-Based Modelling approach

by Ospina-Alvarez, Andres, PhD

Abstract (Summary)
Knowledge of the factors influencing the vertical distribution of fish early stages, and consequently influencing the transport, is a crucial issue in fisheries science. 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. Other adaptation of anchovy is the diel vertical migration pattern. The usual pattern involves displacement from shallow depths at night to greater depths during the day. We explore the underlying mechanisms generating known early life history dynamics patterns of European anchovy associated with egg-buoyancy and DVM. Subsequent, we focused on the relevance of spawners location and egg production of the anchovy stock as factors influencing the transport of eggs and larvae toward nursery areas and to provide a method to estimate the daily egg production from adult biomass obtained by mean of acoustic surveys and available fecundity data. At last, we examine the relative contribution of the inter-annual variability of spawner distribution and hydrodynamic circulation on the dispersal of European anchovy eggs and larvae. To accomplish our objectives, an IBM was applied to study how physical (e.g., ocean currents, temperature, salinity) and biological (e.g., buoyancy, growth, vertical migrations) factors affect the dynamics of ichthyoplankton using velocity, temperature and salinity fields obtained from an hydrodynamic model. It also allowed us to track virtual drifters and the ocean properties (temperature, salinity, density) encountered by virtual particles. In this study, egg-buoyancy is highlighted as an important biological characteristic that influences the egg position in the water column. Our results clearly showed that anchovy larvae migrating between different depths are subjected to different currents and thus their Lagrangian trajectories change. We have shown that physical events that alter the strength or position of the jet, such as changes in sub-basin scale climatic patterns, changes in the frequency of zonal winds, increases in surface temperature or modification in deep Mediterranean water formation might therefore affect the area prone to yield pre- recruits, and therefore affect regional fisheries. We demonstrate that spatial paths dramatically differ in some years. The results are compatible with an explanation based on the inter-annual variability of the spawning distribution and ocean circulation, ruling out factors such as temperature or salinity at the spawning time.
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Bibliographical Information:

Advisor:Isabel Palomera, Ignasi Catalan

School:Universitat de Barcelona

School Location:Spain

Source Type:Doctoral Dissertation

Keywords:Anchovy, early-stages, anchovy, Mediterranean, Individual Based Model, IBM, Spatial, Ecology, Connectivity, eggs, larvae, dispersion, transport

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Date of Publication:12/14/2012

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