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Patrones de distribución espacio-temporal de los estadíos embrionarios y larvales de la anchoita (Engraulis anchoita Hubbs & Marini) a micro y macro-escala: Su relación con la supervivencia y el reclutamiento
Ramiro Pedro Sánchez Janina Y. Dz de Ciechomski
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This dissertation is focused on the study of implications of spatial patterns on survival of eggs and larvae and subseguent recruitment of the SW Atlantic anchovy, Engraulis anchoita. The study of distribution patterns is encompassed within the conceptual framework of the analysis of reproductive strategies of marine bony fish, as adaptations that enable them to cope with and active y exploit environmental variability, regulating their abundance and avording extinction. The Southwest Atlantic anchovy, is ideally suitable for studies on reproductive biology and recruitment on a comparative basis. Its spawning and nursery grounds are located in very diverse ecosystems. This variety refers to their physico-chemical properties, carrying capacity, the influence of several water masses, and the contribution of fresh water runoffs from different origins. Important physical features are seasonal thermocline formation, and the presence of transitional regions such as oceanic, shelf-break and tidal shelf fronts, an upwelling areas. The aim of this dissertation was to study the biological response to that environmental heterogeneity. The central issue of the discussion was the implication of that apparent lack of association between reproductive activity and environmental conditions, on the rates of growth and mortality during the early developmental stages, and subsequent recruitment. As a working hypothesis we postulated the existence of some egree of dependence between those opulation attributes and the evolution of the distributional patterns during the early ontogeny. To prove this assumption we studied distributions not only in their usual connotation (i.e. spatial arrangement, geographic location),but also in their ecological and statistical sense, in a variety of time-space scales, from the Eulerian and Lagrangian perspectives. The final outcome, based on the identification of factors influencing the survival of the early developmental stages of the species, was the derivation of models that could describe mechanisms o demographrc regulation. Chapter I introduces notions which compound the theoretical basis of this dissertation. Among them are such concepts as: reproductive strategies, marine fish recruitment and population regulation, distributional patterns, time-space scales, and the comparative approach as an alternative to the experimental application of the scientific method. A synthesis on the existing information about reproductive biology and early life history of the species is included. A glossary including terms used frequent y along this dissertation has been prepared, with the aim to clarify their origin meaning and equivalencies, particularly in the case of personal translations. Chapter II contains all the basic details about the samples analyzed, with information on the time-space location of the cruises and stations, on the samplers utilized, on the sampling and laboratory techniques applied, on the statistical handling of information and data processing. The present taxonomic status of the genus Engraulis is discussed in Chapter III. Spawning and nursery grounds of all the Engraulis species are reviewed on a comparative basis. A detail analysis is presented on the current knowledge about the spawning grounds of E. anchoita in the SW Atlantic, including a seasonal composite of environmental conditions prevailing in the spawning grounds of the species of the Argentine Sea and Common Fishing Area with Uruguay. Chapter IV is devoted to the analysis of the monthly evolution of spawning patterns based on a historical data series, covering the period 1966-1989. The methodology involved includes the pooling of available information into 30’ latitude x 30’ longitude statistical rectangles. Monthly maps were constructed representing average spawning, percent incidence by rectangle, identification of reproduction nuclei and location of nursery grounds. Monthly vanation of reproductive intensity is analyzed as a function of temperature, latitude, depth, distance from shore and the abundance of zooplankton an other ichthyoplankton. Monthly regional census of egg and larvae production were calculated on the basis of monthly variations in mean productions an geographical extensions of the spawning and nursery grounds. Patterns of eggs and larvae distributions are statistically analyzed in Chapter V through the application of several indexes and ecological models to our historical data series. A simulation exercise is used to discuss the efficiency of two models for the estimation of population parameters from an increasing number of samples. Also included is a practical application resulting from the fitting of these statistical distributions is the estimation of the sampling effort required in order to detect variation in the population abundance with different degrees of precision. Some characteristics of the spatial pattern of distribution of anchovy eggs, such as patch size and aggregation are studied. A comparative analysis is presented on the ecological implications and adaptive advantages of the evolution of distributional pattern in the course of ontogeny. Growth during the anchovy early life history is the subject of Chapter VI. A model is developed for the age determination of anchovy eggs developed at four different experimental temperatures. Results are reported on the experimental growth of yolk sac larvae. The first results are presented on the daily growth of the species during the larval and post-larval stages from countings of otolith rings. Length-weight functions representing larval growth from hatching to metamorphosis were fitted. Multiple regression analysis was used to derive a model to predict larval growth from morphometric measurements. A detailed comparative analysis is presented on egg and larval growth of related species. Chapter VII deals with mortality during the anchovy early life stages. Major causes or embryonic and larval in marine fish are analyzed. The methodology for the calculation of field estimates of egg and larval mortality is developed. Results are presented on the embryonic mortality during the spring spawning peak on the continental shelf off Buenos Aires Province during the period 1967-1970. Planktonic eggs were grouped into age classes following the methods developed in the previous chapter. The weighted negative binomial distribution was applied for the calculation of larval length class frequencies, covering the period 1973-1989. Instantaneous estimates of egg and larval mortality were obtained applying a model of constant exponential extinction. A detailed analysis is presented on the procedure followed for the calculation of weighting factors for sampler efficiency, mesh selectivity and diurnal avoidance, and corrections for pre and post-mortem larval shrinkage and for the variable duration of each size class. The validity of exponential extinction curves to model early ontogeny mortality by means of log-linear and non-linear fitting procedures is discussed. An attempt to estimate embryonic and larval mortality by Eulerian re-sampling of a plankton patch is reported. Based on the concept of saltatory ontogeny the pre-metamorphic phase was divided into four developmental stages, modeling the evolution of instantaneous mortality estimates through that phase by means of the Weibull function. A detailed comparative analysis is presented on egg and larval mortality of related species. Chapter VIII is devoted to the study of reproductive strategies of marine fish from an analysis of spawning behaviour of the anchovy under variable environmental conditions. Chronologically arranged maps with the distribution of eggs, larvae and atitudinal changes in larval size frequency distributions are reported. Seasonal variations of early life history stages vertical distribution, in both regions, are analyzed. Current knowledge on hydrographical structures and Circulation over the continental shelf and slope is use to infer the final fate larvae at metamorphosis. Based on a comparative analysis of embryonic and larval growth and mortality, larval feeding activity and condition and reproductive parameters a discussion is presented on the potential of the two areas as spawning and nursery grounds. Research detailed in Chapter IX is based on a survey designed to reduce the time-space observational scales and to alter of perspective in the study of egg and larval pattern and survival. Lagrangian changes in distribution and survival within an anchovy egg and larvae patch were studied by means of multiple opening/closing sampling following a free drifting buoy. The drifter was launched on the Buenos Aires continental shelf, off Necochea during the spring spawning peak of 1983. Three discrete depths (within, below and above the thermocline) were repeatedly sampled close to the drogue were monitored at 3/4 hour intervals for a period of three days. The efficiency of the drogue as a Lagrangian marker was examined by means of the application of multifactorial ANOVA to test the significance of variability between days, light regime, sampling depths, population structure and their interactions. Wind drag on the surface unit did not significantly affect the trajectory of the drogue. Patterns of embryonic and larval vertical distribution are discussed by means of the variations in the centre of mass, in the vertical dispersion and patchiness indexes for each developmental stage analyzed. There is evidence of diel bvertical migration in larvae larger than 8 mm SL. Although the incidence of feeding based on observations of the presence of undigested food in the gut content of larvae was low, a daily feeding pattern over a l4-hour period starting after sunrise, was evident. Evening ascent of larger larvae was not related to feeding activity. a single equation two-stage model, assuming age dependent mortality in the embryonic and post- larval period is derived and compared to standard models based on constant exponential decay during each developmental phase. The concepts of recruitment, demographic regulation, reproductive strategies and saltatory ontogeny are revisited in Chapter X, with the aim to develop a stock-recruitment model for the anchovy. A review is presented of the derivation of the main schools of thought and current knowledge on the causes of abundance fluctuations in marine fish populations. The stages where recruitment is controlled were evaluated by means of the elaboration of a life-table using empirical or reasonable values for vital or population parameters. Marked fluctuations in population abundance could be originated by changes in the reproductive parameters and survival rates during the early stages. Density-dependent mortality during the egg, larval and post-larval phases, comprised significant percentages of total mortality at those stages. The magnitude of the density-independent component was found to be related to the processes controlling the distributional pattern or early life history stages. A stock-recruitment Curve for each spring spawning population was constructed by means of a multiple-life-history-stage model, graphically represented by a Paulik diagram. as a result of strong density-dependent mortality operating during the egg and larval stages, a dome-shape curve may be inferred for the northern spawning stock, whereas in the Patagonian region, with less intense regulatory forces, the model generates an asymptotic stock-recruitment curve.Palabras clave – provistas por el repositorio digital
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Disponibilidad
| Institución detectada | Año de publicación | Navegá | Descargá | Solicitá |
|---|---|---|---|---|
| No requiere | 1995 | Biblioteca Digital (FCEN-UBA) (SNRD) |
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Información
Tipo de recurso:
tesis
Idiomas de la publicación
- español castellano
País de edición
Argentina
Fecha de publicación
1995
Información sobre licencias CC