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SUMMARY: Southern geoduck is the most long-lived bivalve species exploited in the South Atlantic and is harvested by divers in San Matías Gulf. Except preliminary data on growth and a gametogenic cycle study, there is no basic information that can be used to manage this resource in terms of population structure, harvesting, mortality and inter-population comparisons of growth. Our aim was to analyze the spatial distribution from survey data, population structure, growth and mortality of several beds along a latitudinal gradient based on age determination from thin sections of valves. We also described the spatial allocation of the fleet's fishing effort, and its sources of variability from data collected on board. Three geoduck beds were located and sampled along the coast: El Sótano, Punta Colorada and Puerto Lobos. Geoduck ages ranged between 2 and 86 years old. Growth patterns showed significant differences in the asymptotic size between El Sótano (109.4 mm) and Puerto Lobos (98.06 mm). The maximum age decreased from north to south. Natural mortality was estimated for each bed according to a catch curve (M = 0.105 -0.177 yr -1 ), with a method based on mean age (M = 0.212 -0.233 yr -1 ) and a method based on maximum longevity recorded (M = 0.062 -0.13 yr -1 ). Population features were integrated into the harvest analysis to generate a preliminary management proposal that includes subdivision of the coastal zone, limited entry, harvest rate and individual vessel quotas.Keywords: geoduck, clams, fishery, ageing, population structure, growth, natural mortality. RESUMEN: Estructura poblacional, distribución y explotación de la almeja panopea del sur, PanoPea abbreviata, en el Golfo San Matías (Patagonia, Argentina). -La almeja panopea del sur es el bivalvo más longevo bajo explotación en el Atlántico Sur y es objeto de explotación artesanal mediante buceo en el Golfo San Matías. Salvo datos preliminares de crecimiento y un estudio del ciclo gametogénico, se carece de información relevante para el manejo del recurso como estructura poblacional, mortalidad y diferencias interpoblacionales de crecimiento. Los objetivos de este trabajo fueron analizar la distribución espacial de datos de relevamientos, la estructura poblacional, el crecimiento y la mortalidad en bancos situados a lo largo de un gradiente latitudinal a partir de determinación de edad mediante secciones delgadas de valvas. También se describe la distribución espacial del esfuerzo pesquero de la flota y sus fuentes de variabilidad a partir de datos colectados a bordo. Tres bancos de panopea fueron localizados y muestreados a lo largo de la costa: El Sótano, Punta Colorada y Puerto Lobos. La edad de los individuos osciló entre 2 y 86 años. El patrón de crecimiento mostró diferencia significativa entre la talla asintótica en El Sótano (109.4 mm) y Puerto Lobos (98.06 mm). La edad máxima evidenció una tendencia decreciente Norte -Sur. La mortalidad natural fue estimada en cada banco mediante curva de captura (M = 0.105 a 0.177 año -1 ), un método basado en...

Even though Glycymeris longior is a clam widely distributed in the SW Atlantic Ocean, little is known about its biology and life history. The present study assessed the periodicity of the internal growth increments of G. longior using thin shell sections. Each internal growth increment was composed of two alternating bands: a translucent band (lightcoloured when viewed with transmitted light) and an opaque band (dark-coloured). Annual formation for each pair of bands was demonstrated. The formation of the annual growth increments was synchronous among individuals. Growth was determined from live clams collected at El Sótano, Argentine Sea (age range = 29 to 69 years). According to the growth model, G. longior grows fast during the first 5 years of life and then growth becomes slower in later years; individuals reached 50% and 90% of maximum size at 5 and 13 years of age, respectively. High variability was found in shell height for the first 10 years: differences up to 5-7 mm among individuals were registered for the first 2 years of age, and up to 11 mm between the ages of 3 and 9 years. The growth performance index phi-prime (φ′) and the index of growth performance (P) of G. longior were compared with those of other Glycymeris species. Our results indicate that G. longior is a slow-growing species with a long lifespan (maximum longevity = 69 years).