Population structure, distribution and harvesting of southern geoduck, Panopea abbreviata, in San Matias Gulf (Patagonia, Argentina)

Southern geoduck is the most long-lived bivalve species exploited in the South Atlantic and is harvested by divers in San Matias 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 Sotano, 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 Sotano (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.