Uso de técnicas geoestadísticas en la estimación de la abundancia de vieira patagónica (Zygochlamys patagonica).

To evaluate absolute biomass, a research cruise was conducted on three scallop (Zygochlamys patagonica)beds (38°S-56°W, September 1998). The estimated bed surface was 1,162 nm(2). Sampling stations were regularly spaced at 5 nm intervals. A total of 118 trawls were performed with a non-selective dredge 2,5 m wide (efficiency 16-21. ). Trawls duration and speed were 10 minutes and 3 nm.h(-1)respectively. Samples were taken to estimate total and commercial (greater or equal than 55 mm total height)scallop weight and size frequency distribution. Coefficients of variation (CV)of the estimated biomass were calculated for each bed using geoestatistical techniques and a simple random sampling alternative with the same number of samples. The CVs for total scallop biomass as estimated in the three beds using geostatistical techniques were 50,8. , 20,5. and 5,6. lower than the respective CVs obtained using a simple random design-based alternative. In the case of commercial scallop biomass, the reduction in the CVs was 51,4. , 20,5. and 5,6. , respectively. An important decrease in the associated uncertainty in biomass estimation of the three beds was found using a geoestatistical approach instead of the randomized sampling alternative. Given the spatial distribution and sedentary characteristic of Z. patagonica, once detected, grounds are particularly vulnerable to overfishing. Thus, reliable biomass estimates and precise maps of commercial and non commercial individual densities are useful tools to define sustainable management strategies.