Keywords: catch statistics - pelagic fisheries - population dynamics - shared stocks - stock assessment

Abstract

Sardine (Sardina pilchardus, Walb.) is one of the most important commercial species of the Adriatic Sea. Stocks of sardine, living in the Northern and Central Adriatic Sea, is shared between Italy, Slovenia and Croatia. This assessment is relative to the sardine stock of the Northern and Central Adriatic Sea (GFCM GSA 17), pooling together data coming from Italy, Slovenia and Croatia. It has been carried out in the context of the AdriaMed-SP research programme. The annual catch of sardine for the three countries mentioned was obtained for the time interval 1975-2002. These quantities were distributed into fish age classes, so that catch-at-age data were available. That represented the basic input data of Virtual Population Analysis (VPA), employed for this stock assessment. Annual values of mid-year stock biomass at sea, annual values of the unweighted mean fishing mortality rate over the age class range 0-5, annual values of mid-year spawning biomass and corresponding ratios between catch and mid-year spawning biomass were obtained. In addition, annual exploitation rates were calculated and compared with a threshold derived from literature and suggested for small pelagics. Since decline of stock biomass is observed after the peak in the first half of the 1980s, and lowest values of this series only correspond to recent years, it would be unwise for fishing effort to be allowed to rise. An apparent increase in estimated biomass is observed in the last year, 2002: caution has to be taken when considering this, as VPA may have difficulties with incomplete cohorts; in addition, change in discarding phenomenon (particularly for small size sardines) could play a role in an apparent increase such as the one described. Therefore, monitoring of discarded quantities, as well as pattern as a function of sardine size, is also suggested. Concerning the South Adriatic (GFCM GSA 18), not enough catch and effort data and biological data on the sardine is currently available to perform stock assessment. Data collection in the South Adriatic is being carried out in the framework of the AdriaMed-SP research programme; the retrieval of past data is also going on. Therefore, in the near future, a joint stock assessment will also be possible in this area.