Analysis of Atlantic bluefin tuna catches from the last Tonnara in the Mediterranean Sea: 1993–2010

Abstract

In the last 20 years, several factors have heavily impacted the Atlantic bluefin tuna fishery. They include management policies, market changes, the ban of the drift-net fishery, expansion of the modern purse seine fleet, and implementation of a stock recovery plan. To enhance current knowledge about the population's status, we conducted a long-term analysis (1993–2010) of scientific data and standardized catch-per-unit-of-effort (CPUE) from the traditional trap fishery of Sardinia (Western Mediterranean, Italy), which is the last active bluefin trap fishery in the Mediterranean. We detected a significant increase of the standardized CPUE and a significant decrease in mean weight over time. Cluster analysis conducted on 29,000 specimens revealed three different size groups that were distinct by time period: the 1993–1995 period was characterized by a significant presence of large bluefin; a decrease in mean weight occurred in the 1996–2006 period; and 2007–2010 was characterized by the prevalence of young adults in the history in the trap fishery. This trend, which needs to be confirmed over longer time and spatial scales, raises some ecological questions. In particular, is the occurrence of these young adults a consequence of changes in the migratory behavior of bluefin tuna in the Mediterranean, or does it reflect the actual demography of this population? The results of this study emphasize that data from traditional traps provide valuable long term scientific information about population parameters through time, and thus the use of traps as monitoring stations should continue in the future.