Abstract
Fishing pressure is often expressed in terms of vessel’s physical attributes, like tonnage and engine power, while a common definition of fishing capacity identifies vessel size as a convenient proxy for the size of gear used. Nevertheless, these definitions remain arguable, and the refinement of these fishing descriptors is increasingly receiving growing consideration. A stronger understanding of the relationship between the standard measures of effort and capacity and fishing mortality remains a primary objective, followed by the need to overcome a traditional approach that simply describes effort, capacity and mortality as linearly related, conferring to larger vessels a greater fishing power. In this perspective, the analysis of trawls’ technical features in relation with the size and power of the vessel might constitute an essential step. This study specifically investigated a collection of trawl gears technical specifications collected by CNR-IRBIM, Ancona. The dataset used includes records from several Mediterranean fisheries, and involves three trawling techniques, including single trawl, twin trawl and pair trawling, and diverse trawling gear categories, comprising demersal/bottom 2-panel trawls (OTB2), demersal/bottom 4-panel trawls (OTB4), pelagic 4-panel trawls (PTM4), semi-pelagic 2-panel trawls (OTM2), semi-pelagic 4-panel trawls (OTM4), and Mediterranean bottom beam trawl (TBB). We analyzed and described the relationships between vessels’ technical features (LOA, towing force, engine power), some among the main trawl-metrics (headline length, footrope length, trawl length, square width; fishing circle) and otterboard’s technical features (height, width, projected area) in the attempt to enhance fishing capacity definition through the inclusion of the fishing gear deployed. Self-Organizing maps were used to explore the empirical relationships among different parts of the fishing trawl gears, as well as between some of these parts and the otterboard size and the engine power of the vessel.
Highlights
Fishing activity regulation is aimed at the management of exploited fish populations while ensuring maximum sustainable yield and maximum economic yield
The original database contained more than 600 trawling gear records, 589 of which were effectively analyzed during this research study
Trawling gear records belong to eight different countries, with approximately 44% of the records belonging to Italy, 40.77% coming from Spain, 6.26% from Greece, 4.56% from Turkey and 3.55% from France
Summary
Fishing activity regulation is aimed at the management of exploited fish populations while ensuring maximum sustainable yield and maximum economic yield. Mortality management is generally achieved through a couple of competing and alternative approaches, the input control, regulating the extent at which fishing activity is performed, and the output control, with a core concept that revolves around limitations in catches of one or more selected species. The former approach finds its management tools in restrictions in fleet capacity, fishing gears used and the number of licenses, limitations on technological updates and on the spatial and temporal distribution of fishing activity. Management redundancy, namely the simultaneous application of measures pertaining to both strategies, is sometimes a possibility (Caddy and Defeo, 2003; Gutiérrez et al, 2011; Santiago et al, 2015) in the pursue of profitable, sustainable and long-lasting fishing activity
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