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TECTAC Report Summary

Project ID: Q5RS-2002-01291
Funded under: FP5-LIFE QUALITY
Country: France

Production of a fishing effort model accounting for technological developments and fleets adaptation

Three separate investigations were carried out to analyse the elements of fleet dynamics, the first two focusing on fishing tactics and strategies, and the latter on technological development. The scope of the first investigation is to quantify, for a wide selection of European fisheries, fishing tactics and strategies, and to evaluate the benefits of adjusting the definition of fishing effort using these elements. Fishing tactics and strategies were identified by metiers choices and a series of indices.

These indices have been derived to reflect shifts in tactics (within a fishing trip) and in strategies (within a year). The Shannon-Wiener spatial diversity indices of tactics (FT_SW) and strategies (YE_SW) had the greatest impact on catch rates. In particular, FT_SW was always negatively correlated to catch rates. One may anticipate that during a fishing trip, vessels with high FT_SW have been searching fish aggregations for a long time, while vessels with low FT_SW have been more efficient in finding these aggregations. The linkage between YE_SW and catch rates was of a more complex nature.

The second study has investigated some properties of fishermen�s foraging, using Levy flights theory. The case studies examined were a selection of North Sea Dutch and French vessels, for which catch and effort data were collected on a haul-by-haul basis. Foraging behaviour could reasonably be represented by a Levy flight process for both fleets. The properties of fishers� foraging were further investigated for the Dutch fleet using time series analysis. Efficient foraging led to high value per unit effort, while the knowledge of fishing grounds with high stock density is shown to increase foraging efficiency in the short-term future. Efficient foraging resulted in high levels of fishing effort 4 or 7 months later. By contrast, High levels of fishing effort may induce local depletion on fish stocks, and subsequently adversely affect foraging efficiency. The linkage between foraging and fish prices was complex. It could be explained by fish prices only partially reflecting the economic drivers of fishers� behaviour.

Regarding the third investigation, face-to-face interviews have been undertaken to identify the main changes in gear and vessel technology, which have improved the fishing efficiency of a number of French, Danish and Basque fleets, over the past decades. Important features are the gradual appearance of twin trawls (Danish and French trawlers) and of trammel nets (French gill-netters), and the increased polyvalence of Basque bottom-trawlers. The results suggest that fishing effort descriptors which are not traditionally measured (gear type, ground rope type, length of net used per day, headline length, crew size, number of winch or net drums) may have a substantial impact on catch rates.


Paul MARCHAL, (Senior scientist)
Tel.: +33-3-21995600
Fax: +33-3-21995601
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