, Volume 6, Issue 3, pp 319-352

On bycatches

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Abstract

This paper attempts to provide a synthesis of several issues relevant to the study and management of bycatches. It includes a proposed set of definitions for the different fractions of the harvest (catch, bycatch, release) and for other impacts of the fishing process, either at sea or in port. It also provides a system for the classification of bycatches that shows some basic similarities and differences among fisheries.

The classifications are based on different criteria, including the degree of spatial or temporal ‘aggregation’ of bycatches, the degree of control that the fishers have, the frequency of occurrence, its predictability, its ecological or random origin, the level of impact of bycatches, and whether bycatches are the result of market conditions or regulations.

One of the main issues to address in plans to deal with bycatches is defining the objectives to be pursued. These objectives can include ecological or socio-economic goals, and some of the possible goals are briefly discussed. Once the targets are set, it is necessary to find the strategies to achieve them. The bycatch process is quite simple because it has only two controls: the average impact per unit of effort and the total level of effort. The definition of effort used is not always equivalent to the one used in fisheries models.

If a decision is made to reduce the ecological impacts of a fishery, three sets of tools are available to achieve it, acting over the two controls mentioned above: technology, training of fishers, and management measures. Five possible lines of defence are available to reduce bycatches: (1) increasing the selectivity of the fishery by choices of gear, areas, or seasons; (2) modifying deployment conditions; (3) increasing the fraction released alive either from the gear, or (4) later, from the deck; or (5) increasing the utilization to make catches out of the incidental captures.

One of the options more commonly used to manage fisheries problems is the development of incentive/disincentive programmes, with both positive and negative responses applied to the fishers in accordance to their level of performance. Some examples are mentioned.

Some of the challenges facing scientists, managers, the fishing industry and the environmental community to tackle the bycatch problems in coming years are also presented.