Publication Abstract

Measuring fish behaviour: the relevance to the managed exploitation of shared stocks

J.D. Metcalfe and M.G. Pawson

From a management perspective, a fish "stock" can be defined as that part of a species’ population within which the effects of exploitation on population structure are recognizable. It is a relatively straightforward task to manage the exploitation of fish that remain within the same fishing area throughout their lives, and it is also an advantage if this stock unit has a high degree of biological integrity. However, this is rarely the case. Most fish move between different environments through their lives, and many commercial species exhibit extensive seasonal migrations. Consequently, the identification of individual stocks, as well as knowledge of their spatial distribution and dynamics, are important for any rational management of their fisheries. This applies particularly in situations where a large element of management policy concerns shared fish stocks. Genetic and conventional tagging studies can provide a limited understanding of stock structure and population movements, but they do not provide the resolution needed to understand and quantify the spatial and temporal scales of mixing and movements within populations that is needed to model the interactions and dynamics in relation to providing management advice. Since the late 1960s, CEFAS has developed an approach to overcoming this limitation, using electronic tags to monitor the movements and behaviour of individual free-ranging fish in the open sea for periods from a few days to longer than a year. Such work is advancing our understanding of the stock structure and dynamics of commercially exploited fish species. We illustrate this by reference to plaice stocks around the UK and the influence that stock mixing has on the assessment of stock status. The challenge now is to ensure that this knowledge is built into future assessment and management methodologies.

Reference:

J.D. Metcalfe and M.G. Pawson. 2004. Measuring fish behaviour: the relevance to the managed exploitation of shared stocks. Management of Shared Fish Stocks; 303-315