A computer simulation model for predicting rates and scales of movement of demersal fish on the European continental shelf

Abstract

A quantitative model has been developed which predicts geographical movements of demersal fish on the European continental shelf by combining tidal stream vectors calculated from Admiralty tidal data with known patterns of fish behaviour. The model interpolates the speed and direction of the tidal current at any specified position and allows for the cyclical change of current speed between neap and spring tides. Fish behaviour is specified in terms of swimming speed and direction, as well as times of vertical migration and the duration of the intervening period in midwater. Times of vertical migration to and from the bottom can be specified theoretically in relation to regular tidal events (slackwater, high or low tide, etc.), or practically using actual observations made by sonar or data storage (archival) tags. Simulated tracks can be used singly to predict the behaviour of individual fish in relation to biological problems, or collectively to predict the distribution of whole populations in relation to management problems. These predictions can be formulated so that they can be tested experimentally. The model is being used to reconstruct the ground tracks of fish fitted with data storage (archival) tags and also to predict the theoretical movements of individuals and populations. It has been validated by reconstructing the ground tracks of fish tracked in the open sea using sector scanning sonar and transponding acoustic tags. Potential applications include estimating transfer coefficients for use in spatial assessment models, assessing the exchange of fish between fishable areas and areas closed to fishing for conservation reasons, and providing a theoretical framework for analysing returns from conventional fish tagging experiments.