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Migration, distribution and spatial dynamics of plaice and sole in the north sea

Objective

The major aim is IO describes the migration patterns of two of the economically most important species of flatfish (plaice, sole) in the central and southern North Sea and adjacent areas in relation to their nursery and spawning areas. The research programme aims: (a) to identify and describe patterns of migration of the two species of fish in the southern and central North Sea and adjacent areas (eastern English Channel and Skagerrak) in relation to the location of their spawning and nursery grounds; (b) to identify the underlying biological mechanisms of migration; (c) to establish the link between the behaviour of the fish and key physical factors in the marine environment; and (d) to incorporate the results in a predictive model.
RESULTS TO DATE

collation of all available tagging data on plaice and sole from each of the partner institutions during the first year has allowed the preparation Of a comprehensive inventory of conventional data The inventory identifies information already available in electronic format and additional datasets which should contribute to the final tagging database In addition, identification of those areas where conventional lagging data were missing from the inventory contributed to the planning of tagging cruises.

The first batch of 200 electronic data storage tags was released in the Central and Eastern North Sea, areas with contrasting tidal flow properties. Fish tagged with conventional Petersen tags were released at the same time, and it is expected that the first returns should be recovered early in the second year of the project.
The first year's work provides the framework upon which behaviour patterns of plaice and sole will be analysed and compared, and will contribute to the development of a predictive model of fish movement.

DISCUSSION

This project is expected to enhance our understanding of the migration patterns of two important demersal species in the North Sea and adjacent areas and how they relate to the nursery grounds and spawning grounds of the various populations. It is also expected to demonstrate how patterns of migration and movement in populations depend on the mechanism+ of migration observed in individual fish and how these patterns of behaviour are in turn influenced by environmental factors. the combination of data storage tags to investigate the behaviour of individual fish on a continuous basis with the analysis of conventional tagging experiments will provide a powerful fill research tool.
Understanding how environmental factors affect fish movement is an important step towards understanding population processes. This project should provide important insights about biological stock structure, which in turn are needed to evaluate current management units. New insights about migration and stock identity are also relevant to understanding stock and recruitment relationships, the spread of disease and the effects of pollution on the marine environment

A dynamic model of spatial distributions will be directly applicable to management questions about the effect of closed Areas and could well form the basis for a mixed fisheries model. A genetic model of he spatial dynamics of fish populations may also found the biological basis for bio economic and social models of fisheries needed for evaluating various management systems.

REFERENCES

Metcalfe, J.D., and G.P. Arnold. 1997. Tracking fish with electronic lags. Nature 387:665-666.

Rijnsdorp, A D. and M.A. Pastoors 1994. A simulation model of the spaeal dynamics f North Sea plaice based on tagging data TCF..R CM
INTRODUCTION

This project, which began ill 1996.Will set out to test the two complementary hypotheses that tidal streams provide a transport and guidance system for migratory demersal fish in the North Sea and adjacent areas and that stocks of demersal fish are contained within the boundaries of the tidal stream paths. We are developing a computer simulation model to predict patterns of fish migration and movement in different parts of the study area, across which there are wide variations in the speed and directionality of the tidal streams. Predicted patterns of movement will be compared with observations of the behaviour of individual fish made with electronic data storage tags and observations of the distribution of populations derived fish conventional Lagging experiments. Special emphasis will be placed on comparing the behaviour of fish in areas of fast tidal streams (e.g. Southern Bight and Eastern English Channel), where environmental transport is known to play an important role u1 fish emigration. with behaviour in areas of slow tidal streams (e g central North Sea), where large fish may not be able to gain any energetic advantage by Using tidal stream transport during migration, and where the swimming performance of the fish may therefore by more important. By making these comparisons, it will also be possible to lest the hypothesis that average through-water swimming speeds in the sea are close to the physiologically optimum swimming speeds observed in the laboratory. The project will also examine & effects of temperature on the initiation of seasonal migrations and the effects of long-term m (inter-annual or decadal) changes in average temperatures on population distribution

METHODS

The project builds on three complementary approaches. (1) Electronic data storage tags will be used to obtain in information on the behaviour of free-ranging individual plaice over the long periods associated with migration and seasonal changes in distribution (Metcalfe & Arnold 1997). These data will be interpreted with a tidal stream simulation model, which is based on known patterns of migratory behaviour in the two species (Arnalfl h Holford 19945 {v.) The large body of conventional tagging data on the on the two-species held by the four fisheries institutes involved in the project are being collated and analyzed Using an approach already developed to describe the spatial dynamics of North Sea plaice populations Rijnsdorp & Pastoors 1994). (3). Migration and dispersion indices derived by these two independent methods will be synthesized to produce a predictive model of fish movement that takes account of the basic mechanisms of migration and is applicable to populations as well as individuals.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

University of East Anglia
Address
University Plain
NR4 7TJ Norwich
United Kingdom

Participants (4)

Danish Institute of Fisheries Research
Denmark
Address
101,North Sea Centre
9850 Hirtshals
Ministerie van Middenstand en Landbouw
Belgium
Address
Ankerstraat 1
8400 Oostende
NETHERLANDS INSTITUTE FOR FISHERIES RESEARCH
Netherlands
Address
Haringkade 1
Ijmuiden
THE CENTRE FOR ENVIRONMENT, FISHERIES AND AQUACULTURE SCIENCE
United Kingdom
Address
Pakefield Road
Lowestoft, Suffolk