OBJECTIVES

The overall objective of this project is to develop the conceptual and mathematical basis for advising on how fisheries management measures might be framed to conserve or restore not only stock biomass, but also sub-stock diversity.
At a more detailed level, the objectives of this project are to:

* Establish the current state of, and where possible the trends over the last 40 years in, stock-richness of cod around Iceland and to the west and northwest of Scotland, and relate these to changes in stock biomass.

* Establish the genetic, behavioural and oceanographic basis for the richness of the cod stocks, and the variations in productivity between sub-stocks.

* Compile all the strands of evidence for sub-stock diversity in these cod stocks into a conceptual and mathematical model of the overall population dynamics incorporating sub-stock dynamics.

* Use the models to generate advice on how the dual aims of conserving or restoring stock biomass and sub-stock diversity might be achieved. To achieve these objectives, the following specific tasks will be undertaken:

• WP1 - Document, from historical trawl survey, egg survey, and fishery data, and the indigenous knowledge of fishermen, the past and present day spawning locations of cod around Iceland, to the west of Scotland and in the north-western North Sea.

• WP2 - Relat trends in the distribution of spawning locations to changes in overall stock biomass.

• WP3 - Analyse historical tagging data, and undertake new tagging experiments, to determine the spawning site fidelity of cod, and the annual migration scales of cod from different spawning locations.

• WP4 - Analyse microsatellite DNA and Syp I from samples of cod from different spawning locations, to establish the extent of genetic differentiation of spawning groups and their stability through time. Examine temporal stability by analysing the genetic composition of historical samples of cod (obtained from archived otolith collections) and correlate genetic structures with known changes in population size.

• WP5 - Characterize each of the spawning groups in terms of their otolith elemental fingerprint and otolith shape, for use as a natural tag or marker in tracking subsequent movements.

• WP6 - Assemble and collect information on biological parameters influencing reproductive outputs and estimate total egg production by each spawning component. Construct a population abundance index that can be used to partition the total stock into spawning components

• WP7 - Develop fine scale hydrodynamic models of the spawning regions around southern Iceland, west of Scotland, and the north-western North Sea. Then, conduct particle tracking simulations of the dispersal of eggs and larvae, in order to establish the extent of mixing between offspring from different spawning locations.

• WP8 - Conduct sampling of juvenile cod populations which the tracking models indicate should comprise fish from a mixture of spawning groups, estimate their actual composition from analysis of microsatellite DNA and Syp I genetic markers, otolith elemental composition and growth rates from analysis of otolith microstructure.

• WP9 - Estimate the survival to juvenile stage from different spawning groups using an existing bio-physical model of dispersal, growth and mortality, calibrated using the genetic and otolith data collected from mixed juvenile populations.

• WP10 - Examine the composition of mixed feeding aggregations generally targeted by fisheries, by quantifying the proportions of fish from the various regional spawning components using discrimination techniques developed in workpackages 4 and 5.

• WP11 - Conduct an assessment of the sub-stock structure of the Icelandic, west of Scotland and north-western North Sea cod stocks, to include estimates of the yield per recruit, and stock-recruitment relationships of the main sub-stocks.

• WP12 - Develop advice on how catch and/or effort control measures might be structured in space and time to both manage the population abundance at the scale of whole stock, and conserve or hasten the rebuilding of sub-stock structure.