Description of work
This work package considers the research on indicators at three levels:

Estimation of the health of individuals within a stock
The causes of changes in ‘condition’ between individuals will start from simple measures such as Fulton’s condition factor and be developed through to more complex models that include factors such as density and prey availability. At present, a high condition factor is equated with good condition, however, high condition factor i.e. heavy for a unit length is also equated with obesity and is not a healthy state. The influence of sub-stocks, habitats and inter-species differences in morphology will also be explored. The majority of the research will utilise a range of cod and herring stocks but it is expected that the results and models can be applied to other species.

Estimation of population ‘health´
At the population level the population size is a function of the ‘health’ of a stock and this can influence the ‘health’ of the stock. Factors such as growth rate (and condition factor) are a function of the interplay between stock numbers and the predator-prey relationships. Using tools such as otolith microstructure it is possible to get an indication of the current health or status of a stock and to go back through the historical record to obtain a view of the past ‘health’ of the stock. The case studies to be used here are the Norwegian spring-spawning (NSS) herring and NE Arctic cod.

Estimation of ecosystem condition
At the ecosystem level we are considering two levels the pelagic and benthic ecosystems. The benthic ecosystem is often ignored in the overall fishery management even though it provides prey for many commercial finfish and shellfish fisheries. In both cases the principal is a ‘bottom up’ control on the functioning of the ecosystem. Here we will concentrate on open ocean pelagic systems and inshore, shelf benthic ecosystems. The inshore benthic systems are the richest and arguably the most disturbed of the benthic systems, and is also an important area as nursery ground for many commercial species. Species richness and productivity will be the principal measures. There is a long historical data set that can be used to look at changes and trends in ecosystem ‘health’ in the past.
The second level to be examined at the ecosystem level is the use of seabirds and marine mammals (principally seals) to indicate ecosystem health. The status of seabird populations is often assumed to be a good integrator and indicator of the status of the whole ‘marine ecosystem’ since   both seabirds and seal populations respond to changes in the available abundance of prey species. In both cases there is the necessity of untangling the population dynamics from the ecosystem health i.e. problems associated with e.g. major population explosions in birds and seals which can not be sustained by any marine ecosystem and the top-down control they can exert on a marine ecosystem. In both species we are considering integrating measures of abundance, feeding levels, distributions and population dynamics to provide a measure of ecosystem condition.