engleski

Can an individual tell us something about its population?

Effective decision-making in wildlife management relies on accurate estimates of the current population status, as well as on predictions of its dynamic. The population dynamic is determined by vital rates of individuals, which depend on energy investment into growth and reproduction. The investments depend on the individual’s energy budgets that can be estimated by observing weight and length of individuals. Translating such individual-level measurables to population dynamics, however, is confounded by ecological and environmental feedbacks. We use a DEB-IBM model of European pilchard to look at how environmental conditions – including fishing – affect the relationship between population size and individual-level status. We model how fishing pressure and environmental food availability affect size, reproduction, energy reserves, condition index (CI) and abundance. As expected, both average energy content and average fish condition increase with food availability. Increased fishing mortality results in lower population levels, followed by an increase in energy reserves and CI. Counterintuitively, this implies that very good condition (high CI) of the fish could indicate overfishing. Our results, therefore, suggest that CI may reflect the state of the population. Since CI is a simple metric calculated from commonly available biometric data, it has a great potential of becoming a very simple but powerful addition to existing tools in management of fisheries. We also discuss some limitations of the approach, and applicability to other wildlife.

DEB IBM ; condition index ; population ; fisheries ; fishing mortality ; carrying capacity

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