WP 3: Trophodynamic control of stock dynamics

Description of work

Background

Previous research has demonstrated that, in most European marine ecosystems, predation is the key biological process determining the population dynamics of commercially important fish species (e.g., EU projects: LIFECO, STORE, CORE, STEREO, dst2, BECAUSE). It is a key process determining the survival rates of pre-recruits and hence determines recruitment and stock recovery.  Field sampling programs (e.g., ICES Stomach Data Bases for the North and Baltic Sea) as well as analytical investigations have shown that the predominant fraction of fish prey observed in the stomachs of predatory fish generally consists of early and juvenile life stages. Predation mortality of pre-recruiting fish is determined by the spatio-temporal dynamics of predator - prey overlap in the 3D aquatic environment and the diet selection behavior of the predators. Both processes depend on the hydrographic conditions as well as the sizes and structures of predator and prey stocks (e.g., EU LIFECO, STORE, CORE).
Trophic control of stock recovery can be manifested not only by direct processes but also by indirect processes. Predation can directly affect of recovery target species through cannibalism (intra-specific) and by predation pressure of other species on early life stages of the recovery species. Indirect predatory effects alter the abundance of prey for recovery species, a prey which acts as predator on recovery species, and/or depletion of alternative prey species can increase the predation pressure on recovery species. From the different UNCOVER Case Study areas, there is clear evidence that these processes act at different scales, have a strong influence on stock recovery potentials, and that their magnitudes of impact often depend on the prevailing environmental conditions.

Task 3.1: Description of changes in entire food web structure

In WP 3, all available and relevant data will be synthesized to identify changes in entire food web structures and fluxes experienced during stock decline and the consequences for the prospects of stock recovery will be quantified. The changes will be reviewed and key processes leading to regime shifts will be investigated.

Task 3.2: Resolution of switches in predatory control

Direct and indirect predation processes impacting on recruitment success will be analysed in relation to their environmental dependence and spatio-temporal scale of occurrence. Gained mechanistic understanding will provide process models with realistic behaviour over periods of regime shifts.

Task 3.3: Determination of mesoscale predator-prey interactions impacting on population dynamics

Appropriate methods to take small-scale, high-intensity predation events on early and juvenile life stages of target species into account will be developed by using simulation models, and implemented in large-scale, multi- species fisheries assessment models.
Read more about Task 3.3 here

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