| Summary: | Movements of animals en masse are impressive phenomena that continue to fascinate scientists of all persuasions. Fishes display some of the most striking examples, and an extensive literature has explored the subject in marine species with long histories of commercial harvest, and/or strong, enduring cultural values. Yet, as recognition of the cognitive capacity of fishes grows, and strong inter-individual variability in behavioural traits among sympatric conspecifics is revealed as the norm, fundamental questions on the drivers underpinning both large-scale migrations, and the spatial outcomes of such moves require reexamination. This thesis comprises five papers that focus broadly on understanding the factors that shape movement decisions, distribution patterns and connectivity in schooling marine fishes. Using Atlantic herring (Clupea harengus L.) in Iceland, and striped red mullet (Mullus surmuletus L.) in the North Sea and Eastern English Channel for illustration, the work combines new Bayesian modelling approaches with analyses of otolith (ear stone) chemistry to test the role of intrinsic (i.e. collective behaviour, demographic traits, ontogeny) and extrinsic (i.e. the environment, fishing pressure, prey availability) factors in influencing the spatial dynamics of these commercially-important species. The outcomes highlight the natural synergy between model-based and empirical approaches in addressing questions on the movements of group-living fishes, and demonstrate how these can be integrated to guide fishery-management decisions, both under present conditions, and under future scenarios of environmental change. Hreyfingar og hjarðhegðun dýra er heillandi og áhrifamikil sjónarspil sem hefur verið uppspretta ýmissa rannsókna. Fiskar eru meðal þeirra dýra sem sýna hvað mest sláandi dæmi um hjarðhegðun og margar heimildir eru til um slíkt atferli hjá nytjastofnum sem og öðrum lífverum sjávar. Eftir því sem meiri vitneskja safnast um vitsmunalega getu fiska, sem og um breytileika á meðal einstaklinga ...
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