Social factors affecting stock assessment of the Norway lobster, Nephrops norvegicus (L.): a behavioral deterministic approach

Temporal dimensions of environment, as geophysical cycles, are selective agents for biological rhythms of species. One of the most important and predictable cues to entrain biological rhythms is the day/night cycle. Behavioural rhythms can affect the results on species stock assessment when the timing of sampling is not considered. In this context, the study of behavioural rhythms was introduced in the fishery management models of Nephrops norvegicus that is an evident case of a commercially important species whose rhythmic burrowing behaviour affects fishery. Indeed Nephrops is available to fishery only when emerge from burrow. The aim of this study is acquiring knowledge on burrowing behavioural rhythms of Nephrops to increase the efficiency of management plans. In Norway lobster, territoriality sustained by intraspecific encounters and consequent fighting may inhibit emergence of subordinates, with effect on catchability. It has been already demonstrated the emergence of dominance hierarchies in Nephrops but information on how dominance hierarchies affect circadian rhythms is low. Here we exposed groups of cohoused lobsters to two different light patterns: 12-12 light-darkness conditions (LD) followed by a treatment of constant darkness (DD) to test the hypothesis that social synchronization of the circadian clocks could have an effect on the emergent properties of their dominance hierarchies. The results present here suggest that the diurnal rhythm of agonistic encounters could not be a direct consequence of locomotor activity rhythm. However, we found different positive linear trend among synchronization of fighting against stability of dominance hierarchy observing that fighting behaviour may be an endogenous rhythm. Most importantly, these results stimulate a behavioural oriented research in the natural environment that can provide a solid calibration to stock assessment protocols.