Discrimination of different rhythmic behavioural patterns in Nephrops norvegicus (Linnaeus, 1758), a marine crustacean decapod of commercial interest

Abstract

Nephrops norvegicus represents one of the most important commercial species for EU trawling fisheries. I investigated the existence of different rhythmic behavioural patterns in 52 Nephrops with an innovative actographic method that is able to discriminate 3 geo-referenced components of burrow emergence activity. Recognized patterns were correlated with sex and carapace length and obtained results were extrapolated to the field. The experimental conditions were: 12-12 LD cycle; monochromatic blue (480-nm) light intensity (0.1 lx). The methodological approach produced good time series of locomotor data, since arrhythmic animals are few (8%). Results indicated that Nephrops possesses an unexpected plastic exogenous behavioural rhythm, subdivided into 3 categories related to burrow influence (i.e. Burrow-centred, 60%; Burrow-oriented, 17%; Poorly burrow-oriented, 15%). Sex and carapace length did not influence the expression of reported rhythmic behavioural patterns, but we individuated some differences in overall locomotor activity among sexes. Nephrops should be considered a good model to investigate rhythmic behavioural patterns of deep-sea crustacean decapods. That investigation revealed its potentiality in aquaculture practice (feeding, reproduction and manipulation) and fishery assessment (extrapolation of laboratory data to the Nephrops stock management)