Females of the Norway lobster, Nephrops norvegicus are usually excluded from behavioural research based on the assumption that their reproductive cycle alters the results. A seasonal fluctuation in the sex ratio of commercial catches suggests that females do not emerge from their burrows when berried. Burrow emergence (i.e., catches) and feeding rhythms of berried and unberried females were compared with data on their endogenous locomotor activity rhythm. Catch data and the percentage of empty stomachs already published for a population dwelling on the continental slope (400-430 m) in the western Mediterranean were reprocessed focusing on data for berried and unberried females in October, a month that falls within the breeding season of N. norvegicus in the study area. Catches for both groups significantly increased at daytime, when both displayed the lowest percentages of empty stomachs (i.e., diurnal feeding pattern). To assess the occurrence of alterations in endogenous locomotor patterns depending on the presence of eggs, locomotor rhythms of berried and unberried females were studied under conditions of constant darkness in the laboratory. All individuals showed endogenous circadian and nocturnal locomotion. Taken together, these data suggest that feeding, burrow emergence, and endogenous locomotion rhythms are not inhibited in berried females. A reduction in the duration and range of emergence (i.e., doorkeeping) is hypothesized as the basis for the reported fluctuations in the sex ratio in commercial catches.

Las hembras de cigala Nephrops norvegicus se descartan usualmente de la investigación sobre el comportamiento asumiendo que su ciclo reproductor altere de una forma indeterminada los resultados. Variaciones estaciónales en la proporción de hembras en las capturas sugieren que la emergencia sea inhibida cuando estas ultimas sean ovadas. Datos de captura y de porcentaje de estómagos vacíos publicados en total por una población del talud (400 m) Mediterráneo (Occidental) en Octubre son reprocesados enfocando solo en las hembras ovadas y non ovadas. Otoño representa el periodo de reproducción de esta especie en el área de estudio. La capturas de las hembras en los dos grupos han mostrados claros incrementos diurnos cuando los porcentajes de estómagos vacíosse encontraban en sus mínimos (alimentación diurna). Experimentos de laboratorio sobre el ritmo de locomoción endógena en ambos grupos han mostrado marcados incrementos de actividad en coincidencia de la noche subjetiva. Estos datos sugieren que los indicadores de comportamiento tratados no son alterados por la presencia de huevos. Se propone que las hembras ovadas no supriman sus ritmos de comportamiento si no más bien alteren la duración y la distancia durante sus emergencias fuera de las madrigueras.

The present work was carried out in the context of a national research project funded by the Spanish Inter-Ministerial Commission for Science and Technology (CICYT) (NERIT: MAR98-0935). The Spanish Ministry of Education provided doctoral grant founding (FPI Program) for J. A. The authors wish to thank the crew of the R/V “García del Cid” (CSIC) for their support during sampling.

14 pages, 4 figures, 1 table

Peer reviewed