The effect of light-induced eye damage on the behaviour of Nephrops norvegicus.

Nephrops norvegicus is susceptible to irreversible eye damage following exposure to daylight when brought to the surface during fishing operations. This study investigated the significance of blinding on the behaviour of undersized eye-damaged N. norvegicus after being returned to the sea bed. Field-based and laboratory-based experiments showed that sighted and blinded N. norvegicus possess similar 24 h nocturnal activity rhythms. In the laboratory, N. norvegicus performed a higher level of activity after they were blinded but in the field there was no significant difference in activity levels of the sighted and blinded individuals. The effect of blinding on the predator avoidance behaviour of N. norvegicus was assessed using either the presence or odour of a predatory fish (cod, Gadus morhua). Avoidance behaviour of both sighted and blinded N. norvegicus was elicited by both types of cod stimuli, but blinded N. norvegicus were affected to a lesser extent than the sighted ones. It was also shown that avoidance behaviour of both sighted and blinded N. norvegicus is elicited equally by a predator species (G. morhua) and a non-predatory species (Pollachius virens). Contests between individual N. norvegicus were studied in the laboratory and a full description is given of all types of the agonistic behaviour performed. The relative status of two opponents was unaffected if either the dominant or the subordinate opponent was blinded. The duration and content of contests were largely unchanged after blinding one opponent. There was no evidence from laboratory-based experiments, that blinding has any effect on the ability of N. norvegicus to gain shelter and to locate food items. It was also shown that blinded N. norvegicus are able to find a baited creel in a laboratory situation. These results provide evidence to suggest that, in respect of these important behaviours, there is no major difference between sighted and blinded N. norvegicus.