Seasonal Variations in the Catch Composition of the Norway Lobster, Nephrops norvegicus (L.) around Scotland

Abstract

Scottish research ship sampling, by trawl, shows that the catch of male Norway lobsters does not exhibit any marked seasonal variation in size composition. The males, therefore, provide the most suitable means of comparing year to year variations in the stock and constitute a basis on which to assess seasonal differences in the catchable stock of non-berried and berried females. Females mature at about 23 mm carapace length. The immature sizes show no seasonal variation in abundance. Mature females are mainly caught in the non-berried state between the moulting, which reaches its peak in May, and spawning, which is at its peak in September. The period of incubation is about eight months. Other investigators working on the stocks off North Shields, and at the Faroes, have concluded that Norway lobsters spawn only every second year but their data have certain limitations. Around Scotland the mature female spawns in autumn: hatching occurs in May followed immediately by the moult and mating: the female spawns again in the subsequent autumn. The sex ratio, taken in June and July, reflects the extent of fishing but its use in this regard is limited by the effects on the sex ratio of seasonal variations in fishing intensity.