On the Biology of the Norway Lobster, Nephrops norvegicus(L.)

Abstract

In view of the wide distribution, differences in the biology of Nephrops norvegicus are to be expected. The size composition of the stocks, which varies considerably, appears to be unrelated to latitude. The largest are found off Portugal and the smallest in the Irish Sea. The size of females at maturity also varies in a manner apparently unrelated to latitude. The 50% level of maturity in the High Adriatic is reached at 27 mm carapace length as compared with 33 mm off Portugal and 22 mm in the Moray Firth. The sex ratio varies seasonally because of the lower availability of berried females as compared with nonberried females and males. The percentage of females in the catch is lowest during the period between spawning and hatching. The extent of the seasonal variation is very marked in Scottish and Irish waters, but less so off Portugal and in the Adriatic. The period of eggbearing in the Adriatic extends for about 30 weeks from June-July to January. Off Portugal spawning occurs in August-September and development takes only 28 weeks whilst around Scotland and Ireland spawning occurs around a peak in September and the incubation lasts about 34 weeks until hatching in May. Females are most abundant, relative to males, in the lowest size classes. With the onset of maturity the growth rate of the female decreases in comparison with that of the male of corresponding size. This results in a high percentage of females in the length classes about the maturity size followed by a falling off in the proportion of females to males. Annual spawning is normal throughout the distribution of the Norway lobster.