In experiments in Cornwall and Yorkshire 214 marked lobsters (Homarus vulgaris M. Edw.) were returned after moulting. Of these a number had moulted more than once, and the separation into once-, twice- and three-times-moulted lobsters was achieved using probability paper.
There was no significant difference in growth of lobsters from the two areas. It is concluded that the best method of plotting growth in lobsters is to plot carapace length before moulting against carapace length after moulting.
It is concluded that male lobsters show arithmetic growth over the size range 68–123 mm carapace length, adding a constant mean increment of 9.8 mm carapace length at each moult.
It is concluded that arithmetic growth, with a mean increment of 8.4 mm, adequately describes the growth of female lobsters over a small size range centred on a mean size of about 85 mm, but would lead to inaccuracies over a wider size range.
The concept of arithmetic growth in relation to the general growth pattern is briefly discussed.
In a population study a knowledge of the growth rate is essential. In crustaceans estimation of the growth rate is complicated by two factors: first, it is usually not possible to age the animals, and second, the growth rate is made up of two components, the increase in size at moulting and the frequency with which moults occur.
The present paper presents data on the growth of lobsters at a moult, obtained from field experiments conducted in Cornwall in 1957–59, and in Yorkshire in 1958 and 1960.