Off the coast of Cornwall from the Lizard Head to Padstow there has been, for many years, a small but locally important fishery for crawfish Palinurus elephas (Fabr.).The fishermen had used pots and tangle nets up to the outbreak of the Second World War in 1939. From 1945 tangle nets had been little used and the fishery was pursued mainly by pot fishermen until the early 1960s when divers using self-contained under-water breathing apparatus began to collect crawfish. Tangle nets were re-introduced widely in the late 1960s.

A bloom of the dinoflagellate Gyrodinium aureolum Hulburt in the eastern Irish Sea during September and October 1971 was accompanied by unusual mortalities of Arenicola marina L. and Echinocardium cordatunt Pennant. Observations in the field and laboratory suggest that the mortalities may not have been directly related to the occurrence of Gyrodinium but could have been a consequence of unusual climatic conditions which resulted in oxygen depletion in benthic substrates. The decomposition of the bloom possibly aggravated the situation.

(1932) included the species in his list of British Marine Mollusca, but gave no locality. Dean recorded M. galloprovincialis as 'abundant in Cardiff Docks' (Conchological Soc., 1929), and Gardiner (1945) reported the species as present at Pendine, Carmarthenshire, and St Ives Bay and the Helford River, Cornwall.In spite of these references to M. galloprovincialis in Britain, there seems to be no comprehensive account of the distribution of this species on our shores, or of its abundance relative to our common native mussel M. edulis L., and the present paper attempts to remedy these deficiencies.

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In experiments in Cornwall and Yorkshire 214 marked lobsters (Homarus vulgarisM. 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.IntroductionIn 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.