The Growth Rate of the American Lobster (Homarus americanus)

Abstract

Carapace measurements of lobster larvae caught in the western part of Northumberland Strait showed that in this area the natural growth in length per moult is 34.4 per cent from stage 1 to stage 2, 31.8 per cent from stage 2 to 3, and 30.3 per cent from stage 3 to 4. The seasonal distribution of the first four larval stages was determined from plankton tows made continuously from mid-June to late September each year from 1948 to 1952. To determine natural annual growth, lobsters of 15 to 25 cm., total length, were sorted into five or six size groups and were distinctively marked by means of holes punched through the tail fan. These were liberated on six widely separated fishing grounds in the Maritime Provinces. Recoveries of these marked lobsters four to twelve months after release showed that in the southern Gulf of St. Lawrence, 15- to 20-cm. lobsters grew 8 to 9 mm. (13 to 15 per cent) in carapace length, 22 to 25 mm. (13 to 14 per cent) in total length and 80 to 95 grams (45 to 53 per cent) in weight. In southern Nova Scotia and Grand Manan 20- to 25-cm. lobsters grew 10 to 12 mm. (13 to 15 per cent) in carapace length, 27 to 34 mm. (12 to 15 per cent) in total length and 170 to 220 grams (43 to 54 per cent) in weight. From the carapace length of 4th-stage larvae and straight-line equations relating carapace length before moulting and carapace length after moulting, the average carapace lengths of lobsters in stages 5 to 20 were calculated. From observations and calculations on the growth per moult and moulting frequency, it is estimated that in the Northumberland Strait area lobsters reach a length of 14 cm. (51/2 in.) at the end of the fifth growing season (41/4 years old) and 24 cm. (91/2 in.) at the end of the ninth growing season (81/4 years).