MEPS 326:221-233 (2006)  -  doi:10.3354/meps326221

Growth of juvenile lobster Homarus americanus off the Magdalen Islands (Quebec, Canada) and projection of instar and age at commercial size

Louise Gendron*, Bernard Sainte-Marie

Direction des invertébrés et de la biologie expérimentale, Institut Maurice-Lamontagne, Ministère des Pêches et des Océans, 850 route de la Mer, CP 1000, Mont-Joli, Québec G5H 3Z4, Canada

ABSTRACT: Juvenile American lobster Homarus americanus were quantitatively surveyed in the southeast Baie de Plaisance, Magdalen Islands, from 1995 to 2004. Lobster were collected by SCUBA, in summer and/or early fall after the annual settlement period. Growth for up to 3 yr following settlement was assessed by modal analysis of carapace length (CL)-frequency distributions and was confirmed for the first year by in situ rearing of Stage IV lobster collected from the plankton. In every sampling year, some modes (attributed to instars) were apparent in CL-frequency distributions up to 50 mm CL (estimated to be Instar XVI on average). The mean percent molt increment declined gradually from about 23% at Instar IV to about 15% at Instar XV. Strong year-classes could be tracked reasonably well for up to 2–3 yr after settlement. From this point, we projected growth to fishery recruitment and suggest that lobster reach commercial size at a higher instar and older age than previously believed. This is the first study to explain lobster juvenile growth in such detail, and it constitutes an essential step toward the understanding of potential settler-to-recruit relationships.


KEY WORDS: American lobster · Homarus americanus · Growth · Size-at-instar · Size-at-age


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