EGG DEVELOPMENT TRAJECTORIES OF EARLY AND LATE-SPAWNER LOBSTERS (HOMARUS AMERICANUS) IN THE MAGDALEN ISLANDS, QUEBEC

This study examines egg development in American lobster (Homarus americanus) ovigerous females caught off the Magdalen Islands (MI), Quebec, in September 2002 and kept in tanks for 10-11 months under a simulated natural temperature cycle. The study compares egg development trajectories of 7 early-spawners (ES) that had a well-defined pigmented eye area (Perkins eye index, PEI: 190-246 mu m) at the time of capture and 8 late-spawners (LS) with no visible pigmented eye at the time of capture. Eggs from ES achieved about 80% of their development in the fall, followed by a circa 6-months rest period. Eggs from LS reached approximately 50% development by late fall, and unlike eggs from ES, continued development during winter even at temperatures of 1.0-1.5 degrees C. The two groups experienced different numbers of effective (> 3.4 degrees C) degree-days (ES: 1440.7, LS: 1308.0) for complete embryonic development and late spawning translated into late hatching. Additional observations made on a group of 72 ovigerous MI females caught in September 2006 indicate that early spawning is mainly associated to larger females, most likely multiparous, with a 2-year reproductive cycle, and late spawning mainly to smaller females, most likely primiparous, with a 1-year cycle, molting and spawning the same year. Larvae from ES/multiparous and LS/primiparous may therefore encounter different environmental conditions for survival at hatching and during larval development. The occurrence of females having different patterns of egg development trajectories in American lobster populations can help spread larval production over time. This can be viewed as a mechanism for coping with environmental uncertainty.