Seasonal and interannual variability in larval lobster Homarus americanus size, growth and condition in the Magdalen Islands, southern Gulf of St. Lawrence

Abstract

Seasonal and interannual patterns in lobster larvae and post-larval stage size (mean carapace length: CL), percent size increase at molt, growth rates (mg protein d-1), and nutritional condition (TAG/sterol and TAG/total protein ratios; TAG: triacylglycerols) are presented for the lobster population at the Magdalen Islands, southern Gulf of St. Lawrence (Canada) for 3 yr (1996 to 1998). The effects of water temperature on stage duration and larval protein growth rates seem to determine the seasonal pattern of variability in size of lobster larvae. Stage I larvae CL showed no seasonal decline each year, but diminishing size increases at the first molt following the warming of the water column were apparently responsible for declining stage II and III larvae CL. Under warmer and more stable water temperature conditions in mid-summer (August), higher protein growth rates during the third larval stage compensated for inverse temperature effects on post-larvae size; as a consequence, the seasonal declines in post-larvae CL were not significant except during 1998, when water temperature in late August was colder. The lipid-based condition indices suggest that seasonal larval growth was not affected by changes in food availability in any year of the study. Lobster postlarvae can vary by up to 10 and 20% in CL and biomass (total protein), respectively, within a season. It would appear that the great range in size at age reported in lobsters might originate during the conditions for growth and development of the larval stages.