Spatiotemporal variation in sexual maturation and hatching of American Lobster (Homarus Americans) in Eastern Canada: patterns, processes and implications to fisheries

Abstract

The American lobster supports the most valuable fishery in eastern North America, involving over 15,000 fishers and $1.5 billion in annual revenue. The species’ range extends 10° latitude from North Carolina to Newfoundland, exposing lobster to considerable variation in environmental conditions. The lobster’s environment also changes over time, for example in relation to rapid climate change, exploitation rates, and pronounced changes in lobster abundance (e.g., record high last 3-4 decades). Consequently, spatiotemporal variability in life-history traits is expected, but has been investigated relatively little. In this thesis, I investigated spatiotemporal variation in female size-at-maturity (SM) and timing of hatching in eastern Canada, as well as inter- and intra-clutch variation in embryonic development at hatching. The most salient findings are: (1) SM of female lobster has declined by 1-3 moults over the past 10-80 years; (2) evidence that declines in SM are due to size-selective harvesting, based on the relationship between spatial variation in the magnitude of SM declines and the degree to which minimum legal size regulations have allowed harvesting of immature females; (3) hatching occurs in eastern Canada during weeks of the year (Jul-Sept) that are predicted (based on a larval dispersal model) to minimise larval drift time; (4) considerable geographic variation in timing of hatching (8-10 weeks), which does not seem related to local variation in when hatching would minimise drift time; (5) considerable variation within and among clutches in embryonic size at hatch, likely as a bet-hedging strategy; and (6) an advancement of ≈5 weeks in the start of the hatching period in the southern Gulf of St. Lawrence over 25 years, seemingly in response to an increase in cumulative degree days available in fall for gonadal development and early embryonic development. These findings show considerable variability in reproductive traits of lobster, and highlight the need to consider such variability in fisheries management and research.