Patterns and mechansims of American lobster (Homarus americanus) movement in the Northumberland Strait, Canada

The Northumberland Strait, Canada, is a unique habitat in the southern Gulf of St. Lawrence (sGSL), which supports the only fall fishing season in the sGSL, established in part because of the belief that lobster migrate into the Strait. This thesis employs both Eulerian and Lagrangian methods to study the patterns and mechanisms of lobster movement in the Strait. In Chapter 2, an experimental trap survey documents a sequential increase in lobster catch from the north-west to the south-east, consistent with the observations of fishermen. While the increase in catch is largely a result of increased catchability associated with warm water, sequential increase along the axis of the Strait suggests immigration from the north-west. Both the change-in-ratio analysis and a trawl survey completed before and after the trap survey, indicate a three-fold increase in lobster abundance in the central part of the Strait in July. These results are remarkably consistent with trap catches in Shediac Bay 1932 and Egmont Bay 1981. Such a mass movement or migration may be associated with seasonal inshore/offshore migration, may be part of an ontogenetic shift or result from density-dependent dispersal. In Chapter 3, a mark/recapture tagging study found no directional bias in lobster movement during the summer, and the movement of lobster was consistent with a correlated random walk, such that the observed mass movement could result from diffusion along a gradient in lobster abundance, possibly associated with settlement hotspots. Further, female lobster had a higher mean displacement (13.89 km) than male lobster (10.89 km), which is consistent with female-biased dispersal associated with male territorial behaviour and female mate choice. In Chapter 4, I present the tracks of three resident lobster over three weeks. Of the eight lobster tagged with acoustic tags, the three lobster that stayed within the radio acoustic telemetry (RAPT) hydrophone array had a very limited home range (MCP < 1502 m2) which is ideal for study with RAPT. The very different spatial scale of the movement documented in the second and third chapters demonstrates heterogeneity in American lobster movement behaviour in the Northumberland Strait. Research in other areas suggests that individual lobster are capable of a wide range of movement behaviour. However, if the heterogeneity of lobster movement documented here is associated with a mixing of populations with different movement behaviours, the intense fishery in the Northumberland Strait may undermine metapopulation structure.