Diffusion of American lobster (Homarus americanus) in Northumberland Strait, Canada

We tested the hypothesis that American lobster (Homarus americanus) movement can be described as diffusion. In 2001 and 2002, 3689 lobsters, captured by experimental trap and trawl surveys, were tagged and released in Northumberland Strait, Canada. Recaptures (n = 413) were reported by roughly 200 commercial fishermen, up to 3 years after release. Only six lobsters, all females, were recaptured more than once. Recapture rates were marginally higher for males (male 12%, female 10%) and varied with area of release (range: 5%-12%) and the fishing gear used for tagging (trap 12%, trawl 11%). Maximum and mean displacements between release and recapture were 58.3 and 12.3 km, respectively. The positive linear correlation between mean square displacement (MSD) and time between release and recapture provides evidence for diffusion. We calculate a diffusion coefficient (D)of13km²-week^-1; there was no difference in D between sexes. A power analysis showed that MSD is underestimated at small sample sizes. There were insufficient data to test for differences in D associated with sexual maturity or shell hardness at time of release. During the summer in Northumberland Strait, the lobster population spreads about 20 km. The demographic consequences of seasonal diffusion of lobster warrant study.