Two species of lobster Jasus edwardsii and Sagmariasus verreauxi are found in New Zealand and Australia. Previous work shows that J. edwardsii is genetically indistinguishable between Australia and New Zealand, whereas S. verreauxi may be genetically different between the two countries.

Satellite altimeter data are used here to test the hypothesis that Australia acts as a source of larvae for New Zealand populations, and to investigate if there is a physical mechanism for the lack of gene flow for S. verreauxi. A Lagrangian approach is used in which the Tasman Sea is seeded with a number of numerical drifters to build up a statistical summary of the likely distribution of larval trajectories.

Ignoring biological factors, about 7% of J. edwardsii, and about 3% of S. verreauxi larvae might be expected to arrive in New Zealand within their respective larval lifetimes. The shorter larval life cycle of S. verreauxi is compensated for to some extent by the fact that these animals are more likely to get entrained in the relatively fast moving Tasman Front, whereas J. edwardsii are likely to drift more slowly across the southern Tasman Sea. It appears that larval flow across the Tasman Sea should be sufficient to maintain trans-Tasman genetic homogeneity in both species.

One reason that S. verreauxi may not be genetically homogenous is that in order to cross the sea within one year, they have to cross north of the productive Subtropical Front, where there may not be sufficient prey to sustain the larvae.