Rock lobster Jasus edwardsii larval retention by the Wairarapa Eddy off New Zealand

In February 1998, Jesus edwardsii larval catches off the east coast of New Zealand were binomial in size and stage of development. Mid-stage larvae (presumed to be from the 1997 cohort) appeared to be contained within a large permanent eddy found offshore, known as the Wairarapa Eddy. Late-stage larvae (1996 cohort) have a different distribution from the mid-stage larvae, being found closer inshore of the eddy. Pueruli (also 1996 cohort) were found well inshore of the eddy. Surface currents derived from TOPEX/Poseidon altimeter measurements of sea level are used to simulate larval concentrations. The numerical simulations show that the different distributions of the 3 groups cannot be explained on the basis of advection alone. Mid-stage concentrations appear to be well described by passive drift alone, but the simulations suggest some mechanism inducing shoreward transport is needed for both pueruli and late-stage phyllosomas. Observed puerulus concentrations are best matched by adding a shorewards-directed speed of 8 to 10 cm s(-1) for between 1 and 3 wk before the date of the cruise. Late-stage phyllosoma concentrations are best matched by adding speeds of 4 to 6 cm s(-1). Sustained shorewards swimming speeds of 8 to 10 cm s(-1) are well within the estimates of swimming speed that have been reported elsewhere for pueruli. To our knowledge, extended directed horizontal swimming has not been reported for phyllosomas, yet in the final stage, the pleopods are almost as well developed as they are in the pueruli. These final stage larvae could well use forward pleopod propulsion, in conjunction with exopodal setai beating, to allow them to swim.