Lobster larvae can cross the Tasman
Science Centres: Fisheries
Both New Zealand’s common lobster species, the red rock lobster (Jasus edwardsii) and the green or packhorse lobster (Sagmariasus verreauxi), are also found in Australia. Genetic data suggest that Australian red lobster larvae may be crossing the Tasman Sea and settling in New Zealand, whereas those from Australian packhorse lobsters do not make it across the Tasman.
Simulated trajectories for movement of larvae released off Bass Strait.
Why should this be? Both species have a similar lifecycle, except that the duration of the larval stage of the red rock lobster is about twice that of the packhorse lobster. This led us to hypothesise that the time for larvae to cross the Tasman Sea is between 1 and 2 years, and is therefore longer than the larval life of packhorse lobsters but shorter than that of red rock lobsters.
Satellite maps showing sea level are the oceanographic analogue of weather maps, and can be used to compute daily changes in the patterns of oceanic surface currents. Surface currents computed from these maps were used to model larval lobster movements across the Tasman Sea, simulating the trajectories that larvae hatched off the east coast of Australia would follow. From our simulations we obtained statistics on the probable larval crossing times for each species.
Contrary to our expectations, we found that there is a similar probability, of about 3–7%, that the larvae of each species can reach New Zealand from Australia within their larval life cycle. This is because packhorse lobsters are found farther north and their larvae tend to cross the Tasman Sea where flow is faster than in the more southerly parts where the red rock lobster larvae tend to be crossing. The faster transit of packhorse larvae compensates for their shorter larval life.
Our simulations suggest that both species should show significant gene flow across the Tasman Sea. Other factors must therefore be responsible for the genetic diversity between the stocks of packhorse lobsters on either side of the Tasman. One possible explanation is that the northern Tasman Sea, where the packhorse larvae tend to cross, is a region of low biological productivity in which the larvae may not find enough food to sustain them, even for the shorter duration crossing.
We have yet to determine whether larval recruitment from across the Tasman Sea is a significant factor in either the red rock lobster fishery or the supply of puerulus for aquaculture in New Zealand.