No abstract

The introduced, mytilid bivalve Musculista senhousia (Asian date mussel) occurs on the east coast of New Zealand in the Auckland region. Eighteen sites were searched within the Tamaki Estuary: six had extensive mats of mussels and three contained small, isolated clumps. Core samples were taken monthly during 1994/95 from two of the mat-forming populations. Densities reached 16 000 m -2 at Bucklands Beach and 5000 m -2 at Farm Cove. Both populations were dominated by a single cohort of mussels. Mussels grew to about 20 mm in 12 months, after which growth virtually ceased. Recruitment was sporadic into existing mats, but occurred adjacent to the monitored mat at Bucklands Beach in April 1995. The area occupied by the initial mussel bed at this site decreased by 60% over 1 year. Further core sampling revealed significantly fewer macrofaunal invertebrates under mussel mats compared to control samples taken from areas of beach without mussels. Infaunal bivalves were most adversely affected by M. senhousia, showing an 8-fold decrease in abundance within mats compared to cores in the control area. Our results reveal that M. senhousia in the Auckland area has similar life history features to those reported from populations Received 2 September 1996; accepted 13 February 1997 outside New Zealand. We suggest that any adverse environmental effects caused by M. senhousia are likely to be local and short-lived. M96071

Around the world there is strong interest in the aquaculture of spiny lobsters (family Palinuridae). However, there is little published information about the economic feasibility of spiny lobster aquaculture. For more than 20 yr there has been experimental grow out of the spiny lobster Jasus edwardsii in New Zealand in land‐based systems using seed animals (puerulus) taken from the wild. These studies provide sufficient information on growth, mortality, food conversion, handling and capital costs to enable an assessment of the economic feasibility of the commercial culture of spiny lobsters in temperate waters. This assessment suggests that profitable spiny lobster aquaculture will rely on greatly reducing the infrastructure and operating costs of land‐based farming operations, as well as lowering feed and labor costs. Financial simulations suggest that increasing productivity through faster growth rates and lowered culture mortalities will only have a minor effect on profitability unless infrastructure and operating costs can be reduced significantly. Seacage culture or sea ranching of spiny lobsters may offer a means of avoiding high infrastructure costs associated with land‐based farming operations. The development of a cost‐effective artificial feed would also appear to be a priority for improving the economic outlook for culturing spiny lobsters. The results of this study are relevant to the economics of spiny lobster culture developments in other temperate regions of the world.

No abstract

The relations between growth and mortality rates and water temperature are important in determining the economic success of spiny lobster aquaculture. Captive juvenile lobsters (Jasus edwardsii) were grown at a site in north-eastern New Zealand where ambient sea-water temperatures in the culture tanks ranged from 23.3°C in summer to 13.4°C in winter, with an annual mean of 17.2°C (s.d. = 2.8). The growth and mortality rates of three size classes of juvenile lobsters were examined over one year in captivity. All lobsters were fed cultured mussels. Lobsters in the smallest size class grew to an average of 39 mm carapace length (31 g) in their first year from settlement. Growth to 200 g was estimated to take three years. Total mortality of lobsters was 12.8% and was greatest in the 0+ size class, for which most mortality occurred in a single tank. Of the total mortality, 64% occurred during two summer months (January and February). The growth and mortality of J. edwardsii are compared with previously unpublished information.