Ensuring a sustainable Ross Sea toothfish fishery
Food matters for seahorses
Lobster larvae can cross the Tasman
What happens under that mussel farm?
Overfishing leads to loss of genetic diversity
Encouraging results from freshwater eel culture
Farming paua in recirculation systems - fad or future?
Overfishing can harm the genetic diversity of marine fish populations to a much greater extent than was previously thought, according to a paper published recently*.
Genetic diversity in Tasman Bay snapper.
Genetic diversity in a population is critical to a species’ ability to adapt to environmental changes and for the continued productivity of a fish stock.
In theory, genetic diversity begins to decline only when populations decline to very small numbers. Even overexploited stocks consist of several million fish, apparently protecting them from loss of genetic diversity.
The international market for cultured eels exceeds 100 000 tonnes. Both Southeast Asia and Europe, which are the primary markets, have experienced significant reductions in supplies of glass eels over recent years, limiting the possibilities for further growth of their eel farming industries. There is increasing interest in eel farming in New Zealand to supply these overseas markets.
A huge size range of eels was evident after only 9 months of culture.
Growth of cultured shortfinned eels.
Eel farming was trialled in New Zealand in the 1970s, but proved uneconomic.
NIWA has been carrying out research on toothfish biology and the exploratory longline toothfish fishery in the Ross Sea for several years, initially as a PGSF project, but more recently under contract to the Ministry of 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?
New Zealand has over 550 mussel farms totalling 4500 hectares, most of them in the Marlborough Sounds. Large farms proposed for open coastal regions could result in a 10-fold expansion in area in the near future, and increased awareness of mussel farming’s impact on the marine environment.
Side-scan sonar images of the seabed beneath mussel lines.
Photographs of mussel farm seabed corresponding to the areas marked on the sonar images.
Mussels produce faecal material which may accumulate on the seabed, depending on the amount of water movement under the farm.
Six-month-old juvenile paua.
Growth of two groups each of European and Japanese abalone reared in a recirculation system.
New Zealand paua farmers are increasingly interested in recirculation technology, but is this a likely future direction for the industry or just a current fad?
Culturing seahorses for aquaria or for the dried medicines trade is still a young and largely unproven industry in New Zealand. The supply of sufficient nutritionally adequate food for the seahorses, which are voracious feeders, is a major bottleneck.
Food for seahorse food
Many commercial culturists still rely to various degrees on culturing live prey, such as brine shrimp and copepods, to feed their seahorses. What the brine shrimp and copepods are themselves fed on critically influences their nutritional value, and therefore affects seahorse growth, survival, coloration, and health.
