Blue moki

Blue moki are very similar to the copper moki in shape and size, but they differ in colour throughout the adult stage of their lives.[2] Blue moki are knowing for their piercing colours, which is an array of pink and olive.[3] A blue moki's phenotype is true to its name - they are dark blue/grey.[2] They have a black edge to the caudal and soft dorsal fin.[3] Blue moki belongs to the family Latridae commonly known as trumpeter,[4] which has 4 subspecies of abundance in New Zealand waters. The copper moki which is another member of the genus is located in New South Wales and Tasmania but is rarely seen in New Zealand waters.[5] The colouration of blue moki changes throughout its life time from juvenile to adolescences, their body colours change from green in juveniles to green/grey and through to blue/grey in large adults.[3]

Blue moki are found in the continental shelf north south of the Chatham islands in depths of 10–200 metres.[6] Many adults take part in an annual migration between Kaikoura and East Cape.[7] Juvenile blue moki are then found inshore in coastal rocky reefs; whereas adults tend to school offshore over open bottom areas. There are some adults that tend to remain on coastal reefs in shallower waters.[8] Juvenile blue moki have been observed to prefer rocky-reef type habitats in shallow waters,[9] most of the adult blue moki school offshore on sandy open bottom habitats but some adult blue moki do not join the schools and stay in the rocky-reef type habitats.[10]

Blue moki grow at a rapid rate growing between 5–6 centimetres per year, growth potentially slows with fish between the age of 10–20 years reaching 60 centimetres and there have also been fish recorded at 33 years of age with them being over 80 centimetres long.[7] Blue moki can weigh up to 10 kg.[11] The blue moki reach sexual maturity at 40 centimetres which equates to 5–6 years of age.[3] Migration occurs annually. It begins in May/June (Winter) when blue moki begin to travel from Kaikoura on the East Coast on the South Island up to the only known spawning ground for blue moki in New Zealand, which is in the Mahia Peninsula to the East Cape region. Spawning occurs from August to September.[7] They then pass back by Kaikoura in October.[6] The larvae period of the blue moki spawn lasts about six months; from there juveniles are then found inshore in coastal rocky reefs, whereas adults tend to school offshore over open bottom areas. There are some adults that tend to remain on coastal reefs in shallower waters New Zealand.[7] Blue moki morality other than for commercial fishing reasons is low.[11]

Blue moki feeds at the bottom, on a wide range of benthic invertebrates.[5] It consumes a mouthful of turfing substrate, it then winnows out the prey.[12] Blue moki intestines are often found with ingested sand and mud. This is a result of them feeding on benthic species such as crabs, gastropod, bivalve molluscs, polychaete worms and Munida gregaria.[5] They also feed on juvenile sea urchins.[12] Juvenile blue moki are located on reefs and eat small crustaceans amongst seaweeds, while adults prey on crabs, other crustaceans, shellfish and worms, which they suck from the sand or mud.[13]

Blue moki are seen as a ‘game’ fish in New Zealand and are commercially fished, this is why Humans are seen as one of blue moki's predators.[8] Blue moki stocks were seriously depleted in New Zealand in 1975.[8] Humans are the blue moki's largest predator, which fishes them commercially using set nets in the areas between East Cape and Kaikoura. Catches have been consistent at around 400 tonne per year; fish mortality other than commercial fishing is low.[14] Moki are also caught recreationally through spear fishing and boat fishing in small catch.[14]

Maori view blue moki as having special significance in community and life believing that blue moki spawn in Cape runaway and that there are traditional fishing grounds for blue moki where customary fishing practices took place in earlier times. Iwi also consider fishing blue moki by set nets in the area a cultural offence.[16]

Blue moki is mostly caught on the east coast of New Zealand between Otara and Kaikoura it is a low value fishery. The commercial catch is caught as a bycatch of trawling and set netting for other target species. There are management practices in place for the blue moki fisheries such as a minimum catch size of 40 cm, area restrictions on certain types of fishing methods and a minimum net size of 114mm for target set net fishing of blue moki[17]

Blue moki are a very popular fish targeted by recreational fishermen, they are caught in a variety of ways such as spearfishing, catching on the rod and reel and set netting like commercial fisheries they are legally required to be above 40 cm in length and a minimum set net mesh size of 114 mm. There is also a bag limit of 15 fish per person.[17]