Fish that live on or near the sea floor are known as demersal. They occupy different habitats – open sea floor (consisting of sand, gravel, mud) or rocky sea floor. Those on the open sea floor can be divided into northern, southern and New Zealand-wide groups.
This mid-water predator (Zeus faber) can hardly be seen front-on because it is so thin. However, from the side the John dory looks quite large. Distracting its prey with an eye-shaped spot on its side, it scoops up the hapless creature in its large, protrusible mouth. The species is widespread north of Cook Strait and occupies a variety of habitats, from sandy sea floor through to reefs.
The bluish-green porae (Nemadactylus douglasii) grows to 70 centimetres and is found in northern waters over reefs and sand or gravel bottoms. Porae are long-lived – large fish may be up to 30 years of age. They freely take bait and put up a good fight, yielding palatable white flesh.
This commercial fish (Pseudophycis bachus) is often seen laid on ice in fish shops. It is restricted to New Zealand and southern Australia, and more common along the South Island’s east coast, where large schools form over sand and muddy bottoms. The cod uses a barbel (fleshy filament) on the lower jaw to detect prey buried in mud or sand.
The blue moki (Latridopsis ciliaris) is found throughout New Zealand but is more common in the south, especially on the east coast in depths of 20–100 metres. They feed on a wide range of crabs, shellfish and worms on the sea floor. This is a commercially significant species.
A rather ugly species, the monkfish (Kathetostoma giganteum) looks a bit like a bulldog. Also known as a giant stargazer, it is caught commercially and has firm, tasty flesh. While widespread in New Zealand waters, it is more common around the South Island. Using well-developed pectoral fins it burrows into the sea floor, grabbing fish with its large mouth.
Turbot and brill
These brownish-green flatfish resemble flounder and sole, and are taken by coastal trawlers. The turbot (Colistium nudipinnis) has dark blotches, while the brill (Colistium guntheri) is mottled. Both are endemic to New Zealand, and very good eating.
The tarakihi (Nemadactylus macropterus) is found throughout New Zealand. It feeds below 25 metres, scavenging worms, crabs, brittle stars and shellfish from the bottom. At night it rests on the sea floor, where its colouring becomes blotchy. This species also occurs in southern Australia where it is known as morwong.
Recreational anglers know the tarakihi well – when lifted from the water it often squeaks as air is expelled from its air bladder. Red gurnard often grunt when they are captured.
From the mid-1940s the annual commercial catch was around 4,000–6,000 tonnes, but this has declined.
The red gurnard (Chelidonichthys kumu) is found in fairly shallow water to depths of around 180 metres. It also occurs off southern Australia and South Africa.
Red gurnard feed on crustaceans such as small crabs and shrimps. Their large pectoral fins rest on the bottom and are used to detect food. Shallow coastal trawlers have exploited the gurnard since the 1930s, and by the 1970s it was the fourth most important coastal species.