Deep sea fish take ugliness to new level, says Niwa

Hatchetfish. Photo / Peter Marriott, NIWA

Scouring the depths of New Zealand's sea floor has revealed new-to-science and very rarely sighted fish, many of them fascinating in their ugliness.

Lanternsharks, ghost sharks and black lizardfish were among the rare specimens found at depths greater than 1500 metres by National Institute of Water and Atmosphere (Niwa) scientists.

Researchers onboard the RV Tangaroa trawled the Chatham Rise, a series of underwater hills which run eastward from Banks Peninsula to beyond the Chatham Islands.

Niwa fisheries scientist Peter McMillan said the discoveries revealed how little we knew about the ocean's riches - less than 0.002 per cent of the deep sea environment has been sampled.

"The deeper we go, the less we know. Our knowledge of fishes decreases with increasing depth."

Some of the fish he had never seen in 30 years of sampling around New Zealand.

The fish evolve into bizarre body forms to adapt to the intense water pressure, cold water and scarcity of light and food at great depth.

Living in relative darkness, many had small eyes or produced their own light.

The rarest find was a species of lanternshark, which was yet to be formally named. A sleek fish with lurid green eyes, it was believed to be able to produce light from the bottom of its body to search for food on the sea floor.

The lanternshark has no swim bladder - which allows fish to regulate buoyancy - so it could dive to greater depths.

Scientists also captured a basketwork eel, a deep sea predator found around New Zealand, Australia and South Africa with distinctive wickerwork markings on its skin.

Because the eel may have to last long periods without food, it has a large jaw and distendable stomach to allow it to swallow huge meals.

Mr McMillan said it could eat prey half its size, such as a whole squid.

One of the deepest-dwelling fish Niwa found was the sinister-looking black lizardfish, which was captured at 1800 metres.

Trawling to that depth was expensive and complicated. To send a net to the bottom of the sea floor could take three hours. It required 4000 metres of wire, with winches capable of holding the weighted net and anything it dragged out of the ocean.

The fishing gear was subject to huge pressures, about 200 times that encountered at the sea's surface. The scientists used specialised floats which would not burst in the deep sea.

The study was part-funded by the commercial fisheries industry, which was investigating the possibility of trawling deeper for orange roughy. In June scientists found one specimen of orange roughy below 1500 metres.

Mr McMillan said the scientists did not find an abundance of the fish in the deep sea on this voyage.

The scientists were also seeking to increase their knowledge of fish distribution and ecology at great depths.

Niwa has gifted the captured fish to Te Papa to be stored in its National Fish Collection.

Only one fish has been captured at a depth greater than 6000 metres in New Zealand - the Kermadec snailfish, which was found between 6660 and 6890 metres.