Common New Zealand Fishing Methods

Trawling

A specialised net is used in trawling. Steel paravanes (trawl doors) are adjusted to ‘fly’ through the water in opposing directions and hold the mouth of the net open. The trawl doors are attached to winches on the boat by heavy steel cables (trawl warps).

Marine life that cannot out-swim a trawl net is caught when it is towed across fishing grounds. The net herds marine life into its mouth, fish become tired from swimming and end up in the net’s narrow tail (cod end). The net’s mesh size allows some fish to escape from the trawl. In New Zealand, most trawling is carried out near the bottom, in water depths ranging from around 10 metres to more than a kilometre.

Set netting

This type of fishing involves setting a net, either in mid-water, or on or near the bottom. Set nets are made from fine nylon, so fish can’t see them. They may be up to 10 metres high and several hundred metres long.

These nets catch marine life that swims into them and gets tangled. Fish bigger than the net’s mesh size get tangled in the net by their gills or fins; smaller fish swim through the net. Set netting usually occurs in shallow waters, within a few miles of the coast.

Longlining

Longlining involves setting a single line with many baited hooks on it. Commercial longlines vary in length from tens of metres to several kilometres in length and can have tens to thousands of hooks on a single line. These lines catch marine predators with a mouth large enough to take in the bait and hook.

Surface longlines are usually set in the open ocean, at depths of 50-200 metres or more below the surface. Conventional bottom longlines are set along the sea floor, in water depths ranging from around 10 metres down to around two kilometres. Bottom ‘droplines’ are set vertically, and have only a few hooks on each line.

Dredging

Involves towing a steel net (dredge) across the seabed.

Most dredges in New Zealand are around two-four metres across the mouth. They catch anything that lives on the bottom and can’t swim away. Dredging usually occurs in shallow waters, between 10 and 100 metres deep.

Potting

These are baited traps on the sea floor.

Some are made of nylon mesh and others from steel and wire. They have one or more entrances animals find easy to enter, but difficult to leave. They also have ‘escape’ holes so under-sized animals can get out easily.

Seining

Seining involves setting a net to surround and trap schools of fish before being hauled in.

Purse seining catches surface-schooling fish. A small boat lays a specialised net around the school and a drawstring around the bottom of the net is pulled tight, preventing escape. The net is then drawn into a smaller and smaller circle, trapping the fish in a tiny area. They are then scooped out with smaller nets.

Danish seining catches schools of fish near the bottom, particularly in inshore waters where trawling is not practical (eg areas surrounded by rocks and reefs). Danish seines are like trawl nets, but with long ‘wings’ and weighted ropes either side of the net opening. The net and ropes surround the schools of fish. As the weighted ropes are drawn in, they drag across the bottom, scaring the fish towards the net, which is then hauled onto the boat.