The term billfish is used for marlin and their relatives. They are large migratory fish, with a distinctive upper jaw that forms a pointed spear or bill. Along with the swordfish, five species are known to frequent New Zealand waters seasonally.
Marlin are likely to feed on a broad range of pelagic fish and squid, and small tuna in open waters. Nearer the coast, they also eat bottom-dwelling fish. Marlin are caught commercially, and are sought by anglers fishing off the northern North Island.
In the past, marlin were rumoured to make unprovoked attacks on boats. It is more probable that the fish were lashing out with their bills as fishermen hauled them into the boat.
The striped marlin (Tetrapturus audax) occurs in cooler waters and is the most abundant marlin around New Zealand. It grows up to 3.5 metres long and weighs up to 180 kilograms, but averages around 130 kilograms.
Blue marlin (Makaira mazara) taken from New Zealand waters average around 100–200 kilograms. The heaviest caught in New Zealand was 412 kilograms. Like other marlin, they arrive in the peak of summer and are known from the Bay of Plenty northwards, most notably off Northland’s east coast.
The large black marlin (Makaira indica) typically weighs between 100 and 200 kilograms and is around 2–3 metres in length. The heaviest caught in New Zealand was 444 kilograms. These fish are widespread in the tropical and subtropical waters of the Indian and Pacific oceans.
The broadbill swordfish (Xiphias gladius) is widely distributed and moves from tropical to temperate waters. Although it swims near the surface, it is thought to descend to deeper waters. The bill, which is longer and flatter than the marlin’s, is used for defence and to herd, stun and slice prey such as squid and small fish.
Armed but not dangerous
In 1875 a swordfish over 3 metres long was stranded on Shelly Beach in Auckland. It was examined and described by the Auckland Museum curator, Thomas Cheeseman, who wrote:
It has been said to attack the whale with its sword, but this is extremely improbable ... Instances not unfrequently occur of ships’ bottoms being perforated by the sword, but there is no good reason to think that an intentional attack is ever made. 1
The average length is 2–3 metres. Specimens weighing 100–300 kilograms are taken by anglers off the New Zealand coast.
Commercial fishing of the species is now prohibited, so any swordfish catch is taken by boats fishing for other species such as tuna.
Other billfish occasionally seen in New Zealand waters include the shortbill spearfish (Tetrapturus angustirostris) and the sailfish (Istiophorus platypterus).