Jack Mackerel (Trachurus novae-zelandiae) back home
Not only is the Jack Mackerel found in New Zealand, it is found everywhere in the world from the tropical to subtropical seas.
They are a schooling pelagic fish common all around New Zealand, and swim between mid water to the bottom rather than on the surface, and from near the shore to depths of about 300m or 1000 feet.
It is a very fast swimmer for a fish so small, and swimm in huge schools. Many predators depend on it for food.
The Jack Mackerel is an elongate fish with a pointed head, and similar in shape and appearance to the koheru. It is a slow grower, but grows to a larger size.
They average 35 to 40cm or around 1' in length. It is easily distinguished from the koheru by having a blunter snout, larger eyes, and a line of large and conspicuous bony scutes along the entire lateral line.
The mackerel has small fins behind the dorsal and anal fins. The head has no scales, but the body is covered with lots of very small scales.
Jack mackerel are a pale blue green with a touch of brown on the back, and silver white colour beneath. The tail is a yellowish colour.
Jack mackerel eat plankton and small pelagic fishes. They spawn in groups during summer, and schools of the mirrorlike juveniles are seen close to reefs during autumn.
Juveniles are found sheltering within the stinging tentacles of jellyfish. They grow to 25 cm in 3-4 years, and may live up to 25 years.