Watch the surface on a calm morning off the east coast of the North Island. If silver rain appears to fall upwards, that is koheru. They break the water in flickering sheets. Thousands of bodies move as one. They herd plankton and small crustaceans into their open mouths. Fast, sleek and nervous, they are the ocean's equivalent of a hyperactive schoolchild. Always moving. Never still. Prone to sudden explosive dashes in any direction. The fish cannot sit still. Koheru belongs to the jack family, Carangidae. This group includes trevallies and kingfish. Unlike its larger, more glamorous cousins, koheru stays small. It reaches twenty-five to forty centimetres in length. A big one weighs half a kilogram. Its sleek silver body and deeply forked tail make it a strong swimmer. It is well suited to life in surface schools. It filters food from the water using fine gill rakers. This method works well when plankton is thick. Dawn and dusk are mealtimes. This is when tiny creatures rise toward the light. The Māori name Hature is also used for jack mackerel. The two species look similar and behave similarly. They swim together in mixed schools. These attract seabirds, dolphins and predatory fish like kahawai and kingfish. For the koheru, being bait-sized is not a flaw. It is a role. Its oily flesh is not popular on dinner plates. Game fishers seek it out for hooks. In Māori tradition, surface schools of koheru meant that kahawai and kingfish were close by. It was a sign of the ocean's abundance. It showed the skill required to read the water. A small fish, but a useful one. The surface is calm. The koheru break it, silver rain falling upwards, flickering and flashing. The kahawai are close. The kingfish are closer. The koheru do not know they are bait. They just want to eat plankton.