Jack The Knife: Predator Of The Reef
Dedicated in loving memory to Jackie McCall who swam on this earth from 12/23/89-7/19/2021.
Hawaii's rocky shores are teaming with living creatures, both fast and slow moving. Nature being what it is, these reefs attract their share of predators, above the water and below. Of the ocean predators, sharks immediately come to mind. However, the jack family plays the most significant role in establishing reef communities, and is extremely important to humans as well.
There are about 150 species in the family Carangidae, but about 24 known species that live in Hawai'i. Locally, the large jacks are called ulua, and the juveniles are called papio. These fish range in size from five inches to five feet. Two jacks which are favorites in the traditional Hawaiian diet include akule (bigeye scad) and 'opelu (scad mackerel). Jack fishing contributes millions of dollars annually to the local economy.
Although diverse in size, all of the jacks are carnivores and have developed characteristics that sustain their position at the top of the food chain. Their coloration is typically silver on their sides and undersides with blue green scales on the top. This color pattern makes them difficult to see from above and below. The large jacks search for prey on the outer reef and deep drop-offs. Being top predators, they are sleek, swift, and strong with a streamlined body designed for agility.
Jacks are favored sport fishes, especially the large ulua. It is the most popular fish of shoreline and spear fishermen.
The scad mackerel, or akule, move about in large schools in shallow coastal waters. Akule are the prize catch of throw net fishing, an ancient skill passed down through generations. The "hukilau" song describes how Hawaiians worked together to pull in the fish. Today fishermen can be seen on the reefs, observing patiently and waiting to cast their nets and gather the evening meal.
Long ago, fish were the main source of protein for Hawaiians. The sustainability of life in those times depended upon a renewable and dependable yield. Hawaiians practiced natural conservation to assure the replenishment of fish by observing and respecting the life cycles of the fish. Laws of kapu (prohibitions) were placed on certain species of jack during the spawning season. This ensured that a fishing area was never depleted and that fish would remain abundant.
In recent years, jacks have, at times, been associated with ciguatera poisoning. The problem begins when small reef fish have eaten a specific marine microorganism. If the larger jacks eat a certain number of contaminated smaller fish, the poison accumulates in their bodies and can then be transmitted to humans who eat them. Fortunately, poisonous incidents are infrequent. The best way to avoid the problem altogether is to test the fish you catch. There is an approved test kit that is sold locally in fishing supply stores.
Jacks can be seen in snorkeling and diving areas. Most of the time they'll be swimming in schools, but it is not uncommon to see them swimming alone. It's safe to swim near jacks because even though they are carnivorous, they won't approach you with dinner on their minds.
