About Guy:
Guy Harvey

On just about any dive site in the Cayman Islands, as you roll into the water, the first type of fish you will encounter will be a jack, probably a bar jack. Numerically the bar jack is the most common neritic pelagic fish in the Caribbean and occupies a wide variety of niches, both shallow and deep water. This species epitomises this large, widespread and successful family of fishes, the Carangidae.
 
Here in the Cayman Islands we can expect to encounter seven different species of jacks on a typical wall dive; bar jack, blue runner, the yellow jack, horse-eye jack, permit, black jack and the rainbow runner. The yellow jack is similar to the bar jack but has a more golden/yellow wash, and lacks the typical black bar running along the back and lower caudal fin. Both species form large schools. The blue runner is bland looking, sometimes exhibiting soft vertical bars, but often schools with bar jacks and are prolific offshore associated with flotsam.
 
The horse-eye jack lives up to its name, has large eyes for night feeding, with a silvery body and bright yellow tail, this species often forms schools at the drop off or just in the deep water, and loves the attention of divers. Permit are frequently seen cruising the deep fore-reef or in conjunction with tarpon at Tarpon Alley. The black jack will swim up the wall as shallow as 60 feet, often hanging out near caves and tunnels, but are typically a deep water jack.
 
Another common species of deep water jack is the amberjack or AJ. They are not common here in Cayman, but they are important in recreational fisheries in Florida and the Bahamas and often associate with wrecks and deep sea mounts. If you dive out on 12 Mile Bank, or go to 150 feet off Northwest Point, you may see amberjacks or a similar species the almaco jack.
 
Almaco jacks are frequently encountered offshore hanging out under flotsam, so are caught as juvenile by anglers looking for dolphin fish by the flotsam. Rainbow runners, called ocean salmon here or mongoose jack in Jamaica, are long, slender brightly coloured jacks that are found on the deep fore-reef, and just offshore, often amongst bar jacks or horse-eye jacks.
 
Rainbow runners can form large schools at East End and at 12 Mile Bank, easily seen if you want to do a drift snorkel in these locations. You may encounter black fin tuna, bonito and wahoo while doing this. Blue water snorkelling is very cool.
 
One culprit conspicuously absent from Cayman’s waters but common everywhere else in the Caribbean, particularly in association with river mouths is the jack crevalle.
 
This is one of the largest species, characterised by a steep forehead and a stern face, with a gray silver body and yellow fins and tail. They grow to 60 pounds and are a very fast and aggressive shallow water predator. They feed voraciously on mullet, anchovies and herring, often driving prey species up the beach or over sea walls in their panic to escape.
 
As you cruise the beautiful shallow reefs of the Cayman Islands you may encounter a stingray browsing over the sandy bottom accompanied by a bar jack or two. These jacks are swimming with the ray as it occasionally stops to excavate the soft substrate. The jacks are quick to pounce on any small crustaceans or juvenile fish exposed by the ray.
 
Turtles are often accompanied by bar jacks for the same reason. Bar jacks, rainbow runners and blue runners will also accompany Caribbean reef sharks or black tip sharks. Juvenile bar jacks often ride the pressure wave on the nose of the cruising shark. Larger jacks will often scrape their skin moving forward along a shark’s body to scrape off parasites. Other jacks swim with mantas, whale sharks, and large reef predators such as barracuda and large groupers.
 
Occasionally occurring in the Cayman Islands are a number of other jack species such as the African pompano and the lookdown jack and the palometa which can sometimes be seen in shallow water near the surf zone along Seven Mile Beach. These jacks are hunting small crustaceans disturbed by waders and swimmers over the sand bottom.
 
Jacks are numerous in the Pacific as well. One of my favourites in the blue spotted trevally, which grows to 30 pounds and has a yellow/green skin covered in a myriad of iridescent blue spots. They are outrageous looking, aggressive fore-reef predators that feed mostly upon creole fish. Divers in the Galápagos or Cocos Island will see this reef bandit hacking into vast schools of creole fish along with yellowfin tuna.
 
Almaco jacks up to a hundred pounds patrol the deep reefs in these locations. Green jacks take the place of blue runners in this ecosystem, and are a primary fodder species for all mid-sized pelagic predators. Big-eye jacks and crevalle form enormous schools over seamounts, in association with mullet snapper, a large pelagic snapper. Crevalle often school with young yellowfin tuna way offshore, something you never see in the Caribbean.
 
Further west in the Hawaiian Islands and in the western Pacific, the number of jack species proliferates, the biggest is the giant trevally or ulua. This species grows to 150 pounds and has become one of the most sought after species for shallow water anglers and fly fishermen.
 
All jack species have great value as game fish. No matter what the size or species they give a great fight on light tackle. Bruisers like almacos, amberjacks and giant trevally will test heavy tackle to the limit. Shallow water species such as permit, African pompano, horse-eye and jack crevalle are all powerful adversaries.
 
There is considerable commercial extraction of the larger amberjacks and almacos in many places around the Bahamas and Caribbean. The bar jack is caught in fish traps and artisanal seines all around the Caribbean and are great to eat, as are other white meat species such as the blue runner, black jack, yellow jack, permit and rainbow runner.
 
Jacks that have dark meat such as the crevalle and horse-eye are not considered good table fare. Fortunately jacks are so successful and grow so fast that they have not been over-exploited commercially (apart from the AJ) anywhere in their range. I love to take a small spinning rod armed with a small lure or spoon and catch a few bar jacks for the table. They also make good bait for catching marlin around the banks.

It is our collective responsibility to conserve the marine environment and to maintain the biodiversity of the planet.

Fish responsibly, dive safely.

Guy Harvey PhD.
www.guyharvey.com