It is a beautiful fish with its high, blunt head, slate to bluish-black back, silvery- yellow undersides and bright yellow anal fin. This sickle-shaped yellow anal fin can cause identification problems for those new to coastal fishing. In 30 years as a fisheries biologist, I had to disappoint more than a few anglers by telling them that their prized catch wasn't a yellowfin tuna.
The crevalle jack, scientifically known as Caranx hippos, is a member of the large jack family, Carangidae. Twenty-eight species of jacks occur in North American Atlantic and Gulf waters, including not just the familiar amberjack and delectable pompano, but also the hardtail (blue runner), the cigar minnow (round scad) and the absolutely gorgeous rainbow runner.
The crevalle jack is found on both sides of the Atlantic Ocean. On this side, it occurs from Nova Scotia south all the way to Uruguay in southern South America. In the eastern Atlantic, it ranges from Portugal south to Angola in southern Africa.
One of the heavyweights of the clan, the record weight for this fish in Louisiana is 57.88 pounds, caught by Leon D. Richard in 1997. At the time of its catch, it was a new all-tackle IGFA world-record fish, and was recognized as the Louisiana Fish of the Year by the Louisiana Outdoor Writers Association.
After that catch was made, a new world-record crevalle jack of 58 pounds, 6 ounces was recorded in 2000. Caught by Nuno A.P. de Silva, it was taken off the country of Angola, the southernmost extremity of the species' range in the eastern Atlantic.
Females mature at five to six years old; males mature a year earlier. Crevalle jacks spawn from February to October, with a peak in April-June. In spawning, large schools of a thousand or so fish gather shortly after a full moon. At these aggregations, individual males pair up and chase-court individual females. The courted females turn black on the upper half of their bodies, as do their whole heads.
Larvae end up spread far and wide, from estuaries to far offshore. Juveniles use mostly nearshore and inshore areas, and can be found on seagrass beds and in brackish mud-bottom estuaries. By one year old, they reach 9-10 inches in length, with females growing faster than males, a trend that continues through life.
Juvenile crevalle jacks, 6 to 10 inches long, are commonly caught by anglers fishing in the surf for other species. At that size, they are easy to recognize by their bright yellow dominant color and by the fact that they grunt like little piglets when removed from the water. The spines in their fins make them prickly to handle.
Mature crevalle jacks can be found in very low-salinity estuaries, but more commonly they range from brackish marshes out to the open sea. Crevalle jacks can be found anywhere and everywhere they can find something to eat.
Adult crevalle jacks can be solitary predators, but usually form small, fast-moving schools to hunt. They school by size, with the largest fish forming the smallest schools.
When prey species are sighted, often near the surface, they make spectacular slashing attacks, with prey fish leaping away in panic in every direction. After the attack, the jacks regroup for their next assault.
Pound-for-pound it would be difficult to find a harder-fighting fish in salt water or fresh water. They never give up. Because they will fight to the point of complete exhaustion, release mortality can be quite high.
Crevalle jacks are a poorly researched species, perhaps because they have little perceived food value. One interesting piece of research work, published in 1984, was done on the food habits of the species in the Gulf and South Atlantic.
For the study, fish were captured by hook and line and seine from five areas. Each fish was measured and had its stomach removed and preserved for later analysis. A total of 3,623 fish were examined in this study. Almost 40 percent of the stomachs were empty. More smaller fish than larger fish had empty stomachs, indicating that larger fish probably ate more often, ate larger food items, or regurgitated (up-chucked) less often when caught.
Jack crevalles sampled off of Louisiana ate more fish than invertebrates (animals without backbones). Fish were found in over 82 percent of the stomachs that had food, and invertebrates were found in 49 percent of the stomachs with food. Interestingly, two percent of the stomachs had pieces of wood in them.
The dietary breakdown of Louisiana jack crevalles in the study was as follows:
When the total volume of all the stomach contents was compared, 78 percent was fish and 22 percent was invertebrates. The researchers concluded that, in general, jack crevalle were a major predator on small schooling fishes in the Gulf of Mexico and south Atlantic.
Jerald Horst is an author of the Angler's Guide to Fishes of the Gulf of Mexico, a 444-page, color-illustrated book on fishes written for saltwater fishermen. The book is available in better bookstores or can be ordered by calling (800) 843-1724.