The offshore waters of the Gulf of Mexico are teeming with pelagic fish. The fertile waters, combined with many offshore structures such as oil rigs, create the ideal situation to catch fish. One of the more popular sport fish is the tuna. They come in all sizes and flavors, but generally they are hard fighters and prized for their table fare. Most can be eaten as sushi or ceviche, or seared and grilled in a variety of ways. Tuna is normally a reddish flesh and is often described to taste more like meat than fish. Fresh tuna is nothing like what you get from a can, so don’t judge it by that standard.
Some of the more prized tuna like yellowfin have size and bag limits that apply, while others have none, like the blackfin. Anglers should always check the current laws and licenses required to possess tuna. Permits for possession and landing reports are often required for some species. Often they are free to boaters, but you must get them before the fishing trip.
Since various species of tunas are regulated differently, fishermen must be able to tell which kind they have captured. Below is a guide of some distinguishing characteristics to help you determine which tuna you have captured. Some characteristics are internal, like striations of the liver, but this does not help you know whether to release it or not. For this reason we will focus on the external features that will help you make the call while the fish is still alive.
Yellowfin Tuna
The yellowfin tuna (Thunnus albacares) is one of the most popular and targeted species. They are excellent eating and amazing fighters. They can reach a size of 400 pounds, but that is not the norm. Fish in the 20- to 200-pound range are more commonly caught. This species does have size and bag limits so check the current regulations for the area you will be fishing. All tuna have a fusiform body, like a football, but yellowfin are more slender than related bluefin and bigeye tuna. The second dorsal fin is longer than any other tuna, and it and the anal fin can get longer with age. The pectoral fins on the side are longer when laid against the body than the origin of the second dorsal fin but not longer than the end of the second dorsal’s base. These tuna have a blue/black back and a yellow band on their sides along the lateral line. Below the yellow band, the rest of the sides and belly are a silvery gray. Juveniles often have white bars and dots on their sides. The second dorsal and anal fins are bright yellow, and the small fins down the top and bottom of the tail, finlets, are yellow with a thin black margin.
Yellowfin tuna are caught in a variety of ways, but trolling lures and natural baits, live bait and chunking are popular. Plugging topwater chugging lures and vertical jigging metal jigs into feeding schools is effective, too.
Blackfin Tuna
Blackfin tuna (Thunnus alanticus) are another more commonly-caught species. Much smaller than yellowfin, they average around 28 inches in length and grow up to 40 inches. These tuna are often mixed with yellowfin and skipjack tuna. They are also good eating but not quite as prized as yellowfin. Still, they are great fun to catch and best when eaten fresh.
Blackfin tuna can be distinguished by the lack of yellow finlets. They are dusky colored and may have a white edge and at most a trace of yellow. Their body shape is not as slender as that of the yellowfin. The dorsal fins are both dusky colored, as well as the anal fin, and may have a silvery sheen. The lateral line can have more of an amber color, and the sides and belly are a gray/silverish white. The back is black/blue, and younger fish may show the white bars and spots pattern.
Bigeye Tuna
Bigeye tuna (Thunnus obesus) are less frequently caught but still a possibility in the Gulf. They can be very similar to yellowfin tuna when they are juveniles. Bigeye have a dark, metallic blue back and upper sides, while the lower sides and belly are whitish/silver. The first fin on their back is a deep yellow color, while the second dorsal and anal fins are brownish/yellowish in color with narrow black margins. The finlets are bright yellow like the yellowfin tuna, but the bigeye has a much broader black edge on its finlets. The eye is larger than most other species, hence the name. Bigeye tuna can grow to 66 inches and are prized eating.
Bluefin Tuna
Bluefin tuna (Thunnus thynnus) are less frequently caught but can be the largest of all the tunas. These giants are pursued around the world for their excellent sushi-grade flesh. They are highly regulated and under tremendous fishing pressure around the globe so check the current regulations. Bluefins are distinguished by their stocky compressed body shape, and their pectoral fin does not reach the origin of the second dorsal fin. Also, the height of the second dorsal is taller than the first dorsal. The back and upper sides are black/blue with a greenish sheen. The rest is silvery and marked with gray spots and bars. The second dorsal fin is reddish-brown, and the anal fin is brownish-yellow. The finlets are yellow with black margins. The caudle peduncle is colored black in adults but not in young fish. Bluefin grow up to 118 inches and can weigh up to 1,400 pounds.
Skipjack Tuna
The skipjack tuna (Katsuwonus pelamis) is a very common species offshore and swims and feeds in great schools. Often mixed in with other species, these tuna are easier to recognize because of the dark longitudinal lines down their silver body. When freshly caught, they exhibit fluorescent deep purple lines in their pattern. They have very compressed bodies, and they carry their thickness right up to the tail. They have short pectoral and anal fins, and the dorsal fins are separated by a small gap. The flesh of the skipjack is very soft, but some say that it makes great sushi and steamed tuna salad. They are commonly caught between 16 and 25 inches.
Little Tunny
The little tunny (Euthynnus alletteratus) is another very common catch and will venture nearer to shore than many others. They also feed in great schools and are a common catch while trolling or vertical jigging. They are easy to recognize due to the wavy pattern on their back that begins behind the first dorsal. Their back is a green/black color while the sides and belly are a bright silver. The have a pattern of dark spots below the pectoral fins.
They are often referred to as “bonita” and are more often considered great bait as their meat is strong and almost black/red in color. They can be eaten but are best used to catch something better. Used as cut bait chunks for bottom fishing or trimmed into strips for trolling, they are a fish favorite. They are commonly caught in the 12 to 30 inch range and, like all tuna, are very strong fighters.
Whichever tuna you catch, it will give you quite the fight on the appropriate tackle, and most will give you some amazing dinner.
Get familiar with the look of these fish before you go. Tuna must swim forward constantly and are a very frail fish. You must keep their time out of water to an absolute minimum (about 30 seconds max) in order for these fish to survive release. Therefore knowing what you’re looking for will help you to quickly decide if you can keep your catch or release it to fight another day. Louisiana has a great tagging program and even has tagging tournaments in the Louisiana Saltwater Series. These tagging studies are furthering our knowledge about these popular gamefish.
