Mangrove Jack

A jack eats at the edge of cover and goes home with what it eats. Fishes of Australia describes it as an active predator that feeds mainly at night on fish, crustaceans, gastropods and cephalopods. The fly angler’s window is the edge of that: the first and last hours of light, and the change of the tide. Cast short and accurately, strip short, and strike with the line hand rather than a lift of the rod. The Murray cod timber page describes a similar contest in fresh water, a fish that eats beside timber and heads straight back into it, and its advice on the strip-strike applies here too.

Mostly tropical, with a long tail down the east coast. The sources draw the edges a little differently. The Australian Faunal Directory gives Ningaloo Reef in Western Australia to Sydney. Fishes of Australia gives Perth around the tropical north to Jervis Bay. NSW DPIRD puts the range from Shark Bay through Torres Strait and Queensland to Lake Illawarra, with fish occasionally found in estuaries further south. Read all three together and the practical answer is clear: this is a fish of northern Western Australia, the Northern Territory, Queensland and the northern half of New South Wales, and a southern fish is a stray.

The species also ranges widely through the Indo-west-central Pacific.

Young fish in the estuaries, adults out on the reef. The Australian Faunal Directory says juveniles inhabit mangrove estuaries and tidal creeks and are occasionally found in the lower reaches of freshwater streams. Fishes of Australia says they move offshore when they reach 40 to 50 centimetres, and that adults gather around coral reefs.

So the estuary fish are the sub-adults, and they behave like it: each holds close to a snag, a rock bar, an undercut mangrove bank or a pylon, and every take is an ambush followed by a dash for cover. Fishes of Australia gives a maximum of 120 centimetres, with fish commonly to 80; NSW DPIRD gives about 1.2 metres and 16 kilograms. Fish that size are reef fish, not creek fish.

The red bass, Lutjanus bohar, is the lookalike, and the difference matters: NSW DPIRD notes that mangrove jack are often confused with red bass on colour alone. Look in front of the eye. A red bass has a deep pit in front of each eye, and a mangrove jack does not. Fishes of Australia adds that red bass are usually darker. Juvenile jacks are easier: about eight whitish bars on the sides and one or two blue lines across the cheek.

Names cause their own confusion. The Australian Faunal Directory records a long list of common names for this fish, among them red bream, river roman and rock barramundi, so a report of a “rock barra” may be a jack and not a barramundi at all.

The fly-fishing advice here comes from an angling magazine, Hooked Up, not from a fisheries agency, and its message is that light tackle loses jacks.

Short, accurate casts beat long ones near a snag. On a rock bar, Hooked Up suggests casting long and up-current, letting the line sink, and stripping back over the rocks with a varied, slow retrieve; casting downcurrent lifts the fly out of the zone too quickly. The saltwater depth control page covers that problem in more detail, and streamer fishing covers the stripping. Most of what a jack eats is small fish and crustaceans, so the baitfish and fry page is the right place to think about profiles.

Low light matters most. Hooked Up puts the best of it in the first two hours of the morning and the last two of the afternoon, with tide changes as the other trigger.

When one eats, do not let it turn. Strip-set hard with the rod low, and pull the fish away from the structure before you think about anything else. Unhook it with pliers and keep your fingers clear of the front of its mouth.

Out of reach of the estuary angler. Fishes of Australia says mangrove jack spawn on deeper offshore reefs during the summer months, releasing pelagic eggs, and that the young settle in coastal estuaries before moving back offshore as they grow. The creek fish you catch are not spawning fish.

Rules differ by state and change, so check the current guide before you keep one.

Fishes of Australia lists the species as Least Concern on the IUCN Red List.

Because the fish is closer to its snag than you are to the fish. Hooked Up’s answer is tackle: a 9 or 10 weight for subsurface flies and leaders up to 40 lb, so the first pull turns the fish’s head instead of testing the knot.

Look in front of the eye. NSW DPIRD’s test is the deep pit before each eye that a red bass has and a mangrove jack lacks. If you are offshore and unsure, treat the identification as unconfirmed and check the local rules before keeping it.

Rarely. Fishes of Australia says jacks move offshore at 40 to 50 centimetres, so the largest fish are reef fish. A creek fish near that size is about as big as estuary jacks get.