Category: High Risk
MAHI MAHI, or dolphinfish, have to be one of the most colourful and acrobatic targets for recreational anglers in Western Australia. Generally found well offshore, these spectacular speedsters, with the colour-changing abilities of a chameleon, are a highly valued recreational species. Experienced offshore anglers always investigate floating objects to see if any mahi mahi have taken up residence beneath them. The sight of the lit up shoulders and pectoral fins of a school of mahi mahi is welcome indeed, for they are frequently the preferred fish anglers would like to take home to the family for a meal. The flesh is sweet but soft and does not lend itself to freezing or careless handling. Nevertheless it is highly prized on the table fresh.
Mahi mahi are voracious eaters and consume just about anything that's edible in the upper layers of the ocean, and it is for this reason that they are viewed as an effective sampler of what lives near the surface. Recently off Perth a juvenile broadbill swordfish was found in the stomach contents of a mahi mahi, providing new evidence that broadbill almost certainly breed offshore between Geraldton and Perth. Mahi mahi have also been known to eat plastic and other junk that ends up in the ocean.
It is very difficult to confuse mahi mahi with anything else with fins. The colour of this fish is truly unique and varies from dull silver flanks and blue/grey back on schooling fish through to vivid yellow and blue/green with iridescent turquoise spots on hunting or captured fish. Mahi mahi also have the ability to "light up" when hunting, as do billfish, and this is best seen in their pectoral fins which frequently take on a striking iridescent blue when they come in for a bait or lure. The colour shift is truly amazing. The males, or bulls, can easily be distinguished from the females, or cows, by their blunt heads. The females have a much gentler sloping head.
Most anglers encounter fish in the range from two to ten kilos, but mahi mahi up to 15.3 kilos have been recorded off Exmouth/Coral Bay. In NSW monsters up to 38 kilos have been recorded. The larger specimens are always males - they reach twice the size of females.
Mahi mahi are one of the fastest growing fish in the sea and small fish of two kilos which recruit onto the Rottnest FADs in January can be as heavy as seven to nine kilos by May. Now that's some growth and it's probably why aqua culturists have been keen to breed and rear them in captivity for the table. I understand that from an egg to 20 kilos can take as little as nine months! I understand this work is continuing at Fremantle in conjunction with South Metropolitan College of TAFE.
Mahi mahi are widely distributed in the warmer waters along the west coast with their normal range extending down to around 33 degrees south. However, in years of a strong Leeuwin Current they can turn up as far south as Albany.
Breeding and migration
In captivity female mahi mahi spawn every few days, so the egg production from a female would be very significant over a 12-month period. The general migration pattern along the west coast is southward from the tropical zone following the warm Leeuwin Current. Mahi mahi can be found in water as cold as 19deg but prefer temperatures of above 23deg.
Given that mahi mahi migrate annually into the southern waters of WA, it is possible that local stock depletion could occur as a result of excessive fishing pressure. The increasing activities of Australian longliners will certainly reduce the numbers of these fish available for recreational anglers, but because of their very wide distribution they are unlikely to become threatened in the near future.
Tackle and bait
Mahi mahi will at times take baits, lures and flies with relish. At other times they will just ignore anything you put in front of them, which is surprising given the amount of food they must surely need to fuel their phenomenal growth rates. My favourite tackle for fish up to ten kilos is a spin stick with six-kilo line or braid if I'm hungry. Drifting a mulie near a FAD is probably the most popular way of catching a fish, but many regular mahi mahi anglers favour live baiting. Live herring, yellowtail scad or blue mackerel are all irresistible at times - and at others they are useless. Such is fishing for mahi mahi. Cut baits of fresh fillet will also catch them but the bait needs to be straight to ensure that it doesn't spin in the current or during retrieve, when fish often pounce. A single hook tied to a 15 to 24-kilo trace with a 6/0 hook will handle most mahi mahi you are likely to encounter in WA waters when bait fishing. Tackle can be very simple indeed.
One of the great things about mahi mahi is that when they shut down to one fishing method they will still be susceptible to others. If I were fishing FADs, or around any floating object for that matter, I would start by trolling small flashy skirted lures, such as Christmas trees or feathers, past the floating object. I might even put a bibbed minnow in short in the prop wash to increase the range of options. Mostly mahi mahi respond positively to lures presented at speed. If the fish turned shy to that approach I would switch to live bait or mulies. And stay watchful, for often mahi mahi will leave the floating object they call home and move away to feed. When this happens look for feeding birds not too far from the floating object and fish there.
Trolling for mahi mahi away from floating objects and FADs is generally not worthwhile, though they occasionally turn up as a very welcome bycatch when chasing more widespread species such as tuna, or when trolling for marlin. I have caught numerous good sized mahi mahi during marlin fishing trips on lures carrying a pair of 16/0 hooks. At times mahi mahi can be so keen to eat your offering that you can easily exceed the daily bag limit of four, so crushing down barbs on hooks is a good idea if you want to keep fishing.
Kailola, Williams, Stewart, Reichelt, McNee and Grieve Australian Fisheries Resources 1993. Hutchins and Swainston Sea Fishes of Southern Australia 1986. Compiled with the assistance of Dr Julian Pepperell.