SHARK mackerel (Grammatorcynus bicarinatus) are regularly encountered by anglers fishing near coral reefs along Australia’s north eastern and north western coastlines.
Also known as scaly mackerel or large scaled tuna, this species is only known to occur along Australia’s northern coasts, and the southern coastline of Papua New Guinea. In Western Australia, this species can be reliably encountered prowling inshore and offshore coral reef edges and flats from the Kimberleys south to Shark Bay, and seasonally much further south, even to Rottnest Island in some years. On the east coast, shark mackerel occur throughout the Great Barrier Reef and seasonally have been recorded as far south as Cook Island and Ballina in northern New South Wales.
Shark mackerel have occasionally been recorded by anglers in the Northern Territory and Gulf of Carpentaria, but due to the relative scarcity of well developed coral reefs in these areas, often these encounters were not with shark mackerel, but instead the closely related and more widely distributed double-lined or scad mackerel (Grammatorcynus bilineatus).
Like shark mackerel, the scad mackerel is greenish above, grading to silver yellow along the flanks with a distinctive double lateral line, a feature that separates both Grammatorcynus species from all other mackerels. Indeed, the two species are so similar, for over 100 years scientists considered them to be one species. However, by the early 1980s it was confirmed that the scad mackerel was a separate species, distributed throughout the Indo-Pacific region, that was essentially a smaller cousin to the shark mackerel.
Scad mackerel possess a noticeably bigger eye, more gill rakers, smaller teeth and grow only to around 60cm and 3kg in weight. In contrast, shark mackerel can grow to around 110cm and over 13kg, while smaller specimens can be easily distinguished from the scad mackerel due to the presence of numerous black spots along the belly of the shark mackerel. These spots are always absent in scad mackerel.
Early scientists can be forgiven for thinking scad mackerel were immature shark mackerel. Besides the absence of the belly spots and a slightly larger eye (features that are known to vary in other fish species as they mature), both species also have flesh which posesses a distinctive shark-like ammonia smell when filleted (thus the name shark mackerel for G. bicarinatus).
For shark mackerel, this odour can be masked by brushing the fillets with lemon juice, or other more creative cooking techniques. However, scad mackerel have an even stronger ammonia odour, which together with their much darker, oilier flesh means scad in Australia are more popular as bait for larger fish, particularly as troll baits for big marlin. In some South Pacific countries, where scad mackerel are commonly eaten, their colloquial name of “urine fish” suggests they are not held in the highest esteem as a food fish!
