The narrow–barred Spanish mackerel is large and fast pelagic predator that is abundant in the tropical and sub-tropical waters of the Indo-west Pacific. It is commonly associated with island and reef environments and is most frequently caught in depths less than 100m. The Spanish mackerel is world-renowned by anglers as an excellent light game fish and is also recognised for its agreeable culinary qualities including good nutritional and storage characteristics. The global catch of this species is considerable, as indicated from landings of around 170,000 tonnes in 1995 to almost 205,000 tonnes in 2000 (FAO Fisheries Production Statistics). The total catch of Scomberomorus commerson in Northern Australia is thought to be in the range of 2000-3000 tonnes. This includes the catches of commercial, recreational and indigenous groups.

The principal fishing locations for Spanish mackerel in the Northern Territory are island, shoal and reef habitats that are easily accessible from the ports of Darwin and Nhulunbuy. The annual catch of Spanish mackerel by recreational anglers in the Northern Territory is estimated to be around 5,751 individuals or 40.3 tonnes (Lyle et al. 2003). Indigenous people are thought to catch between 2.7 and 4 tonnes (Coleman et al. 2003). These estimates are based on a mean weight of 7kg for S. commerson. 

Spanish mackerel spawn in oceanic conditions on reef edges. The eggs have a large oil droplet that aids in buoyancy and keeps the egg at the top of the water column which is warmer, well oxygenated and has a more abundant planktonic food supply for the larvae once hatched. It is believed that S. commerson, when in the larval stage, stay in their own species specific groups and are not normally found with other mackerel larvae of the same genus, such as S. semifasciatus and S. queenslandicus. This is not always the case with adult mackerel as occasional mixing of different species within the same genus can occur.

Spawning is seasonal but protracted in the warmer waters of the tropics. Many of the fisheries that target this species are based on pre-spawning feeding aggregations. A significant percentage of the female fish caught in NT waters between July and December have either recently spawned or are close to spawning (Buckworth and Clark 2001). In general, spawning times for Spanish mackerel tend to be associated with higher water temperatures that promote optimal food availability for the rapid growth and development of the larvae (Jenkins et al. 1985).

As the young larvae grow they move from the offshore spawning grounds to inshore and estuarine habitats where they are frequently encountered in the juvenile phase of their growth cycle. In the inshore environment they feed mostly on the larvae and juveniles of small fish and crustaceans until they become large enough to tackle small fish and squid (McPherson 1988). Australian studies of this species suggest that males and females differ in size, with females being larger than males (McPherson 1992; Buckworth 1998; Mackie et al. 2003). Female Spanish mackerel mature at about 2 years of age or around 80cm in length.

The longevity of Spanish mackerel is regarded as moderate. The oldest specimens from the east coast fishery are around 16 years (McPherson 1992), 12 years in the NT fishery (Buckworth 1998) and 22 years in north west Western Australia (Mackie et al. 2003). S. commerson is thought to be highly migratory but there are also resident sub-stocks (Collette and Nauen 1983). Allozyme and mitochondrial DNA studies indicate that there are three broad genetic stocks in the Australian region. One extends from PNG down the east coast of Australia and a separate population occurs in the Torres Strait. Another population ranges from southern PNG across Northern Australia and down the West Coast of the continent.

The Spanish mackerel fishery is generally reliant on hook and line technology with occasional captures in trawl and gill nets of other fisheries. The annual commercial catch in the NT over the last two decades has been as little as 54 tonnes in 1986, to as much as 385 tonnes in 2001 (Figure 4.3; logbook data, Fisheries Group, NT Department of Business Industry and Resource Development). Between 1995 and 2001 the catch of Spanish mackerel by anglers during guided fishing tours in the NT has more than doubled from 1165 to 2423 fish, with more than 60% released in most years (NT Fisheries logbook data). From a historical perspective, the biggest impact on the Spanish mackerel population of the NT was from the Taiwanese fishing fleet that fished Australian waters outside the 12 nautical mile limit between 1974 and 1986. After this time fishing became uneconomical due to net restrictions placed on each vessel. The net restrictions (a maximum of 2500m in length) were implemented as a response to concerns over the entanglement and drowning of whales and dolphins in the Taiwanese nets. The annual catch of all mackerel species by the Taiwan fleet, according to logbook and observer data, was between 400 to 500 tonnes. This represented less than 10% of the total annual catch by the Taiwan fleet. There were however, reports of annual catches of Spanish mackerel exceeding 1000 tonnes in the late 1970s (Rohan and Church 1979).

It has been known for many years that the consumption of seafood is a significant contributor to the health and wellbeing of humans. This anecdotal knowledge was recently confirmed in a study by CSIRO and the Fisheries Research and Development Corporation, which indicated that Australian seafood is high in oils such as Omega-3 (Nichols et al. 2002). Some of the beneficial effects of these polyunsaturated fatty acids are that the heart and arteries are afforded some protection from the ravages of the modern diet. Other effects of Omega-3 fatty acids on human health, is a lowering of blood pressure and prevention of rheumatoid arthritis and possibly some cancers. Another revelation from the study indicated that Australian fish, particularly those species from the warmer tropical waters, such as mackerel, have higher levels of these fatty acids than fish from the northern hemisphere.

Buckworth, R.C. 1998. Age structure of the commercial catch of the Northern Territory narrow barred Spanish mackerel. Project T94/015. Final Report to the Fisheries research & Development Corporation. Northern Territory Department of Primary Industry and Fisheries, Darwin, Australia. Fishery Report 42, 28 p. ISBN 0 7245 3037 1.

Buckworth, R.C. and Clarke, R. 2001. Fishery Assessment Report for the Northern Territory Spanish Mackerel Fishery – 1999: Summary of Assessment Information. Department of Primary Industry and Fisheries, Darwin, Australia. Fishery Report 52, 28 p. ISBN 0 7245 3072 X.

Coleman, A.P.M., Henry, G.W., Reid, D.D. and Murphy, J.J. 2003. Indigenous fishing survey of Northern Australia. In: The National Recreational and Indigenous Fishing Survey. Fisheries Research & Development Corporation Project 99/158. G.W. Henry and J.M. Lyle (eds). NSW Fisheries, Sydney, Australia. pp. 98-123.

Collette, B.B. and Nauen, C.E. 1983. FAO Species Catalogue. Vol 2. Scombrids of the world. An annotated and illustrated catalogue of tunas, mackerels, bonitos and related species known to date. FAO Fisheries Synopsis 125 (2), 137 p.

Jenkins, G.P., Milward, N.E. and Hartwick, R.F. 1985 Occurrence of larvae of Spanish mackerels, Genus Scomberomorus (Teleostei; Scombridae), in shelf waters of the Great Barrier Reef. Austustralian Journal of Marine and Freshwater Research 36: 635-640.

Lyle, J.M., Henry, G.W., West, L.D., Campbell, D., Reid, D.D. and Murphy, J.J. 2003. National recreational fishing survey. In: The National recreational and Indigenous Fishing Survey. Fisheries Research and Development Corporation project 99/158. G.W. Henry and J.M. Lyle (eds). NSW Fisheries, Sydney, Australia. pp. 27-97.

McPherson, G.R. 1988. A review of large coastal pelagic fishes in the South Pacific Region, with special reference to Scomberomorus commerson in north-east Australian waters. South Pacific Commission /Inshore Fisheries Resources/WP.15.

McPherson, G.R. 1992. Age and growth of the narrow-barred Spanish mackerel Scomberomorus commerson (Lacepede,1800) in north-eastern Queensland waters. Austustralian Journal of Marine and Freshwater Research 43: 1269-1282.

Nichols, P., Mooney, B., Virtue, P. and Elliott, N. 2002. Nutritional Value of Australian Fish: Oil, Fatty Acid and Cholesterol Composition of Edible Species. Final Report, CSIRO Marine Research, Hobart (Australia); Fisheries Research and Development Corporation Project1995/122. ISBN 0643061789.

Rohan, G. and Church, A. 1979. A review of the Northern Territory mackerel and reef fisheries. Northern Territory Department of Primary Production, Fisheries Division, Darwin, Australia. Fishery Report 3, 9 p.