Trachurus murphyi

The Chilean jack mackerel (Trachurus murphyi) sometimes called the Inca scad, is a species of jack mackerel in the genus Trachurus of the family Carangidae. Since the 1970s, it has become one of the world's more important commercial fish species. High volumes have been harvested, but the fishery may now be in danger of collapsing. Chilean jack mackerels are commonly 45 cm (18 in) long, though they can grow to 70 cm (28 in). They have elongated and laterally compressed bodies. The head is large with well-developed transparent protective membranes (the adipose eyelid) covering the eyes. The mouth is also large, with the rear edge of the lower jaw aligning with the front edge of the eyes. It possesses small teeth. Each opercle of the gill covers has a distinct notch on its rear edge. The second dorsal fin is much longer than the first. The pectoral fins are long and pointed. The origin of the pelvic fins is below the bottom point of attachment of the pectorals. The anal fin is also long, but shorter than the second dorsal fin. At its front are two strong spines. The upper parts of the body are metallic blue in color, while the bottom surfaces are a silvery white. The Chilean jack mackerel is an epipelagic fish that swims in schools around coasts and in the open ocean. Normally it swims at depths between 10 and 70 m, but it can swim as deep as 300 m. They are found in the south Pacific off the coasts of Chile and Peru, around New Zealand and south Australia, and in a band across the open ocean in between. In 1993, Elizarov et al. referred to this band on the high seas as the 'jack mackerel belt'. The jack mackerel belt ranges from 35 to 45°S, which means it has a north-south breadth of 10° (about 1100 km). 'Spawning groups concentrate mainly in the north of 40°S in spring and summer and south of 40°S in autumn and winter to feed'. Chilean jack mackerel normally spawn in summer. Their eggs are pelagic, that is, they float free in the open sea. Not enough data are available to know for sure the Chilean jack mackerel stock structure. However, four separate stocks have been proposed: 'a Chilean stock which is a straddling stock with respect to the high seas; a Peruvian stock which is also a straddling stock with the high seas; a central Pacific stock which exists solely in the high seas; and, a southwest Pacific stock which straddles the high seas and both the New Zealand and Australian EEZs.' Chilean jack mackerels mainly eat fish larvae, shrimp, and other small crustaceans such as copepods, although they also eat squid and small fishes. They can live up to 16 years. Not a lot is known about their predators, though they have been found in the stomachs of albacore tuna and swordfish. Tunas, billfish, and sharks are known to prey on other carangid mackerels, and will presumably also prey on Chilean jack mackerels. Chilean jack mackerels are the most commonly fished species which is not a true mackerel. They are caught commercially with surround nets designed for small pelagic purse seining, or with midwater trawls, or by trolling or longlining. In the early 1970s, Chilean jack mackerels started flourishing along the west coast of South America, and became important as a commercial species. The mackerel then expanded in a westward movement out into and across the open ocean, eventually reaching the coastal waters around New Zealand and Australia. During 1997 and 1998, a precipitous decline occurred in the catch (see the graph on the right), which can be attributed to changes in the sea surface temperature that accompanied the 1997–98 El Niño. On the eastern side of the south Pacific, the Chilean fishery operating mainly within its own EEZ has taken 75% of the global catch over the years. The Peruvian fishery captured 800,000 tonnes in 2001, but overall is an order of magnitude smaller. On the western side of the south Pacific, New Zealand fishes jack mackerel mainly inside their own EEZ, peaking modestly at 25,000 tonnes in 1995–96. From 1978 to 1991, the USSR fishing fleet intensively fished the jack mackerel belt on the high seas, taking 13 million tonnes. In subsequent years, other distant fishing nations, such as Belize, China, the Netherlands, and the Republic of Korea, have joined Russia fishing the jack mackerel belt, and by 2007, these nations were taking 18% of the global catch.