Trachurus Mediterraneus

– Mediterranean Horse Mackerel-

-(Bluejack Mackerel) –

The Mediterranean horse mackerel (Trachurus mediterraneus), also known as the Black Sea horse mackerel, horse mackerel, Mediterranean scad, common scad, or simply scad, is a species of mackerel in the family Carangidae found in the eastern Atlantic from Bay of Biscay to Mauritania, including the Mediterranean Sea. It is a benthopelagic, subtropical, marine fish that can reach up to 60 cm (24 in) in length. In the countries near the Mediterranean and Black Seas, it makes up a significant portion of fish catch, 54% of fish caught in the latter. Despite overfishing in the 1980s, catch numbers have leveled out and it is listed as least concern by the International Union for the Conservation of Nature.

Description

The Mediterranean horse mackerel has an elongated, compressed body (up to 60 cm (24 in) in length, common length 30 cm (12 in)) with a large head and projected lower jaw. The nostrils are small and close-set and the eyes are protected by a well-developed adipose eyelid. Its upper jaw, or maxilla, is also large and wide. Its body is a dusky color, blue to grey to black in color dorsally and on top of the head, while the lower two-thirds of the body is white to silver in color. Its caudal fin is yellow and it has a distinct black mark just posterior to the operculum. It has 36-41 gillrakers and the anal fin is preceded by two separate spines.^[3]

The body of horse mackerel is fusiform, slender and laterally compressed , with an average length of 30 cm (maximum 60 cm).
The fins, especially the caudal , are yellowish , made up of thorny rays. It has a dorsal fin in 2 very distinct parts .
The lateral line shows a clear inflection in the middle of the body . It is marked by large bony scales, transparent in the form of escutcheons. A second line, near the back , stops at the start of the second dorsal.
The size of the pecs does not exceed the curve of the lateral line. The caudal fin, forked, is not thick. The last ray of the second dorsal and anal is slightly separated from these fins.
The mouth is protractile *, the muzzle pointed, the mandible * prominent. The scales are cycloid *.
The general coloration is silvery gray , marked by a black spot spread over the operculum .

Distribution and Habitat

The Mediterranean horse mackerel is found in subtropical waters throughout the eastern Atlantic Ocean from the Bay of Biscay to Mauritania, as well as the Mediterranean Sea, Black Sea, the Sea of Marmara, and the southwestern Sea of Azov. Its latitudinal range extends from 49°N to 28°N and its longitudinal range extends from 13°W to 43°E.^[2] The subspecies T. m. mediterraneus is found in the Mediterranean Sea,^[4] while the T. m. ponticus subspecies, also called the Black Sea scad, is native to the Black Sea, the Sea of Marmara, and the Sea of Azov.^[2] T. m. ponticus is found in the territorial waters of every country bordering the Black Sea: Bulgaria, Georgia, Romania, Russia, Turkey, and Ukraine.^[5] Subspecies populations are not isolated and some limited migration between seas occurs. Hybrid offspring have been found in the wild.^[4][6] Its typical depth range is 5–250 m (16–820 ft), though it can be found as deep as 500 m (1,600 ft). It lives near the ocean floor, though it sometimes schools near the surface.^[2]

Biotope

It is a migratory fish in open water, able to adapt to brackish water. It is found near the bottom or on the surface, from 5 to 250 m, and even 500 m, in depth. He is a very good swimmer.
He lives in schools.
In winter, it moves away from the coast and lives deeper (between 50 and 400 m).

Taxonomy and Phylogeny

The Mediterranean horse mackerel was first described in 1868 by Austrian ichthyologist, zoologist, and herpetologist Franz Steindachner, who gave it the name Caranx trachurus mediterraneus. It was also described two other times, by Y. G. Aleev in 1956 and J. Dardignac and A. Vincent. Its generic name comes from the Greek roots trachys meaning “rough” and oura meaning “tail”.^[2]

Similar Species

Trachurus trachurus , the less elongated horse mackerel, is very similar but its second lateral line ends at the end of the second dorsal. In addition, the spot marking the operculum is rounded and the size of the pectorals exceeds the curve of the lateral line. It is greenish gray and the undersides of the pecs are dark. Finally, its range is wider.

Trachurus picturatus , the blue horse mackerel, has a slender body with the second lateral line extending beyond the beginning of the second ridge. The last ray of the dorsal and anal is slightly separated from these fins. The back is dark blue, the fins pink. It is a species from the open sea.

Trachurus suareus is a rarer species. Its back is iridescent, its sides silver. The anal is pink.

Schools of yellowtail horse mackerel resemble schools of mackerel ( Scomber scombrus ), especially since they pursue the same prey.

Biology and Ecology

A marine species that prefers brackish water and subtropical temperatures, the Mediterranean horse mackerel is oceandromous, that is it migrates within its native bodies of water. It feeds primarily on sardines, anchovies, and small crustaceans.^[2] It shoals with other members of its genus, such as T. trachurus and T. picturatus.^[3]

Like other mackerels, the Mediterranean horse mackerel’s reproduction is oviparous. Its reproductive cycle is divided into three distinct stages, the prereproductive, reproductive, and postreproductive. The prereproductive stages occurs from January to April and the postreproductive stage occurs from September to December. During these periods, the gonads are much smaller than the reproductive stage. Mating occurs in the summer from May to August, during which testes and ovaries grow significantly in size. The ovaries become a dark orange color and eggs are visible on the surface.^[7] Embryonic development occurs in 24–26 hours.^[8] Eggs are pelagic^[2] and 0.71–0.92 mm (0.028–0.036 in) in length.^[9] Sexual maturity is reached at 2 years of age and around 16 cm (6.3 in) in length for both males and females.^[7]

It is parasitized by the monogeneans Gastrocotyle trachuri, Pseudaxine trachuri, and Cemocotyle trachuri.^[10]

Alimentation

Mainly piscivorous, it feeds more particularly on sardines and anchovies, but also sometimes on small crustaceans. Young people eat only crustaceans.
It hunts in schools, vertically. It is a voracious fish.

Reproduction

The breeding season takes place from June to September. 100,000 to 200,000 eggs are scattered at sea: they are pelagic *, as are the fry.
Upon hatching, the larva * measures 2.5 mm. Larvae and fry live in small groups, often in the shade of floating objects.

Associated Life

The larvae and the fry often settle in the shelter of the parasols of jellyfish, such as Cotylorhiza tuberculata or Rhizostoma pulmo , benefiting from the protection of the stinging cells of their host. They leave this protection when they reach 4 cm in length.

Various Biology

A subspecies, Trachurus mediterraneus ponticus , lives in the Sea of ​​Marmara, the Black Sea and south of the Sea of ​​Azov.

The longevity of this horse mackerel can reach 15 years.

Human Interaction

The Mediterranean horse mackerel is an important resource in the Mediterranean Sea and the Black Sea region.^[6] It makes up 54% of catches in the Black Sea and 39% in the Sea of Marmara. In the Aegean and Mediterranean Seas, it only totals 3-4% of annual catches. Fixed nets and seines are common methods used to catch Mediterranean horse mackerel.^[1] Along with T. trachurus, it is one of two Trachurus species in the Mediterranean. Because it forms dense schools and lives in shallower waters, the Mediterranean horse mackerel is the more commonly caught species.^[11] Along with Engraulis encrasicolus, it makes up 59% of seafood production in Turkey.^[9]

Despite being regularly caught in mixed-species fisheries, the Mediterranean horse mackerel is listed as least concern by the IUCN. Its wide range buffers it from steep population declines, and none has been observed in recent years, with catches leveling out in the past decade. Overfishing in the 1980s led to a steep decline in catches in the Black and Marmara Seas, but has since become stable. Some conservation measures are in place in certain European countries. Minimum catch lengths are 15 cm (5.9 in) in the EU, 10 cm (3.9 in) in Ukraine, 12 cm (4.7 in) in Romania and Bulgaria, and 13 cm (5.1 in) in Turkey.^[1]