Trachurus Trachurus

– Atlantic Horse Mackerel –

The Atlantic horse mackerel (Trachurus trachurus), also known as the European horse mackerel or common scad, is a species of jack mackerel in the family Carangidae, the jacks, pompanos and trevallies. It is found in the eastern Atlantic Ocean off Europe and Africa and into the south-eastern Indian Ocean. It is an important species in commercial fisheries and is listed as a Vulnerable species on The IUCN Red List of Threatened Species.

Description

The Atlantic horse mackerel has quite a slender, quite compressed body with a large head in which the rear of the upper jaw reaches the front of the eye and the lower jaw projects beyond the upper jaw. The eye has a well developed adipose eyelid.^[4] It has two dorsal fins,^[5] the first is tall^[3] and has seven thin spines, with the final spine being much shorter than the others. The second dorsal fin is separated from the first by a narrow gap and is considerably longer than the first^[5] with 29-33 soft rays.^[6] The anal fin is about as long as the second dorsal fin and there are two separate spines at its anterior end.^[5] The moderately sized pelvic fin has a single spine and five soft rays and has its origin below the end of the pectoral fin base.^[4] A curved line of 33-40 bony scutes runs from the head to the tail, each having a small spine which increase in size and become bonier towards the tail.^[7] The lateral line has a total of 66-67 scales, of which 31-36 are scutes.^[5][6] It is dark blue in colour with silvery flanks and a white belly, there is a dark spot on the operculum. This species attains a maximum fork length of 60 centimetres (24 in),^[6] although they are normally around 25 centimetres (9.8 in) and a weight of 1.5 kilograms (3.3 lb).^[5]

Horse mackerel is a spindle-shaped fish with pearly sides and a darker back. Metal shards are characteristic of this fish which belongs to the Carangidae family.

It can be recognized by the presence of about seventy-five thickened scales called scutes , which clearly show the bayonet pattern of the lateral line . A second side line, accessory , is hardly visible. She runs along the back almost reaching the tail. A black spot is usually clearly visible on the operculum. The eye is very large and the mouth is protractile * . The dorsal fins are two in number. The first is high but narrow , while the second goes from the middle of the back almost to the tail . The caudal fin is very forked, the caudal peduncle * is narrow, the pectoral fins are longer than the head. The anal fin is almost symmetrical to the second dorsal, it is preceded by two small characteristic spines . The fins are more or less transparent .

Another characteristic of this fish is that one has the impression of seeing the “ribs” at the level of the belly.

Distribution

The Atlantic horse mackerel occurs in the north and eastern Atlantic Ocean, the Mediterranean Sea and Sea of Marmara and the Black Sea. In the Atlantic it is found from Norway to South Africa where it may extend around the Cape of Good Hope along the southern African Indian Ocean coast Maputo in Mozambique.^[1] However, if Trachurus capensis is considered to be a valid species then this species is restricted to the north east Atlantic.^[8] It has been recorded in Cape Verde but is thought to occur there only as a vagrant.^[1]

Biotope

Horse mackerel are gregarious and pelagic * fish. They are generally found from the surface to a depth of 100 m, but can go down to 1,050 m, especially in winter.

They congregate in large schools above sandy bottoms. In summer, they get closer to the coast, but rarely remain visible in shallow water.

Taxonomy and Naming

The Atlantic horse mackerel is the type species of the genus Trachurus but when Constantine Samuel Rafinesque created the genus in 1810 he used Trachurus saurus as the type species but Carolus Linnaeus had used the name Scomber saurus and had already described Scomber trachurus so Rafinesque’s name was invalid.^[10] The genus Trachurus is part of the subfamily Caranginae of the family Carangidae, which is the largest family in the order Carangiformes.^[11] The generic and specific names are a compound of the Greek trachys meaning “rough” and oura meaning “tail”, this appears to be an ancient name for horse mackerels, presumably in reference to the spiny scutes on the caudal peduncle.^[12]

The common name horse mackerel has been said to derive from the belief that other fishes rode on its back but it may derive from the old Dutch word Horsmakreel which means a mackerel which spawns over a shallow or bank, a hors, and this was taken into English as “horse mackerel”.^[13]

The Cape horse mackerel (Trachurus capensis) is considered to be the subspecies T. trachurus capensis of the Atlantic horse mackerel by some authorities and it is thought that there is no adequate series of these specimens of this taxa along the coast of Africa available to confirm the validity of this taxon.^[8]

Similar Species

From a distance, horse mackerel looks like bugs ( Boops boops ) or even mackerel ( Scomber scombrus ).
Up close it is difficult to distinguish in situ from other horse mackerel.

The yellow-tailed horse mackerel ( Trachurus mediterraneus ) is longer, the accessory lateral line reaching the junction between the two dorsal fins. Its fins and tail are often yellowish, hence its name.

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

Comet kia-kia ( Decapterus punctatus ), a subtropical cousin of horse mackerel, is also very close. It is distinguished in particular by the presence of scutes only in the posterior third of the lateral line. Its presence is yet to be confirmed in the Mediterranean.

Habitat and Biology

The Atlantic horse mackerel is a benthopelagic species which normally occurs over sandy substrates at depths of 100–200 metres (330–660 ft), although it has been reported as deep as 1,050 metres (3,440 ft) and it is sometimes found nearer the surface waters.^[4] It is a migratory species, moving northwards in the summer months and returning southwards when the sea temperature starts to fall.^[7] In the north east Atlantic two stocks are recognised, the western stock spawns in a wide area from Ireland to the Bay of Biscay in the early Spring and moves northward to the southern coats of Norway and the northern North Sea in the summer. The North Sea stock spawns in the southern part of the North Sea during the summer and then migrates northwards into the central North Sea, the Skagerrak and the Kattegat. Off Mauritania this species has its main spawning season in November to January while the related Cunene horse mackerel (Trachurus trecae) spawns in June and August.^[1] Off Ireland spawning occurs irregularly during the summer from June to August reaching its peak in July. The females spawn in batches, each of up to 140,000 eggs and hatching larvae 5 millimetres (0.20 in) in length. Spawning is indeterminate meaning that the total number of eggs a female can produce is dependent on factors which can change over the course of a spawning season.^[7] The eggs and larvae are pelagic.^[4]

The juveniles of thus species frequently often shoal with the juveniles of other fish species, mainly Atlantic herring (Clupea clupea) and with other species of horse mackerels such as the Mediterranean horse mackerel (T. mediterraneus) and blue jack mackerel (T. picturatus).^[4] Juveniles are also often encountered sheltering in the tentacles of jellyfish. In South Africa the maximum recorded age is 24 years while 40 years of age has been recorded in the northeast Atlantic. They are thought to breed from two to four years old for females. Off Mauritania, the juveniles are caught at depths of 200–300 metres (660–980 ft) while mature fish are taken in shallower waters of less than 100 metres (330 ft).The age and growth of the Atlantic horse mackerel vary across its extensive range and are affected by the levels to which stocks are exploited.^[1]

The diet of this species, in both juveniles and adults, is copepods, shrimps, small fishes and squids.^[6] An examination of the stomach contents of Atlantic horse mackerels caught in the Aegean Sea recorded a total of 60 different prey species which belonged to five major systematic groups, polychaetes, crustaceans, molluscs, arrow worms and bony fish. Copepods, Euphasids and Mysids made up the highest percentage of food eaten. Bony fish were the secondmost numerous food ingested, while polychaeta and arrow worms were infrequently recorded food items. The diet showed very little seasonal variation with copepods and mysids making up the largest proportion of prey throughout the year, with fishes being most frequent prey except in the spring. Larger fish, over 16.9 centimetres (6.7 in) fed largely on the larvae of bony fishes. No less than 45 species of copeopod were identified in this study, and Acartia clause and Oncea media were numerous and important throughout the year. Crustaceans were the most important prey to be eaten by this species in all seasons, however, bony fish were the most important prey items for larger fish.^[9]

Alimentation

The food of horse mackerel is varied, consisting of fish, crustaceans and cephalopods. It sometimes attacks jellyfish, when weakened, they arrive on the shore (editor’s observation).

This predatory fish hunts in schools, it is more active at night than during the day.
The daily vertical migrations are important. At night, horse mackerel follow the plankton * and come up close to the surface to feed while during the day, they descend to the bottom.

Reproduction

Sexual maturity is reached around three years old for females, around five years old for males, when horse mackerel reaches 20 cm. The sexes are separate and fertilization is external.

Horse mackerel has a high reproduction rate. The female can lay up to 140,000 yellow-brown, spherical and smooth eggs, which are released in open water during the summer season. When hatching, the larvae * measure barely 5 mm.

Their lifespan is estimated at 22 years.

Associated Life

Juveniles are often found under jellyfish (classic association with Cotylorhiza tuberculata and Rhizostoma pulmo ), even among their tentacles *, and other drifting objects to protect themselves from predators.

Various Biology

Common species offshore, with an interest in fishing, but which remains rare on our coasts.

The species migrates according to the seasons. A large group spawns from the Bay of Biscay to Ireland in spring and then migrates into the northern North Sea and southern Norway, while another group spawns in the southern Black Sea in summer and then moves up to the North.

Further Information

Called severeaux in Provence, horse mackerel are popular with both professional and recreational fishermen who offer multiple recipes to accommodate them …

Fisheries

The Atlantic horse mackerel is fished for commercially using trawls, longlines, purse seines (using artificial light), traps and on line gear. In 1999 the Food and Agriculture Organization stated that the total catch reported to it was 322 207 tonnes with the largest catches being in the Netherlands and in Ireland.^[4] There is a total allowable catch (TAC) in the North Sea for this species and landings have consistently been below this level^[14] but the TAC is not in line with the scientific advice. There have been calls to create a management plan for the Atlantic horse mackerel in the North Sea but currently there are no specific management objectives for it. The stock needs to be assessed and management objectives should be set before the fishery can be shown to be sustainable.^[15]

Conservation

The IUCN classify the Atlantic horse mackerel as Vulnerable because even if there has been no decline in the population in European waters there have been greater than ninety percent declines off the West African coast which means that this species will have undergone a decline of at least 35-40% decline over the past three generation lengths, which are estimated at 30–35 years.^[1] The International Council for the Exploration of the Sea (ICES) classifies the population of this species as below the safe biological limit for exploitation.^[7] The populations are experiencing a slow decline with increased fishing pressure at the maximum sustainable yield since 2006 with low recruitment since 2004.^[7]

Human Uses

The Atlantic horse mackerel is consumed fresh. It may be preserved by freezing, salting and drying, smoking and canning. It can be prepared by frying, broiling or baking.^[4] The flesh is said to have a pleasant flavour with an oily delicate texture which is a good sourse of omega-3 fatty acids.^[16] Nutritionally 100g of the flesh of the Atlantic horse mackerel provides 97 kcal of energy and is made up of:^[17]

Chicharros en escabeche

• Water: 77.4 g
• Protein: 19.8 g
• Fat: 2 g
• Cholesterol: 64.4 mg
• Total minerals: 1.3 g
• Phosphorus: 224 mg

In Iberia it may be prepared as an escabeche while some are exported to Japan as aji to be used in sushi.^[18] They are also an important ingredient in Sicilian cuisine.^[17]