Mackerel

The name "mackerel" covers more than 30 species of open-ocean fish, most of which belong to the family Scombridae. These fish live in warm and cool seas worldwide, usually far from shore but sometimes near coastlines. They are recognized by deeply forked tails and iridescent blue-green backs marked with vertical, tiger-like stripes. Many species have limited ranges and form separate populations, or stocks, based on geography. Some stocks travel in large schools along coasts to shallow spawning grounds, then return in smaller groups to feeding areas, often near upwellings. From there they may move into deeper water and spend winter in a less active state. Other stocks migrate across entire oceans.

Smaller mackerel serve as forage for larger predators, including bigger mackerel, Atlantic cod, seabirds, whales, dolphins, sharks, tuna, and marlin. These predators follow mackerel schools and attack with sophisticated, cooperative tactics. Mackerel flesh is rich in omega-3 oils, and humans harvest them heavily—commercial fishermen landed over 5 million tons in 2009. Sport fishermen prize the king mackerel for its fighting ability.

**Species** More than 30 species, mainly from Scombridae, are called mackerel. The word itself comes from Old French and may have meant "marked" or "spotted," but also "pimp" or "procurer." The latter link is unclear, though mackerel spawn enthusiastically in coastal shoals, and medieval ideas about animal reproduction were imaginative.

**Scombroid mackerels** About 21 Scombridae species are called mackerel. The type species is the Atlantic mackerel, *Scomber scombrus*. Until recently, Atlantic chub mackerel and Indo-Pacific chub mackerel were considered subspecies of the same fish. In 1999, Collette used molecular and morphological evidence to show they are separate species. Mackerel are smaller and have shorter lifespans than their close relatives, the tuna, which belong to the same family.

**Scombrini, the true mackerels** True mackerels belong to the tribe Scombrini, which has seven species split between two genera: *Scomber* and *Rastrelliger*.

**Scomberomorini, the Spanish mackerels** Spanish mackerels belong to the tribe Scomberomorini, a cousin group to the true mackerels. This tribe has 21 species total—18 in *Scomberomorus*, two in *Grammatorcynus*, and one in the monotypic genus *Acanthocybium*.

**Other mackerel** Some species from the families Carangidae, Hexagrammidae, and Gempylidae are also called mackerel due to similar features. The Pacific jack mackerel (*Trachurus symmetricus*) and the heavily harvested Chilean jack mackerel (*T. murphyi*) were once thought to be the same species but are now recognized as distinct.

The term "mackerel" also modifies the common names of other fish, often because they have vertical stripes like scombroid mackerel: mackerel icefish, mackerel pike, mackerel shark (several species), shortfin mako shark, mackerel tuna, and mackerel tail goldfish. By extension, it applies to the mackerel tabby cat and to cloud formations like the altocumulus mackerel sky.

**Characteristics (Scombridae)** Most mackerel are in Scombridae, which also includes tuna and bonito. Mackerel are generally smaller and slimmer than tuna, though they share many traits. Their scales, if present, are tiny. Like tuna and bonito, they are voracious feeders, fast and agile swimmers that retract fins into grooves to streamline. They lack a swim bladder, have cylindrical bodies, and sport numerous finlets behind the dorsal and anal fins. Unlike deep-bodied tuna, they are slim.

The type species, Atlantic mackerel, has an iridescent blue-green back, a silvery belly, and near-vertical wavy black stripes along the upper body. These stripes are not for camouflage against a background—mackerel live in midwater with no background. Instead, fish have an optokinetic reflex sensitive to moving stripes. For efficient schooling, mackerel need feedback to align with neighbors and match speed. The stripes act as "schooling marks," signaling changes in relative position. The lateral line also aids orderly schooling.

Some mackerel stripes contain a layer of thin, reflecting platelets. In 1998, E. J. Denton and D. M. Rowe argued these platelets convey extra information about a fish’s movement. As the fish’s orientation shifts relative to another, the amount of reflected light changes. This orientation sensitivity gives mackerel "considerable advantages in being able to react quickly while schooling and feeding." Mackerel range from small forage fish to larger game fish. Coastal mackerel tend to be small; the king mackerel is an example of a larger species.