Green jack
Encyclopedia
The green jack, Caranx caballus (also known as the horse jack), is an abundant species
of coastal marine
fish
in the jack family Carangidae
. The species is distributed in the eastern Pacific Ocean
along the America
n coastline from Santa Cruz Island
off California in the north to Peru
in the south, as well as a number of islands including the Galapagos and recently, Hawaii
. The green jack is distinguished from other similar carangid species by a number of features including gill raker
and lateral line
scale counts, and the presence of an adipose eyelid. It is a moderately large species, growing to at least 55 cm in length and 2.81 kg, although unconfirmed reports suggest a much larger maximum size. It lives in a wide range of continental shelf
environments including estuaries, bay
s, reef
s and offshore seamount
s, living both pelagically and demersally. The green jack is a predatory species, preying on a variety of fish, crustacean
s and cephalopod
s, as well as zooplankton
. Most fish are sexually mature
by the time they attain 38 cm, with spawning
occurring between May and October. The species is of high importance to fisheries throughout its range, caught by pelagic trawls, a variety of netting
methods and hook and line. The green jack is also of interest to angler
s, taken by bait and lures, although is considered to only be fair in eating quality.
Caranx
, one of a number of groups of fish referred to as jacks and trevallies. Caranx is further classified in the family Carangidae
, itself part of the suborder Percoidei
and the order Perciformes
; the perch-like fishes.
The species was first scientifically described by the French biologist
Charles Frédéric Girard
in 1858, who named the species Trachurus boops, placing the species in the horse mackerel
genus based on the holotype
taken off of San Diego, California
.
With the instability of carangid taxonomy
at the time, the species was reassigned to a number of genera, including Caranx, which created a taxonomic homonym
with the Caranx boops described by Georges Cuvier
in 1833. In 1868, British zoologist Albert Günther unaware of the prior naming independently renamed the species Caranx caballus based on specimens collected from Panama
, one of which was designated to be the holotype. The species was further renamed in 1870 by Franz Steindachner
, who attempted to remove the Caranx boops homonym by simply renaming the species Caranx girardi. Later reviews of the Carangidae revealed this synonymy, and due to Gunther's' earlier naming, his species name was kept and attributed to him, while Cuvier's' Caranx boops was later moved to Selar boops. The specific name caballus is Latin
for 'horse', reflecting the common name of horse mackerel given to this and many similar species at the time. William Smith-Vaniz has suggested the possibility C. caballus is conspecific with a very similar Atlantic
species; Caranx crysos, but no studies into this relationship have been undertaken. Its position in the genus Caranx has also been questioned recently by John Randall due to its unusual dentition. The common name
'green jack' is in reference to the species common coloration, while 'horse jack' is derived from the Latin name. In Spanish
speaking nations, it is often known under broadly applied names including 'Cocinero' and 'Caballa'.
similar to a number of other carangids, having an elongated, moderately compressed fusiform body with dorsal and ventral profiles of approximately equal convexity and a slightly pointed snout. The posterior section of the eye is covered by a moderately well developed adipose eyelid, and the posterior extremity of the jaw
is vertically under the center of the eye. The dorsal fin
is in two parts, the first consisting of 8 spines and the second of 1 spine followed by 22 to 25 soft rays. The anal fin consists of 2 anteriorly detached spines followed by 1 spine and 16 to 21 soft rays. The lobes of both the second dorsal and anal fin are slightly elongated and almost entirely covered in small scale
s, but are still much shorter than the head length. The lateral line
has a pronounced but short anterior arch, with the curved section intersecting the straight section below the spine of the second dorsal fin. The straight section contains 0 to 7 scales followed by 42 to 56 very strong scute
s, and 43 to 47 scales overall. The chest is completely scaled. The upper jaw contains an irregular series of outer canine
s with an inner band of small, regularly spaced teeth, while the lower jaw contains a single band of small teeth. The species has 40 to 45 gill raker
s in total; 10 to 15 on the upper limb and 27 to 30 on the lower limb, with this the only feature that differs between C. caballus and C. crysos. There are 25 vertebrae present.
In life, the green jack has a greenish blue colour overall, with an olive green to dark blue back and a golden to grey coloured belly, with a distinct back blotch on the outer edge of the operculum
. Individuals in schools
often have a very evident pearly white marking near this black blotch. Juveniles have 7 dark vertical stripes on their flanks which fade with age. The caudal fin is grey with dark tips, with all other fins being light grey to hyaline
in colour.
. Its range extends along the coast of the Americas from Santa Cruz Island
, California
, south through Mexico
and Central America
, and down to Peru
. The species also inhabits a number of offshore islands including the Galápagos Islands
. The species had been captured on occasion from the Hawaiian Islands
since 1923, but was misidentified until William Smith-Vaniz re-examined the specimens in 1981 and identified them as Caranx caballus. Due to the heavy fishing pressures throughout Hawaii and the rarity of captures, it was concluded these few individuals were strays carried by ocean current
s from the eastern Pacific, as these were the only known specimens. In 1998 however, the species appeared in fishermen's catches in large numbers, and has ever since, indicating a population has been established in the island chain.
The green jack inhabits a variety of continental shelf
environments to a depth of at least 100 m, predominantly inshore reef
systems, as well as shallow bay
s, estuaries and lagoon
s. It leads both a demersal and pelagic lifestyle, forming large schools which can move large distances offshore, allowing them to reach offshore island as well as deep, isolated seamount
s.
s are formed by juveniles when entering shallower waters including bays and estuaries. The species is predatory in nature, taking small fish, cephalopod
s, crab
s, shrimp
s and other crustacean
s, either in midwater or on the sea floor. Green jack are also known to consume zooplankton
, especially in deeper waters around islands and seamounts where the plankton is aggregated. Throughout its range, the species is one of the most abundant species, making it an important part of the ecology
, not only as a predator but as prey. It is known to be taken by larger fish such as marlin
and shark
s, as well a variety of other animals.
Reproduction in the species has been quite well studied, with the commercial value of the species having led to a number of growth and population dynamics
studies being undertaken. Spawning
appears to take place from May to October, with peaks in June and October. Larval
growth has been extensive described, with the larvae identifiable by their pigmentation pattern and meristic count of 25 vertebrae. The body shape of early larvae resembles that of Chloroscombrus orquetu, however, differences in pigmentation, particularly on the dorsal body margin, differentiate the species Studies off the coast of Mexico have found the larvae tend to occur in deeper waters than most other carangid larvae inhabit, from 90 to 100 m depth, possibly indicating spawning occurs in deeper waters. Otolith
studies indicate that both the females and males grow at the same rate; 16.82 cm after the first year, 27.78 after the second, 34.66 after the third, with modelling suggesting the maximum length of 55 cm is reached at around 8 years of age. Most individuals reach sexual maturity
before they reach 38 cm in length. Juveniles tend to move to protected waters such as estuaries, moving to deeper waters at adulthood.
is one exception. Record from 1980 onward show a catch between 9 and 250 ton
, with an average of 93 ton, with the catch best between September and December. Like most carangid species in the area, it is considered a lower class product, fetching between 0.50 and 0.80 US dollars per kilogram, making it accessible to the low income population. The fish are sold both for consumption and as bait
, either fresh, smoked or salted
. There is some hope that the Hawaiian population becomes commercially viable in the future, as they are often landed in other carangid catches at the present.
The green jack is also of modest interest to angler
s in the region, with the species a good light tackle fish. Lure
s are most often used on the species, including jigs, spoons and squids, although baits of live fish and strip baits work equally as well. As mentioned previously, the species is considered to be a fair to poor quality table fish.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of coastal marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
in the jack family Carangidae
Carangidae
Carangidae is a family of fish which includes the jacks, pompanos, jack mackerels, and scads.They are marine fish found in the Atlantic, Indian and Pacific Oceans...
. The species is distributed in the eastern Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
along the America
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...
n coastline from Santa Cruz Island
Santa Cruz Island
Santa Cruz Island was the largest privately owned island off the continental United States, but is currently part-owned by the National Park service . The island, located off the coast of California, is long and from wide...
off California in the north to Peru
Peru
Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....
in the south, as well as a number of islands including the Galapagos and recently, Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
. The green jack is distinguished from other similar carangid species by a number of features including gill raker
Gill raker
Gill rakers in fish are bony or cartilaginous processes that project from the branchial arch and are involved with filter feeding tiny prey. They are not to be confused with the gill filaments that compose the bony part of the gill. Rakers are usually present in two rows, projecting from both the...
and lateral line
Lateral line
The lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...
scale counts, and the presence of an adipose eyelid. It is a moderately large species, growing to at least 55 cm in length and 2.81 kg, although unconfirmed reports suggest a much larger maximum size. It lives in a wide range of continental shelf
Continental shelf
The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...
environments including estuaries, bay
Bay
A bay is an area of water mostly surrounded by land. Bays generally have calmer waters than the surrounding sea, due to the surrounding land blocking some waves and often reducing winds. Bays also exist as an inlet in a lake or pond. A large bay may be called a gulf, a sea, a sound, or a bight...
s, reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
s and offshore seamount
Seamount
A seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface , and thus is not an island. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of depth. They are defined by oceanographers as...
s, living both pelagically and demersally. The green jack is a predatory species, preying on a variety of fish, crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s and cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s, as well as zooplankton
Zooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
. Most fish are sexually mature
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
by the time they attain 38 cm, with spawning
Spawn (biology)
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
occurring between May and October. The species is of high importance to fisheries throughout its range, caught by pelagic trawls, a variety of netting
Netting
In general, netting means to allow a positive value and a negative value to set-off and partially or entirely cancel each other out.In the context of credit risk, there are at least three specific types of netting:...
methods and hook and line. The green jack is also of interest to angler
Angling
Angling is a method of fishing by means of an "angle" . The hook is usually attached to a fishing line and the line is often attached to a fishing rod. Fishing rods are usually fitted with a fishing reel that functions as a mechanism for storing, retrieving and paying out the line. The hook itself...
s, taken by bait and lures, although is considered to only be fair in eating quality.
Taxonomy and naming
The green jack is formally classified within the genusGenus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Caranx
Caranx
Caranx is a genus of tropical to subtropical marine fish in the jack family Carangidae, commonly known as jacks, trevallies and kingfishes. They are moderate to large sized, deep bodied fishes which are distinguished from other carangid genera by specific gill raker, fin ray and dentition...
, one of a number of groups of fish referred to as jacks and trevallies. Caranx is further classified in the family Carangidae
Carangidae
Carangidae is a family of fish which includes the jacks, pompanos, jack mackerels, and scads.They are marine fish found in the Atlantic, Indian and Pacific Oceans...
, itself part of the suborder Percoidei
Percoidei
Percoidei is one of eighteen suborders of bony fish in the order Perciformes. Many commercially harvested fish species are contained in this suborder, including the snappers, jacks, whitings, groupers, bass, perches and porgies.-Divisions:...
and the order Perciformes
Perciformes
The Perciformes, also called the Percomorphi or Acanthopteri, is one of the largest orders of vertebrates, containing about 40% of all bony fish. Perciformes means perch-like. They belong to the class of ray-finned fish and comprise over 7,000 species found in almost all aquatic environments...
; the perch-like fishes.
The species was first scientifically described by the French biologist
Biologist
A biologist is a scientist devoted to and producing results in biology through the study of life. Typically biologists study organisms and their relationship to their environment. Biologists involved in basic research attempt to discover underlying mechanisms that govern how organisms work...
Charles Frédéric Girard
Charles Frédéric Girard
Charles Frédéric Girard was a French biologist specializing in ichthyology and herpetology.Born in Mulhouse, France, he studied at the College of Neuchâtel, Switzerland as a student of Louis Agassiz. In 1847, he accompanied Agassiz as his assistant to Harvard...
in 1858, who named the species Trachurus boops, placing the species in the horse mackerel
Trachurus
Jack mackerels are marine fishes in the Trachurus genus of the Carangidae family. The type species of the genus is the Atlantic horse mackerel, Trachurus trachurus. The name of the genus is derived from the Greek word trachys, meaning "rough", and the Greek word oura, meaning "tail"...
genus based on the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
taken off of San Diego, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
.
With the instability of carangid taxonomy
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
at the time, the species was reassigned to a number of genera, including Caranx, which created a taxonomic homonym
Homonym
In linguistics, a homonym is, in the strict sense, one of a group of words that often but not necessarily share the same spelling and the same pronunciation but have different meanings...
with the Caranx boops described by Georges Cuvier
Georges Cuvier
Georges Chrétien Léopold Dagobert Cuvier or Jean Léopold Nicolas Frédéric Cuvier , known as Georges Cuvier, was a French naturalist and zoologist...
in 1833. In 1868, British zoologist Albert Günther unaware of the prior naming independently renamed the species Caranx caballus based on specimens collected from Panama
Panama
Panama , officially the Republic of Panama , is the southernmost country of Central America. Situated on the isthmus connecting North and South America, it is bordered by Costa Rica to the northwest, Colombia to the southeast, the Caribbean Sea to the north and the Pacific Ocean to the south. The...
, one of which was designated to be the holotype. The species was further renamed in 1870 by Franz Steindachner
Franz Steindachner
Franz Steindachner was an Austrian zoologist.- Work and career :Being interested in natural history, Steindachner took up the study of fossil fishes on the recommendation of his friend Eduard Suess...
, who attempted to remove the Caranx boops homonym by simply renaming the species Caranx girardi. Later reviews of the Carangidae revealed this synonymy, and due to Gunther's' earlier naming, his species name was kept and attributed to him, while Cuvier's' Caranx boops was later moved to Selar boops. The specific name caballus is Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
for 'horse', reflecting the common name of horse mackerel given to this and many similar species at the time. William Smith-Vaniz has suggested the possibility C. caballus is conspecific with a very similar Atlantic
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
species; Caranx crysos, but no studies into this relationship have been undertaken. Its position in the genus Caranx has also been questioned recently by John Randall due to its unusual dentition. The common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
'green jack' is in reference to the species common coloration, while 'horse jack' is derived from the Latin name. In Spanish
Spanish language
Spanish , also known as Castilian , is a Romance language in the Ibero-Romance group that evolved from several languages and dialects in central-northern Iberia around the 9th century and gradually spread with the expansion of the Kingdom of Castile into central and southern Iberia during the...
speaking nations, it is often known under broadly applied names including 'Cocinero' and 'Caballa'.
Description
The green jack is moderately large in size, growing to a maximum confirmed length of 55 cm and 2.81 kg in weight. Unconfirmed reports indicate the species may grow much larger; up to 1 m in size, but it is most commonly seen at lengths below 40 cm. The green jack is morphologicallyMorphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
similar to a number of other carangids, having an elongated, moderately compressed fusiform body with dorsal and ventral profiles of approximately equal convexity and a slightly pointed snout. The posterior section of the eye is covered by a moderately well developed adipose eyelid, and the posterior extremity of the jaw
Jaw
The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...
is vertically under the center of the eye. The dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
is in two parts, the first consisting of 8 spines and the second of 1 spine followed by 22 to 25 soft rays. The anal fin consists of 2 anteriorly detached spines followed by 1 spine and 16 to 21 soft rays. The lobes of both the second dorsal and anal fin are slightly elongated and almost entirely covered in small scale
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...
s, but are still much shorter than the head length. The lateral line
Lateral line
The lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...
has a pronounced but short anterior arch, with the curved section intersecting the straight section below the spine of the second dorsal fin. The straight section contains 0 to 7 scales followed by 42 to 56 very strong scute
Scute
A scute or scutum is a bony external plate or scale, as on the shell of a turtle, the skin of crocodilians, the feet of some birds or the anterior portion of the mesonotum in insects.-Properties:...
s, and 43 to 47 scales overall. The chest is completely scaled. The upper jaw contains an irregular series of outer canine
Canine tooth
In mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, fangs, or eye teeth, are relatively long, pointed teeth...
s with an inner band of small, regularly spaced teeth, while the lower jaw contains a single band of small teeth. The species has 40 to 45 gill raker
Gill raker
Gill rakers in fish are bony or cartilaginous processes that project from the branchial arch and are involved with filter feeding tiny prey. They are not to be confused with the gill filaments that compose the bony part of the gill. Rakers are usually present in two rows, projecting from both the...
s in total; 10 to 15 on the upper limb and 27 to 30 on the lower limb, with this the only feature that differs between C. caballus and C. crysos. There are 25 vertebrae present.
In life, the green jack has a greenish blue colour overall, with an olive green to dark blue back and a golden to grey coloured belly, with a distinct back blotch on the outer edge of the operculum
Operculum (fish)
The operculum of a bony fish is the hard bony flap covering and protecting the gills. In most fish, the rear edge of the operculum roughly marks the division between the head and the body....
. Individuals in schools
Shoaling and schooling
In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
often have a very evident pearly white marking near this black blotch. Juveniles have 7 dark vertical stripes on their flanks which fade with age. The caudal fin is grey with dark tips, with all other fins being light grey to hyaline
Hyaline
The term hyaline denotes a substance with a glass-like appearance.-Histopathology:In histopathological medical usage, a hyaline substance appears glassy and pink after being stained with haematoxylin and eosin — usually it is an acellular, proteinaceous material...
in colour.
Distribution and habitat
The green jack is distributed throughout the coastal waters of the tropical and subtropical waters of the eastern Pacific OceanPacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
. Its range extends along the coast of the Americas from Santa Cruz Island
Santa Cruz Island
Santa Cruz Island was the largest privately owned island off the continental United States, but is currently part-owned by the National Park service . The island, located off the coast of California, is long and from wide...
, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, south through Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
and Central America
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
, and down to Peru
Peru
Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....
. The species also inhabits a number of offshore islands including the Galápagos Islands
Galápagos Islands
The Galápagos Islands are an archipelago of volcanic islands distributed around the equator in the Pacific Ocean, west of continental Ecuador, of which they are a part.The Galápagos Islands and its surrounding waters form an Ecuadorian province, a national park, and a...
. The species had been captured on occasion from the Hawaiian Islands
Hawaiian Islands
The Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...
since 1923, but was misidentified until William Smith-Vaniz re-examined the specimens in 1981 and identified them as Caranx caballus. Due to the heavy fishing pressures throughout Hawaii and the rarity of captures, it was concluded these few individuals were strays carried by ocean current
Ocean current
An ocean current is a continuous, directed movement of ocean water generated by the forces acting upon this mean flow, such as breaking waves, wind, Coriolis effect, cabbeling, temperature and salinity differences and tides caused by the gravitational pull of the Moon and the Sun...
s from the eastern Pacific, as these were the only known specimens. In 1998 however, the species appeared in fishermen's catches in large numbers, and has ever since, indicating a population has been established in the island chain.
The green jack inhabits a variety of continental shelf
Continental shelf
The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...
environments to a depth of at least 100 m, predominantly inshore reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
systems, as well as shallow bay
Bay
A bay is an area of water mostly surrounded by land. Bays generally have calmer waters than the surrounding sea, due to the surrounding land blocking some waves and often reducing winds. Bays also exist as an inlet in a lake or pond. A large bay may be called a gulf, a sea, a sound, or a bight...
s, estuaries and lagoon
Lagoon
A lagoon is a body of shallow sea water or brackish water separated from the sea by some form of barrier. The EU's habitat directive defines lagoons as "expanses of shallow coastal salt water, of varying salinity or water volume, wholly or partially separated from the sea by sand banks or shingle,...
s. It leads both a demersal and pelagic lifestyle, forming large schools which can move large distances offshore, allowing them to reach offshore island as well as deep, isolated seamount
Seamount
A seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface , and thus is not an island. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of depth. They are defined by oceanographers as...
s.
Biology
The green jack is a gregarious species, forming moderately large schools of fish in the marine environment. Smaller shoalShoal
Shoal, shoals or shoaling may mean:* Shoal, a sandbank or reef creating shallow water, especially where it forms a hazard to shipping* Shoal draught , of a boat with shallow draught which can pass over some shoals: see Draft...
s are formed by juveniles when entering shallower waters including bays and estuaries. The species is predatory in nature, taking small fish, cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s, crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s, shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
s and other crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, either in midwater or on the sea floor. Green jack are also known to consume zooplankton
Zooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
, especially in deeper waters around islands and seamounts where the plankton is aggregated. Throughout its range, the species is one of the most abundant species, making it an important part of the ecology
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
, not only as a predator but as prey. It is known to be taken by larger fish such as marlin
Marlin
Marlin, family Istiophoridae, are fish with an elongated body, a spear-like snout or bill, and a long rigid dorsal fin, which extends forward to form a crest. Its common name is thought to derive from its resemblance to a sailor's marlinspike...
and shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s, as well a variety of other animals.
Reproduction in the species has been quite well studied, with the commercial value of the species having led to a number of growth and population dynamics
Population dynamics
Population dynamics is the branch of life sciences that studies short-term and long-term changes in the size and age composition of populations, and the biological and environmental processes influencing those changes...
studies being undertaken. Spawning
Spawn (biology)
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
appears to take place from May to October, with peaks in June and October. Larval
Ichthyoplankton
Ichthyoplankton are the eggs and larvae of fish. They are usually found in the sunlit zone of the water column, less than 200 metres deep, which is sometimes called the epipelagic or photic zone...
growth has been extensive described, with the larvae identifiable by their pigmentation pattern and meristic count of 25 vertebrae. The body shape of early larvae resembles that of Chloroscombrus orquetu, however, differences in pigmentation, particularly on the dorsal body margin, differentiate the species Studies off the coast of Mexico have found the larvae tend to occur in deeper waters than most other carangid larvae inhabit, from 90 to 100 m depth, possibly indicating spawning occurs in deeper waters. Otolith
Otolith
An otolith, , also called statoconium or otoconium is a structure in the saccule or utricle of the inner ear, specifically in the vestibular labyrinth of vertebrates. The saccule and utricle, in turn, together make the otolith organs. They are sensitive to gravity and linear acceleration...
studies indicate that both the females and males grow at the same rate; 16.82 cm after the first year, 27.78 after the second, 34.66 after the third, with modelling suggesting the maximum length of 55 cm is reached at around 8 years of age. Most individuals reach sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
before they reach 38 cm in length. Juveniles tend to move to protected waters such as estuaries, moving to deeper waters at adulthood.
Relationship to humans
The green jack is one of the most abundant species of fish within its range, and as such is quite important to fisheries throughout its range. It is taken both by pelagic trawls as well as inshore gill nets, purse nets and seines, as well as hook and line gear. Catch statistics are not kept for the fish throughout most of its range; however, the Mexican state of ColimaColima
Colima is one of the 31 states which, with the Federal District, make up the 32 Federal Entities of Mexico. It shares its name with its capital and main city, Colima....
is one exception. Record from 1980 onward show a catch between 9 and 250 ton
Ton
The ton is a unit of measure. It has a long history and has acquired a number of meanings and uses over the years. It is used principally as a unit of weight, and as a unit of volume. It can also be used as a measure of energy, for truck classification, or as a colloquial term.It is derived from...
, with an average of 93 ton, with the catch best between September and December. Like most carangid species in the area, it is considered a lower class product, fetching between 0.50 and 0.80 US dollars per kilogram, making it accessible to the low income population. The fish are sold both for consumption and as bait
Fishing bait
Fishing bait is any substance used to attract and catch fish, e.g. on the end of a fishing hook, or inside a fish trap. Traditionally, nightcrawlers, insects, and smaller bait fish have been used for this purpose...
, either fresh, smoked or salted
Salting (food)
Salting is the preservation of food with dry edible salt. It is related to pickling . It is one of the oldest methods of preserving food, and two historically significant salt-cured foods are dried and salted cod and salt-cured meat.Salting is used because most bacteria, fungi and other potentially...
. There is some hope that the Hawaiian population becomes commercially viable in the future, as they are often landed in other carangid catches at the present.
The green jack is also of modest interest to angler
Angling
Angling is a method of fishing by means of an "angle" . The hook is usually attached to a fishing line and the line is often attached to a fishing rod. Fishing rods are usually fitted with a fishing reel that functions as a mechanism for storing, retrieving and paying out the line. The hook itself...
s in the region, with the species a good light tackle fish. Lure
Fishing lure
A fishing lure is an object attached to the end of a fishing line which is designed to resemble and move like the prey of a fish. The purpose of the lure is to use movement, vibration, and colour to catch the fish's attention so it bites the hook...
s are most often used on the species, including jigs, spoons and squids, although baits of live fish and strip baits work equally as well. As mentioned previously, the species is considered to be a fair to poor quality table fish.