The
shads or
river herrings comprise the
genusIn 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...
Alosa,
fishFish 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...
related to
herringHerring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...
in the
familyIn biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
ClupeidaeClupeidae is the family of the herrings, shads, sardines, hilsa and menhadens. It includes many of the most important food fishes in the world.-Description and biology:...
. They are distinct from others in that family by having a deeper body and spawning in rivers. The several species frequent different areas on both sides of the
Atlantic OceanThe 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...
,
Mediterranean SeaThe Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
.
Alosa can also be found throughout the
Caspian SeaThe Caspian Sea is the largest enclosed body of water on Earth by area, variously classed as the world's largest lake or a full-fledged sea. The sea has a surface area of and a volume of...
. Many are found in freshwater during spawning and some are only found in landlocked freshwater.
Appearance
Alosa are generally dark on the back and top of the head with blue, violet, or greenish tints. However, some species can be identified as having a grey or green back. Spots are commonly found behind the head and the fins may vary from species to species or individually. Most species of
Alosa weigh 300 grams or less with one species,
Alosa pontica, weighing up to 2 kilograms.
Biology
Shads are thought to be unique among the fishes in having evolved an ability to detect
ultrasoundUltrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...
(sound at frequencies above 20 kHz, which is the limit of human hearing) (Mann et al. 2001). This was first discovered by fisheries biologists studying a type of shad known as
blueback herringThe blueback herring is an anadromous species of herring from the east coast of North America from Cape Breton, Nova Scotia to the St. John’s River in Florida. Blueback herring form schools and are believed to migrate offshore to overwinter near the bottom.This fish has, in the past, been used as...
, and was later verified in laboratory studies of hearing in American shad. This ability is thought to help them avoid dolphins that find prey using echolocation.
Alosa are generally pelagic, meaning they live near the surface of the water.They are mostly andromous or semiandromous with the exception of strictly freshwater landlocked species.
Alosa are generally migratory and schooling fish. The biology of these fish seem to vary among species. Males will usually mature about a year before females and spawn in the late spring to summer months. After spawning, mortality occurs in most species.
Alosa are seemingly very adaptive vertebrates and can change readily to adapt to their environment as species are found in a variety of temperatures and waters
Life cycle and Reproduction
As
Alosa are generally anadromous, they are faced with various obstacles to survive. They may have to pass through numerous barriers and waters to get to either their spawning grounds or normal habitat (the sea in most cases). Estruaries are a major factor in numerous
Alosa species migration. Estruaries can be highly variable and complex environments contributing to fluctuating biological interactions. There are shifts in osomolarity, food sources, predators, etc. Since many adult
Alosa species die after spawning, it is the young who generally have to migrate to the sea from the spawning grounds. Duration of migration varies among fish but studies have shown that duration of migration can greatly effect survival.
Reproduction varies form species to species. Studies done on
Alosa in Iranian waters have shown that spawning in
Alosa varies in time, place, and temperature of species.Fecundity may also vary.It is observed that species will spawn as early as April or as late as August. Temperatures range from approximately 11 to 27 degrees Celsius. Fecundity can range from approximately 20,000 eggs to 312,000 eggs. Eggs are pelagic.
The life span of
Alosa can be up to 10 years but is generally uncommon as many die after spawning.
Systematics
Systematics of shads are complex. The genus inhabits a wide range of
habitat* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
s, and many taxa are
migratoryMany types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...
. There are also a few land-locked forms, one from
KillarneyKillarney is a town in County Kerry, southwestern Ireland. The town is located north of the MacGillicuddy Reeks, on the northeastern shore of the Lough Lein/Leane which are part of Killarney National Park. The town and its surrounding region are home to St...
in
IrelandIreland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
and two from lakes in northern Italy. There are species native to the
Black SeaThe Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...
and
Caspian SeaThe Caspian Sea is the largest enclosed body of water on Earth by area, variously classed as the world's largest lake or a full-fledged sea. The sea has a surface area of and a volume of...
, as well as the
Persian GulfThe Persian Gulf, in Southwest Asia, is an extension of the Indian Ocean located between Iran and the Arabian Peninsula.The Persian Gulf was the focus of the 1980–1988 Iran-Iraq War, in which each side attacked the other's oil tankers...
. Alosa species of the Caspian are systemically characterized by the number of rakers on the first gill arch by some scientists. They are classified as being "multirakered," "mediumrakered," or "oligorakered." The multirakered are primarily plankton feeders, the oligorakered have large rakers and are predators, and the mediumrakered generally possess a mixed diet. Most current species of the Alosa genus in North America can be found in Florida, although Florida may not be the only place that these species are found.
MorphologyIn biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
is notoriously liable to adapt to changing food availability in these fish. Several taxa seem to have
evolveEvolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
d quite recently, making molecular analyses difficult. In addition, it appears as if hybridization is a factor to be reckoned with when researching shad phylogeny.(Faria
et al. 2006)
Nonetheless, some trends are emerging. The North American species except the Atlantic shad can probably be separated in a
subgenusIn biology, a subgenus is a taxonomic rank directly below genus.In zoology, a subgeneric name can be used independently or included in a species name, in parentheses, placed between the generic name and the specific epithet: e.g. the Tiger Cowry of the Indo-Pacific, Cypraea tigris Linnaeus, which...
(or even genus)
Pomolobus. On the other hand, the proposed genus (or subgenus)
Caspialosa for the
Caspian SeaThe Caspian Sea is the largest enclosed body of water on Earth by area, variously classed as the world's largest lake or a full-fledged sea. The sea has a surface area of and a volume of...
forms is rejected due to
paraphylyA group of taxa is said to be paraphyletic if the group consists of all the descendants of a hypothetical closest common ancestor minus one or more monophyletic groups of descendants...
.(Faria
et al. 2006)
- Alosa aestivalis (Mitchill, 1814) (Blueback shad)
- Alosa agone
Alosa agone is a species of ray-finned fish in the genus Alosa.Alosa agone is an endangered species of the Alosa genus.-Species Description:...
(ScopoliGiovanni Antonio Scopoli was an Italian physician and naturalist.-Biography:...
, 1786) (Agone)
- Alosa alabamae D. S. Jordan
David Starr Jordan, Ph.D., LL.D. was a leading eugenicist, ichthyologist, educator and peace activist. He was president of Indiana University and Stanford University.-Early life and education:...
& EvermannBarton Warren Evermann was an American ichthyologist. He was born in Monroe County, Iowa, and graduated from Indiana University in 1886. For 10 years, he served as teacher and superintendent of schools in Indiana and California. He was professor of biology at the Indiana State University in...
, 1896 (Alabama shad)
- Alosa algeriensis
Alosa algeriensis is a species of ray-finned fish in the genus Alosa.-Location:Alosa algeriensis is primarily found in the Mediterranean Sea from northern Morocco to northern Tunisia. They are also found in Sardinia, Italy with landlocked populations in Lake Ichkeul, Tunisia and Sardinia, Italy...
Regan, 1916 (North African shad)
- Alosa alosa (Linnaeus, 1758) (Allis shad)
- Alosa braschnikowi (Borodin, 1904) (Caspian marine shad)
- Alosa caspia
Alosa caspia is a shad living in the Caspian Sea* Caspian shad, Alosa caspia caspia Eichwald, 1838)* Enzeli shad, Alosa caspia knipowitschi * Astrabad shad, Alosa caspia persica...
(EichwaldKarl Eduard von Eichwald was a Russian geologist and physician.Eichwald was a Baltic German born at Mitau in Courland...
, 1838)
- Alosa caspia caspia (Eichwald
Karl Eduard von Eichwald was a Russian geologist and physician.Eichwald was a Baltic German born at Mitau in Courland...
, 1838) (Caspian shad)
- Alosa caspia knipowitschi (Iljin, 1927) (Enzeli shad)
- Alosa caspia persica (Iljin, 1927) (Astrabad shad)
- Alosa chrysochloris (Rafinesque, 1820) (Skipjack shad)
- Alosa curensis (Suvorov, 1907) (Kura shad)
- Alosa fallax (Lacépède, 1803) (Twait shad)
- Alosa immaculata E. T. Bennett
Edward Turner Bennett was an English zoologist and writer. He was the elder brother of the botanist John Joseph Bennett. Bennett was born at Hackney and practiced as a surgeon, but his chief pursuit was always zoology...
, 1835 (Pontic shad)
- Alosa kessleri
Alosa kessleri is a species of ray-finned fish in the genus Alosa....
(Grimm, 1887) (Caspian anadromous shad)
- Alosa killarnensis
Alosa killarnensis is a fresh water species of ray-finned fish in the genus Alosa.-Geographic Location:Lough Leane in Ireland is only the place where it is found. Eutrophication and introduction of species such as Rutilus rutilus and Abramis brama are the most probable threats...
Regan, 1916 (Killarney shad)
- Alosa macedonica (Vinciguerra, 1921) (Macedonia shad)
- Alosa maeotica
The Black Sea Shad is a species of fish in the Clupeidae family. It is found in Bulgaria, Georgia, Moldova, Romania, Russia, Turkey, and Ukraine.-Source:* World Conservation Monitoring Centre 1996. . Downloaded on 3 August 2007....
(Grimm, 1901) (Black Sea shad)
- Alosa mediocris (Mitchill, 1814) (Hickory shad)
- Alosa pseudoharengus (A. Wilson
Alexander Wilson was a Scottish-American poet, ornithologist, naturalist, and illustrator.Wilson was born in Paisley, Scotland, the son of an illiterate distiller. In 1779 he was apprenticed as a weaver. His main interest at this time was in writing poetry...
, 1811) (Alewife)
- Alosa sapidissima (A. Wilson
Alexander Wilson was a Scottish-American poet, ornithologist, naturalist, and illustrator.Wilson was born in Paisley, Scotland, the son of an illiterate distiller. In 1779 he was apprenticed as a weaver. His main interest at this time was in writing poetry...
, 1811) (American shad)
- Alosa saposchnikowii
Alewife is a species of ray-finned fish in the genus Alosa....
(Grimm, 1887) (Saposhnikovi shad)
- Alosa sphaerocephala
Alosa sphaerocephala is a species of ray-finned fish in the genus Alosa....
(L. S. Berg, 1913) (Agrakhan shad)
- Alosa tanaica
Alosa tanaica is a species of ray-finned fish in the genus Alosa....
(Grimm, 1901) (Azov shad)
- Alosa vistonica
Alosa vistonica is a species of fish in the Clupeidae family. It is endemic to Greece. Its natural habitat is freshwater lakes. It is threatened by habitat loss.-Source:* Crivelli, A.J. 2005. . Downloaded on 3 August 2007....
Economidis & Sinis, 1986 (Thracian shad)
- Alosa volgensis
Alosa volgensis, the Volga shad, is a species of shad which is endemic to the Russian Federation....
(L. S. Berg, 1913) (Volga shad)
Commercial fishing
| Commercial Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions...
capture production of wild shad in tonnes. |
| 1999 |
2000 |
2001 |
2002 |
2003 |
2004 |
2005 |
| 788 770 |
860 346 |
665 284 |
589 692 |
524 800 |
569 160 |
605 548 |
Management
Shad populations have been in decline for years due to spawning areas blocked by dams, habitat destruction, pollution, and overfishing. Management of shad has called for more conservative regulations, as well as policies to help the species obtain a lower fishing mortality.
Political Significance
Shad serve a peculiar symbolic role in
VirginiaThe Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...
state politics. On the year of every gubernatorial election, would-be candidates, lobbyists, campaign workers, and reporters gather in the town of
Wakefield, VirginiaWakefield is an incorporated town in Sussex County, Virginia, United States. The population was 1,038 at the 2000 census.Wakefield is famous for being the "Peanut Capital of the World" and the location of the famous , as well as the site of Airfield Conference and 4-H Educational Center...
for
shad plankingThe Shad Planking is an annual political event in Virginia which takes place every April near Wakefield in Sussex County. It is sponsored by a chapter of the Ruritans, a community service organization which was originally founded in the small town of Holland about 30 miles to the...
. American shad served as the focal point of
John McPheeJohn Angus McPhee is an American Pulitzer Prize-winning writer, widely considered one of the pioneers of creative nonfiction....
's book
The Founding Fish.
External links