Alosa sapidissimaAmerican shad(Also: Atlantic shad; Common shad; North River shad; Potomac shad)

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Geographic Range

American shad are restricted to temperate climates and spend the majority of their lives in coastal areas of the Atlantic or Pacific Ocean. During spawning season, American shad travel to the rivers of the United States, Canada, and Mexico to lay their eggs. American shad are native to the Atlantic Ocean, ranging from Newfoundland, Nova Scotia and the St. Lawrence River in the north, to areas of coastal central Florida in the south. In the late 1800's, humans introduced American shad to the Pacific Ocean. Today, American shad can be found as far north as Cook Inlet, Alaska and the Kamchatka Peninsula and south to Baja California, Mexico. (Eddy, 1957)

Habitat

Adult American shad are predicted to swim over 19,000 km in their lifetime, during which they are found in many habitats. During summer and fall, American shad can be found in coastal waters, generally at depths from 0 to 250 m. During the winter months, they generally inhabit deeper ocean waters away from the coast at depths up to 375 m. American shad are a migratory species, and toward the end of winter they travel into rivers to spawn. (Eddy, 1957)

  • Aquatic Biomes
  • rivers and streams
  • coastal
  • Range depth
    0 to 375 m
    0.00 to 1230.31 ft
  • Average depth
    125 m
    410.10 ft

Physical Description

The stomach and chest of American shad have sharp scales similar to that of a saw. They have a compressed body, which is dorsally blue and metallic in color and ventrally white. American shad have one or more black spots in a row on their shoulder. Though rare, some American shad have two rows of black spots. When American shad enter rivers to spawn, their colors darken. American shad on average measure 55.85 cm in length and can range from 45 to 76.2 cm. On average, they weigh 2.5 kg and can range from 0.9 to 5.4 kg. Females are typically three times larger in mass than males. (Ford, 2006)

  • Sexual Dimorphism
  • female larger
  • Range mass
    0.9 to 5.4 kg
    1.98 to 11.89 lb
  • Average mass
    2.5 kg
    5.51 lb
  • Range length
    45 to 76.2 cm
    17.72 to 30.00 in
  • Average length
    55.85 cm
    21.99 in

Development

Adult American shad spawn in rivers during late winter. On average, larvae hatch in 10 days. In rivers of higher temperature, larvae may hatch in as little as a week. Newly-hatched larvae average 10 mm long. In late fall or early winter, juveniles make their way from rivers into the ocean. In 2 to 5 years, adult American shad return to their natal rivers to spawn. (Glebe, 1981)

Reproduction

In the late months of winter, American shad enter freshwater rivers of the United States, Canada, and Mexico to spawn. One or more males chase a female up a river and may also nudge her belly until the female releases her eggs in open water. The pursuing males then fertilize the eggs. The eggs separate from each other and may drift many kilometers before they hatch. This mobility of eggs may increase survival rates, as eggs are not all at risk in one location if discovered by a predator. (Page, 1991; Wiley, 1986)

Female American shad spawn for the first time between 3 and 7 years of age (average 4 years). In total, females release 200,000 to 250,000 eggs each year. Individual American shad lay 2 to 150 eggs each season, which are released in cycles as females travel up the river. A cycle lasts from a couple of days to a week and is followed by 1 to 3 days of rest, after which she begins a new cycle. Juveniles hatch after 6 to 10 days and are independent on hatching. (Crossman, 1998; Pfeiffer, 2002)

  • Breeding interval
    American shad spawn once a year.
  • Breeding season
    American shad spawn from late winter to early spring.
  • Range number of offspring
    2 to 150
  • Average number of offspring
    77
  • Range time to hatching
    6 to 10 days
  • Average time to independence
    0 minutes
  • Range age at sexual or reproductive maturity (female)
    3 to 7 years
  • Average age at sexual or reproductive maturity (female)
    4 years
  • Range age at sexual or reproductive maturity (male)
    3 to 7 years
  • Average age at sexual or reproductive maturity (male)
    4 years

Adult American shad do not provide any care for the eggs or larvae after fertilization. (Plachta, 2003; Zool, 1993)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female

Lifespan/Longevity

American shad have a life expectancy of 6 to 10 years in the wild (average 9 years). Migration from rivers to the sea places a heavy toll on their bodies, and increased migration increases mortality. Migrating females have an average mortality rate of 60 % during seasons in which they migrate. In captivity, American shad are expected to live 4 to 7 years (average 6 years). (Eddy, 1957; Ford, 2006; Weiss-Glanz,, 1972)

  • Range lifespan
    Status: wild
    7 to 12 years
  • Average lifespan
    Status: wild
    10 years
  • Range lifespan
    Status: captivity
    4 to 10 years
  • Typical lifespan
    Status: wild
    6 to 10 years
  • Average lifespan
    Status: wild
    9 years
  • Typical lifespan
    Status: captivity
    4 to 7 years
  • Average lifespan
    Status: captivity
    5 years

Behavior

American shad are social animals that swim in schools. As juveniles travel toward the ocean, they avoid larger species of fish which may prey on them. As they grow larger and reach the ocean, American shad live in closer proximity to other fish. (Crecco, 1985; Ford, 2006)

Home Range

American shad do not have a determined home range, nor to they defend a territory.

Communication and Perception

American shad have the ability to detect ultrasonic signals up to 180 kHz. They are often able to escape predators that use ultrasonic signals for communication. Male American shad communicate to females to release their eggs by chasing and nudging the female's belly. (Crossman, 1998; Plachta, 2003)

Food Habits

Juvenile American shad are omnivores with a diet consisting of mostly zooplankton and insect larvae. Juveniles eat more once they have left spawning areas. As they get older, American shad broaden their diet to include small fish, crustaceans, plankton, worms, and occasionally fish eggs. During migration in the late months of winter, American shad eat very little food, if any. However, as water temperatures increase in spring, their diet returns to normal. (Weiss-Glanz,, 1972)

Predation

Adult American shad darken in color on entering rivers to spawn, which helps them blend into their environment. American shad also have the ability to detect ultrasound. When shad detect ultrasound use of predators, such as their major predators, dolphins (Delphinus capensis and Delphinus delphis), American shad hide or flee. Other predators include: striped bass Morone saxatilis, blue fish Pomatomus saltatrix, smallmouth bass Micropterus dolomieu, walleye Sander vitreus and channel catfish Ictalurus punctatus. Additionally, bears and some birds eat American shad. This species is also a sport fish and is consumed by humans. (Crecco, 1985; McPhee, 2003)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

American shad are preyed upon by bigger fish, some birds, humans, bears, and dolphins. However, these predators are not dependent on this species. American shad also eat many riverine crustaceans and fish during migration and may regulate populations of some species. American shad are hosts to a variety of parasites, including nematodes (Hysterothylacium aduncum) and cestodes (Scolex pleuronectis). Individuals that migrate to spawn in northwestern United States are occasionally infected by nematodes (Anisakis simplex), for which American shad act as an intermediate host. In the southern Atlantic, American shad are often infected by one species of trematode (Genitocotyle atlantica). (Shields, 2002; Zool, 1993)

Commensal/Parasitic Species
  • nematodes (Anisakis simplex)
  • cestodes (Scolex pleuronectis)
  • nematodes (Hysterothylacium aduncum)
  • trematodes (Genitocotyle atlantica)

Economic Importance for Humans: Positive

American shad are a sport fish and are also bred in hatcheries. Both their roe and meat are consumed. This species may also encourage ecotourism, drawing sport fishermen. (Dicenzo, 1995; Ford, 2006; Marcy, 2004; Page, 1991; Pfeiffer, 2002)

Economic Importance for Humans: Negative

There are no known adverse affects of American shad on humans. (Dicenzo, 1995; Marcy, 2004)

Conservation Status

American shad have been harvested for meat and eggs for hundreds of years. However, overfishing and habitat destruction have dramatically reduced populations of this species. Both state and federal governments have limited anthropogenic changes to rivers with shed populations and have imposed stricter fishing limits. Hatcheries of American shad have been created by state governments and private organization in a number of states. Dams and rivers that once stopped shad from traveling up rivers to spawn are now equipped with passages to enable migration. (Dicenzo, 1995; Marcy, 2004)

Contributors

Sean Kessler (author), Radford University, Karen Powers (editor), Radford University, Gail McCormick (editor), Animal Diversity Web Staff, Catherine Kent (editor), Special Projects.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

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Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

electric

uses electric signals to communicate

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

freshwater

mainly lives in water that is not salty.

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

phytoplankton

photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)

piscivore

an animal that mainly eats fish

polyandrous

Referring to a mating system in which a female mates with several males during one breeding season (compare polygynous).

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

ultrasound

uses sound above the range of human hearing for either navigation or communication or both

visual

uses sight to communicate

zooplankton

animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

References

Crecco, V. 1985. Effects of Biotic and Abiotic Factors on Growth and Relative Survival of Young American Shad, Alosa sapidissima, in the Connecticut River. Canadian Journal of Fisheries and Aquatic Sciences, 43: 1640–1648.

Crossman, S. 1998. The Freshwater Fishes of Canada. Ontario, Canada: Galt House Publications Ldt.

Dicenzo, V. 1995. Relations between Reservoir Trophic State and Gizzard Shad Population Characteristics in Alabama Reservoirs. North American Journal of Fisheries Management, 16: 888-895.

Eddy, S. 1957. How to Know The Freshwater Fishes. Iowa: WMC Brown Company.

Ford, F. 2006. 77 Great Fish of North America. Ontario: Thomas Alen & Sons Limited.

Fowler, H. 1945. Fishes of the Southern Piedmont. Lancaster, Pennsylvania: Wickersham Printing Company.

Glebe, B. 1981. Latitudinal Differences in Energy Allocation and Use During the Freshwater Migrations of American Shad (Alosa sapidissima) and Their Life History Consequences. Canadian Journal of Fisheries and Aquatic Sciences, 38: 806-820.

Marcy, B. 2004. Early Life History Studies of American Shad in the Lower Connecticut River and the Effects of the Connecticut Yankee Plant. CSA, 9: 155-180.

McPhee, J. 2003. The Founding Fish. New Jersey: Farrar, Straus and Giroux.

Page, L. 1991. A Field Guide to Freshwater Fishes. Boston: Houghton Mifflin Company.

Pfeiffer, C. 2002. Shad Fishing: A Complete Guide Species, Gear, and Tactics. United States of America: Stackpole Books.

Plachta, D. 2003. Evasive responses of American shad to ultrasonic stimuli. Journal of the Acoustical Society of America, 4/2: 25-30.

Shields, B. 2002. The Nematode Anisakis Simplex in American Shad (Alosa sapidisima) in Two Oregon Rivers. The Journal of Parasitology, 88: 1033-1035.

Weiss-Glanz,, L. 1972. Water Temperatures and the Migration of American Shad. Society of Certified Senior Advisors, 70: 659-670.

Wiley, H. 1986. The Zoogeography of North American Freshwater Fishes. New York: Wiley-Interscience Publication.

Zool, C. 1993. Parasites of American Shad, Alosa sapidissima (Osteichthyes: Clupeidae), From Rivers of the North American Atlantic Coast and the Bay of Fundy, Canada. Canadian Journal of Zoology, 71/5: 941-946.