Alosa sapidissima

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.

• Biogeographic Regions
• nearctic nearctic
  • native native
• atlantic ocean atlantic ocean
  • native native
• pacific ocean pacific ocean
  • introduced introduced

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.

• Habitat Regions
• saltwater or marine saltwater or marine
• freshwater freshwater

• Aquatic Biomes
• rivers and streams
• coastal coastal

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.

• Other Physical Features
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger

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.

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.

• Mating System
• polyandrous polyandrous

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.

• Key Reproductive Features
• seasonal breeding seasonal breeding
• sexual sexual
• fertilization fertilization
  • external external
• oviparous oviparous

Adult American shad do not provide any care for the eggs or larvae after fertilization.

• 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).

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.

• Key Behaviors
• natatorial natatorial
• diurnal diurnal
• nocturnal nocturnal
• motile motile
• migratory migratory
• social social

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.

• Communication Channels
• visual visual
• electric electric

• Perception Channels
• visual visual
• tactile tactile
• ultrasound ultrasound
• chemical chemical

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.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • eats non-insect arthropods

• Animal Foods
• fish
• eggs
• zooplankton zooplankton

• Plant Foods
• phytoplankton phytoplankton

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.

• Anti-predator Adaptations
• cryptic 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 ).

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.

• Positive Impacts
• food food
• ecotourism ecotourism

Economic Importance for Humans: Negative

There are no known adverse affects of American shad on humans.

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.

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

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

References

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