Alosa sapidissima

Invasion History

First Non-native North American Tidal Record: 1871
First Non-native West Coast Tidal Record: 1871
First Non-native East/Gulf Coast Tidal Record: 1874

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General Invasion History:

American Shad (Alosa sapidissima) is an anadromous fish native to the East Coast of North America. Native spawning populations range from the St. Lawrence River estuary to the St. Johns River in Florida. Spawning fish migrate up to 800 km upstream to spawn, though dams have limited that movement. Juvenile shad move downstream to estuaries and as adults range widely in coastal ocean waters (Bigelow and Schroeder 1953). American Shad were stocked unsuccessfully in the Great Lakes in 1870-1875 (Emery 1985), and the Gulf Coast in 1875-1900 (Baird 1878; Bowers 1900; USGS Nonindigenous Aquatic Species Program 2014), but plantings in the San Francisco estuary in 1871 resulted in an established population in the estuary, which later developed spawning populations north to the Columbia River (Pearcy and Fisher 2011). Migrating adults move along the coasts from Baja California, north to Alaska, and west to Kamchatka, Russia (Pearcy and Fisher 2011; Hasselman 2012a).

North American Invasion History:

Invasion History on the West Coast:

In June 1871, the first planting of 1000 fry from the Hudson River was made at Tehama on the Sacramento River, which is 443 km upstream of Sacramento. The fish were carried in milk cans and transported by rail. From 1871 to 1881, a total of 600-879,000 American Shad were stocked in the San Francisco Bay watershed. Their successful establishment may have been favored because shad have floating eggs and spawn in deep river channels, and so were less affected by the heavy siltation resulting from hydraulic mining in the watershed (Shebley 1917; Cohen and Carlton 1997; Dill and Cordone 1997). Additional plantings were made in the Columbia River in 1885-1886 (Lampman 1946). American Shad dispersed rapidly up and down the coast, reaching San Pedro Bay in the south and the Columbia River and Vancouver Island in the north by 1880 (Smith 1895; Lampman 1946; Cohen and Carlton 1995; Dill and Cordone 1997).

Adult fish range as far south as Baja California, Mexico and Kodiak Island, Alaska (Pearcy and Fisher 2011; Hasselman 2012a). Adults have strayed as far west as the Kamchatka Peninsula, Russia, but there is no evidence of spawning there (Chereshnev and Zharnikov (1989, cited by Hasselman 2012a). Spawning populations are known from the Salinas, Eel, Klamath River, Coquille River, Coos Bay, Umpqua River, Smith River and Siuslaw River. Migration occurs along the narrow continental shelf, mostly with 50 km of the shore (Pearcy and Fisher 2011).

American Shad are still established in San Francisco Bay, but have declined since the mid-20th century, though not as dramatically as Striped Bass (Morone saxatilis) (Dill and Cordone 1997; Sommer et al. 2007). The only established land-locked freshwater population of American Shad was established in Millerton Lake, a reservoir on the upper San Joaquin River, near Fresno, and ~ 400 km from the sea. The fish may have been accidentally introduced with a planting of Striped Bass in 1955-1957 (Dill and Cordone 1997).

American Shad from San Francisco Bay had reached the Columbia River by 1880. But between 1885 and 1886 additional plantings were made by the US. Fish Commission who planted 910,000 fry in the Willamette River. Spawning populations were established in the Columbia River by the 1940s (Pearcy and Fisher 2011). After 1960, the number of shad passing Bonneville Dam began to increase sharply, peaking at ~6 million fish in 2006 (Hasselman et al. 2011a). Shad have been collected as far upriver as the Granite Dam on the Snake River, Idaho, 600 km from the Ocean, but most of the spawning takes place below the Bonneville Dam. Breeding populations are known from Willapa Bay, the Chehalis River, and Puget Sound tributaries (Pearcy and Fisher 2011). Stray fish were reported in Cook Inlet and Kodiak Island in 1904 and 1926 and the Kamchatka Peninsula, Russia by 1989 (Hasselman 2012a).

Invasion History on the Gulf Coast:

Attempts were made to introduce American Shad to several Gulf of Mexico tributaries, including the Colorado River, Texas (Baird 1874) and Apalachee Bay, Florida, the Econfina-Steinhatchee River in Florida, and Suwannee River in Georgia (Bowers 1900, cited by USGS Nonindigenous Aquatic Species Program 2018). These releases appear to have been unsuccessful (USGS Nonindigenous Aquatic Species Program 2018). The very similar Alabama Shad is native in much of this range (Robins et al. 1986).

Invasion History Elsewhere in the World:

Many attempts have been made to introduce American Shad to inland waters of North America. In 1870, 5,000 American Shad were released in the Genesee River, a tributary of Lake Ontario. In the 1870s and early 1880s, nearly 3.5 million shad were released in the Great Lakes, but few fish were recovered (Emery 1985). Several releases were made in interior rivers and reservoirs, including Great Salt Lake Basin, and the Colorado River in California, mostly in the 19th century. All these releases were unsuccessful (USGS Nonindigenous Aquatic Species Program 2018). There are reports of introductions to Japan and Germany, but no details are available (Food and Agricultural Organization 2018; Froese and Pauly 2018).

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Description

American Shad (Alosa sapidissima) is an anadromous fish in the herring family (Clupeidae), with an extensive ocean range and only one known landlocked population. Its body is streamlined, but deep and laterally compressed. There is a single soft-rayed dorsal fin, a soft-rayed anal fin, and the pelvic fins are abdominal. There are 15-19 dorsal rays, and 18-24 anal rays. The tail is deeply forked. The scales are large and easily loosened. The belly is keeled with prominent bony scutes (external bony plates). Adult fish can reach 760 mm. The body is dark greenish or bluish dorsally and silvery-white on the sides, with a dark spot and one or two rows of dusky lateral spots on the rear of the gill cover (Bigelow 1953; Miller1972; Eschmeyer and Herald 1983). Developmental stages are described by Jones et al. (1978) and Wang (1985).

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Taxonomy

Ecology

General:

American Shad (Alosa sapidissima) is an anadromous fish, whose adults migrate long distances along the continental shelf while feeding, and run long distances up large rivers for spawning (Bigelow and Schroeder 1953; Page and Burr 1991). Only one landlocked population is known, in Millerton Reservoir, San Joaquin River CA (Dill and Cordone 1997). Females tend to reach a larger size (3.6 kg) than males (2.7 kg). The maximum length is 760 mm, but more usually 600 mm (Froese and Pauly 2018). Adults mature at ~380-400 mm, at about 3-6 years. Females produce 100,000 to 600,000 eggs (Bigelow and Schroeder 1953; Murdy et al. 1997).

Adults usually migrate to their river of birth. Some spawn immediately on reaching freshwater, but some fish migrate as much as 630 km upstream, although dams have curtailed many of these migrations (Bigelow and Schroeder 1953; Froese and Pauly 2018). Spawning fish enter freshwater at ~10-13 F in winter to spring. Spawning dates on the east coast are as early as January in Georgia and as late and May-June in Nova Scotia (Bigelow and Schroeder 1953). In the San Francisco estuary, American Shad enter the estuary as early as the fall. Spawning runs occur in March to April-June, mostly above Rio Vista on the Sacramento River in the tidal fresh section of the river (Wang 1986). Spawning migrations in the Columbia River take place from May to July (Pearcy and Fisher 2011). The fish do not feed during the spawning migrations. Spawning takes place in sandy or pebbly shallows. After spawning, the emaciated adults either die, or return downriver to feed, and then go out to sea (Bigelow and Schroeder 1953). On the Pacific coast, most adults die after one spawning (Cohen and Carlton 1995). The eggs are semi-buoyant and move downstream along the bottom with the current. At 12-17 C, the eggs take 6-15 days to hatch into 9-10 mm yolk-sac larvae. After absorption of the yolk-sac, at ~16.5 mm, the larvae are extremely slender, but by late summer or fall the juveniles have reached 40-80 mm and resemble the adults in shape (Bigelow and Schroeder 1953). In some estuaries, they move downstream into brackish or sea water, but most of those in the San Francisco estuary remain in the fresh water of the upper Delta (Wang 1986).

As strong migrators, American Shad can avoid extremes of temperature through migration. On the Atlantic Coast, they have seasonal migrations at sea. Fish from all along the Atlantic coast gathering in the Gulf of Maine to feed in summer, often moving more than 150 km offshore. Adult fish winter in deeper offshore waters (Bigelow and Schroeder 1953). On the Pacific Coast, fish reach the highest abundance from central Oregon to Vancouver island, over the shallow continental shelf (<159 m), at sea surface temperatures of 11 to 17 C, but do not show strong southward migrations. In all their movements, American Shad move in large schools. The spawning migration into freshwater requires a physiological adaptation to freshwater, mediated by hormones. The fish meander during migration, while making this adjustment. They also cease to feed (Leggett and O'Boyle 1976).

The primary food of larvae, juveniles, and adult American Shad is zooplankton. Larval and juvenile fish feed on smaller freshwater and estuarine copepods. They switch to larger marine copepods (e.g. Calanus spp.), mysids, and euphausiids as adults. Occasionally, adults will eat small fish, but this is not a major part of their diet (Bigelow and Schroeder 1953). As noted above, feeding ceases when adults migrate into freshwater. Shad are prey for larger fishes, birds, and seals.

Food:

Copepods, mysids, fishes

Consumers:

Fishes, Birds, Seals, Humans

Trophic Status:

Carnivore

Carn

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Habitats

General Habitat	Nontidal Freshwater	None
General Habitat	Grass Bed	None
General Habitat	Unstructured Bottom	None
General Habitat	Coarse Woody Debris	None
General Habitat	Tidal Fresh Marsh	None
General Habitat	Salt-brackish marsh	None
General Habitat	Rocky	None
Salinity Range	Limnetic	0-0.5 PSU
Salinity Range	Oligohaline	0.5-5 PSU
Salinity Range	Mesohaline	5-18 PSU
Salinity Range	Polyhaline	18-30 PSU
Salinity Range	Euhaline	30-40 PSU
Tidal Range	Subtidal	None
Vertical Habitat	Nektonic	None

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Life History

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Tolerances and Life History Parameters

Minimum Temperature (ºC)	4	Field data (Jones et al. 1978)
Maximum Temperature (ºC)	30	Field data (Jones et al. 1978)
Minimum Salinity (‰)	0	Field data (Jones et al. 1978)
Maximum Salinity (‰)	35	Field data (Jones et al. 1978)
Minimum Dissolved Oxygen (mg/l)	3.2	Field data (Jones et al. 1978)
Minimum Reproductive Temperature	8	Field data (Jones et al. 1978)
Maximum Reproductive Temperature	26	Field data (Jones et al. 1978)
Minimum Reproductive Salinity	0	This is a freshwater-spawning fish.
Maximum Reproductive Salinity	7.5	Bigelow and Schroeder 1953
Minimum Length (mm)	380	Froese and Pauly 2014
Maximum Length (mm)	760	Froese and Pauly 2014
Broad Temperature Range	None	Cold temperate-Warm temperate
Broad Salinity Range	None	Limnetic-Euhaline

General Impacts

American Shad (Alosa sapidissima) was a highly esteemed food-fish on the East Coast, well regarded for its flesh and roe. Its introduction and establishment on the West Coast was regarded as a triumph of fish-culture in the 19th century. Successful fisheries were quickly established from San Francisco Bay to the Columbia River (Smith 1895; Dill and Cordone 1997). However, on the Pacific coast, 'the shad never quite has convinced the western palate, perhaps because of a prodigality of salmon' (Lampman 1946). The commercial net fishery for Shad ended in San Francisco Bay in 1957, but a sport fishery continues with dip nets and fly-fishing. While migrating adult shad do not feed, they will snap at an artificial fly and provide sport for fly-fishers. (Dill and Cordone 1997). Prior to the introduction of Shad into the San Francisco estuary and watershed, large planktivorous fishes were absent from the system. Thus Shad were able to fill and an empty niche (Cohen and Carlton 1995). However, in the Columbia River, where ranges of juvenile salmon (Oncorhynchus spp.) overlap with shad, competition for zooplankton prey is a concern. In coastal Pacific waters, American Shad may be competing with Pacific Herring for food (Ray Buckley, personal communication 2004; Hasselman 2012b).

Economic Impacts 

Fisheries- As noted above, American Shad was a highly esteemed food-fish at the time of its introduction to San Francisco Bay in 1874, and commercial fisheries were underway by 1883. However, shad never reached the popularity that it had on the East Coast, and few people were willing to learn the difficult skill of boning this very bony fish (Dill and Cordone 1997). Nonetheless, fisheries developed at rivers north of San Francisco Bay to the Columbia River by 1888 (Smith 1895). Fisheries on the San Francisco Bay and the West Coast were primarily for the roe. They fluctuated both with the abundance of the fish, and the price, which sometimes fell so low that the fishery was not profitable. In 1957, the state closed the fishery due to pressure from sport fishers, who were concerned about Striped Bass being caught in seine nets. Sports fisheries for Shad continue using dip nets and fly-fishing (Dill and Cordone 1997). ).

Ecological Impacts 

Impacts of American Shad on native species in the San Francisco estuary were thought to be small, because shad were believed to occupy an 'unfilled niche' (Cohen and Carlton 1995). However, abundances of this fish has increased in Oregon and Washington marine, estuarine and fresh waters, raising concern about competition for zooplankton with Pacific Herring (Clupea pallasi) and native salmon (Onorhynchus spp.) (Ray Buckley, personal communication 2004; Hasselman 2012b). The increased population of American Shad after 1988, contributed to an amplified epizootic of the protozoan parasite Ichthyophonus, a potential threat to other marine and anadromous fishes (Hershberger et al. 2010). The increased population of American Shad migrating up the Columbia River also has potential effects on the river system's foodweb by transporting nutrients from the ocean into the river and reservoirs. This import roughly matches the present importation of marine nutrients by migrating salmon, but is much smaller than the historic upstream transport by native salmon populations (Haskell 2018).

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Regional Impacts

P260	Columbia River		Ecological Impact	Competition
Zooplankton predation by American Shad are expected to affect food availability for native fishes, including Pacific salmon (Oncohrynchus spp.) (Haskell et al. 2013).
P260	Columbia River		Ecological Impact	Predation
The increased population of American Shad in reservoirs of the Columbia River appears to have altered the zooplankton population, reducing the abundance of large zooplankton such as Daphnia spp. American Shad are estimated to consume an average of 23% of daily zooplankton production (Haskell et al. 2013).
P260	Columbia River		Ecological Impact	Parasite/Predator Vector
The increased population of American Shad in reservoirs of the Columbia River appears to have amplified the population of a native protistan parasite, Ichthyophonus spp. in freshwater reservoirs of the river. The parasite is regarded as a threat to native Pacific salmon, although prevalence was very low (~4%) in spring Chinook Salmon (Hershberger et al. 2010).
P260	Columbia River		Economic Impact	Fisheries
'Several hundred thousand shad are landed annually by commercial and sport fisheries in the Columbia River (Petersen et al. 2003', cited by Pearcy and Fisher 2011).
P180	Umpqua River		Economic Impact	Fisheries
Commercial fishery, (Mullen and Conover 1973, cited by Pearcy and Fisher 2011)
P090	San Francisco Bay		Economic Impact	Fisheries
By 1874, American Shad were abundant enough to support a small fishery in San Francisco Bay, and from 1900 to 1945, catches frequently exceeded 1 million pounds. Catches decreased in the 1950s, and the commercial fishery was banned in 1957. The sport fishery continues, by dipnet and fly-fishing (Smith 1896; Cohen and Carlton 1995).
NEP-V	Northern California to Mid Channel Islands		Economic Impact	Fisheries
By 1874, American Shad were abundant enough to support a small fishery in San Francisco Bay, and from 1900 to 1945, catches frequently exceeded 1 million pounds. Catches decreased in the 1950s, and the commercial fishery was banned in 1957. The sport fishery continues, by dipnet and fly-fishing (Smith 1896; Cohen and Carlton 1995).
NEP-IV	Puget Sound to Northern California		Economic Impact	Fisheries
Commercial fisheries occurred in the Siuslaw, Umpqua, Smith, Coos, Coquille Rivers in Oregon, where shad spawned, averaging 192 metric tons per year, during 1962–72 (Mullen and Conover 1973, cited by Pearcy and Fisher 2011).
P190	Siuslaw River		Economic Impact	Fisheries
Commercial fishery, (Mullen and Conover 1973, cited by Pearcy and Fisher 2011)
P170	Coos Bay		Economic Impact	Fisheries
Commercial fishery, (Mullen and Conover 1973, cited by Pearcy and Fisher 2011)
P160	Coquille River		Economic Impact	Fisheries
Commercial fishery, (Mullen and Conover 1973, cited by Pearcy and Fisher 2011)
P260	Columbia River		Ecological Impact	Trophic Cascade
Migration by American Shad has partially replaced the transport by native Salmon of nutrients (N and P) from the marine environment to the Columbia River Basin. At present, shad import 2% of the total phosphorus load to the John Day Reservoir, on the lower Columbia. Nutrient imports by shad roughly equal those of native salmon at present, but are much smaller than those from historic salmon population (Haskell 2018).
CA	California		Economic Impact	Fisheries
By 1874, American Shad were abundant enough to support a small fishery in San Francisco Bay, and from 1900 to 1945, catches frequently exceeded 1 million pounds. Catches decreased in the 1950s, and the commercial fishery was banned in 1957. The sport fishery continues, by dipnet and fly-fishing (Smith 1896; Cohen and Carlton 1995)., By 1874, American Shad were abundant enough to support a small fishery in San Francisco Bay, and from 1900 to 1945, catches frequently exceeded 1 million pounds. Catches decreased in the 1950s, and the commercial fishery was banned in 1957. The sport fishery continues, by dipnet and fly-fishing (Smith 1896; Cohen and Carlton 1995).
OR	Oregon		Economic Impact	Fisheries
Commercial fishery, (Mullen and Conover 1973, cited by Pearcy and Fisher 2011), Commercial fishery, (Mullen and Conover 1973, cited by Pearcy and Fisher 2011), Commercial fishery, (Mullen and Conover 1973, cited by Pearcy and Fisher 2011), Commercial fishery, (Mullen and Conover 1973, cited by Pearcy and Fisher 2011)

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