Invasion History

First Non-native North American Tidal Record: 2007
First Non-native West Coast Tidal Record:
First Non-native East/Gulf Coast Tidal Record: 2007

General Invasion History:

Argopecten irradians is native to the Northwest Atlantic from southern Massachusetts Bay to the Gulf of Mexico in shallow coastal waters. Specimens are known from Sable Island, Nova Scotia (Academy of Natural Sciences of Philadelphia 2011), but this bivalve is not established there (Abbott 1974; Morris 1975; Gosner 1978).

North American Invasion History:

Invasion History on the West Coast:

Argopecten irradians is known from the West Coast only from 'old and broken valves' found in South San Francisco Bay in 1963 and 1973 (Wicksten 1976, cited by Carlton 1979), and from a museum specimen from Newport Beach, Oregon in 1923 (Academy of Natural Sciences of Philadelphia 2011). Live animals or dead shells of this bivalve were probably introduced with oysters planted in San Francisco Bay and Oregon waters, from Long Island Sound, in the late 1800s - early 1900s (Carlton 1979; Miller 2000). Alternatively, especially for the Oregon specimen, discarded shells or whole scallops from seafood restaurants are a possibility. There is no evidence that a breeding population existed in San Francisco Bay or Oregon.

Invasion History on the East Coast:

In 1979 and 1989, batches of A. irradians were transported to hatcheries in Nova Scotia, for the development of a 'put and take' scallop fishery. Bay scallops do not survive the winter, but are kept, bred, and reared in hatcheries, then released in Prince Edward Island waters for 'grow-out' in the spring and harvesting in the fall (Whyte et al. 1993; Minchin 2003). In 2007, young Bay Scallops were found settling in Pomquet Harbor, Nova Scotia. Marked scallops survived the winter, and by 2013, a population was apparently established (Williams et al. 2015).

Invasion History Elsewhere in the World:

Argopecten irradians has been introduced to aquaculture facilities in China (Minchin 2003; Zheng et al. 2004). We do not know if it has been released or is established in natural waters.


Argopecten irradians, the Bay Scallop, is round with nearly symmetrical 'wings' on each side of the beak, prominent ribs radiating from the triangular beak, and scalloped edges. The lower valve (left) and upper valve (right) are equally convex. Color patterns of the shells are variable, often with bands of light and dark along the growth lines, and varying among grey, brown, and white. Adult shells typically range from 50 to 75 mm. The adult live animal is marked by the many blue eyes visible when the shell is open and by the rapid, jerky swimming caused by opening and closing its shell. (Description from: Abbott 1974; Morris 1975; Gosner 1978)


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Mollusca
Class:   Bivalvia
Subclass:   Pteriomorphia
Order:   Ostreoida
Family:   Pectinidae
Genus:   Argopecten
Species:   irradians


Aequipecten irradians (Lamarck, 1819)

Potentially Misidentified Species



Juvenile Argopecten irradians use byssus threads to attach to substrates such as gravel and eelgrass, but move freely as adults, swimming when disturbed. They range through estuarine habitats, but depend on eelgrass for shelter from predators (Gosner 1978; Minchin 2003). These scallops are hermaphroditic, but the eggs are fertilized externally (Zheng et al. 2004). The veliger larvae are planktotrophic.





Trophic Status:

Suspension Feeder



General HabitatGrass BedNone
General HabitatOyster ReefNone
General HabitatUnstructured BottomNone
Salinity RangeMesohaline5-18 PSU
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Maximum Depth (m)36Field (Castagna and Chanley 1973)
Minimum Salinity (‰)14Experimental, field (Castagna and Chanley 1973)
Minimum Duration10Larval duration, at 28 C (Minchin 2003)
Maximum Duration19Larval duration, at 20 C (Minchin 2003)
Minimum Length (mm)25Morris 1975; Gosner 1978
Maximum Length (mm)75Morris 1975; Gosner 1978
Broad Temperature RangeNoneCold temperate-Tropical
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

Argopecten irradians is a highly prized food item, because of the delicious taste and firm texture of its adductor muscle meat. Fisheries on the East Coast are limited, and declining, because of poor water quality, and the loss of eelgrass (Zostera marina) beds in many estuaries. The high status and price of this scallop has led to introductions for aquaculture in China, and a hatchery-dependent 'put and take' fishery in Atlantic Canada (Minchin 2003). No impacts have been reported for this species in its introduced range.

Regional Impacts

NA-S3NoneEconomic ImpactFisheries
Although it does not survive the winter in the Gulf of St. Lawrence, and is dependent on hatcheries for survival and reproduction, A. irradians sustains a 'put and take' fishery in estuaries of Prince Edward Island (Whyte et al. 1993; Minchin 2003). Discovery of a protozoan parasite, Perkinsus karlsoni in the scallops caused a 2-year suspension of Bay Scallop stocking, before experiments showed that this organism was not transmissible to other shellfish (Whyte et al. 1993).
NWP-4aNoneEconomic ImpactFisheries
Argopecten irradians is an important aquaculture organism in China, because of the high quality of its meat and its rapid growth. Selective breeding is underway (Minchin 2003; Zheng et al. 2004). We do not know if 'wild' populations occur in Chinese waters.
NWP-3aNoneEconomic ImpactFisheries
Argopecten irradians is an important aquaculture organism in China, because of the high quality of its meat and its rapid growth. Selective breeding is underway (Minchin 2003; Zheng et al. 2004). We do not know if 'wild' populations occur in Chinese waters.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NA-ET2 Bay of Fundy to Cape Cod 0 Native Estab
NA-ET3 Cape Cod to Cape Hatteras 0 Native Estab
CAR-VII Cape Hatteras to Mid-East Florida 0 Native Estab
CAR-I Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida 0 Native Estab
CAR-III None 0 Native Estab
NEP-V Northern California to Mid Channel Islands 1963 Def Failed
CAR-IV None 0 Native Estab
CAR-V None 0 Native Estab
NEP-IV Puget Sound to Northern California 1923 Def Failed
NWP-3a None 1982 Def Unk
NWP-4a None 1982 Def Unk
P090 San Francisco Bay 1963 Def Failed
NA-ET1 Gulf of St. Lawrence to Bay of Fundy 0 Native Unk
NA-S3 None 2007 Def Estab
CAR-II None 0 Native Estab
P210 Yaquina Bay 1923 Def Failed

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Abbott, R. Tucker (1974) American Seashells, Van Nostrand Reinhold, New York. Pp. <missing location>

Academy of Natural Sciences of Philadelphia 2002-2024a Malacology Collection Search. <missing URL>

Carlton, James T. (1979) History, biogeography, and ecology of the introduced marine and estuarine invertebrates of the Pacific Coast of North America., Ph.D. dissertation, University of California, Davis. Pp. 1-904

Carlton, James T. (1999) Molluscan invasions in marine and estuarine communities., Malacologia 41(2): 439-454

Castagna, M.; Chanley, P. (1973) Salinity tolerance of some marine bivalves from inshore and estuarine environments in Virginia waters on the western mid-Atlantic coast., Malacologia 12(1): 47-96

Gosner, Kenneth L. (1978) A field guide to the Atlantic seashore., In: (Eds.) . , Boston. Pp. <missing location>

Lutaenko, Konstantin A.; Furota,Toshio; Nakayama, Satoko; Shin, Kyoungsoon; Xu, Jing (2013) <missing title>, Northwest Pacific Action Plan- Data and Information Network Regional Activity Center, Beijing, China. Pp. <missing location>

Miller, Alexander Whitman (2000) <missing title>, University of California at Los Angeles, Los Angeles. Pp. <missing location>

Minchin, Dan (2003) Introductions: some biological and ecological characteristics of scallops., Aquatic Living Resources 16: 521-532

Morris, Percy A. (1975) A field guide to shells of the Atlantic, Houghton-Mifflin, Boston. Pp. <missing location>

Whyte, S. K.; Cawthorne, R. J.; McGladdery, S. E.; McMillan, R. J;, Montgomery, D. M. (1993) Cross-transmission studies of Perkinsus karlssoni(Apicomplexa) from bay scallops Argopecten irradians to native Atlantic Canadian shellfish species., Diseases of Aquatic Organisms 17: 33-39

Williams, Jim; Polk, Zephyr C. S.; Smit, Laura A.; Macinnis, Gina (2015) Establishment and overwintering of Bay Scallops (Argopecten irradians Lamarck) in a Gulf of St. Lawrence estuary, Journal of Shellfish Research 34(3): 737-741

Zheng, Huaiping; Zhang, Guofan; Liua,Xiao; Zhang, Fusui; Guo, Ximing (2004) Different responses to selection in two stocks of the bay scallop, Argopecten irradians irradians Lamarck (1819)., Journal of Experimental Marine Biology and Ecology 313: 213-223