The Bay Scallop, Argopecten irradians, in Florida Coastal Waters WILLIAM S. ARNOLD Introduction tions by transplantation of field-collect- the grass blades and assume a benthic ed specimens or by rearing scallops in a existence. They achieve a shell height The bay scallop, Argopecten irradi- hatchery setting and then planting them of 50–55 mm by June of the follow- ans, supports one of the most popular at sites targeted for restoration (Arnold ing year, at which time growth slows and family-oriented fisheries currently et al., 2005). Regardless of the methods considerably and energy is devoted to pursued in Florida coastal waters. Har- used to restore scallop populations in reproductive development and spawn- vesting bay scallops has a long history Florida, the species remains imperiled in ing (Barber and Blake, 1983). in both peninsular (Marelli and Arnold, the face of continued human population 2001) and panhandle (Mikell, 1992; growth and concomitant loss of suitable Species Distribution and Status 1994; Thomas and Campbell, 1993) bay scallop habitat. Three species of Argopecten occur Florida dating to at least A.D. 900, but in Florida including the calico scallop, in recent years the popularity of the Life History Argopecten gibbus; the nucleus scal- scallops as a target for recreational and Bay scallops are short-lived, and in lop, Argopecten nucleus; and the bay commercial fishermen appears to have Florida their life span rarely exceeds scallop, Argopecten irradians (Abbott, contributed to local declines and the 18 months (Barber and Blake, 1985). 1974). The calico scallop inhabits implementation of more stringent man- Their primary habitat is seagrass beds, deeper offshore waters and has been agement measures (Arnold et al., 1998). particularly Thallassia and Syringo- the target of an occasionally lucrative Those declines also have instigated dium, but it is not uncommon for scal- commercial fishery (Moyer and Blake, many efforts to rebuild scallop popula- lops to be found in open sand areas or 1986; Blake and Moyer, 1991). In con- lying on algal mats among the seagrass trast, the bay scallop and the nucleus William S. Arnold was with the Fish and Wild- beds. Bay scallops may or may not have scallop inhabit shallow inshore waters. life Research Institute, Florida Fish and Wildlife the physiological apparatus to support Their range appears to overlap in south Conservation Commission, 100 Eighth Avenue gregarious behavior, but they are com- Florida and particularly Biscayne Bay S.E., St. Petersburg, FL 33701. His current address is the Southeast Regional Office, NOAA, monly found in patches that are densely (Waller, 1969), but otherwise the range National Marine Fisheries Service, 263 13th Ave. populated relative to background abun- of the nucleus scallop is more southerly South, St. Petersburg, FL 33701 (email: Bill. dance. The patchy distribution pattern than that of the bay scallop. [email protected]). may facilitate successful reproduction. Nucleus scallops occur throughout Scallops are broadcast spawners, so the the Caribbean and northern South likelihood of successful fertilization America (Waller, 1969) whereas the ABSTRACT—The bay scallop, Argopec- is enhanced by proximity (Levitan, most southerly record of the bay scallop ten irradians, supported a small commer- 1995). is from Tuxpan in the Veracruz region cial fishery in Florida from the late 1920’s Peak spawning activity appears to of Mexico (Wakida-Kusunoki, 2009). through the 1940’s; peak landings were occur in the fall season in Florida, in There are published reports of calico in 1946 (214,366 lbs of meats), but it cur- rently supports one of the most popular and contrast to the situation with bay scal- scallops occurring in Biscayne Bay family-oriented fisheries along the west lops in New York to Massachusetts (Coleman et al., 1994), thus creating coast of Florida. The primary habitat of where spawning is a summer or even a situation where all three species co- the short-lived (18 months) bay scallop is spring event. However, ongoing studies occur, and the author has many records seagrass beds. Peak spawning occurs in the by the author show that spring spawning of calico scallop recruits collected from fall. Human population growth and coastal development that caused habitat changes occurs in some years, and recruitment inshore bays on both the east and west and reduced water quality probably are the has been recorded in almost every coast of Florida. main causes of a large decline in the scallop’s month of the year. Fertilized larvae Within the species Argopecten ir- abundance. Bay scallop restoration efforts spend about two weeks in the pelagos, radians, three extant subspecies are in bays where they have become scarce have centered on releasing pediveligers after which they settle and attach to recognized including A. i. irradians and juveniles into grass beds and holding seagrass blades. At a shell height of from the northeastern United States, A. scallops in cages where they would spawn. about 15–20 mm, the scallops drop off i. concentricus from the Mid-Atlantic 71(3) 1 region and eastern Gulf of Mexico, and north, somewhat consistent with human ing, and wet weather during the spring, A. i. amplicostatus from the western development patterns in the state. Bay but no definitive correlations could be Gulf of Mexico including Mexico. A scallops appear to have disappeared discerned. fourth subspecies (A. i. taylorae) oc- first from the southeast coast of the Bay scallop population density sur- cupying Florida and the eastern Gulf state, then from Pine Island Sound in veys were initiated at several sites along of Mexico has been suggested but not southwest Florida, followed by loss of the Gulf of Mexico coast of Florida codified (Marelli et al., 1997a). If that populations in Sarasota Bay and Tampa beginning in 1993 and have continued subspecific designation is accepted, Bay, then Anclote, and finally Homosas- to the present. Survey sites were selected then the A. i. concentricus designation sa and Crystal River (Fig. 1). However, based upon the historical and anecdotal would be dropped and bay scallops from bay scallops also have disappeared from information described above and have North Carolina north would be lumped western panhandle Florida, suggesting been continued (and expanded) since into the A. i. irradians group (Marelli a more complex pattern of loss. their initiation at Homosassa in 1993. et al., 1997b). Anecdotal information gleaned from At each survey site, 20 stations were The three subspecies are in many telephone and personal interviews with randomly selected from within the 2 ft respects similar in appearance al- fishermen, owners of marine-dependent to 6 ft (0.61 m to 1.83 m) depth contours though they can be distinguished by businesses (dive shops, bait shops, ma- (Arnold et al., 1998). At each station, morphological details such as hinge rinas), and coastal managers conducted two scuba divers swam the length of a width and the number of ribs on the during 1991, 1992, and 1993 supports 984 ft (300 m) transect line and counted shell surface (Waller, 1969). They also the pattern of disappearance described all scallops within 1.1 yds (1 m) on share a dependence on marine seagrass above (Arnold and Marelli1). Responses either side of the line, thus surveying an as a habitat (Thayer and Stuart, 1974), were divided into three geographically area of 718 yds2 (600 m2) at each station although the particular species of sea- representative areas including south- or 14,352 yds2 (12,000 m2) at each site. grass upon which the scallop depends west Florida (from Tampa Bay south), At the Cedar Key site, where the extent differs from site to site according to the central west coast of Florida (i.e. of seagrass beds is relatively small, only seagrass distribution patterns. That the Big Bend, from Tampa Bay north 6 rather than 20 stations were surveyed dependence upon seagrass has con- to approximately Apalachicola Bay), each year. tributed to the decline of bay scallops and northwest Florida (from Apala- Initial survey results supported the in Florida and throughout the range of chicola Bay to the Florida–Alabama historical and anecdotal information the species, because the seagrasses are state line). reported above. Scallops have been becoming scarcer. In the southwest region, scallops were essentially nonexistent in Pine Island Museum collections indicate that the reported only from Pine Island Sound, Sound (Table 1) in southwest Florida distribution of bay scallops in Florida where they were scarce and their inter- and in Pensacola Bay and St. Andrew once extended from Palm Beach on the annual abundance was inconsistent. In Bay in northwest Florida. In the central southwest coast of the state to Pensacola the central region, scallops were rare region, scallops were rare in the Homo- and westward to the Chandeleur Islands from Tampa Bay north to the Pepperfish sassa/Crystal River area through 1998 in Louisiana (Waller, 1969). Although Keys area, but from Pepperfish Keys but abundance has been highly variable no definitive information is available, it north to Keaton Beach (i.e. the Stein- in Anclote. In contrast, although interan- is likely that the scallops were not con- hatchee area) scallops were abundant, nual fluctuations are apparent at both the tinuously distributed within this range. although abundance varied from year to St. Joseph Bay and Steinhatchee study Instead, the population was composed year. Respondents reported that scallops sites, at least through 1998 scallop abun- of many discretely distributed sub- “used to be” abundant in areas such as dance at those sites has been an order populations that inhabited the bays and Anclote and Homosassa and suggested of magnitude greater than at most other estuaries that characterize the Florida that declines in these populations were sites during most years. Since 1998, coast.