is about 14 days and that the spat are about 

 0.25 mm in shell height when first set. 



A few observations have been made on the 

 shell growth of young calico scallops following 

 setting. Calico scallops (apparently small spe- 

 cimens) collected from fouling arrays in the 

 northeastern Gulf of Mexico grew at a minimum 

 rate of 3.1 mm (presumably in shell height) per 

 week in April (Pequegnat and Pequegnat, 1968) . 

 Oflf the Florida east coast, young calico scallops 

 found in spat collecting traps after 10 weeks' 

 exposure time had a maximum size of 27 mm 

 in shell height (Allen, see footnote 8). 



Shell growth of large scallops was estimated by 

 Bullis and Ingle (1959) for calico scallops caught 

 in the northeastern Gulf of Mexico. From re- 

 portedly "inadequate" size frequency data, they 

 tentatively estimated that scallops averaging 

 54 mm (probably in shell diameter) were 24 

 months old. 



Growth of calico scallops from the North Car- 

 olina grounds was estimated using several tech- 

 niques and reported as increases in shell depth by 

 Kirby-Smith (1970). In this case, shell depth 

 refers to shell height (Kirby-Smith, see footnote 

 3) . For scallops ranging from about 19 to 28 mm 

 in height, maximum growth (converted from the 

 daily rate) was 2.2 mm per month. Calico scal- 

 lops from North Carolina that ranged from 43 

 to 61 mm in shell height were estimated to be 

 2 years old (Wells, Wells, and Gray, 1964). 



Roe, Cummins, and Bullis (1971) estimated 

 growth rates from size frequencies of calico scal- 

 lops collected oif the Florida east coast. They 

 reported that growth (in shell diameter) in- 

 creases rapidly up to about 50 mm. For scallops 

 having mean sizes from 13.9 to 37.8 mm, average 

 growth was 4.0 mm per month. For scallops 

 having mean sizes from 63.5 to 65.5 mm, average 

 growth was 0.3 mm per month. These authors 

 concluded that the calico scallop becomes senile 

 at a size of 75 to 80 mm, that maximum size is 

 80 mm, and that maximum age averages 18 to 20 

 months and does not exceed 24 months. 



In a recent innovation, calico scallops were 

 marked with a quick-setting cement to measure 

 growth increments over known time periods 

 (Hudson)." Preliminary studies oh the Cape 



Kennedy grounds indicate that marked scallops 

 reach 40 to 45 mm in shell height in 6 to 8 months 

 (Miller and Hudson)." Age-growth estimates 

 shown by Weeks (1970) are in error. 



Mortality 



The disappearance of calico scallops from an 

 area is common (Bullis and Ingle, 1959; Hulings, 

 1961; Commercial Fisheries Review, 1962; 

 Kirby-Smith, 1970; Roe, Cummins, and Bullis, 

 1971; Porter and Wolfe, in press ; Joyce, see foot- 

 note 12) and has often been attributed to mor- 

 tality or migration, although the ability of calico 

 scallops to migrate has not been shown. Mortal- 

 ity or poor recruitment is indicated when only 

 empty scallop shells are found on formerly pro- 

 ductive scallop grounds. 



Very heavy natural mortality of calico scal- 

 lops was reported to occur in late winter on the 

 northern two-thirds of the Cape Kennedy 

 grounds (Bullis and Cummins, 1961). The 

 joined valves containing scallop flesh indicated 

 very recent mortality. At the same time, live 

 scallops were fairly abundant on the southern 

 third of the Cape Kennedy grounds. Therefore, 

 these authors concluded that factors affecting 

 mortality may be limited to distinct areas. 



The causes of mass mortalities of calico scal- 

 lops are not known. Near Cape Hatteras, N.C., 

 where calico scallops occur, drastic fluctuations 

 of water temperature may cause mortalities of 

 benthic invertebrates ( Cerame-Vivas and Gray, 

 1966) . Some mortalities may be a result of pre- 

 dation. For example, sea stars (Asterias) , which 

 have been observed feeding on scallops, occur in 

 vast numbers on the Cape Kennedy grounds 

 (Roe, Cummins, and Bullis, 1971). Extremely 

 large scallops which are "often in poor condition" 

 and may be "at the end of their life span" are 

 present year around on the Cape Kennedy 

 grounds; the adductor muscle in these scallops is 

 small, discolored, and often too weak to close the 

 shell (Bullis and Cummins, 1961). According 

 to Carpenter (1967) , calico scallops in the north- 

 eastern Gulf of Mexico die in the late summer, 

 "presumably after spawning" and following 



'* Hudson, J. H. Marking scallops with quick-setting 

 cement. Submitted to Proc. Natl. Shellfish Assoc, for 

 1971, vol. 62, 7 MS p. 



" Miller, G. C. and J. H. Hudson. 1971. Growth of 

 calico scallops, Argopecten gibbus. Unpublished manu- 

 script filed at the National Marine Fisheries Service, 

 Southeast Fisheries Center, Miami Laboratory, Miami. 

 Fla. 33149. 



