ROE, CUMMINS, and BULLIS: CALICO SCALLOP OFF FLORIDA 



OCT DEC 



am juc 



AUG OCT 



Figure 10. — Average number of pounds of scallop meats 

 per 30-min drag by month during the 1967-68 Florida 

 east coast survey. 



tober or December cruises, indicating spawning 

 occurred much later in 1968 than in 1967. 



DISCUSSION 



Reproduction in calico scallops is related to 

 age rather than size. It is probably triggered 

 by water temperature as Loosanoff and Davis 

 (1950) have shown that raising the ambient 

 water temperature induces spawning in some 

 bivalves. Since spawning generally occurs in 

 the spring, rising temperatures would be ex- 

 pected to be the initiating mechanism. 



Maturation, taking 7 to 9 months beginning 

 in late summer, is easily detected in the field 

 by coloration changes in the ovaries. Resting 

 ovaries are whitish-yellow but as maturation 

 progresses their color changes through various 

 stages of deepening yellow-oranges to a reddish- 

 orange at the ripe condition. Ripe gonads have 

 been collected from a wide size range indicating 

 that the minimum age of sexual maturity is 

 quite low. Data indicate maturation does not 

 begin simultaneously in all scallops within even 

 the same bed. This presumably accounts for 

 the 2- to 3-month differential in maturation time. 



Spawning begins in late February or early 

 March and continues to June. In some areas 

 the season is protracted since small scallops are 



caught throughout most of the year. This is 

 probably due to variation in sexual maturation 

 rate, growth rates, and water temperature. The 

 lowest frequency of small scallops occurred in 

 February indicating decreasing temperatures 

 in the fall terminate any protracted spawning. 



Protracted spawning during one season con- 

 ceivably leads to protraction during the next. 

 Since growth is related to temperature, scallops 

 spawned early in spring have a longer growing 

 season than do those spawned later in the year. 

 Therefore, the older individuals in a year class 

 would undoubtedly be larger at spawning than 

 the younger individuals. Further, maturation 

 is probably controlled by hormones which in 

 turn are influenced by some environmental fac- 

 tor such as water temperature. This interaction 

 between age, environment, and reproduction 

 needs clarification. 



Growth curves through all sizes ranges can- 

 not be calculated from the survey data since 

 the earliest stages are omitted. The curve is 

 sigmoid from seed size to senility, rapidly in- 

 creasing from 5 to 50 mm. Then the rate de- 

 creases through senility with maximum size 

 about 80 mm. 



Data from 1967 and 1968 indicate only one 

 year class is present in spring but two year 

 classes are present from early summer through 

 winter. Therefore, the maximum age reached 

 by calico scallops must not be greater than 24 

 months and averages 18 to 20 months. 



Mortality rates computed from the survey 

 data support a 2-year maximum life span. Post- 

 spawning mortality averages 23 '^r per month. 

 At that rate only 20% of the year class would 

 remain by early fall. Assuming that some mor- 

 tality occurs during the pre-spawning period, 

 the remaining population in 18 to 20 months 

 would be exceedingly small. 



Scallops are not randomly distributed but 

 form north-south windrow configurations. 

 These configurations, established at spat set, are 

 heavily influenced by currents. Olsen (1955) 

 indicates that windrow-like configurations result 

 from strong tides, their orientation running 

 lengthwise to the tide. He also shows strong 

 linear configurations result in eddy systems. 



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