ROE, CU\L\11NS. and BL'LLIS: CALICO SCALLOP OFF FLORIDA 



catch curves. To test this possibility, data from 

 a bed of known age composition were used to 

 construct a catch curve. This bed, located at 

 lat 29° 16' N in 22 to 27 fm on transect C, was 

 established in August 1967 and can be accurately 

 traced through October 1968 with length-fre- 

 quency data. 



The catch curve for the bed (August 1967 

 to October 1968) is given in Figure 4. Recruit- 



Figure 4. — Catch curve for transect C, 22 to 27 fm. 

 Data are for the 1967 year class. 



ment in late summer and fall was strong. Re- 

 cruitment and mortality seem balanced from 

 October to February, but neither can be accu- 

 rately determined. The convex descending limb 

 (February to October) indicates a nonuniform 

 mortality rate, increasing rapidly after June 

 with the termination of spawning. 



The February to October segment was treated 

 linearly to estimate monthly mortality. Results 

 were / = —0.231 and a = 21 Si (see Table 1). 

 Mortality rates for the dome (October to Feb- 

 ruary) were not calculated. 



Although these rates are similar to those in 

 Table 3, enough discrepancy exists to indicate 

 more than one year class might have been in- 

 cluded in Table 3 data, causing some differences 

 in mortality rates. This does not jjreclude mor- 

 tality rate differences on the grounds. 



The major calico scallop predator appears to 

 be the starfish {Asterias) which is often taken 

 in large numbers in dredge tows (Figure 5) and 



has been seen by submarine observers feeding 

 on scallops (Figure 6). Rays and skates may 

 feed on calico scallops (Struhsaker, 1969) and 

 puffers (Sphoeroides) have been taken with 

 numerous small (2 to 5 mm) scallops in their 

 stomachs. Other predators are not known. 



Little is known about those environmental fac- 

 tors affecting scallops though water temperature 

 is considered most important. Past explorations 

 have shown evidence of occasional mass mortal- 

 ities that may have been due to temperature 

 fluctuation. Dickie and Medcof (1963) reported 

 that mass mortalities often occur in sea scallops 

 when water temperatures fluctuate rapidly. 

 Further, temperature changes may indirectly 

 cause death through dehabilitation, thereby 

 rendering scallops highly susceptible to preda- 

 tion. 



DISTRIBUTION AND ABUNDANCE 



Calico scallops occurred in 13 to 37 fm with 

 greatest concentrations between 19 and 30 fm 

 (Figure 1). 



Depth distributional differences north and 

 south of the Cape were noted (Figure 7). Scal- 

 lops south of the Cape were generally found 

 shallower than north of the Cape. The reasons 

 for this are unknown though the thermal struc- 

 ture may be different in these areas. Also the 

 shelf is narrower with a steeper gradient south 

 of the Cape, and available habitat is restricted. 

 Optimum bottom may occur 4 to 5 fm shallower 

 in that area. 



A slight seasonal change in depth distribution 

 occurred in both areas. Scallops were in slightly 

 deeper water in winter than summer, this dif- 

 ference being less noticeable north of the Cape. 



Yearly differences in bed distribution were 

 noted during the survey. In 1967 beds were 

 primarily located between 19 and 30 fm; how- 

 ever, in the fall of 1968 very few scallops oc- 

 curred in that depth range and a developing bed 

 was found at lat 29° 10' N in 15 to 17 fm. This 

 bed extended northward beyond lat 29°25' N. 



Scallops were usually found in north-south 

 windrows several hundred yards to a quarter 

 mile long. Bed size varies but without a means 



403 



