Table l. — Monthly summary of size, molting activity, and 

 condition of spiny lobsters, and water temperatures in eastern 

 Biscayne Bay, Fla., 1976-77. 



technicians. The mean error was 0.3 mm, with a 

 range of -1.8 to +2.1 mm. Consequently, only 

 changes in carapace measurements >2.0 mm were 

 recorded as growth, others were considered mea- 

 surement errors. 



Two factors appeared to affect growth rates: 

 water temperature and lobster condition. Growth 

 rate did not vary with either sex or size within the 

 range observed. Mean intermolt periods were es- 

 timated by doubling the time interval over which 

 SO*??^ of the lobsters observed had molted. This as- 

 sumed that at the time of tagging the lobsters were 

 randomly distributed throughout their molting 

 cycle (Munro 1974). This appeared reasonable 

 since we observed molting activity throughout the 

 year (Table 1), and direct observations of indi- 

 vidual lobsters through periodic recaptures con- 

 firmed the mean values obtained for the popula- 

 tion in this manner (Davis 1978). For example, 

 during winter, the percentage of tagged lobsters 

 that had molted increased weekly from 12% after 1 

 wk to 22, 31, 32, 40, 44, and 58% after 8 wk, 

 indicating that 50% had molted after about 7.5 wk, 

 resulting in a mean intermolt period of 15 wk 

 (Figure 1). In contrast, the mean intermolt period 

 during summer was only 8 wk (Table 2). The mean 

 intermolt period of injured lobsters was 15 wk, and 

 for uninjured lobsters it was 10 wk (Table 2). The 

 mean growth increments were estimated by exa- 



980 



O 





• Uninjured — 



* Injured -- 



• Summer — 



* Winter ' -- 



9 11 13 15 17 



Weeks 



Figure l.— Comparison of molting activity as a function of 

 condition ( Ai and season i B) for .spiny lobsters in Biscayne Bay, 

 Fla. 



Table 2.— Mean growth variables determined from 1,688 

 observations on 534 tagged juvenile spiny lobsters in Biscayne 

 Bay Fla., 1976-1977. 



mining frequency distributions of observed 

 changes in carapace length. Mean single molt 

 growth increments were significantly larger dur- 

 ing the summer and for uninjured lobsters than 

 during the winter and for injured lobsters, respec- 

 tively (Table 3). Effects of season and lobster con- 

 dition on growth rate were independent (Table 4). 

 Predictably, higher summer (May-October) 

 temperatures and longer daylight periods were 

 related to a greater growth rate (0.75 mm CL/wk) 

 than that observed during winter, November 

 through April (0.31 mm CL/wk). This 59% de- 

 crease in growth rate between summer and winter 

 was apparently related to the 8.0° C decrease in 

 mean water temperature, from 29.1° to 21.1° C, and 

 the increased frequency of injuries incurred dur- 



