Table 3. — Comparison of mean molt increments (millimeters of 

 change in carapace length) of juvenile spiny lobsters, in Biscayne 

 Bav. Fla. 



Season 



Conditions 



Item 



Summer 



Winter 



Injured 



Uninjured 



X 



Sx 



t. 306 df 



6.0 4.7 



32 3.6 



7.75" 



4.7 

 3.8 



5.2 

 38 



2.25- 



••Ps0.01;-Ps0 05. 



Table 4. — Two-way fixed factor ANOVA of effects of season and 

 spiny lobster condition as evidenced by growth rate. 



Source of variation 



df 



SS 



MS 



ing the fall and winter fishing season. Growth 

 rates were lowest for injured lobsters during 

 winter and highest for uninjured animals during 

 summer, but injured lobsters grew faster in sum- 

 mer than injured ones in winter. Both of these 

 factors, reduced temperature and injuries, caused 

 increased intermolt periods and reduced molt in- 

 crements, which resulted in reduced growth rates 

 {Table 2). Change in the length of the intermolt 

 period was the major effect of both factors, but by 

 inspection of the values in Tables 2 and 3, it was 

 apparent that intermolt period was propor- 

 tionately more important for the injury-caused 

 reduction, whereas decreased molt increment was 

 proportionately more important for the season- 

 related growth reduction. 



Discussion 



The growth data presented here generally con- 

 form both in magnitude and character to that in 

 the published literature for decapod crustaceans, 

 but the precise effect of injuries in the wild and 

 definition of their origin is apparently new infor- 

 mation, particularly for P. argus. Estimated 

 growth rates for juvenile P. argus in the Carib- 

 bean, Florida, and Bermuda, range from 0.43 to 

 0.65 mm CL/wk (Smith 1951; Travis 1954; 

 Sutcliffe 1957; Buesa M. 1965; Witham et al. 1968; 

 Sweat 1968; Little 1972; Eldred et al. 1972; Ting 

 1973; Munro 1974; Peacock 1974; Olsen and Koblic 

 1975). The estimates for Biscayne Bay from this 

 study ranged from 0.31 to 0.75 mm CL/wk, but the 

 mean of 0.41 mm CL/wk was the lowest reported. 

 The 1977 winter in Biscayne Bay was the coldest 



in the previous century (Molinari et al. 1977; 

 McGuirk 1978), and the Bay is already near the 

 northern limit of P. argus distribution. That cold 

 winter depressed the mean growth rate somewhat, 

 but another significant factor was that the Bis- 

 cayne Bay lobster population was the most heavily 

 fished by sport divers of all of those for which 

 growth rates were reported. The injuries resulting 

 from diver activity also depressed the growth rate. 

 It appeared that a combination of cold weather and 

 extremely high fishing activity caused the low 

 growth rate reported in this study. 



Variations in growth rates of lobsters have been 

 attributed to several factors, the most common of 

 which is temperature (Crawford and De Smidt 

 1922; Newman and Pollock 1974; Phillips et al. 

 1977). Limited food (Sutcliffe 1957; Chittle- 

 borough 1970; Newman and Pollock 1974), shelter 

 (Chittleborough 1970), salinity and light (Travis 

 1954), and injuries (Chittleborough 1974a; Aiken 

 1977; Ford 1977) have also been cited as factors 

 affecting lobster growth (see Aiken 1977, Dall 

 1977, and Ford 1977 for a review of lobster growth i. 

 The effects of these factors are translated into 

 growth rate variations by changing either inter- 

 molt period, molt increment, or both. Most com- 

 monly, intermolt is shortened by warm tempera- 

 tures, darkness, or autotomy of appendages; and 

 lengthened by age, cold, or low salinity. Under 

 some conditions, as in this study, both changes in 

 molt increment and intermolt period occurred 

 (Mauviot and Castell 1976; Aiken 1977; Pollock 

 and Roscoe 1977). 



While autotomy may stimulate molting, Chit- 

 tleborough (1974a) reported that repeated loss of 

 two or three legs or a large number of appendages 

 resulted in decreased molt increment, so the net 

 result was a reduction in growth rate. The results 

 of the current study in Biscayne Bay also clearly 

 demonstrated the adverse impact of injuries on 

 growth rates. However, our observations did not 

 demonstrate any proportional relationship be- 

 tween the degree of injury and the degree of molt 

 increment depression as demonstrated for shore 

 crabs by Kuris and Mager (1975). Most injured 

 lobsters in Biscayne Bay were missing one or both 

 antennae and one or two legs. The growth rate of 

 P. argus with these minor injuries, five or fewer 

 missing appendages, was virtually identical to the 

 growth rate of more seriously injured lobsters that 

 survived and which were missing up to nine legs 

 and both antennae. It appeared that even minor 

 losses caused a significant shift in growth pattern. 



981 



