Schmid: Marine turtle populations of the east-central coast of Florida 



141 



not well defined. In this study, the term "juvenile" 

 has been reserved for immature turtles in the pe- 

 lagic stage of development. A turtle is considered "sub- 

 adult" when it has recruited to its respective coastal- 

 benthic habitat and "adult" when sexually mature. 

 Loggerhead turtles greater than 80-cm carapace 

 length were considered adult, based on the length 

 frequencies of Cape Canaveral nesting females (Carr, 

 1986, and references therein) and earlier investiga- 

 tions of Henwood (1987a). Kemp's ridley turtles 

 greater than 60-cm carapace length were considered 

 adult (Pritchard and Marquez, 1973). 



Monthly trawling effort was calculated and stan- 

 dardized according to Henwood and Stuntz (1985) 

 by using the formula 



E 



( Nets  Length V Min 

 { 305 A~60~ 



where E is the trawling effort in hours towed by a 

 single 30.5-m headrope length net, Nets is the num- 

 ber of nets towed, Length is the headrope length (m) 

 of a net, and Min is the number of minutes fished. 



Capture records were analyzed to evaluate species 

 composition within the study area, length-frequency 

 distribution of each species, and patterns of seasonal 

 distribution and movements. Linear regression 

 analyses were performed for carapace width on 

 length for loggerhead turtles. The morphometric data 

 for loggerhead turtles were subdivided into a sub- 

 adult group (<80 cm SSCL) and an adult group (>80 

 cm SSCL) because the carapace dimensions of this 

 species change as the animals mature (Henwood and 

 Moulding, 1987). Carapace width was regressed on 

 length, and weight regressed on length for Kemp's 

 ridley and green turtles. Turtles with carapace 

 wounds or deformities were not included in the analy- 

 ses. Regression residuals for length-weight relation- 

 ships were analyzed graphically to assess the appro- 

 priateness of the straight-line model (Sokal and 

 Rohlf, 1981; Kleinbaum et al., 1988). 



Curved carapace lengths (CCL) of stranded turtles 

 were converted to straight-line carapace lengths 

 (SCL) by using the following regression equations of 

 Teas (1993): 



SCL = -1.442 + (0.948 x CCL) 

 for loggerhead turtles; 



SCL = 0.013 + (0.945 x CCL) 

 for Kemp's ridley turtles. 



Total straight-line carapace lengths (TSCL) of log- 

 gerhead turtles were converted to standard straight- 



line carapace lengths (SSCL) with the regression 

 equation of Henwood and Moulding (1987): 



SSCL = (0.9964 x TSCL) - 0.775. 



Yearly growth rates were calculated from the formula 



G = 



A Length 

 Days 



365 



where G is the growth rate in cm/yr, ALength is the 

 difference between the recapture length and the ini- 

 tial length, and Days is the number of days out. The 

 von Bertalanffy growth interval equation was fitted 

 to the recapture data with a nonlinear least-squares 

 regression procedure (SAS, 1988). The von 

 Bertalanffy growth interval equation (Fabens, 1965) 

 for recapture is as follows: 



CL 2 =a-(a-CL 1 )e kt , 



where CL 2 is the carapace length at recapture, a is 

 the asymptotic length, CL 1 is the length at first cap- 

 ture, K is the intrinsic growth rate, and t is the time 

 in years between captures. 



Results 



Trawling effort 



Monthly trawling effort varied from year to year 

 ( 1989-91 ); however, monthly totals for all three years 

 indicate that the majority of effort occurred from May 

 to December (Table 1). This corresponds to the sum- 

 mer-fall fisheries for brown and white shrimp, the 

 target species during this study. Monthly turtle cap- 

 ture rates were also variable, probably as a result of 

 the combined seasonal fluctuations in trawling ef- 

 fort and turtle abundance. A structured sampling 

 scheme with equal monthly effort would be required 

 to make accurate calculations of monthly changes in 

 turtle abundance. Loggerhead turtle catch per unit 

 of effort (CPUE) ranged from 0.02 turtles/net hour 

 in October 1989 to 1.09 turtles/net hour in August of 

 1991. Maximum CPUE of 0.25 turtles/net hour was 

 obtained for Kemp's ridley turtles in May 1990 and 

 0.05 turtles/net hour was obtained for green turtles 

 in January 1989 (Table 1). 



Species composition 



A total of 774 (83%) loggerhead, 113 (12%) Kemp's 

 ridley, and 41 (4%) green turtles were captured, 

 tagged, and released during the course of the study. 

 A leatherback turtle, Dermochelys coriacea, was also 



