588 



Fishery Bulletin 93(3), 1995 



10% of the weight of the turtle, in accordance with 

 the safety recommendations of Brander and Cochran 

 (1969), Bradbury et al. (1979), Aldridge and 

 Bringham (1988), and Byles and Keinath ( 1990). 



Tracking 



Turtles were released at their capture sites between 

 0900 and 1600 hours. We used a Telonics TR2/TS1 

 receiver-scanner connected to a directional 5-element 

 Yagi antenna to monitor radio transmitters until they 

 became detached from turtles. Maximum radius of 

 signal reception with this equipment is approxi- 

 mately 16 km. When weather prohibited tracking by 

 vessel, turtles were monitored from land. Sonic trans- 

 mitters were monitored by using a Dukane direc- 

 tional hydrophone with a receiving range between 

 0.6 and 1.1 km. Sonic tracking alone was used when 

 a turtle had lost its radio transmitter but retained 

 its sonic transmitter or when a second turtle was 

 present in the area of a turtle being monitored by 

 radio. 



Data were collected for 12 hours each day. All hours 

 of the day and night were included by offsetting each 

 day's start time by two hours from that of the previ- 

 ous day. We attempted daily to locate every turtle 

 with a functioning transmitter. Up to five turtles were 

 tracked during each day. Geographic location was 

 recorded when a turtle was sighted or its position 

 obtained with sonic telemetry. Reference marks were 

 painted at 50-m intervals on jetty boulders, west- 

 ward from the seaward tip of each jetty. Locations of 

 turtles were determined with respect to reference 

 marks and to visual estimates of perpendicular dis- 

 tance from the jetties. When possible, turtle locations 

 >40 m from the jetty were recorded by means of a 

 portable global positioning system. The total time 

 spent between jetty reference marks was calculated 

 for each turtle. Each turtle position was given a 

 weight equal to time spent at that position. These 

 weighted positions were then used to calculate a 

 mean position for each turtle. Minimum observation 

 time used for this analysis was 5 minutes. Range 

 (area containing 95% of locations) and core area (area 

 containing 50% of locations) were developed by us- 

 ing the minimum convex polygon method (Mohr, 

 1947), modified to exclude nonwater areas. To dis- 

 cern differences in movement patterns, the ranges 

 and core areas for each turtle were determined for 

 dawn (0500-0900 h), day (0900-1700 h), dusk (1700- 

 2100 h), and night (2100-0500 h) if at least three 

 days were sampled and >5 h of tracking information 

 were available for a turtle within a time period. To 

 obtain an index of turtle movements, the distance 

 and time between surfacing events were calculated 



for each turtle and used to estimate mean speed of 

 movements for dawn, day, dusk, night, and all times 

 combined. 



Surface and submergence behavior 



Surface and submergence times were calculated for 

 each turtle affixed with a radio transmitter. Data 

 collected on the day of release were omitted from 

 analyses of ranges and of surface or submergence 

 behaviors. Surface time was considered to be the in- 

 terval between the beginning and ending of radio 

 signals (i.e. when the turtle was within 40 cm of the 

 ocean surface). Submergence time was denned as the 

 interval between the end of a radio signal and the 

 beginning of the next signal (i.e. when the turtle was 

 deeper than 40 cm). Overall mean surface and sub- 

 mergence times, and day, night, dawn, and dusk 

 means were calculated for each turtle. A surface or 

 submergence interval overlapping two time periods 

 was included in the period containing the majority 

 of the interval. 



Statistical methods 



Distribution of variables (surface and submergence 

 times, movement speed) were tested with the 

 Shapiro-Wilk test for normality (oc=0.05). The 

 Kruskall-Wallis analysis was used to test for differ- 

 ences in means between dawn, day, dusk, and night 

 (a=0.05) (Sokal and Rohlf, 1981) when the null hy- 

 pothesis (normal distribution) was rejected. If a sig- 

 nificant difference was indicated, a means test de- 

 scribed by Conover (1980) was used to determine 

 which means differed, again by using a=0.05. 



Results 



Sea turtle movement patterns 



Nine green turtles (29.1-47.9 cm straight carapace 

 length [SCL], 2.6-14.8 kg) were tracked from 14 to 

 58 days from 31 July to 26 September 1992 (Table 

 1). Differences in tracking periods were due to dif- 

 ferent capture dates and variable tag retention. In 

 addition, on some days certain turtles could not be 

 located owing to inclement weather. All turtles moved 

 away from the jetties immediately following release. 

 Those released between the jetties entered the deeper 

 waters of the channel, but T8, released on the Gulf 

 side of the south jetty, moved south, roughly parallel 

 to the beach. Seven turtles returned to the jetties 

 within an hour. T6 and T7 went offshore after enter- 

 ing the channel and returned to the jetties the next 



