Long term movement of Green Turtles Chelonia mydas in Gladstone Harbour: advantages of acoustic telemetry

Juvenile, sub-adult and adult green turtles were tagged with acoustic tags within two arrays of acoustic receivers in Gladstone Harbour. At Pelican Banks, 33 animals (5 juveniles, 7 sub-adults and 21 adults) were tagged while... [ view full abstract ]

Juvenile, sub-adult and adult green turtles were tagged with acoustic tags within two arrays of acoustic receivers in Gladstone Harbour. At Pelican Banks, 33 animals (5 juveniles, 7 sub-adults and 21 adults) were tagged while at Wiggins Island 16 juveniles were tagged. Between May 2013 and September 2014, over 1.4 million detections of tagged turtles were recorded by 44 acoustic receivers within Gladstone Harbour.

Individual turtles were detected up to 240 000 times with the median number of detections greater than 17000. The average detection span for all turtles was 273 (± 19) days with turtles at Wiggins Island having a greater detection span (337 ± 34 days) than turtles at Pelican Bank (242 ± 31 days). The average number of days turtles were detected on was 218 (± 20) with turtles at Wiggins Island being detected on more days (295 ± 34 days) than turtles at Pelican Bank (181 ± 25 days).

Home range estimates (50 and 95 % KUD) were calculated for those individuals that were detected for more than 30 days on two or more receivers (n = 42). Green Turtles at Gladstone had small home ranges which persist for months. The average 50 and 95 % KUD of animals at Pelican Banks was 1.4 ± 0.2 km2 and 6.7 ± 0.9 km2, respectively which was significantly greater than animals at Wiggins Island (0.7 ± 0.1 km2 and 3.8 ± 0.4 km2), however, like many animals where long term data are now becoming available, a large proportion move away from previously established home range and set up a home range tens to hundreds of kilometres away. In Gladstone, after 1 year of monitoring nearly 20 % of turtles at Wiggins Island and 53 % of turtles at Pelican Banks had moved outside the array of receivers within Gladstone Harbour. Implications for management with respect to ship strike and food resources in Gladstone are discussed.