Temporal, spatial, and body size effects on growth rates of loggerhead sea turtles (Caretta caretta) in the Northwest Atlantic |
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Authors: | Karen A Bjorndal Barbara A Schroeder Allen M Foley Blair E Witherington Michael Bresette David Clark Richard M Herren Michael D Arendt Jeffrey R Schmid Anne B Meylan Peter A Meylan Jane A Provancha Kristen M Hart Margaret M Lamont Raymond R Carthy Alan B Bolten |
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Affiliation: | 1. Archie Carr Center for Sea Turtle Research, University of Florida, Gainesville, FL, 32611, USA 2. Department of Biology, University of Florida, Gainesville, FL, 32611, USA 3. NOAA, National Marine Fisheries Service, Silver Spring, MD, 20910, USA 4. Florida Fish and Wildlife Conservation Commission, Fish and Wildlife Research Institute, Jacksonville, FL, 32218, USA 5. Florida Fish and Wildlife Conservation Commission, Fish and Wildlife Research Institute, Melbourne Beach, FL, 32951, USA 6. Inwater Research Group, Inc., Jensen Beach, FL, 34957, USA 7. Marine Resources Division, South Carolina Department of Natural Resources, Charleston, SC, 29412, USA 8. Environmental Science Department, Conservancy of Southwest Florida, Naples, FL, 34102, USA 10. Smithsonian Tropical Research Institute, Balboa, Panamá 9. Florida Fish and Wildlife Conservation Commission, Fish and Wildlife Research Institute, St. Petersburg, FL, 33701, USA 11. Natural Sciences Collegium, Eckerd College, St. Petersburg, FL, 33711, USA 12. InoMedic Health Applications, Kennedy Space Center, Merritt Island, FL, 32899, USA 13. US Geological Survey, Southeast Ecological Science Center, Davie, FL, 33314, USA 14. US Geological Survey, Florida Cooperative Fish and Wildlife Research Unit, University of Florida, Gainesville, FL, 32611, USA
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Abstract: | In response to a call from the US National Research Council for research programs to combine their data to improve sea turtle population assessments, we analyzed somatic growth data for Northwest Atlantic (NWA) loggerhead sea turtles (Caretta caretta) from 10 research programs. We assessed growth dynamics over wide ranges of geography (9–33°N latitude), time (1978–2012), and body size (35.4–103.3 cm carapace length). Generalized additive models revealed significant spatial and temporal variation in growth rates and a significant decline in growth rates with increasing body size. Growth was more rapid in waters south of the USA (<24°N) than in USA waters. Growth dynamics in southern waters in the NWA need more study because sample size was small. Within USA waters, the significant spatial effect in growth rates of immature loggerheads did not exhibit a consistent latitudinal trend. Growth rates declined significantly from 1997 through 2007 and then leveled off or increased. During this same interval, annual nest counts in Florida declined by 43 % (Witherington et al. in Ecol Appl 19:30–54, 2009) before rebounding. Whether these simultaneous declines reflect responses in productivity to a common environmental change should be explored to determine whether somatic growth rates can help interpret population trends based on annual counts of nests or nesting females. Because of the significant spatial and temporal variation in growth rates, population models of NWA loggerheads should avoid employing growth data from restricted spatial or temporal coverage to calculate demographic metrics such as age at sexual maturity. |
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