Movements of Juvenile Green Turtles (Chelonia mydas) in the Nearshore Waters of the Northwestern Gulf of Mexico

Abstract

Satellite telemetry is a valuable tool for examining long-term, large scale movements of highly migratory species. Tracking data can be used by resource managers to protect habitat and ensure recovery of threatened and endangered species. Few tracking studies have focused on habitat use patterns of juvenile, neritic stage turtles. Satellite tracking surveys were conducted to assess juvenile green turtle movements in the northwestern Gulf of Mexico during 2006-2010. Fifteen turtles were equipped with platform terminal transmitters (PTT; 3 rehabilitated, 12 wild). Mean track duration was 129 days (range: 16-344 days). A hierarchical switching state-space model (hSSM) was applied to extrapolate population level foraging/resident versus migratory movements. All turtles displayed residency in Texas bays during summer months (March-November) while five individuals exhibited seasonal migrations into Mexican waters following passage of strong cold fronts in December and January. Winter (e.g., Mexico) versus summer (e.g., Texas) core areas were not significantly different. Winter 95% contours were significantly larger than summer (summer: 125.4 ± 47.5 km 2 , n = 15; winter: 274.4 ± 252.9 km 2 , n = 5). Space-time hot spot analysis provided a new and unique approach for conducting spatiotemporal cluster analysis, and was applied to migratory turtles to determine monthly changes in distribution and habitat associations. Changes in hot spots over time were detected within the lower regions of the Laguna Madre with punctuated intervals of hot spot activity. Upper regions of the Laguna Madre were identified as new hot spots in the later part of the year (e.g., Fall/Winter). Within core areas in Texas, seagrasses comprised an average density of 32.4% while 87.5% of the total available seagrass habitat occurred within the 95% KDE contour. Based on PTT and historic tide station surface water temperatures, all turtles tracked over winter migrations and residencies (n = 5) remained within waters > 15 • C, suggesting a threshold temperature at which migration behavior may be initiated. Continued recovery of threatened and endangered sea turtle populations depends on a comprehensive examination of patterns in habitat use. These data suggest cooperation between the United States and Mexico is needed to protect critical habitat and enhance recovery of this species.

CARACTERIZACIÓN DEL MICROHÁBITAT DE Chelonia mydas (CHELONIDAE) EN LA COSTA CENTRAL DE VERACRUZ, MÉXICO

“…Los datos de temperatura oscilaron de 24.8 a 30.3 °C (promedio ± DE= 28.4 ± 2.66) (Tabla 1). Las tortugas marinas suelen encontrarse activas a diversas temperaturas, con distintos umbrales a favor de la zona geográfica en la cual residan (Mendonça, 1983;Hazel et al, 2009;Lamont et al, 2015;Álvarez-Varas et al, 2017;Metz et al, 2020); no obstante, registros desmesurados, durante lapsos prolongados, alteran su comportamiento e incluso conllevan a la muerte (Bitón-Porsmoguer, 2009).…”

“…Las tortugas marinas mitigan el efecto de la temperatura mediante acciones alternativas tales como el adormecimiento temporal, disminución de las actividades (Contreras-Salazar, 2008), hábitos migratorios (González-Carman et al, 2012;Metz et al, 2020), cambio en la distribución dentro de la columna del agua (Lamont et al, 2015), entre otras. La sensibilidad de los organismos a dicho parámetro varía en razón de la edad (Sevilla, 1977) estado de salud o tamaño de los individuos (Márquez, 1996).…”

Variation in Species Composition, Size and Fitness of Two Multi-Species Sea Turtle Assemblages Using Different Neritic Habitats

“…Juvenile turtles throughout the world have been shown to exhibit multi-year fidelity to foraging areas (González Carman et al, 2016;Metz et al, 2020;Siegwalt et al, 2020), which further highlights their importance in the conservation and recovery of these species. In Australia, green turtles and loggerheads remained in foraging habitats for 17 and 23 years, respectively.…”

“…In Australia, green turtles and loggerheads remained in foraging habitats for 17 and 23 years, respectively. The size of these home ranges varies greatly among species and studies, most likely a factor of study methods used, duration of tracking periods, and environmental conditions (Metz et al, 2020). For example, mean size of core use areas for green turtles in Northeast Florida was 4.4 ± 1.3 km 2 (Wildermann et al, 2019) while along the Texas coast, the mean size for green turtles in summer was much larger (125.4 ± 47.5 km 2 ) and when examining only winter core use areas, the mean size in Texas was even greater (543.7 ± 230.6 km 2 ).…”

Inter-Nesting Movements, Migratory Pathways, and Resident Foraging Areas of Green Sea Turtles (Chelonia mydas) Satellite-Tagged in Southwest Florida

“…Research using telemetry to track juvenile green turtles in the Gulf of Mexico has revealed that they generally use small core use areas in nearshore foraging habitats at this life stage Lamont et al, 2015;Wildermann et al, 2019), although seasonal differences in foraging ranges have been reported (Metz et al, 2020). Satellite tracking data for adult green turtles nesting on United States Gulf of Mexico beaches are currently limited to studies at Dry Tortugas, where post-nesting movements have been documented both within the park and the surrounding areas of the Florida Keys (Hart et al, 2013).…”