Juvenile Green Sea Turtle Studies

Large rocks piled into a line bordering the waters edge along two sides of a channel filled with blue-green water.
The Mansfield Jetty at the southern end of Padre Island National Seashore.

NPS Photo.

The Laguna Madre and the Mansfield Channel (located at the southern end of Padre Island National Seashore) provide critical habitat for foraging, developing, resting, and migrating sea turtles like hawksbill, Kemp's ridley, and loggerhead sea turtles. However, these locations are particularly important to juvenile green sea turtles (Shaver 1994, 1998, 2000), which were once commercially exploited in south Texas. In the late 1990’s and early 2000’s, stranded, netted, and satellite-tracked green sea turtles were studied from the Laguna Madre and Mansfield Channel to determine residency, seasonality, relative abundance, distribution, movements, and migration patterns in Texas (Shaver 1994, 1998, 2000, 2005, Shaver et al. 2013, Shamblin 2017, Shaver et al. 2020, Meylan et al. 2020).

Netting and satellite tracking data support that the Mansfield Channel is an important developmental habitat for juvenile green turtles. Some netted and tracked green turtles remained at the Mansfield Channel jetty area, some used the Mansfield Channel as a passageway between the Laguna Madre and Gulf of Mexico, and some moved southward along the Gulf of Mexico coast to waters off the coast of Mexico (Shaver 1998, 2000, 2005, Shaver et al. 2013).

Tissue samples collected from stranded juvenile green turtles in Texas and from nests in Mexico demonstrate that Texas is an important foraging habitat for turtles of Mexican origin (Shamblin et al. 2017). The connection between Mexico and Padre Island National Seashore has been well documented where stranded turtles tagged in Mexico have been found stranded in Texas and vice versa (Shaver et al. 2020).

 
A young sea turtle swims between algae covered rocks with its head out of water.
A juvenile green sea turtle at the Mansfield Channel.

NPS Photo.

The Laguna Madre and the Mansfield Channel are not only important for green turtles hatching in Mexico, it is also used by green turtles from other natal locations. Analysis of mitochondrial DNA in tissue samples from Texas green turtles genetically match rookeries in other locations in the western Gulf of Mexico and northern Caribbean, with smaller contributions from the western and southern Caribbean, and potentially the Mediterranean Sea (Anderson et al. 2013).

Researchers at the park are also studying juvenile green turtles in other areas within and around the National Seashore, specifically at the Packery Channel which was opened in 2005 north of the park. The opening of the Packery Channel provided a new direct water exchange to the Gulf of Mexico from the Laguna Madre and Corpus Christi Bay, providing additional habitat and a new avenue for sea turtles to enter the system. In 2019, a large recruitment pulse of juvenile green turtles was observed along the island and at the Packery Channel. During this event, hundreds of juvenile green turtles were observed in nearshore waters and found washed up on the beach within the park and at the Packery Channel. Park researchers are currently documenting and collecting samples from these juvenile green turtles to determine their origin, inform future management policies, educate the public, and assess the importance of the Packery Channel to juvenile green turtles in south Texas waters.

While some green sea turtle nesting occurs at Padre Island National Seashore, research shows that most of the juvenile turtles in the area are from a variety of different locations. Protection of foraging grounds and natal beaches are important for conservation of the species and the identification of these locations is vital. Results from these studies have been and will continue to be used by managers to develop and evaluate regulations and protection measures and improve restoration programs undertaken for green sea turtles. These studies also underscore the im­portance of continued international partnership for the recovery of threatened green sea turtle populations in the western Gulf of Mexico.

 

Literature Cited:

Anderson, J.D., D.J. Shaver, and W.J. Karel. 2013. Genetic diversity and natal origins of green turtles (Chelonia mydas) in the Western Gulf of Mexico. Journal of Herpetology 47(2):251–257.

Meylan, A., R.F. Hardy, P.A. Meylan, J. Gray, B.M. Shamblin,H.R. Frandsen, D.J. Shaver. 2020. Chelonia mydas (Green sea turtle). Developmental migration. Herpetological Review 51(1):107.

Shamblin, B.M., P.H. Dutton, D.J. Shaver, D.A. Bagley, N.F. Putman, K.L. Mansfield, L.M. Ehrhart, L.J. Peña, and C.J. Nairn. 2017. Mexican origins for the Texas green turtle foraging aggregation: a cautionary tale of incomplete baselines and poor marker resolution. Journal of Experimental Marine Biology and Ecology 488:111–120. doi: 10.1016/j.jembe.2016.11.009.

Shaver, D.J. 1994. Relative abundance, temporal patterns, and growth of sea turtles at the Mansfield Channel, Texas. Journal of Herpetology 28(4):491–497.

Shaver, D.J. 1998. Report on netting of green sea turtles at the Mansfield Channel, Texas during 1997. Report to the National Marine Fisheries Service under Interagency Agreement purchase order NA96AANFG0417. U.S. Geological Survey, Department of the Interior. 8 pp.

Shaver, D.J. 2000. Distribution, Residency, and Seasonal Movements of the Green Sea Turtle, Chelonia Mydas (Linnaeus, 1758), In Texas, PH. D. Dissertation. Texas A&I University, 2000. 273 pages.

Shaver, D.J. 2005. Movements of juvenile green turtles in and from a south Texas developmental habitat. In: Proceedings of the 21st Annual Symposium on Sea Turtle Biology and Conservation, Feb. 24-28, 2001, Philadelphia, Pennsylvania, p. 70–71. M.S. Coyne and R.D. Clark (compilers). NOAA Technical Memorandum NMFS-SEFSC-528.

Shaver, D.J., K.M. Hart, I. Fujisaki, C. Rubio, and A.R. Sartain. 2013. Movement mysteries unveiled: Spatial ecology of juvenile green sea turtles. In: Reptiles in Research: Investigations of Ecology, Physiology, Behavior from Desert to Sea, p. 463–484. W. Lutterschmidt (editor). Nova Science Publishers, Inc. ISBN: 978-1-62808-599-0.

Shaver, D.J., H.R. Frandsen, J.S. Walker, J.A. George, R.J. Gonzales Diaz Miron. 2020. Chelonia mydas (Green sea turtle). Bi-national recapture. Herpetological Review 51(2):310–311.

 

Last updated: December 3, 2020

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