Pacific turtle tracks: Turtle-Safe Seas Project

Keywords: Observation, Occurrence, Occurrence,Radio transmitters,Animal movements
Temporal coverage: 1997/2001

Original provider:
Blue Ocean Institute

Dataset credits:
Blue Ocean Institute

Abstract:
The oceanic movements of loggerhead turtles (<i>Caretta caretta</i>), green turtles (<i>Chelonia mydas</i>), and a Pacific ridley turtle (<i>Lepidochelys olivacea</i>) were monitored with satellite telemetry between 1996 and 2001 in the Pacific Ocean. During this time, several turtles migrated across the Pacific Ocean, covering more than 11,500 km between Santa Rosalita, Baja California, Mexico (28 degrees 40 minutes N, 114 degrees 14 minutes W), and Sendai Bay, Japan (37 degrees 54 minutes N, 140 degrees 56 minutes E). These findings are consistent with the hypothesis that loggerheads feeding in the eastern Pacific eventually return to nest on western Pacific beaches. Baja California loggerhead turtles have been shown, through molecular genetic analysis and flipper tag returns, to be primarily of Japanese origin. 
We conclude that loggerhead turtles are capable of transpacific migrations and propose that the band of water between 25 and 30 degrees north latitude, the Subtropical Frontal Zone, may be an important transpacific migratory corridor. Recent findings indicate that juvenile loggerheads in the North Pacific move westward against weak (0.1 - 0.3 km/hr) eastward geostrophic currents, demonstrating that passive drift may not entirely explain the dispersal of loggerheads.

Purpose:
The objective of the study was to monitor the oceanic movement, using satellite telemetry, of a Pacific loggerhead turtle initially captured on feeding grounds along the Baja California coast. Movement data also were examined with respect to oceanographic and meteorological information in an effort to gain insight into the navigational cues that guide adult sea turtles and to identify possible transpacific movement corridors. 

Juvenile loggerhead turtles, <i>Caretta caretta</i>, in the 20 - 85 cm straight carapace length (SCL) size range have been observed in the offshore waters along the Pacific coast of California, USA, and the Baja California peninsula, Mexico. It was suggested that these turtles might be of western Pacific origin, migrating 10,000 km and feeding on pelagic red crabs (<i>Pleuroncodes planipes</i>) along the Baja California coast. Subsequently, Pacific loggerheads appear to utilize the entire North Pacific during the course of development in a manner similar to Atlantic loggerheads' use of the Atlantic Ocean.  After a period of more than 10 years, mature turtles evidently cross the Pacific Ocean from pelagic waters and foraging areas along the Baja California coast to return to natal beaches, a journey of more than 12,000 km in each direction.
This is the first effort to document pelagic movements of North Pacific loggerheads from feeding grounds to nesting areas using satellite telemetry. Previous telemetry studies of loggerhead turtles have documented post-reproductive movements, pelagic movements, home ranges, navigational abilities and homing behavior. However, few studies of sea turtles have documented pre-nesting movements from feeding grounds to breeding areas.  Notably, documented movement of a Kemp's ridley turtle (<i>Lepidochelys kempii</i>) from feeding grounds in Louisiana, United States, to its successful nesting in Rancho Nuevo, Mexico.
A unique opportunity to track the movements of an adult-sized loggerhead turtle, rarely encountered along the Baja California coast, emerged in 1996. The turtle had been raised in captivity and used in the initial genetic analysis of Baja California loggerhead turtles. Its mature size, genetic affinities with Japanese turtles, and the existence of a previous tag return from Japanese waters of a captive-raised, Baja California loggerhead turtle were the deciding factors in choosing this particular turtle for the study. This turtle is included in the dataset as series 7667, named Adelita. 

Adelita was monitored following release at Santa Rosalita, Baja California, Mexico (28 degrees 40 minutes N, 114 degrees 14 minutes W). The turtle was first captured in October 1986 by sport fishermen in Bahia de Los Angeles, Baja California, and maintained in captivity at the Centro Regional de Investigaciones Pesqueras, Sea Turtle Research Station (CRIP-STRS). At the time of capture, it had a straight carapace length (SCL) of 29.9 cm and weighed 4 kg. The turtle was used in a study of captive growth rates and in genetic analysis of Pacific loggerhead stocks. Genetic studies suggested that this individual was of Japanese origin. At the time of release, the turtle measured 83.4 cm (SCL) and weighed 95 kg. The tail measured 3.5 cm from the edge of the carapace to the tip.

Sixteen other satellite tagged turtles are included in this dataset. Each turtle is identified by series number, name, species, and life stage. The shortest track consists of 20 locations, and the longest track includes 787 locations. Most of the tracked turtles were adult females, one turtle was an adult male, and the remainder were juveniles. 

A model ST-3 backpack transmitter manufactured by Telonics, Inc. (Mesa, Arizona, United States) was programmed with a duty cycle of 6 hours on, 6 hours off. The transmitter was attached to the second vertebral scute (counting from the anterior) of the turtle's carapace using a modified version of the attachment technique. Specifically, we substituted a thin layer (&lt;1 cm) of tinted two-part marine epoxy (Marine-Tex; Montgomeryville, Pennsylvania, United States) for Silicone Elastomer. Epoxy was also used to create a small faring on the leading and trailing edges of the transmitter to reduce drag. Release of the telemetered turtle occurred about 2 km offshore of Santa Rosalita, Baja California, Mexico (28 degrees 40 minutes N, 114 degrees 14 mintes W), on 10 August 1996, 10 years after initial capture. Transmission data were received via the Argos/NOAA satellite-based location and data collection system, which interprets and classifies signal locations in categories called location classes (LC). In addition to the date and location, data included surface time for each 12-hour period, average dive time for each 12-hour period, last dive time and temperature. Only positions with LCs of 0, 1, 2 or 3 were included in the analysis of distances traveled and swim speeds. LCs of 1 or greater have known error factors of &lt;1,000 m and accuracy increases with location class (LC = 2, accuracy within 350 m; LC = 3, within 150 m). Distances and headings were calculated using variations of the Great Circle Equation. Each segment of the track, or distance traveled between quality locations, is presented and swim speeds for these segments are calculated by dividing the distance traveled by the time between locations. The straightness index, or the ratio between the great circle distance (shortest line between the release location and the final location) and the calculated distance traveled, was calculated using endpoints of the track.

Supplemental information:
[UPDATE 2013-03-20] The following animals were removed as these are included in <a href="/dataset/317">Pacific Turtle Tracks: Grupo Tortuguero</a>
1085, 20750, 20780, 21217, 3851, 5524, 7667, 5521