Recapture of a Lifetime
Early in my career, Larry Ogren would tell me our investigations of free-ranging marine turtles in the waters of western Florida were long-term endeavors. These "ancient mariners" live as long, if not longer, than the humans studying them and information can be gathered for some time after a research project has ended or a researcher has retired. Marine turtle tagging studies have the potential for the collection of data over extended periods of time. The trick, however, is affixing some sort of unique identifier to the turtle that is recognizable when someone subsequently encounters (recaptures) the individual and then has the wherewithal to report the unique identifier back to a researcher.
In 1955, Dr. Archie Carr and David Caldwell with the University of Florida initiated one of the first west Florida tagging studies for marine turtles. There was still an active turtle fishery at this time and their study animals were acquired from a fish house in the Cedar Keys. Early efforts to identify individual turtles involved circular metal discs wired to the outer edge of their shell. Metal cow-ear tags were later applied to the trailing edges of a turtle’s front flippers. A unique number and contact information (mailing address) were imprinted on the tags for those who may encounter the turtle after release. For this one-year study, it was west Florida turtle fishermen who first captured the turtles for tagging and then recaptured some of the tagged turtles on the same feeding grounds after a few months at large.
Some 30 years later, I was hired by Larry at the National Marine Fisheries service (NMFS) lab in Panama City to assist with his studies of Kemp’s ridley turtles in the Cedar Keys. The species was heading for extinction and there was little information on the immature Kemp's ridleys inhabiting U.S. coastal waters. We too called upon the knowledge of local fishermen to help us capture turtles for research rather than food. Cattle ear tags applied to the flippers had become the standard tool for identifying marine turtles. We soon discovered, however, there were shortcomings to using these tags in nearshore waters. Kemp's ridleys were being captured with conspicuous notches in their flippers where tags had been applied. In the absence of distinguishing wounds or other unique features, there was no way to identify who had tagged the recaptured turtle.
Our recapture of Kemp’s ridleys with their tags still attached began to reveal a troubling trend. Barnacles were fouling the metal tags, forming large clusters that added weight and drag in the water. Additionally, the growing barnacle cluster damaged the tissue around the tagging site which led to the eventual loss of the tag and scarring on the flippers. We tried using plastic cattle ear tags but these too became fouled with barnacle clusters in theses productive estuarine waters. Barnacles were settling on tags within a couple weeks and most tags were subsequently lost within a year.
Starting in 1992, we began using a new technology to identify individual turtles in our west Florida studies. Passive integrated transponders (PIT) were being injected under the scaley skin of a turtle's flipper. These internal microchips, the same kind used with family pets, require a special reader to scan the tag and display the unique code. Potential problems include someone who recaptures a turtle not realizing it has an internal tag and they may not have a PIT tag reader to identify the individual. Regarding the former, flipper tags are still applied despite their limited retention times as tag scars would indicate the turtle may have a PIT tag. For the latter, PIT tags and scanners are now a common tool for studies of marine turtles inhabiting U.S. coastal waters and those for female turtles that come ashore to nest.
PIT tags should be retained for the life of the turtle, although there may be problems with tag loss soon after injection or movement of tags within the body. In more recent collaborations with Wayne Witzell at NMFS Miami Laboratory and Dr. Tony Tucker formerly with Mote Marine Laboratory, we observed barnacle growth and loss of flipper tags but no loss or noticeable movement of PIT tags with any turtles tagged and recaptured during our collective west Florida studies. In fact, the recapture history of a Kemp’s ridley originally tagged in the Cedar Keys and subsequently observed nesting on Texas beaches offers testament to the longevity of these internal microchips.
Female Kemp’s ridley turtles come ashore to nest in the western Gulf of Mexico from Texas, USA to Veracruz, Mexico. Dr. Donna Shaver and her staff with the National Park Service have been monitoring Padre Island National Seashore (PAIS) as part of long-term marine turtle conservation efforts in Texas. On 26 April 2011, they encountered a nesting female with a PIT code that did not match those of any turtles tagged in this region. Several years later, thanks to the diligence of Dr. Cathi Campbell with the Archie Carr Center of Sea Turtle Research, the PIT tag was matched to a Kemp’s ridley tagged on 9 September 1992 in the Cedar Keys. The turtle had been at large for 18.6 years.
Not only was this the first Kemp’s ridley recapture reported outside of the Cedar Keys study area, long after our research efforts had ended there in 1995, this was the first record of an immature Kemp’s ridley from west Florida feeding grounds subsequently nesting as an adult on Texas beaches. At initial capture, Dr. Lisa Gregory was conducting a study of Kemp’s ridley stress and sex hormones as part of her Master’s research at University of Florida. This particular turtle was predicted to be female and her subsequent emergence on a nesting beach supports the use of hormone concentrations for sexing immature marine turtles.
As if one nesting emergence was not enough, this female Kemp’s ridley was observed on Padre Island beaches again in 2011, once in 2013, twice in 2017, and twice in 2018. Furthermore, Dr. Peter Dutton and Amy Frey with NMFS Southwest Fisheries Science Center used kinship analysis to match this turtle to two more nests in 2007 and another in 2013. For this analysis, PAIS researchers collect tissue samples from nesting females as well as dead hatchlings salvaged from nests where the females were not observed and genetic markers are used to match the identity of females with the unknown nests. Dr. Shaver and her staff calculated that the 10 nests from the recaptured Kemp’s ridley had a mean clutch size of 91 eggs and a mean hatching success of 90%. This female turtle has produced as many as 825 hatchlings during an 11 year period.
To our knowledge, the 25.7 year recapture history for this female Kemp’s ridley is the longest interval recorded for the species and we can only hope she continues even longer in subsequent years. This recapture not only demonstrates the connectivity of feeding grounds with nesting beaches but also that of the many researchers who spend their careers providing information on these long-lived marine creatures. The life and times of a single turtle has brought together six and a half decades of collective wisdom in our continuing quest to solve the many “riddles of the ridley”.