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From 1979 to 1991, carapace tags were used as an alternative to Monel flipper tags to improve tag retention and continuity of individual sea turtle identification prior to the introduction of less corrosive Inconel flipper tags. The carapace tags consisted of two 1 7/16 inch 18/8 stainless steel fender washers attached to the dorsal and ventral sides of a posterior left (or right) marginal scute (Hopkins 1979; LeBuff 1990). The washers were attached with a 1 1⁄4 - 1 1⁄2 inch long hex-headed machine bolts through a 1⁄4 inch diameter hole drilled though the thinnest part of the carapace and secured with a nylon insert 18/8 stainless steel locking hex nut (Hopkins 1979; LeBuff 1990). Each tag was stamped with a unique number (LeBuff 1990; Murphy 2019). Tags were applied to nesting loggerhead sea turtles on Sanibel Island, Florida and on South Island, South Carolina in the United States, as well as on flatback turtles (Natator depressus) in Queensland, Australia (LeBuff 1990; Murphy 2019). Carapace tags were applied to both returning and newly sighted turtles in addition to a new or existing Monel flipper tag applied to the trailing edge of one front flipper (Hopkins 1979; LeBuff 1990). At least 102 individual loggerheads were tagged on Sanibel Island in 11 years starting in 1980. Tags were applied sequentially with the series starting at 101 (LeBuff pers. comm. 2020). Forty-eight tags were attached on South Island, South Carolina in 1979 (Hopkins 1979). The two series had notably different number stamps (Fig. 1B & 1C) and Sanibel Island tags carried a prefix “SAN” on one washer, while the South Island tags had a return address (Hopkins 1979; LeBuff 1990).

Figure 1. Images of (A) carapace tag observed on Casey Key, Florida in 2016. Photo credit: James Grimes; (B) Example carapace tag from Sanibel Island, Florida. Photo credit: Charles LeBuff; (C) Example carapace tag from South Island, South Carolina. Photo credit: Tom Murphy.

Turtles with carapace tags sighted on Casey Key were originally tagged on Sanibel Island, which is a loggerhead sea turtle nesting beach located approximately 80 km south of Casey Key. Exchange of nesting turtles between Casey Key and Sanibel Island has been documented on other occasions based on flipper and PIT tag recaptures (Mazzarella K.T. unpubl. data). Historical tag records from Sanibel Island were lost (LeBuff pers. comm. 2020); thus, original tag dates are not available for all individuals from that period. An archived letter from Caretta Research, Inc. dated 28 July 1986, provided documentation that one turtle had received a carapace tag “SAN132,” and a Monel flipper tag “CR5142” on Sanibel Island approximately one month prior to being sighted on Casey Key. The turtle was identified on Casey Key by the carapace tag and the flipper tag was missing. Two additional carapace-tagged loggerheads, “SAN170” and “SAN180,” were sighted on Casey Key on one to three occasions, in 1992 and 1993, respectively. Based on the tag sequence, these sightings are estimated to be one to six years after their original tagging on Sanibel Island. Loggerhead sea turtle “203” was sighted on Casey Key in 1992, 1997, 2001 and 2016. This turtle’s carapace tag lacked the “SAN” identifier but matched the “3” stamp of the Sanibel Island tags. The lack of the “SAN” prefix on this tag may be due to an error in application such that the “SAN” washer was applied to the ventral side of the carapace. This tag documents carapace tag retention of at least 26 years (Table 1).

Table 1. Original and recapture data from four carapace tags observed on Casey Key Florida. Tags were originally applied sequentially on Sanibel Island, Florida between 1980 and 1991 but original tag data were lost. Tagging dates and tag retention are estimated based on first recapture.

Nocturnal tagging projects may not identify the presence of a carapace tag due to tag location on the carapace and high potential to be concealed by epibionts. In 2016, epibionts were removed from the “203” tag in order to read the tag number, which was still legible after 26 years. On nine additional Casey Key encounters of carapace tagged turtles, individuals were identified by flipper tag or PIT tag number, but no carapace tag was noted. A characteristic notch or hole in the posterior marginal scute may indicate the loss of a carapace tag (LeBuff pers. comm. 2020). In addition, tags may loosen over time and create an enlarged hole (Murphy 2019). Tagging projects are encouraged to remain alert for evidence of carapace tags, whether the tag remains in place or the notch is observed.

The value of a long-term tagging dataset is dependent upon the recapture and proper identification of tagged individuals. Thus, tagging projects should conduct thorough examinations of nesting turtles for all possible tags, even when some tags are evident. Researchers are encouraged to locate and communicate with historic tagging programs in their region. Identification of historic tags may lead to discovery of longer recapture times than previously documented. This investigation of historic tags highlights the importance of utilizing multiple tag types to improve likelihood of recapture and backing up data to prevent loss and ensure effective use by future scientists.

Acknowledgements. Much appreciation goes out to Sally R. Murphy and Charles LeBuff for designing these tags and providing consultation for this paper. I also thank Mote tagging staff, volunteers, and interns who documented the encounters of individuals with carapace tags, without which this paper would not be possible, especially Jim Grimes who observed and investigated this tag in 2016. Thanks to Jennifer Johnson for her help with photo preparation. Tagging on Casey Key was conducted under Florida Marine Turtle Permit 155 and Mote Marine Laboratory IACUC 16-01-KMz1.

HOPKINS, S.R. 1979. Experimental carapace tag. Marine Turtle Newsletter 13:9-10.

MURPHY, S.R. 2019. Turning the Tide: A Memoir. Evening Post Books, Charleston, SC. 320 p.

LEBUFF, C.R. 1990. The Loggerhead Turtle in the Eastern Gulf of Mexico. Caretta Research Inc., Sanibel, FL. 216 p.