Marine Turtle Newsletter 77:1-6, © 1997
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Marine Turtle Newsletter 77:1-6, © 1997
In 1996, the U. S. National Marine Fisheries Service's (NMFS) Galveston Laboratory, Gladys Porter Zoo (GPZ, Brownsville, Texas USA) and Instituto Nacional de la Pesca (INP) of Mexico initiated tagging of hatchling Kemp's ridleys (Lepidochelys kempii) at Rancho Nuevo, Tamaulipas, Mexico. NMFS, GPZ and INP personnel tagged 3,336 hatchlings with non-magnetized wire tags (Patrick Burchfield, GPZ, pers. comm., January 1997). The tags (manufactured by Northwest Marine Technology, Shaw Island, Washington USA) were injected into the right foreflipper. Plans are to wire-tag up to 10,000 more hatchlings in the left foreflipper in 1997, thus distinguishing them from the 1996 year-class.
The purpose of this paper is to alert the sea turtle research community to this tagging program, to provide background information concerning how and why it came about, and to provide criteria for distinguishing captive-reared from wild Kemp's ridleys.
In 1992, Eckert et al. (1994) conducted a peer review of the Kemp's ridley head-start experiment, clarified its objectives, developed testable hypotheses and made recommendations for improvements (see also Wibbels, 1989 and Donnelly, 1994). They stated explicitly that head-started turtles were the experimental group and wild turtles were the control group. However, a direct comparison between headstarted and wild year-classes was not possible, because ages of the wild turtles were unknown. There had been no tagging program for known-age wild turtles (see recommendations of Byles et al., 1996) comparable in magnitude to that for known-age, head-started turtles.
To provide a control, Eckert et al. (1994) recommended tagging as large a sample of wild hatchlings as possible in each of two consecutive seasons at Rancho Nuevo, using archival type tags (either internal wire or PIT, passive integrated transponder). The Galveston Laboratory is conducting PIT-tagging experiments on loggerhead (Caretta caretta) hatchlings, but use of this tag on large numbers of hatchlings released into the wild is cost-prohibitive, especially when the rate of tag returns is expected to be low. Eckert et al. (1994) recognized there were biases in using wild hatchlings as a control. Most head-started year-classes were released during years in which turtle excluder devices (TEDs) were not required in shrimp trawls, whereas the tagged wild turtles will be exposed to trawling with mandatory TEDs. The wild turtles are being tagged and released as hatchlings, but the captive-reared turtles were seven months old or older when released (Caillouet et al., 1995).
At its October 1993 meeting in North Padre Island, Texas (USA), the Kemp's Ridley Working Group (KRWG) requested laboratory tests of wire-tagging hatchlings, using loggerheads followed by Kemp's ridleys. The KRWG also expressed concern that magnetized wire tags might interfere with magnetic orientation and navigation of hatchlings (see also Eckert et al., 1994), and requested only non-magnetized wire tags be applied to large numbers of hatchlings at Rancho Nuevo. These non-magnetized tags cannot be detected using magnetometers unless they are first magnetized (see Fontaine et al., 1993 for details). However, wire tags can be detected by X-ray.
Galveston Laboratory experiments comparing non-tagged to two wire-tagged (non-magnetized and magnetized) groups of hatchlings were conducted on loggerheads of the 1993 year-class, and repeated on Kemp's ridleys of the 1994 and 1995 year-classes (see Table 1). Tagging was done at Rancho Nuevo to simulate on a small scale the situation that would occur in a large scale wire-tagging operation. There were no significant differences in survival, growth or tag retention rates among groups in either species, and tag retention (as confirmed by magnetometer and X-ray) was near 100%. For both year-classes of Kemp's ridleys, the three groups all had magnetized wire tags when released (Table 1). At its November 1995 meeting in College Station, Texas USA, the KRWG cautioned against wire-tagging more than 5,000 hatchlings in 1996, because this method had never been attempted on large numbers of hatchlings under field conditions.
We consider head-started turtles to be the 22,205 "yearlings" of the 1978-1992 year-classes obtained as hatchlings from Padre Island National Seashore (PINS) near Corpus Christi, Texas USA or from Rancho Nuevo, captive-reared by the Galveston Laboratory for 7-15 months, tagged and released into the Gulf of Mexico (Table 1). Hatchlings from PINS were produced from eggs collected at Rancho Nuevo. Additional Kemp's ridleys were captive-reared for longer periods (e.g., to develop a captive brood stockduring the early years of the head-start experiment). Some of these socalled "super-head-started" turtles (Phillips, 1989:103) were eventually released. We do not consider them typical of head-started turtles, because extended rearing may have habituated them to artificial conditions and predisposed them to exhibit aberrant behavior when released (Caillouet et al., 1995). Any Kemp's ridleys of the 1978-1992 year-classes that may have been captive-reared by other organizations are not considered head-started. Finally, those of the 1993 and later year-classes captive-reared by the Galveston Laboratory are not considered head-started. Regardless, we have included in Table 1 all captive-reared Kemp's ridleys released by the Galveston Laboratory or transferred to other organizations which released them. The Galveston Laboratory maintains tag-release records for these turtles, and therefore is the clearing house for their tag returns.
Tags applied to captive-reared turtles (Table 1) are the keys to distinguishing them from wild ones, whether tagged or not. Researchers at Galveston Laboratory applied external, metal, foreflipper tags to every turtle released, and applied additional types of tags to most of them (Fontaine et al., 1985; Caillouet et al., 1986; Manzella et al., 1988; Fontaine et al., 1988, 1989a, 1989b; Phillips 1989; Fontaine et al., 1993; Caillouet et al., 1995). In 1996, the first documentation of head-started Kemp's ridley nestings (one each from 1983 and 1986 year-
Table 1. Numbers of captive-reared Kemp's ridleys tagged with various types of tags and then released into the wild (includes head-started,"super-head-started" and other captive-reared turtles). "Internal-tagged" refers to turtles wire-tagged in either the left or right foreflipper. "External-tagged" refers to yearling turtles receiving external metal foreflipper tags.
| ------------------------------------------------------------------------------------------------------------------- | ||||||
| Year- | Internal-tagged | Living- | PIT- | External- | ||
| class | (left) | (right) | tagged | tagged | tagged | Total |
| ------------------------------------------------------------------------------------------------------------------- | ||||||
| 1978 | 9 | 1 | 8 | 2018 | 2028 | |
| 1979 | 1363 | 1370 | ||||
| 1980 | 180 | 1723 | 1723 | |||
| 1981 | 1639 | 1639 | ||||
| 1982 | 12 | 12 | 436 | 12 | 1324 | 1336 |
| 1983 | 183 | 190 | 190 | |||
| 1984 | 1041 | 1041 | 23 | 1017 | 1041 | |
| 1985 | 1533 | 1533 | 1533a | 1533 | ||
| 1986 | 1726 | 1492 | 97 | 1629b | 1726 | |
| 1987 | 1280 | 1265 | 5 | 1230 | 1280 | |
| 1988 | 910 | 870 | 102 | 808 | 910 | |
| 1989 | 1914 | 1447 | 69 | 1845c | 1914 | |
| 1990 | 1979 | 1979 | 1979 | 1979 | 1979 | |
| 1991 | 1944 | 1944 | 1944 | 1944d | 1944 | |
| 1992 | 1963 | 1963 | 1963 | 1963 | 1963 | |
| 1993 | 188 | 188 | 188 | 187 | 188 | |
| 1994 | 170 | 142 | 170 | 170 | 170 | |
| 1995 | 168 | 160 | 168 | 168 | 168 | |
| Total | 13458 | 1391 | 14824 | 6728 | 22730e | 23102 |
classes) relied on more than one type of tag (Shaver, 1996a, b). Despite being tagged with one to four types of tags, captive-reared turtles can still be misidentified as wild if tags are (a) lost, (b) retained but not detected by persons unfamiliar with the tags or who lack appropriate detection equipment and training or (c) detected but not correctly reported.
One or more of the following criteria are necessary to distinguish captive-reared from wild turtles:
1. Captive-reared turtles tagged with magnetized wire tags totaled 14,837 (Table 1), but wire tags in wild hatchlings released at Rancho Nuevo were non-magnetized. Distinguishing captive-reared from wild turtles based on this difference will require retention of magnetism by the magnetized tags, and the non-magnetized tags remaining non-magnetized in the wild. Under these conditions, wire tags in the captive-reared turtles should be detectable with a magnetometer, and those in the wild will have to be magnetized with a magnet before they can be detected with a magnetometer (Fontaine et al., 1993).
2. All captive-reared Kemp's ridleys of the 1978-1995 year-classes (23,102 turtles) were tagged with Hasco Style 681, external, metal, foreflipper tags bearing unique individual codes (manufactured by National Band and Tag Company, Newport, Kentucky USA). However, these tags are not permanent. When lost, they leave scars, but the scars sometimes heal and are not recognizable. As long as they are retained, these tags distinguish captive-reared from wild turtles by their unique codes. No other tags are needed to identify a captive-reared turtle when the external, foreflipper tag is retained, observed, correctly read and reported.
3. Most (14,824 turtles) captive-reared Kemp's ridleys were tagged with "living tags" (formed by grafting a small, light-colored piece of plastron tissue to the darker carapace). "Living tags" were placed on different scutes to distinguish year-classes (Caillouet et al., 1986; Fontaine et al., 1988). To our knowledge, no wild Kemp's ridleys have been "living tagged" and released. However, even trained observers sometimes fail to observe "living tags" (Fontaine et al., 1993). It is essential that observers scrub the carapace to remove adhering algae, mud or other debris before examining it carefully for a "living tag."
4. PIT tags (400 kHz; Biosonics, Inc., Seattle, Washington USA) bearing unique individual codes were placed in 6,728 captive-reared Kemp's ridleys. Captive-reared turtles should be distinguishable from wild nesters and other PIT-tagged wild turtles by these codes, assuming they are detected, correctly read and reported.
5. No captive-reared Kemp's ridleys of year-classes 1979-1981 and 1983 were wire-tagged. Only nine of the 1978 year-class and 12 of the 1982 year-class (see Table 2 in Fontaine et al., 1985) that were "super-head-started" and eventually released were wire-tagged.
6. All captive-reared Kemp's ridleys should be larger than the wild turtles tagged as hatchlings at Rancho Nuevo in 1996. Captive-reared turtles of the 1996 year-class have not yet been released.
We expect the wire-tagged wild turtles of the 1996 year-class to enter the neritic habitat following 1-2 years in the pelagic stage (see Ogren, 1989; Byles et al., 1996). There they may be encountered by "in-water" researchers, or be found stranded by the Sea Turtle Stranding and Salvage Network (STSSN). It may take more than a decade before any appear on nesting beaches (Byles et al., 1996). On the other hand, we expect captive-reared Kemp's ridleys to be reported for many years hence. Eckert et al. (1994) recommended that nesting beach coverage efforts be increased to examine all nesters and that all field teams be outfitted to detect head-started turtles (Pritchard, 1990; Byles, 1993; Williams, 1993). We urge participants in the STSSN, "in-water" research and nesting beach operations to examine all Kemp's ridleys they encounter, using criteria presented herein (see also Fontaine et al., 1993).