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Marine Turtle Newsletter 48:19-20, © 1990

Occurrence of Physical Abnormalities in Caretta Caretta at Hobe Sound National Wildlife Refuge, 1987 and 1988

Daniel J. Drennen
Eufaula National Wildlife Refuge, Rt. 2, Box 97-B, Eufaula, Alabama 36027 USA

The occurrence of abnormalities in turtles has received limited attention in the literature since Agassiz first noted this phenomenon (Agassiz, 1857). In particular, systematic studies describing and quantifying embryonic abnormalities in natural, undisturbed nesting areas are largely lacking. Information collected in this regard is often buried in longer papers of chelonian biology. Several theories and explanations for various abnormalities are summarized by McGehee (1979) and Dodd (1988). In any case abnormalities may be considered relatively rare and may indicate negative changes in the turtle's biology due to environmental factors. For this reason, physical abnormalities occurring in loggerhead sea turtles (Caretta caretta) are reported in this note.

In conjunction with a nesting success study on Hobe Sound National Wildlife Refuge (27°06'N, 80°08'W, Martin county, Florida USA), eggs and hatchlings were sampled from loggerhead sea turtle nests (n=213) and examined for developmental abnormalities. Physical abnormalities were noted in past due (unhatched) embryos and hatchlings remaining in the nest 3 days or more after a 55-day incubation period. Unhatched eggs were opened in the field; embryos found to display abnormalities were examined in the lab. Minute abnormalities, such as scale anomalies, not apparent in the field could have been overlooked.

"Abnormality" was defined as any external gross deformity of the head, body or appendages, lack of color (albinism), head tumors and twinning. When an individual embryo or hatchling displayed multiple abnormalities, each abnormality was categorized separately. Terminology was based on Miller (1985), Rhodin et al. (1984), and McGehee (1979).

Twenty-five (11.74%) of the 213 loggerhead nests examined contained at last one example of abnormal development. Forty different abnormalities were recorded (Table 1). The total number of eggs containing malformed embryos was 37, or 0.17% of the total eggs (n=21,130). This compares favorably to the 0.17% reported by Miller (1985) in 90,000 "marine turtle eggs".

Albinism was the most common abnormality noted (24.35% of total), followed by cleft palate and appendage abnormalities (bifurcation and/or stunted growth): 15.7% and 11.4% of total, respectively. The majority of body and head abnormalities (prognathia, anophthalmia, compressed carapace, monopthalmia, synopthalmia, micrognathia, encephalocele) occurred in albinistic individuals. However, one non-albinistic advanced embryo had head tumors. In the three pairs of twins, five embryos appeared normal in external development while one embryo had a compressed carapace. Partners in two pairs of twins were of vastly unequal sizes, while partners in the third pair were roughly equal.

TABLE 1. Abnormalities observed in loggerhead sea turtle embryos exhumed in situ during 1987 and 1988 at Hobe Sound National Wildlife Refuge, Florida USA.

The occurrence of scoliosis (8.6% of total) and kyphosis (1.45% of total) in adult sea turtles and hatchlings is discussed by Rhodin et al. (1984). In the present study, six specimens (two living hatchlings and four near term dead embryos) had a scoliotic condition. One additional (loggerhead) hatchling was kyphotic. In conclusion, physical abnormalities may be more common in natural settings than is commonly believed. Closer examination of hatchlings and past-due eggs by persons who regularly move clutches to safer beaches or hatcheries (or persons studying nesting success on undisturbed beaches) could provide valuable information on embryonic and hatchling abnormalities, and perhaps the environmental, physiological or genetic factors that influence this phenomenon.

Agassiz, L. 1857. Contributions to the natural history of the United States of America. First Monograph, Vol. II. Little, Brown and Co., Boston, Massachusetts.

Dodd, C. K., Jr. 1988. Synopsis of the biological data of the loggerhead sea turtle, Caretta caretta (Linnaeus 1758). U. S. Fish & Wildl. Serv., Biological Report 88(14):1-110.

McGehee, M. A. 1979. Factors affecting the hatching success of loggerhead sea turtle eggs (Caretta caretta). Master of Science Thesis, Univ. Central Florida, Orlando, Florida.

Miller, J. D. 1985. Embryology of marine turtles, p.269-328. In: C. Gans, F. Billett and P. F. A. Maderson (eds.), Biology of the Reptilia, Vol. 14 (Development A). Academic Press, New York, USA.

Rhodin, A. G. J., Pritchard, P. C. H. and Mittermeier, R. A. 1984. The incidence of spinal deformities in marine turtles, with notes on the prevalence of kyphosis in Indonesian Chelonia mydas. Br. J. Herp. 6:369-373.