Annual Occurrence and Winter Mortality of Marine Turtles in New York Waters

Abstract

Cold-stunned sea turtles, both moribund and dead as a result of hypothermia, were collected along the shorelines of Long Island, New York, during three consecutive winters. A total of 130 juvenile Lepidochelys kempii, Caretta caretta, and Chelonia mydas was collected. Lepidochelys kempii represented 75% of all individuals encountered. The size distribution of L. kempii (straight-line carapace length 22.5 cm to 37.6 cm; i = 29.4 cm, SD = 3.1) was unlike any other assemblage reported within the species' range. The regular occurrence of relatively small turtles suggests that New York waters are utilized on an annual basis by L. kempii during early developmental stages. The numbers observed in this study, coupled with historical records, indicate that New York represents an important portion of the range of L. kempii. There is a continuous distribution of this species from the Gulf of Mexico to New England waters. Sea turtles are usually considered inhabitants of the tropics and the subtropics. However, in recent years it has become evident that many sea turtles also frequent northern temperate latitudes (Bleakney, 1965; Carr, 1980; Lazell, 1980; Shoop, 1987), where they may be exposed to very low temperatures. In transitional climates, there is evidence that both green turtles (Chelonia mydas) and loggerhead turtles (Caretta caretta) escape low winter temperatures by burying themselves in bottom sediments (Felger et al., 1976; Carr et al., 1980). However, unlike some freshwater turtles (Jackson and Ultsch, 1982) and some terrestrial turtles (Gatten, 1987; Claussen et al., 1991) that can withstand prolonged periods at very low temperatures of 3 C and 5 C, respectively, sea turtles have been reported to suffer from hypothermia, or coldstunning, at temperatures between 3.5 and 9 C in outdoor tanks (Schwartz, 1978) and below 8 C in the wild (Witherington and Ehrhart, 1989). The decline in water temperatures each year in northeastern U.S. waters raises some questions as to this region's suitability as habitat for marine turtles and as to the role of the area in life histories of certain species (Carr, 1980; Hendrickson, 1980; Lazell, 1980). Cold-stunning of sea turtles has provided valuable information from which we can approximate lower thermal tolerance limits and other physiological aspects of these reptiles. The most commonly observed response of sea turtles to very low temperatures is to become buoyant and float to the surface (Schwartz, 1978). This phenomenon makes it possible to sample large numbers of free-ranging, and otherwise healthy, sea turtles over a short time, and can provide new insight into the population structure and life history of species that are affected. Witherington and Ehrhart (1989) were able to describe some key demographic characteristics of green and loggerhead turtles in east-central Florida based on data collected from 467 coldstunned turtles over a 9 yr period. In the more northern waters of New York, four species of sea turtles, loggerheads, greens, Kemp's ridleys (Lepidochelys kempii), and leatherbacks (Dermochelys coriacea), have been repeatedly documented over the past century (Murphy, 1916; Babcock, 1919; DeSola, 1931; Brongersma, 1972). One specimen of a hawksbill turtle (Eretmochelys imbricata) was also collected in New York in 1938 (Morreale et al., 1989). Each autumn, temperatures in this region decline rapidly, and any sea turtles that remain through the winter must face water temperatures that drop below 1 C. In the winter of 1985, 56 cold-stunned sea turtles of three species were retrieved along New York's shoreline (Meylan, 1986). These observations initiated an effort to i vestigate the role of New York waters in the life history of sea turtles. The objective of this portion of the study was to examine demographic characteristics of sea turtles in New York waters based on cold-stunned animals collected