Archie Carr

Handbook of Turtles

Two hundred million years ago the reptiles, newly arisen from an uncommonly doughty set of amphibians, were on the verge of great adventures. They bore the mark of destiny in the shape of impervious scales and the new cunning to lay shelled eggs, and these devices insured them against the age-old disaster of drying out, both before birth and after, and let them gratify their growing curiosity about the vast and almost empty land. Along with the new equipment they had imagination and no end of notions for novel body designs. Today we call these old beasts cotylosaurs, or stem reptiles, because all the lines of vertebrate life above the amphibian level lead back to them as branches converge in the trunk of a tree.

Impact of nondegradable marine debris on the ecology and survival outlook of sea turtles

Sea turtles of all kinds are peculiarly prone to eat plastic scraps and other buoyant debris and to tangle themselves in lines and netting discarded by fishermen, and records of such mishaps have increased markedly in recent years. Advances in our understanding of the developmental ecology of sea turtles shed new light on the impact of buoyant wastes on the juvenile stages. The initial developmental stages of all species are passed in the open sea. In the case of the loggerhead Caretta this period of pelagic life is likely to include 3–5 years of planktonic open-ocean travel, which may involve multiple transatlantic crossings. During this time both the young turtles and their buoyant food are drawn by advection into fronts (convergences, rips, driftlines) and the same process also brings in and aligns persistent plastics and lost fishing gear. This effect exacerbates survival problems for sea turtles that are dependent on driftlines for their food supply or shelter.

Reproduction and migrations of the Ascension Island green turtle (Chelonia mydas)

TOME, M. A., AND F. H. POUGH. 1982. Responses of amphibians to acid precipitation, p. 245-254. In: Acid rain fisheries. R. E. Johnson (ed.). Proceedings of an International Symposium on Acid Precipitation and Fisheries Impacts in Northeastern North America, 2-5 August 1981, Ithaca, New York. American Fisheries Society, Bethesda, Maryland. (BAP) DEPARTMENT OF BIOLOGY, BAYLOR UNIVERSITY, WACO, TEXAS 76798 AND (JMH) DEPARTMENT OF ZOOLOGY, CONNECTICUT COLLEGE, NEW LONDON, CONNECTICUT 06320. Accepted 17 April 1986.

Social facilitation in green turtle siblings

Abstract 1. 1. Tests made at the green turtle nesting ground at Tortuguero, Costa Rica, show that turtles hatching singly have reduced prospects of emerging from the nest, and even less chance of reaching the sea. 2. 2. Observations through glass nest sides, and of young going from the nest to the sea, show that group facilitation, probably involving both mechanical and psychological factors, occurs. 3. 3. Data from tests at Ascension Island, extending Hendricksons results (1958) in the China Sea, indicate that metabolic heating raises the temperature in nests of developing green turtle eggs and suggests that this may constitute thermal co-operation affecting the fitness of the sets of eggs and young as evolutionary units.

Reproductive biology of the Hawksbill Eretmochelys imbricata at Tortuguero, Costa Rica, with notes on the ecology of the species in the caribbean

Abstract From 1955 through 1983, 246 hawksbills Eretmochelys imbricata have been tagged as they came ashore to nest at Tortuguero, Costa Rica, a beach they share with a large colony of green turtles Chelonia mydas . Nesting hawksbills average 82 cm in straight carapace length and grow at a mean rate of 0·3 cm year −1 . Mean clutch size is 158 eggs; clutch size is poorly correlated with female body size. Average time from egg deposition to hatching emergence is 58·5 days. Mean emergence success ff hatchling is 58·3% in all clutches and 91·6% in clutches that produced hatchlings. The internesting interval averaged between 16 and 17 days. Site-fixity of females both within and between seasons was examined; a greater degree of site-fixity was exhibited between seasons than within. The distribution of hawksbill nesting activity at Tortuguero is spatially similar to, but temporally different from, that of the green turtle. There is increasing evidence from tag returns that the Tortuguero hawksbill may also share the feeding grounds of the Tortuguero green turtle in the Miskito Cays, Nicaragua. Notes on the movements and feeding habits of juveniles on their feeding grounds are included. Following a decline from 1956, there has been no consistent trend in the number of hawksbills nesting at Tortuguero since 1972. However, the mean carapace length of hawksbills has shown a steady decline, suggesting that the population is not demographically stable. The stability of an entire population cannot be determined from monitoring the number of nesting turtles each year.

The Ascension Island Green Turtle Colony

Recoveries of Atlantic green turtles tagged at the Ascension Island nesting ground confirm an exclusively Brazilian origin for the island colony and show its renesting and remigration periodicity and its site tenacity to be similar to those of the more extensively sampled Tortuguero (Costa Rica) colony. Implications of the dual origin of the Brazilian resident colony, where Ascension Island turtles mix with turtles from a Surinam breeding ground, are discussed; and the probable composite nature of Chelonia mydas, for which Ascension Island is the type locality is pointed out.

Site Fixity in the Caribbean Green Turtle

Although tagged green turtles that return to Tortuguero Beach to nest show definite site fixity, their site discrimination is not absolute. The modal distance between successive returns, whether after the 2—week internesting period of a given season or after the 2— or 3—year remigration interval between nesting seasons, is .2 km; average separation of return points is 1.2 km. In view of the steady reworking of the Tortuguero foreshore by wind, waves, and longshore currents,it seems unlikely that olfaction could be an important cue in landfall and nest—site discrimination, and new delimitation of the homing goal reinforces that belief. The straying of nesting females as far as 7 km from previous nesting sites suggests how colony proliferation may occur. No Tortuguero turtle has ever been found nesting on any other shore. See full-text article at JSTOR

Modulated Reproductive Periodicity in Chelonia

After 15 yr tagging at the nesting ground of Chelonia mydas at Tortuguero, Costa Rica, 447 remigration returns have been recorded. These confirm previous indications that some Tortuguero females return to nest every 2 yr and some every 3 yr, with the latter being the more frequent cycle. Returns after absences of 4 yr are so frequent that it seems probable that a regular cycle of this magnitude also exists. Longer absences recorded (up to 9 yr) probably can be attributed to missed encounters or to weak site tenacity by the returning turtles. A growing list of two—time and three—time returns shows that although an individual usually maintains a constant cycle, modulation of this may occur, and that the change may be either from 3 to 2 yr, or vice versa. It is suggested that the modulation reflects ecological conditions on the feeding ground. A sudden extensive shift to a 2—yr cycle, by turtles that had been nesting on a 3—yr cycle, probably contributed to the heavy nesting that occurred in 1969, after several previous weak seasons.

The role of vision in the sea-finding orientation of the green turtle (Chelonia mydas)

Summary Two tests of sea-finding orientation were used to determine the nature of the visual cues that guide green turtles to the sea after hatching or nesting. The orientation performance, in day-light, during 143 trials with adult female turtles was evaluated quantitatively while they were wearing spectacles containing different filters; and a total of 525 hatchlings was tested at various times of day and night in a circular arena near the sea, where direction preferences might be observed when the view of the horizon was unobstructed, or when it was blocked by a low wall. Blindfolded turtles were unable to find the sea except by chance; their performance was worse than that of any other group. Red, blue, and 0·4 neutral density filters significantly decreased orientation scores. Turtles with green filters, and those with neutral density filters and depolarizing-diffusing filters to which the animals had been pre-adapted, were able to orient as well as control animals with clear filters. Hatchlings placed in the low-walled arena headed in a landward direction nearly 50 per cent of the time despite a clear view of the sky. Sea-finding orientation was highly successful in the unwalled arena during both day and night, although there was no direct view of the sea. Theere was little correlation between hatchling direction preferences and the pattern of light intensity in the sky above the horizon, as measured by a photometer. Some conclusions based upon these results are as follows: o 1. Sea-finding orientation is primarily a visual process. 2. There was no evidence of an ‘innate’ compass direction preference based on celestial information. 3. A direct view of the sea or surf is not necessary for seaward orientation of either adults or hatchlings. 4. Light polarized by reflection from the surface of the sea is not used as a primary orienting stimulus when the water, itself, is not in sight. 5. Orientation is not impaired when the details of visual images are blurred by a diffusing filter. 6. It is unlikely that true colour preference forms the behavioural basis of the sea-finding guidance system. The results of the spectacle experiments with colour filters may be interpreted to mean that marine turtles are less sensitive to red light than are fresh-water turtles. 7. The principal sea-finding process is visual inspection of the beach horizon and landscape features. It is not clear whether an avoidance of dark areas or an attraction to open, brighter portions of the beach is involved; the two may co-exist, and further studies are necessary to resolve the problem. A comparison of our results with those of previous studies suggests that fresh water and marine turtles have solved the problem of water-finding in the same way.

Observations on the ecology and survival outlook of the hawksbill turtle

Abstract The hawksbill turtle ( Eretmochelys imbricata ) has declined to endangered status before its ecology has been adequately investigated. A limited amount of data on the species has accumulated at the Green Turtle Station at Tortuguero, on the Caribbean coast of Costa Rica. Stomach contents of 29 mature turtles (11 males, 13 females and 5 unsexed), killed by shell hunters on Tortuguero Bank, are listed. Tag returns that have been recorded add to knowledge of remigratory and renesting intervals, multiple nesting, philopatry and post-breeding movements. The bearing of the reproductive isolation of separate island colonies on the survival position of the genus is briefly discussed.