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During the period February 13 to 20, 1973, a visit was made to Canton Island for the purpose of conducting a preliminary survey of marine turtle nesting populations. Although previous investigators have described the sea birds (Buddle, 1938; Murphy G., 1954), insects (Van Zwaluwenburg, 1943, 1955), and vegetation (Hatheway, 1955), very little is known about the marine environment of Canton or the other seven atolls (Enderbury, Birnie, Phoenix, Sydney, Hull, Gardner and McKean) which comprise the Phoenix group. Publications dealing with marine life are limited to a description of fishes collected during the 1939 Bushnell Expedition at Canton, Hull, Enderbury and McKean (Schultz, 1943) and to an identification of some marine algae at Canton Island (Degener and Gillaspy, 1955 Dawson, 1959).

Tongatapu, like Tahiti, was visited by many early European navigators and was one of the first of the South Pacific islands to be charted in any detail. Though it was discovered (and named Amsterdam Island) by Tasman in January 1643 (Sharp 1968, 152-158), the first comments on the sand cays of the surrounding reefs were made by Cook during his second voyage, with the Resolution and Adventure, in October 1773. On this occasion Cook spent less than a week at Tongatapu, anchored in the northwest, and commented that "it would have taken up more time than I could spare to have surveyed these parts Minutely as there are a number of small Islots and reefs of rocks extending to the NE even further than we could see" (1961, 261). His naturalists, the Forsters, did not describe the cays, though Georg Forster remarked on the emersion of reef limestones on Tongatapu and its similarity to the continuing emergence of the land in Scandinavia (1777, I, 453). Cook returned on his last voyage in 1777, with the Resolution and Discovery, and stayed for a month. He anchored near modern Nuku'alofa and landed on Pangaimotu and possibly other islands (1967, 124-125, 155, 890). He charted the area but gave no description of the cays.

Rarotonga and Aitutaki form the summits of separate volcanic masses rising from depths of 4000 m, at which depth the cones are 45-55 km in diameter (Summerhayes and Kibblewh 1966, 1967).The lower slopes of the cones average 15-25 increasing to 30 in the upper 750 m and becoming very steep the surface reef is approached. The Mauke-Aitutaki line of islands is thought to be of early Tertiary age: the surface volcanics are much eroded, with a subdued topography, or are capped with limestones (Wood, 1967; Wood and Hay, 1970). On Rarotonga, where the relief is much stronger (maximum altitude 640 m), radiometric ages of 2.3-2.8 million years date the 1 as Pliocene (Tarling, 1967). Mangaia, with a cap of Oligoce Miocene limestones, must be much older (Marshall, 1927). Evi dence from the deep-sea drilling programme indicates that th ocean floor in the area of the southern Cooks is Paleogene (22.5-65 million years) in age (Winterer, 1973), thus provid a maximum age for the islands. It is probable that the gross history of the Cooks resembles that of other, better-known reef-capped Pacific volcanic cones known to have been initia in the early Tertiary.