We found rats throughout the Southern Leeward Islets and 

 learned from the Faleoners that they are an abundant nuisance 

 on Ana-Ana. They trapped over 1 .300 animals in 2 years and. 

 like the pioneers before them, rely upon a dog to help keep them 

 at bay. 



Marine Mammals 



On March 14, 1990, members of the Line and Phoenix 

 Islands Expedition observed a minimum of 1 Pacific bottlenose 

 dolphins (Tursiops gilli) in the open sea about 500 m off the 

 southeast corner of South Island. 



Coconut Crabs 



The coconut crab (Birgus latro, Coenobitidae), the largest 

 terrestrial invertebrate on earth, ranges throughout the tropical 

 Indo-Pacific (Subchapter 1.1, PI. 56). It is highly esteemed as 

 a source of food throughout its range, and for this reason is rare 

 or absent on or near most inhabited islands. Because it is 

 heavily exploited by man, it is under consideration for 

 endangered species status (Reese, personal communication). 

 Since March 1990, dozens of Caroline's coconut crabs have 

 been killed for food and for preservation in formalin as curios 

 for the Tahiti tourist market. Because of the increasing numbers 

 of visitors to Caroline over the past 2 years, it is important that 

 Caroline's coconut crabs receive protection. 



History : Young (ca. 1 922) was the first to mention coconut 

 crabs on Caroline. In 1910 he wrote that "hundreds of great 

 Coconut Crabs were seen: 40 large ones were caught by the 

 crew of the schooner in an hour" on South Island. 



It is hardly credible that these enormous crabs, the dominant 

 terrestrial animal of the atoll environment, could have been 

 overlooked by all visitors prior to the 20th century. Perhaps 

 their populations had been reduced or extirpated by earlier 

 inhabitants. It is of interest in this regard that members of the 

 1934 Mangarevan Expedition saw no coconut crabs on nearby 

 Flint Island ( Fosberg, personal communication ), nor were they 

 mentioned in a historical summary paper on Flint by Maude 

 (ca. 1942b). Today Flint has perhaps the greatest density of 

 coconut crabs in the world (Kepler, 1990b). 



Young ( ca. 1 922 ) noted that coconut crabs were considered 

 a great nuisance by plantation laborers, who killed them 

 mercilessly. Evidently the crabs dug up newly planted nuts and 

 snipped off emerging shoots. On the smaller islets, visited less 

 frequently than South, Nake, and Long, these depredations 

 were difficult to control. Thus the small motu plantations were 

 abandoned within a tew years of initial planting, resulting in a 

 remarkably rapid recovery of the original vegetation (see 

 Subchapter I.I. Ecological Succession section). 



Distribution and Habitat Preference : In 1988 and 1990, 

 coconut crabs were abundant in the Cocos plantations of South 

 and Nake, and present, in varying densities, on 1 2 other motus 

 (Fig. 18). Although generally associated with ( 'ocos, we found 

 them in woodlands of Pisonia, Cordia, and Toumefortia, as 

 well as on rubble beaches (especiallj alter dusk). Although 

 capable of survi\ ing without coconut palms, these crabs appear 

 to seek them out. In the open understory of the tall plantations. 



or in groves of only one or two palms, telltale piles of shredded 

 coconut husk fibers (Subchapter 1.1. PI. 57) disclosed the 

 crab's presence. 



Because the prevalent coarse rubble substrates on Carol ine 

 are hard to burrow into, coconut crabs occupied a variety of 

 shelters: mounds of fallen coconuts and rotting palm fronds ( to 

 1.5 m high), piles of rubble pushed against tree roots, sand 

 burrows, tunnels within the/<?» (Subchapter 1.1, PI. 22), or 

 large cavities in the boles of mature Pisonia trees. Coconut 

 crabs also use a variety of shelters on the Tokelau Islands 

 (Yaldwyn & Wodzicki. 1979) and Flint (AKK. personal 

 observation). 



Numbers : Though conspicuous and slow-moving, coconut 

 crabs are very difficult to count. Environmental variables such 

 as rainfall, tide, lunar cycle, and population size and age classes 

 all affect their activity (Reese. 1965: Helfman. 1977a,b). 

 Although unable to conduct mark-recapture studies, we did 

 make incidental observations on the numbers of individuals 

 seen during transect and perimeter surveys. Coconut crabs are 

 generally nocturnal, but we often found them during daylight, 

 at times exposed on coral gravel beaches close to the waterline. 

 Reese (personal communication) suggests that the abundance 

 of rats occupying the same habitat may "force" the crabs to be 

 more diurnal, as has been reported from the Indian Ocean. Our 

 estimate of the population on Caroline is approximately 

 2, 200 individuals, based on the number of daytime observations, 

 the area covered, and the fact that only one out of every three 

 or four individuals may be present on any given night ( Helfman, 

 1977b; Reese, 1987). 



Foraging : Since the first detailed description of coconut 

 crabs in 1 705, their shy, curious habits have been the subject of 

 folklore, speculation, and misinformation (see Reyne. 1939). 

 No scientist has yet published a documented account of a 

 coconut crab actually opening a coconut (Helfman. 1979), 

 which is widely held to be their consummate foraging behavior. 

 Helfman is convinced that they do so, as he has found piles of 

 coconut fiber and observed crabs walking w ith husked, opened 

 nuts in places where he was the only other possible coconut 

 husker. We repeat Helfman's ( 1979) assertion that coconut 

 crabs do husk fallen coconuts. The piles of finely separated 

 fibers (Subchapter 1.1, PI. 57) we encountered are totalis 

 different from those produced by stick or machete husking, the 

 two methods commonly employed by Pacific peoples. The 

 crab tears virtually every fiber off individually, a process so 

 painstakingly slow it probably takes days. We did not observe 

 this on Caroline, but in March 1 990, AKK. on uninhabited Flint 

 Island, observed a large male coconut crab that had just husked 

 a coconut and was enlarging a small crack in the center of the 

 smooth nut in a manner similar to that described by Gardiner 

 (1907) in Reyne (1939, p. 297). 



On Caroline we observed the aftermath of coconut crab/ 

 sooty tern predation or scavenging. On Brothers Islet, several 

 entrances and pathways leading to coconut crab holes were 

 strewn with the feathered skeleta of adult sooty terns (and 

 possibly brown noddies ), along w ith numerous, freshly snipped 

 branches of Pisonia up to 0.7 m long (Subchapter 1.1. 

 Description and Ecology of the Motus section). This was also 



150 



