These animals were loaded DEVELOPMENT OF THE aboard the Tahitien bound for Papeete. During the journey, INTRODUCED GREEN SNAIL the molluscs were kept alive in a metal tank (an empty metal POPULATION IN FRENCH drum) filled with sea water, renewed by intermittent pump­ POLYNESIA ing. At the end of the 12<lay jour­ Introduction IllllllpSliipiiliinpil ney, 42 green snails arrived l|||iii|Mi||^i|^l alive but very weak in Papeete on 9 April 1967, They were In the late 1950s, the production immediately transported to the of mother-of-pearl from the liiilil intended introduction site. black-lipped pearl oyster Pinc- tada margarittfera was in sharp decline in French Polynesia. It iliiiiiPliiii)llliiilllli Establishment on Tautira reef Was therefore decided to intro­ duce other pearl shell varieties guehi, 1987), the green snail's Transferring the animals to the site to offset this shortage, adaptation to the waters of French Polynesia would appear The imported specimens were The proximity of the western to be the first known successful transported to Tautira, the cho­ Indo-Pacific region, very rich in introduction of this species sen site, on their day of arrival. nacreous molluscs and with a (Yamaguchi & Kikutani, 1989). Because of the long distance coral environment comparable between Papeete and the site, to that of French Polynesia, This 23-year experiment has so they first travelled by road in prompted the authorities of the far not been documented, else­ tanks filled with aerated sea day to seek a commercial spe­ where. This study is a report on water and were then carried out cies within that region. The the introduction of this shellfish to the reef by boat. trochus Trochus niloiicus was to French Polynesia and an at­ thus introduced from Vanuatu tempt to appjrajse tfye size of the Site description in 1957 (Yen, 1985). This first present population^and its introduction was atotal success consequences for the" fishery. The chosen site lies on the and the experiment was re­ From a purely biological stand­ soutn-east coaSt of the penin­ peated in 1966 with Turbo point, the•••oppatibn. can be sula, at the.end Of the island, in marmoratus, also from Vanuatu. termed a sucee^, afi&frc|m the,, Tautira district figure 1). It is 'commercial1. fit|ndpoiri£ also; "close tSth|f;siteusfed for trochus The giant green turban shell, since' gree|fcisnalr poaching intj^tiction 10'years previ­ Turbo marmoratus Linne 1758, is (harvestings as yet illegal), is ously, and was chosen for the regularly reported around the following reasons: a nacreous gastropod mollusc ; of the order ArchaeO-gastro- island of Tahitir ;,^ ' ' ,,,. ^•:; pods, belonging to the family ; — relative remoteness from Turbinidae. More commonly 3§^ m> highly-urbanised areas, reduc­ known as the 'green snail', this Introduction of the green ing the risk of poaching; large shellfish, which may snail to the island of Tahiti weigh over 3 kg, has a green to — exposure to the prevailing browny-green shell lined with Transport from Vanuatu to east winds, creating an envi­ mother-of-pearl, making it at a Tahiti ronment of strong current and highly-prized raw material in high oxygenation, favourable to the mother-of-pearl industry In March 1967,300 'adult' green this species; and the handicrafts trade. snails weighing over 1 kg were collected in the New Hebrides —extreme south-easterly posi­ Contrary to the trochus, which (now Vanuatu) on the island of tion, exposed to the prevailing has been successfully intro­ Efate. The available information winds, favourable for larval duced to a number of Pacific does not state the exact place of migration along the coast, par­ countries (Gillett, 1986; Yama- collection. allel to the winds. 28 SPC Fisheries Newsletter #58 DEVELOPMENT OF THE INTRODUCED GREEN SNAIL POPULATION IN FRENCH POLYNESIA Figure 1: Map of the island of Tahiti and 1967 green snail introduction site The specimens were placed on bottoms ranging from 7 to 8m a recent dive enabled the author the outer slope of Teaiatia bar- in depth (see Figure 1). No de- to sketch the lagoon floor rier reef, approximately 100m scription of this site was made (Figure 2). from the Vaionifa passage, on at the time of introduction, but B C Figure 2: Diagram of the introduction site 29 SPC Fisheries Newsletter #58 DEVELOPMENT OF THE; INTRODUCED GREEN SNAIL POPULATION IN FRENCH POLYNESIA The site features the presence of thejFaabrte fringing reef (Figure —Presence of green snail along an extensive reef flat (Zone B) 1). They were gathered at night the whole length of the east approximately 80 to 100 m at depths of 0.5—0.8m. coast of/Tahiti, with a greater wide, very gently sloping be­ density near the introduction fore the sharper drop-off. A The harvesting of these young site; predominance of Pocillopora spedmens made it possible to colonies is observed, with some confirm that the species'had — Absence of green snail in al­ Acropora and Pontes amongst adapted to the reefs of T/ahiti most every west coast location, them. The algal vegetation is and was spreading along the apart from occurrences in the generally encrusting, except the island's east coast. extreme south-west near i!he macrophytes of genus Turbi- introduction site; naria which are probably not a source of food for the green 1979 Survey — Green snail presence was snails. The molluscs introduced recorded at depths of between in 1967 were placed on the reef Between September 1979 and 1 and 15 m; beyond this no drop-off. During our recent in­ January 1980,13 years after the specimen was observed. spection, most were found introduction, an initial popula­ scattered over Zone B, not tion survey was carried out on In certain areas in the immedi­ hidden in the fissures and all the reefs of Tahiti. However, ate vicinity of the introduction crevices, which are uncommon the information gathered dur­ site, as many as 80 green snails at this location. ing this operation was not ac­ were counted in 30 minutes' curate enough to provide an diving time by four divers. Al­ There is no information avail­ appraisal of the stocks of green though this figure may have no able about the state of living snails present around the is­ real significance where overall substrate when the specimens land. Precious information stock estimation is concerned, it were introduced in 1967, but the about the proliferation of these is comparable to the figure re­ geomorphology of the site was animals ata time when virtually corded on Aneityum in the certainly the same then as it is no inter-reef transplanting had New Hebrides in 1961 (13 ani­ now. been carried out around Tahiti mals /lOmins/ 2 divers) where was nevertheless obtained, to­ Devambez estimated that the gether with data on the relative stocks had risen to exploitable Development of the popu­ stock sizes in each district levels again. lation around Tahiti Eadi dive involved 2—4 divers The spread of the population Initial observations working outside the barrier along the east coast was there­ reef. The dive times were gen­ fore confirmed by this survey, The results of inspections car­ erally recorded and distances but it was slow compared to the ried out by the Fisheries De­ travelled alongside the reef proliferation of trochus, for partment from 1967 to 1971 are were sometimes registered. which commercial fishing be­ nowhere to be found. Depths were usually noted also. came possible a mere 14 years The specimens present were after its introduction (Yen, A visual inspection carried out counted as divers progressed 1985). at the introduction site in De­ along prearranged transects, cember 1971 revealed the pres­ Some relatively deep dives, ence of seven adult green snails between 15 and 25 m, were Recent observations at depths of 7—11 m, but no performed during this inspec­ young specimens were found. tion to verify whether or not No population survey was car­ During the same period, two green snails were present a t this ried out between 1979 and 1990, fishermen reported collecting depth. but a number of dives have two juveniles on the outer slope been made in the urban area of the barrier reef at Pueu, a Figure 3 shows the relative between Punaauia and Mahina district close to Tautira (see stock size as it emerged reef by since 1987. They showed that Figure 1). reef during the survey. The in­ green snails were present on all formation gathered during this the reefs within this zone and In October 1972, fishermen study was as follows: that stock sizes had diminished from Faaone collected two ju­ from 1987 to 1990. To quote veniles weighing under 1 kg on only the example of the Venus 30 SPC Fisheries Newsletter #58 DEVELOPMENT OF THE INTRODUCED GREEN SNAIL POPULATION IN FRENCH POLYNESIA Inter-island transplants Many trans­ planting op­ erations were carried out be­ tween 1980 and 1981 to the Leeward Is­ lands and some of the Tuamotu atolls (Table 1). In 1982, it was the turn of the Gambier Is­ lands to receive transplanted stocks. Other, more recent, introductions have taken place, chiefly in the Tuamotu Archipelago in 1985,1987 and 1989. None of these introduc­ Figure 3: Results of the survey carried out between September 1979 and January 1980. tions have ever (The figures represent the number of green snails found on each separate reef.) really been properly moni­ tored, but, according to the few Point reef at Mahina, 96 speci­ where stocks would appear observations reported by fish­ mens were collected and re­ adequate to sustain commercial ermen, these molluscs appear to leased in a 40-mrnute dive by poaching.