Secretariat of the Pacific Community ISSN 1025-7462 Issue 14 – July 2008 TROCHUS and other marine molluscs information bulletin Editorial Contents A year after the last publication, we are proud to present issue #14 of the SPC Trochus Information Bulletin. With the help of excellent contributors Trochus niloticus (Linnae 1767) from various fields, we have managed to put together a substantial and growth in Wallis Island well-balanced issue, offering you an array of research results, reviews and S. Lemouellic and C. Chauvet p. 2 reflections on topics related to the harvesting, aquaculture and manage- ment of marine molluscs in the Indo-Pacific. Growth rate of Trochus niloticus (L., 1767) fed different food types For starters, two studies on the growth of trochus in Wallis Island and Viet Do Huu Hoang et al. p. 7 Nam, contributed by Soazig Lemouellic and Claude Chauvet (University of New Caledonia) and by Do Huu Hoang and collaborators (Institute of Oce- Appraising the resilience anography, Viet Nam), respectively. Then, Simon Foale (James Cook Uni- of trochus and other versity, Australia) writes on the resilience of trochus and other nearshore artisanal fisheries in the Western Pacific, and Antoine Teitelbaum (SPC) nearshore artisanal fisheries and Sompert Rena (Vanuatu Fisheries Department) provide an update on in the Western Pacific marine gastropod and bivalve aquaculture in Vanuatu. Last but not least, Simon Foale p. 12 Antoine Teitelbaum and Kim Friedman (SPC) outline the outcomes of the Update on aquaculture reintroduction of giant clams to the Indo-Pacific region. As usual, we have included for your perusal a list of pertinent abstracts published in different of marine gastropods sources over the past 18 months. and bivalves in Vanuatu A. Teitelbaum and S. Rena p. 16 As you can see, we continue to make progress in broadening the scope and increasing the appeal of the bulletin – sincere thanks to those of you who Successes and failures have shared in this adventure. Our dream for the next issue (#15) would in reintroducing giant clams be to receive an even larger selection of articles dealing with a diversity in the Indo-Pacific region of marine molluscs from a wide range of geographical areas. We remind A. Teitelbaum and K. Friedman p. 19 readers and potential contributors that while this publication will remain focused on species of commercial significance to Indo-Pacific communities, Abstracts and publications p. 27 such as giant clam, conch and trochus, we are always looking for comple- mentary information on other species (of marine gastropods and bivalves), regions (i.e. Caribbean, Mediterranean, etc.) and endeavours (e.g. regional Editors: surveys, emerging aquaculture or fisheries programmes, workshops and Jean-François Hamel & Annie Mercier Ocean Sciences Centre (OSC) conferences, relevant biological data, aquarium trade information). All Memorial University forms of contributions are welcome, as are suggestions from scientists, hob- St. John’s (Newfoundland) byists, managers and stakeholders regarding possible topics of interest. Canada A1C 5S7 Email: [email protected] We are counting on you all to help us get the next issue ready for publica- Email: [email protected] tion in a year or so – maybe even less. Seize this opportunity to make your- Production: self and your work known and perhaps get feedback from others involved Information Section, Marine Resources Division in this constantly evolving field of research and business. We cannot wait to SPC, BP D5, 98848 Noumea Cedex hear about new projects and novel findings. New Caledonia. Fax: +687 263818 Meanwhile, enjoy issue #14 and please share it with your friends and Email: [email protected] colleagues. www.spc.int/coastfish Jean-François Hamel and Annie Mercier Produced with financial assistance from Australia, France and New Zealand 2 SPC Trochus Information Bulletin #14 – July 2008 Trochus niloticus (Linnae 1767) growth in Wallis Island Soazig Lemouellic1 and Claude Chauvet1, 2 Abstract A study of the Wallis Island Trochus niloticus stock was undertaken between 2004 and 2006. The growth of individuals was studied by tagging. Results are presented and compared with growth trends in other regions of the Pacific. Introduction T. niloticus inhabits the intertidal and shallow sub- tidal zones. Its preferred habitat is the moderately Trochus niloticus (Linnae 1767) is a marine gastropod. exposed coral reef shore (McGowan 1956; Gail It belongs to the Prosobranchia subclass, Archaeo- 1957; Smith 1979). Its diet is herbivorous, and it gastropoda order and Trochidae family (Hickman forages on small green and red seaweeds (Cyano- and McLean 1990). Wild populations of T. niloticus phycae and Phaeophycae), benthic diatoms and occur between longitudes 90° W (Andaman Islands, Foraminifera (Asano 1944). Trochus spp. are gono- India) and 180° W, and latitudes 20° N and 25° S. choric, without any external sexual dimorphism. The Wallis T. niloticus population is therefore on Females and juveniles, however, have green gonads, the edge of the species’ area of natural occurrence whereas males have white gonads (Amirthalingam (Fig. 1). During the last century, some populations 1932a, b). Spring tides mark the breeding period, were artificially transplanted to the east, north and with external fertilisation and nocturnal spawn- southeast of the species’ occurrence zone in the wild ing. Female spawning is induced by the presence (Gillett 2002). Although there were some failures, as of sperm (Amirthalingam 1932c; Nash 1985). In in the Loyalty Islands with New Caledonian juve- Micronesia, Australia and the Andaman Islands, niles, most of these populations settled successfully spawning occurs all year round (Rao 1936). In New (Hoffschir et al. 1989; Chauvet et al. 1998). Caledonia, T. niloticus spawns between October and Northern Mariana Islands Andaman Islands Guam Palau Caroline Is. Marshall Islands Phoenix Islands PNG Marquesas Is. Solomon Islands Wallis French Polynesia Fiji Is. Samoa Tuamotu Is. Society Is. New Caledonia Australia Cook Islands Figure 1. Distribution of Trochus niloticus. Natural stocks occur west of the dotted line. To the east, implanted populations of the Northern Mariana, Guam, Yap, Chuuk, Marshall and Phoenix Islands originated in Palau; the Society Islands population was implanted from Vanuatu and New Caledonia, whereas the Cook Islands population came from Fiji Islands. 1. University of New Caledonia, BP R4, Noumea, New Caledonia. 2. Email: [email protected]; ph: +687 265 828, fax: +687 273 272. SPC Trochus Information Bulletin #14 – July 2008 3 April (Bour 1989). Heslinga and Hillmann (1981) horizontally on an openwork surface, facilitating and Nash (1985) described the species’ reproduc- the different steps of the tagging: tive behaviour and larval development in Australia 1. the shell is scratched clean with a knife on a 5 x 2 (Great Barrier Reef) and Palau, respectively. Ferti- cm surface; lised eggs are covered by a thick chorion. The first 2. this surface is then polished with a sandpaper- division occurs between 30 and 60 minutes after ing machine; fertilisation and the trochophore larva hatches 3. the surface is air-dried with a diving bottle; after 12 hours. At the end of the first day, the larva 4. the surface is cleaned with acetone to improve becomes a veliger. Although the larva is teleplanic, the resin’s sticking power; its metamorphosis into a juvenile occurs classically 5. the first thin coat of epoxy is applied; the resin during the third day of its life (Heslinga and Hill- must remain tacky for ca. 7 minutes and must mann 1981; Nash 1985). Metamorphosis and settle- then be hardened in 2 minutes; ment are stimulated by the presence of red algae or 6. the number (Dymo tag) is placed; and humic acids (Heslinga and Hillmann 1981). 7. a second coat of resin is applied to cover the tag. The shells of T. niloticus are used as raw materials The specimens are then placed in an immersion net by the nacre button industry. The value of this natu- until they are individually released at the place of ral material has increased steadily since the emer- their capture. The best colours for tags are orange gence of plastic materials. Artisanal jewellers put and yellow because they are easily discernible in the shells to a variety of uses and designs, such as shallow water. As concretions will cover up the inlaying and incrustation. Commercial demand for mark in 4–6 months, it is advisable to double the these products has been on the rise for more than tagging with an internal shell inscription made with 30 years. It is therefore necessary to manage stocks a pencil. carefully, particularly on small islands. Knowledge of growth rates is the basis of good management. The tagged specimens are then returned one by one Mean individual growths were studied in differ- to their natural habitat. Care should be taken dur- ent islands of the Pacific Ocean and fitted to the ing this step to ensure survival of the specimens Von Bertalanffy model, which has proven robust. and success of the tagging experiment. To prevent Although similar, growth rates in different loca- them from being turned over by waves or current, tions, such as Japan (Honma 1988), New Caledonia the specimens are repositioned so that they can (Bour et al. 1982), the Great Barrier Reef in Australia quickly re-attach themselves to the substrate. When (Nash 1985) and Vanuatu (Bour and Grandperrin a T. niloticus is upside down it becomes vulnerable 1985), differ sufficiently to suggest that they are to predation and can be eaten by small fish, such specific to geographical units. In that case, manage- as Labridae. Whenever possible, each trochus is ment advice and practices should be adapted to released in an environment that matches the foul- each stock. The present study, designed as a follow- ing of its shell, the best option being to take it back up to a short study of T.