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ISSN 1025-4943 Secretariat of the Pacific Community ECHE-DE-MERB Number 15 — September 2001 INFORMATION BULLETIN Editor and group coordinator: Chantal Conand, Université de La Réunion, Laboratoire de biologie marine, 97715 Saint-Denis Cedex, La Réunion, France. [Fax: +262 938166; E-mail: Chantal.Conand@univ-reunion.fr]. Production: Information Section, Marine Resources Division, SPC, B.P. D5, 98848 Noumea Cedex, New Caledonia. [Fax: +687 263818; E-mail: cfpinfo@spc.int; Website: http://www.spc.int/coastfish]. Produced with financial assistance from France and Australia. Editorial Inside this issue Welcome to the 15th issue of the Bulletin. The ‘New Members’ section on page 42 and the great number of hits on the Bulletin’s The Torres Strait beche-de-merweb-pages (www.spc.int/coastfish/News/bdm/bdm.htm) are (sea cucumber) fisheryproof of the increasing interest raised by our publication. by D. D'Silva p. 2Thanks to all contributors who helped me in keeping the Bulletin alive and informative. Sexual reproduction of Stichopus chloronotus, a fissiparous sea We start the ‘New Information’ section with an article on the cucumber, on Reunion Island, Torres Strait beche-de-mer fishery (p. 2) followed by two articles Indian Ocean on the different aspects of the biology of sea cucumbers sexual re- by T. Hoareau & C. Conand p. 4 production (p. 4 and p. 13). The ‘Aquaculture News’ column in- Assessment of the ‘tubulecludes three original articles presenting new projects in Vietnam recruitment model’ in three(p.17), Marshall Islands (p. 27) and New Zealand (p. 28). tropical Aspidochirote holothuriansInformation on beche-de-mer prices is difficult to get. INFOFISH Trade News is one of the best sources of information for seafood by C. Ramofafia & M. Byrne p. 13 market trends and we are thankful to them for allowing us to re- Preliminary sandfish growth produce a table presenting beche-de-mer prices on the Asian mar- trials in tanks, ponds and pens kets (p. 31). We also thank the National Fisheries Authority (NFA) in Vietnamof Papua New Guinea for providing information on their beche- by R. Pitt et al. p. 17de-mer export prices (p. 30). Sharing information is the main aim of this bulletin and we encourage other fisheries departments from The new Marshall Islands within and outside the Pacific region to follow NFA’s example. Science Station inaugurates a sea cucumber aquaculture I draw again your attention to the ‘Echinoderms Newsletter’ that research programme is available on the Web (www.nmnh.si.edu/iz/echinoderm) by J.-F. Hamel & A. Mercier p. 27and to the echinoderms forum that was created after the International Conference in Dunedin. You can subscribe by Sea cucumbers: farming, contacting sabine.strohr@nrm.se or by sending an e-mail to production and development listserv@nrm.se and including on the first line of the message of value added products SUBSCRIBE ECHINODERM-L, your surname and first name, by A. Morgan p. 28 but no other text. and more. . . Chantal Conand MARINE RESOURCES DIVISION – INFORMATION SECTION SPC Beche-de-mer Information Bulletin #15 – September 20012 new infobeche-de-mer The Torres Strait beche-de-mer (sea cucumber) fishery 1Dallas D’Silva Management and licensing tasks are administeredBrief history by the Australian Fisheries Management Authority The beche-de-mer fishery is an important commer- (AFMA) and the Queensland Fisheries Service cial fishery for Torres Strait Islanders. There is no (QFS) based at Thursday Island and Brisbane, re- definite record of when beche-de-mer fishing began spectively. The Queensland Boating and Fisheries in Torres Strait but by the early 18th century it had Patrol (QBFP) perform surveillance and enforce- become important to the economies of both Torres ment duties from officers based on Thursday Island. Strait and coastal Papua communities (Williams 1994). In the past, the fishery was based primarily This fishery, in common with all other Torres Strait on sandfish (Holothuria scabra); however, harvesting fisheries, has the policy that if an increase in fishing of this species has since been discontinued. Current effort is allowed, then it must be reserved exclu- fishing effort focuses on surf redfish (Actinopyga sively for Torres Strait Islanders. mauritiana), black teatfish (Holothuria nobilis), white teatfish (Holothuria fuscogilva) and to a lesser extent, Key management measures a couple of lower value species. Regulations implemented in the fishery include: limiting the method of collecting beche-de-mer toManagement arrangements either hand, or hand-held, non-mechanical imple- Commercial and traditional fishing within the ments; a ban on the use of hookah gear; limiting Australian section of the Torres Strait Protected Islander dinghies to less than 7 metres in length; Zone (TSPZ) is managed under the Commonwealth and a competitive total allowable catch (TAC — Torres Strait Fisheries Act 1984 by the Protected Zone measured in wet weight gutted) for commercial Joint Authority (PZJA). The PZJA is comprised of species and minimum size limits. the Commonwealth and Queensland Ministers re- sponsible for fisheries. Current fishery trends Fisheries resources of the TSPZ are managed in ac- Fishing for beche-de-mer in Torres Strait is mainly cordance with the provisions of the Torres Strait by free diving from dinghies crewed by 2–3 fishers Treaty, ratified in 1985. The Treaty requires Australia or by hand collection along reefs at low tide. Once and Papua New Guinea to cooperate in the conser- collected, the animal is gutted, graded, cleaned, vation, management and optimum utilisation of re- boiled, smoked and dried. This is a labour-inten- sources of the region primarily for the benefit of tra- sive process usually carried out on processing ves- ditional inhabitants of the two countries. sels or at shore-based facilities. 1. Queensland Fisheries Service, GPO Box 46, Brisbane, Qld, 4001, Australia SPC Beche-de mer Information Bulletin #15 – September 2001 3 Beche-de-mer are especially susceptible to over- fishing because they are large, easily seen and col- lected, and do not require sophisticated fishing techniques (Skewes et al. 2000). As a result, the Torres Strait beche-de-mer fishery is subject to a suite of output and input controls aimed at pre- venting overfishing but also allowing Islanders to benefit from the use of beche-de-mer stocks. A total of 148 traditional vessels are presently li- censed for the fishery. One non-islander operator is licensed in the fishery with additional conditions that primarily involve the participation of is- landers in those activities. Sandfish (Holothuria scabra) Overexploitation of sandfish Sandfish is a high-value species occurring in rela- tively shallow waters and vulnerable to over-har- A third survey of the sandfish population on vesting. The population on Warrior Reef has been Warrior Reef was undertaken by CSIRO in January subject to excessive levels of fishing effort during 2000. The work revealed that sandfish stocks are the early 1990s and 1995 in particular. A similar still severely depleted with only a very slight re- boom on the PNG side of the TSPZ preceded this in covery since the extremely low abundance the late 1980s and early 1990s. recorded in 1998. The heavily depleted population was also confirmed by estimates of the standing Following concerns of serious resource depletion stock, which suggest it is unlikely there are more and overexploitation of sandfish stocks on Warrior than 100 tonnes of adult animals remaining on Reef, two independent fishery surveys were com- Warrior Reef. The present stock size is also very missioned to assess the level of reduction in sand- low compared to virgin biomass estimates of over fish abundance from November 1995 to January 1600 tonnes (Skewes et al. 2000). 1996 and in January 1998. The collection of sand- fish was primarily for export to Asia. Harvesting The findings from the most recent survey were has been prohibited since early 1998, following rec- noted by the PZJA at its meeting in April 2000 and ommendations from Commonwealth Scientific the existing closure for sandfish has been contin- Industrial Research Organisation (CSIRO) re- ued. The PZJA referred the findings to the Beche- searchers who surveyed the remaining stock on de-mer Fishery Working Group and requested the Warrior Reef, and determined it was approxi- group to develop long-term management arrange- mately 80 per cent less than in November 1995. In ments, including monitoring and enforcement for 1995, the sandfish stocks were considered overex- the fishery. ploited, therefore the subsequent reduction indi- cated a serious depletion (Skewes et al. 2000). Recovery of sandfish stocks Sandfish stocks were regarded as being in a Experience elsewhere in the Pacific indicates recov- downward spiral, with progressively smaller ery of overfished sea cucumber stocks is a lengthy breeding populations leading to smaller and process, taking several years. This is because smaller recruitments. The CSIRO survey also led holothurians, like many other invertebrates are to the introduction of severe management mea- broadcast spawners, and fertilisation success is sures. Further fishing pressure on sandfish may highly dependent on population density. have led to a total collapse of the stock and a con- Reduction of population densities by fishing may tinued closure was recognised as the only feasible render remaining individuals incapable of success- strategy for rehabilitation. ful reproduction. Because the fishery had been closed for two years, The possibility of reseeding sandfish stocks on it was decided that another survey should be car- Warrior Reef is also being explored as a viable op- ried out to determine if there had been any recov- tion to assist recovery. The fishery has several char- ery in the population. This was recognised as a acteristics that make it suitable to reseeding and high priority by management agencies and would benefit from recent work conducted by Islander fishing representatives at a beche-de-mer ICLARM in Solomon Islands where propagation workshop held on Thursday Island in July 1999. techniques for sandfish have been investigated. CSIRO Division of Marine Research SPC Beche-de-mer Information Bulletin #15 – September 20014 While reseeding may be a viable option to assist re- Status of other commercial species habilitation in future management agencies are more concerned with the effective sustainable The status of black and white teatfish, surf redfish management of other commercial species being and other lower value species remains unknown at fished at present. present. It is possible these species may be the tar- get of increased fishing pressure in future due to the growing export market demands for qualityRecent catch estimates beche-de-mer. Combined log returns from individual islands in- dicate that 15 tonnes of prickly redfish, 23 tonnes of References black and white teatfishes, and 12 tonnes of all other species were harvested during 1999. The 1998 Williams, G. 1994. Fisheries and Marine Research catch included 80 tonnes of prickly redfish, 20 in Torres Strait. Bureau of Rural Sciences, tonnes of teatfishes and 15 tonnes of all other Department of Agriculture, Fisheries and species combined. The 1997 catch comprised 57 Forest, Australia. 84 p. tonnes of prickly redfish, 29 tonnes of teatfishes and 29 tonnes made up of all other species com- Skewes, T., D. Dennis and C. Burridge. 2000. bined. These figures are in wet weight and gutted. Survey of Holothuria scabra (sandfish) on Warrior Reef, Torres Strait, January 2000. Official figures for 1995 revealed the total harvest CSIRO Division of Marine Research. of sandfish was around 1000 tonnes. Industry esti- mates place the total catch between 1200 and 1400 tonnes wet weight, with all but approximately 50 tonnes being sandfish. Sexual reproduction of Stichopus chloronotus, a fissiparous sea cucumber, on Reunion Island, Indian Ocean Thierry Hoareau and Chantal Conand Marine Ecology Laboratory, University of La Reunion should provide a better understanding of the re-Introduction spective roles of sexual and asexual reproduction Stichopus chloronotus is a holothurian of the order and facilitate the interpretation of population ge- Aspidochirotes, family Stichopodidae, that is widely netics (Uthicke et al. 1999 and 2001). distributed across the tropical Indo-Pacific region. It is mainly found on reef flats and slopes with con- Materials and methods siderable hydrodynamic energy. The species’ den- sity is relatively low, but sometimes reaches up to Sites 2several specimens per m (Franklin 1980; Conand 1989; Uthicke 1994; Conand et al. 1998). The Trou d’Eau station is located on Reunion Island’s west coast on the Saline-les-Bains reef com- Similarly to nine other Aspidochirotes sea cucum- plex that spans five kilometres. It is a fringing reef bers, they can reproduce both sexually and asexu- that is swept by the trade winds, but with little hy- ally (Uthicke 1994, 1997, 2001; Conand et al. 1998). drodynamic activity. Most sampling was conducted Their sexual reproduction has been studied in on this site, which is a back reef forming a channel Australia (Franklin 1980) and Malaysia (Tan Shau- made up mainly of detrital coral sediment littered Hwai and Bin Yasin 2000). Asexual reproduction is with large basalt blocks. Small amounts of brackish achieved by transverse fission resulting in two an- water well up into this 0.70-m deep area at the imals that each regenerate the missing part shoreline, providing algal cover for the substrate at (Uthicke 1997; Conand and Uthicke 1998; Conand certain times of the year. et al. 1998). Seawater surface temperature was selected as a The aim of this study was to describe the sexual re- reference parameter and recorded hourly through- production cycle on Reunion Island. The results out the study, ie from March to April 2001, using a SPC Beche-de mer Information Bulletin #15 – September 2001 5 VEMCO minilog-T sensor set three metres deep at GI follows the Conand (1989) calculation method. the Pointe des Galets harbour exit (F. Conand The monthly average (+/- standard deviation) was pers. corr.). The temperature curve throughout calculated and the patterns indicated maturity, the study was obtained by five-day averages of spawning and sexual resting periods. hourly readings. GI = (100 x Wg) / We Stichopodidae gonads have two tufts of tubules lo- cated on either side of the mesentery. The tubules branch out distally and are joined at the base in a sac, which bulges out from the dorsal mesentery. Saccules, ie dilations developing during matura- tion, are generally observed in this family (Conand 1993a). This characteristic form is not found, how- ever, in S. chloronotus, which has tubular distal tips. The gonads’ macroscopic and microscopic charac- ters were determined using samples fixed in for- malin. The lengths of gonad tubules were mea- sured from the gonad base to the distal tip to within 5 mm (Lg). Tubule diameters were also measured (Dg). Both values were used to describe S. chloronotus maturity stages by comparing them with macroscopic gonad characteristics such as colour, morphology and consistency and by using other descriptive methods, such as gonad indices, microscopic observations and histological sections. Figure 1. Sampling sites of It was possible to determine the sex in females dur-Stichopus chloronotus ing advanced stages of maturation using a binocu- lar magnifier, but it was generally necessary to re- sort to a microscope. Also, oocyte diameter distri-Sampling bution was established based on samples pre- Twenty adult specimens were collected monthly at served in formalin and was used to determine ma- the Trou d’Eau station from March 2000 to April turity stage characteristics. 2001. They were selected from among the longest and heaviest category, so as to avoid any bias aris- Atresia was related to undischarged germ cell dis- ing from the relation between size and the gonad integration. These germ cells were, therefore, ob- index value (Franklin 1980). Such sampling based served as coloured clusters in several areas of the on a uniform size category is recommended for gonad tubule lumina. A new parameter was de- studying reproduction cycles. Small specimens fined and used to determine the end of the sexual were also sampled to determine the population’s cycle, because the proportion of clusters increased size at first sexual maturity. Further sampling was as reproductive activity declined. A semi-quantita- conducted at the Planch’Alizés station (Fig. 1), fol- tive value or atresia index was allocated to each lowing early results, so as to obtain extra females. specimen using the formalin samples. • no atresia (0): no degenerative cell clusters ob-Gonad dissection and processing served anywhere in the gonad Specimens were anaesthetised in a 37 % magnesium • low atresia (1): small scattered coloured clusters chloride solution and dissected on arrival at the lab- mainly distributed at the tubules’ distal tips oratory after a one-hour journey. The length to • medium atresia (2): much larger and more numer- -1within 0.5 cm (Lt) and total weight to within 10 g ous clusters, still mainly concentrated in the (Wt) were measured for each specimen. The gonads distal tips. Clusters clearly visible to the -2were weighed to within 10 g (Wg) and fixed in for- naked eye. malin (10 %). Finally, the eviscerated weight (We) • high atresia (3): clusters replaced by structures was obtained, which is more representative than taking up the entire lumen volume in the the total weight that includes the coelomic fluid gonad’s main tubules. Some clusters re- and digestive tract contents, which cause consider- mained in the distal tips of tubules that ap- able variability (Conand 1989). The gonad index or peared fairly empty. SPC Beche-de-mer Information Bulletin #15 – September 20016 An atresia development curve was obtained and at their highest. GI values obtained for March (Fig. correlated with mean GI curves throughout the 3a) differed from one year to the next, however, study. with a mean GI in 2000 of 1.64 ± 0.45 and for March 2001 of 3.31 ± 1.10 (t = -6.27, 5% significant differ- Histological sections were prepared to provide ence threshold). more accurate descriptions of the observed matu- rity stages. Two stains were used, ie Trichrome and An analysis of gonad tubule diameters indicated HPS (hematoxylin-phloxin-saffron). that this parameter generally followed the mean GI curve. From March to June, tubule diameters slowly narrowed at the same time as gonad indicesResults dropped off for the first time. When gonad indices rose to their initial peak in mid-November, tubuleSex ratio diameters increased considerably. As with diame- Out of the entire year’s sampling of 260 specimens, ters, gonad tubule lengths also varied in line with only 8 females were collected, giving a sex ratio of the monthly GI curve. Average lengths dropped 97.3% males (Fig. 2). In the extra sample collected with the first GI trough and rose again with the at Planch’Alizés, 5 of the 12 specimens obtained first GI peak. were female and 7 male, which was a more bal- anced sex ratio. Providing a macroscopic description of gonads in terms of the maturity stage was more difficult than with other sea cucumber species (Conand 1989,Gonad and gonad index study 1993b). There was no major variation in appear- Monthly mean GI variations (Fig. 3a) indicated ance during the sexual cycle. The following phases several phases in the year. From March to late May, were nevertheless identified: 1) a maturing stage; values remained fairly stable between 1.64 and 2) a pre-spawning or ripe stage; and 3) a post- 1.69. From late May onwards, a sharp GI fall was spawning stage (Fig. 4). No immature specimens observed, reaching 0.83 ± 0.29 in July. A gradual re- were observed, other than in the extra sampling turn to the mean GI was then noted, followed by a conducted to determine weight at first maturity. maximum in early November at 3.22 ± 0.93, ie the first GI peak. Gonad indices subsequently fell With regard to atresia, the mean atresia index curve slightly up until late December (2.41 ± 1.36). In during reproduction (Fig. 3a) generally followed January, GI rose very steeply again to reach a sec- the opposite path to mean gonad indices. When the ond peak in late January (4.58 ± 1.36). Values then initial GI peak occurred in mid-November, atresia gradually declined until late March (3.31 ± 1.10). was falling sharply, reaching nil in late November. Two peaks were therefore noted on the GI curve, ie After rising steeply again in January, between the around mid-November and late in January. Falling two spawning seasons, it declined once again. values coincided with the two spawning seasons Mean atresia index increases occurred during GI (Conand 1989). Both peaks occurred in the warm falls, immediately after spawning. season (Fig. 3b), when seawater temperatures were 100% 90% 80% 70% 60% 50% 40% 30% 20% FFemellesemales 10% MalesM les 0% 1234567891011213 Figure 2. Monthly sex ratio in Stichopus chloronotus population from Trou d’Eau, La Reunion (monthly sample of 20 individuals, March 2000 – April 2001) SPC Beche-de mer Information Bulletin #15 – September 2001 7 6.0 3.5a Mean gonad index Mean atresia index 3.0 5.0 2.5 4.0 2.0 3.0 1.5 2.0 1.0 1.0 0.5 0.0 0.0 29 b 28 27 26 25 24 23 22 mamjjasondjfm Month Figure 3. Monthly variations of gonad index and atresia index (±SD) of Stichopus chloronotus and sea water temperatures (La Reunion) A B C D Figure 4. Morphology of Stichopus chloronotus gonads. A: Testis. B: Mature testis tubule. C: Mature ovarian tubule. D: Post spawning testis showing atresia. Mean gonad index Temperature °C Mean gonad index Temperature ¡C Mean atresia index Meann atresia index SPC Beche-de-mer Information Bulletin #15 – September 20018 The oocyte diameter frequency distribu- 15tion based on formalin samples is pre- b maturing 10sented for each stage in Figure 5. During the post-spawning stage (Fig. 5a), oocytes 5 were distributed between 12 µm and 048 µm, the mode being 30 µm. During 15 maturecmaturation (Fig. 5b), developing oocytes 10have diameters ranging from 36 µm to 78 µm, the average being 64 µm. The only 5 three females collected during the spawn- 0 ing season (Fig. 5c) had oocytes measur- 30 aing 30 to 114 µm with the mature oocyte 25 mode being 84 µm. post-spawning 20 A more accurate appreciation of these 15 stages was obtained through the histolog- 10ical study. It provided a clearer distinc- tion between immature and maturing 5 specimens. Four maturity stages were de- 0 scribed using the histological approach, ie 315273951637587991 Oocyte diameter frequencies (m)1) immature; 2) maturing; 3) pre-spawn- Oocytes diameter frequency (µm) ing or mature; and 4) post-spawning (Fig. 6). These stages are described in Figure 5. Oocyte diameter frequency distributions Table 1. of Stichopus chloronotus A B C D Figure 6. Histological characteristics of Stichopus chloronotus gonads. A. Ovary, vitellogenis oocytes. B. Post spawning ovary with degenerating oocytes. C. Mature testis with spermatocytes and sperm. D. Post spawning testis. Number Number Number Number Number SPC Beche-de mer Information Bulletin #15 – September 2001 9 Maturity stage variations during First maturity the yearly cycle First maturity was determined on the basis of 20 Figure 7 presents the proportions of specimens atsmall specimens from the extra samples collected each stage over time supported by the variousat Trou d’Eau (11/03/01). Weight at first maturity methods. Most post-spawning specimens were ob-was estimated at 50 g. All specimens weighing served from March to July and declined as matur-more than 50 g proved to have gonads, while those ing specimens increased from August to October.weighing less did not. Pre-spawning speci- mens rose sharply in November and fell in100% December. They in- creased abruptly again 75% in January and gradu- ally waned in February 50% and March. The cycle was therefore charac- terised by a minor ini-25% tial spawning season in November, followed by 0% the main season inMAMJJASONDJFM February/March dur-Month ing the warm season. Maturing Mature Post-spawning Figure 7. Stichopus chloronotus’s reproductive cycle on Reunion Island Table 1. Macroscopic and microscopic characteristics of Stichopus chloronotus gonads at different maturity stages Various stages Gonad anatomical and Microscopic characteristics macroscopic characteristics Immature stage Small tubules with little branching Some sparse villi against tubule walls. Few germ cells. Maturing stage Whitish tubules already branching Males: Increasing villi. Few germ cells in tubule out considerably; villi clearly visible lumina. Females: Oocytes tightly packed and filling en- tire tubule lumina.At this stage, oocytes mea- sure 36 to 78 µm, the average being 64 µm. Mature stage Slight colour change from whitish Males: Villi are less prominent and remain on to off-white and even creamy walls. Maturing spermatocytes are clearly visi- brown in both sexes.Tubules are ble. Sperm appear in the form of thick granules bulging. in the tube lumina. Females: Oocytes are not attached to tubule walls, which still hold oogonia.At this stage, most oocytes are mature, measuring an average 84 µm with the largest reaching 114 µm.They have a very wide, clearly visible nucleus and an eccentric nucleolus. Post-spawning stage Tubules are more or less empty, More or less empty tubules are observed in but have residual, undischarged both sexes. Undischarged cells and oocytes at sperm or oocytes undergoing various stages of deterioration are noted in fe- atresia (yellowish clusters) males and atresia clusters in males. SPC Beche-de-mer Information Bulletin #15 – September 200110 The reproductive cycle was described using stan-Discussion dard methods. Average monthly GI data can differ This study follows on from an analysis of asexual depending on the species or site under considera- reproduction by fission in Stichopus chloronotus tion. The bimodal curve observed with Stichopus (Conand et al. 1998) and is the first on sexual re- chloronotus on Reunion Island indicates a biannual production on Reunion Island. It was conducted reproductive strategy, which confirms previous at the Trou d’Eau site, where there is a high fission studies on this species (Franklin 1980; Tan Shau- rate. The site benefits from an upwelling of nutri- Hwai and Bin Yasin 2000). There is a significant dif- ent-rich water (Cuet 1989), which enables algae to ference between the peaks’ average values (ie sta- develop and results in high organic-matter con- tistically significant at a threshold of 5%), which tent in sediment. These conditions are highly con- implies different reproductive activity rates at each ducive to settlement and proliferation by this spawning season. This has been observed before species, which is a detritus feeder (Conand 1989; by various authors, namely Franklin (1980), with Uthicke 1997). regard to S. chloronotus, as well as by Conand (1989 and 1993b) and Hamel et al. (2001) with regard to When using microscopic sex determination, a Holothuria scabra. Mean gonad indices for March highly male-biased sex ratio of 0.97:0.03 was ob- 2000 (1.64 ± 0.45) and March 2001 (3.31 ± 1.10) dif- served. This is unusual among other sea cucum- fered significantly (p = -6.27 at a 5 % threshold). ber species in which the ratio is often close to 1:1 (Conand 1989; Hopper et al. 1998; Uthicke 1997; Water temperatures in March 2001 exceeded the Hamel et al. 2001). multi-year average by approximately 1° C. This prolonged warm season brought about a shift Other S. chloronotus populations studied in the and/or extension of the reproductive cycle. This past have displayed balanced sex ratios, ie in phenomenon has previously been observed by var- Australia (GBR) (Franklin 1980), Indonesia (Tan ious authors, particularly Hopper et al. (1998), who Shau-Hwai and Bin Yasin 2000) and Reunion demonstrated how temperature severely disrupted Island (Planch’Alizés site) (Conand unpub. obs.). the reproductive cycle in Actinopyga mauritiana. A comparable sex-ratio bias has, however, been de- scribed by Uthicke et al. (1999) on Great Palm When values are compared with other authors’, Island (GBR). Only one female was observed out of several similarities can be observed, such as two re- 59 specimens. productive seasons and greater activity in the warm season, but so can a number of differences. There are four possible explanations for these Such comparisons can only be made in terms of results: general reproductive activity trends, however, as 1) high adult female mortality; each author’s selected gonad indices restrict the 2) a higher fission rate among males; values than can be compared (total weight, open or 3) low female recruitment owing to high fe- eviscerated). The reproductive cycle described in male mortality among larvae or juveniles; Malaysia (Tan Shau-Hwai and Bin Yasin 2000), for and example, appears to extend over a longer period 4) sex inversion during the life cycle at the than on Reunion Island. As there is a longer inter- planktonic larval or adult stages. val between the two reproduction peaks (Fig. 8), the end of the cycle occurs later. Also, an earlier Weight distribution was identical among males peak has been recorded. The data obtained on the and females, however, indicating that age and Great Barrier Reef (Franklin 1980) indicates the survival rates were also equally distributed across same interval between peaks as on Reunion Island both sexes, which would exclude the first hypoth- (Fig. 8). Values are also too small to discern any dif- esis. No differences in fission rates between the ference in reproductive activity rates between the sexes have been observed either (Uthicke et al. two spawning periods. The cycle on the Great 1999), which excludes the second hypothesis. Barrier Reef appears to last the same time as on Reunion Island, although the two reproductive cy- The fact that size is evenly distributed among both cles seem to occur at slightly different times. males and females and that no hermaphrodite specimens have been recorded is incompatible Gonad morphology was examined from two an- with the sex-inversion hypothesis at the adult gles: tubule diameter and tubule length. Data on stage. The heavy sex-ratio bias at Trou d’Eau can tubule diameters indicated that they were widest therefore be explained either by higher female during spawning, as observed by Franklin (1980). mortality during recruitment or a differential dis- The longest tubule lengths were recorded during persal ability according to sex, as on the GBR the high reproductive activity period. Tubules (Uthicke et al. 1999). were present throughout the year in S. chloronotus