Aquacult. Sci. 63(3),273-282(2015) Population characteristics of Monetaria annulus (Linnaeus, 1758) (Gastropoda: Cypraeidae) from temperate to tropical areas 1 2,* Shiela VILLAMOR and Tomoko YAMAMOTO Abstract: The aim of this study was to describe the population characteristics of Monetaria annulus (Linnaeus, 1758), including the density, abundance of different developmental stages, sex ratio, and size dimorphism between sexes, which are significant factors for resource management. We surveyed populations in the Philippines (tropical area) for comparison with populations in Japan (subtropical and temperate areas). The population density in the tropical area was interme- diate between that in the sub-tropical and temperate areas, although density varied among stations in the same geographical area. There was a low proportion or absence of immature cowries in the habitat shared with adults, except for Nogas Island in the Philippines. Because marine protected areas (MPAs) include a nursery area, which is a protective area for immature cowries, further study was required to determine where juveniles are recruited and grow. We detected the sex of adult cowries by histological analysis and measured the length of each shell to distinguish sexual dimorphism. Females were larger than males in some sampling sites. When formulating fisheries guidelines, including controlling the collection of larger individuals, we should investigate the sex ratio and size dimorphism in each resource population to avoid a sex ratio that is biased toward males. Key words: Monetaria annulus; Developmental stages; Sex ratio; Sexual size dimorphism The Cypraeidae family (commonly known tropical countries around the Indian and Pacific as cowries) is widely distributed in the Indo- Ocean, where shells and shell craft products West Pacific from tropical to temperate areas. are continuously exported. Cowries are in high Monetaria annulus (Linnaeus, 1758) or the demand by shell collectors, and many tourists gold-ringed cowry is one of the most common buy the crafts as souvenirs, thereby providing species in this family. These gastropods are a source of livelihood for the people in coastal usually found in the middle and lower intertidal fishing communities (Wells 1981; Newton et al. areas in shallow water, tide pools, under stones, 1993; Tiraa-Passfield 1996; Ponder and Grayson or among seagrasses. Their habitats include 1998; Floren 2003; Gossling et al. 2004; Oliver rocky, muddy and sandy shores (Orr 1959; Foin 2004). 1989). The northern limit of their distribution Research has identified habitat degrada- was observed in Boso, Japan (Irie 2006) and tion (Floren 2003; Huang et al. 2008; van der the southern limit in Algoa Bay, South Africa Meij et al. 2009) and overexploitation (Wells (Schilder and Schilder 1939). Cypraeid shells 1981; Newton et al. 1993; Tiraa-Passfield 1996; are beautiful, glossy and colorful, making them Floren 2003; Gossling et al. 2004) as reasons an economic commodity, mainly important in for a decrease in population numbers. Resource Received 12 December 2014; Accepted 1 May 2015. 1 The United Graduate School of Agricultural Sciences, Kagoshima University, Korimoto 1-21-24, Kagoshima 890-8580, Japan. 2 Faculty of Fisheries, Kagoshima University, Shimoarata 4-50-20, Kagoshima 890-0056, Japan. *Corresponding author: E-mail, [email protected] (T. Yamamoto). 274 S. Villamor and T. Yamamoto management based on scientific information with populations in Japan. is greatly required, particularly in the tropi- cal areas, where prolific collection of Cypraeid Materials and Methods shells occurs. A potential method of resource conservation is prohibiting collection during Fig. 1 shows the sampling sites and sta- the reproductive and recruitment seasons; tions in Japan and the Philippines. Sampling however, this practice appears to be difficult to stations were located in the intertidal area of implement in tropical and sub-tropical regions. each sampling site. The sampling sites in Japan In the tropical and sub-tropical areas, repro- included the southern part of Kyushu Island, duction and recruitment of larvae continues the coast of Hanase (with three neighboring throughout the year for these gastropods, and stations), the small islands at the southwest in particular for M. annulus (Frank 1969; Katoh part of Japan, including Tanegashima Island 1989). Another alternative method is to restrict (with five stations around it: Yanagihara, Iseki, the minimum harvest size. Through histologi- Ushino, Kamitateshi, and Shimoneshime), cal analysis, we found that in a temperate area a Amami Island (with one station at Hienhama bias toward females exists in the sex ratio, and in the west), and Tokunoshima Island (with size dimorphism between sexes where the shell three stations around it: Kanami, Shikaura, length of females were significantly larger than and Motokawa). In the Philippines, the sam- those of males (Villamor and Yamamoto 2015). pling sites were located in the central part of If size dimorphism is a general phenomenon the country, including Sulangan Island (Guiuan in this species, the limitation of the minimum Province) in the east, Nogas Island (Antique harvest size may result in a higher pressure on Province) in the west, and Olango Island (Cebu females than on males. Province) (with three stations around it: Sta. Establishing marine protected areas (MPAs) Rosa, Sabang, and Pangan-an) at the center. where egg masses and juveniles can be pro- Surveys in Japan and the Philippines were tected appears to be the most effective method conducted on different dates from 2010 to 2013. of fisheries management. Because egg masses Each sampling station was surveyed once, and brooding females have been observed in except at Hanase and Nogas Island. At Hanase the vicinity where adults were found (Natarajan Station 1 on Kyushu Island, surveys were con- 1957; Kay 1960; Frank 1969; Katoh 1989), it ducted every 2 months from June 2010 to June can be said that the spawning area comprises 2011, and all data were pooled. At Nogas Island almost the entire area of adult stage habitat. in the Philippines, surveys were conducted in However, there is little information regarding 2012 and 2013. The geographical coordinates nursery areas for this species. Katoh (1989) of the sampling sites, range and mean of sea identified both juveniles and adults in the field surface temperatures, and the sampling date at throughout the year but failed to mention the each sampling site are shown in Table 1. habitat difference between the two developmen- Survey areas at Hanase Station 1 in Japan and tal stages. Nogas and Olango islands in the Philippines The aim of this study was to describe the pop- were set at the wide range of the intertidal ulation characteristics of M. annulus, including zone. In each survey area, 2-3 transect lines the population density; abundance of juveniles, with a length of 50-100 m each were laid, and sub-adults and adult cowries occupying the all the individuals in every 1 × 1 m2 quadrat same habitat or fishery ground; sex ratio; and placed within 1 m of both sides of the transect size dimorphism between sexes, which are lines were sampled. At Hanase Stations 2 and significant factors for resource management. 3, all individuals in every 1 × 1 m2 quadrat Because this species is a high-valued resource in the designated survey area were sampled. in tropical areas, we conducted a survey on pop- At Tanegashima Island in Japan, all individu- ulations in the Philippines and compared them als collected at each coast were counted and Population characteristics of Monetaria annulus 275 Fig. 1. Location of sampling sites in (A) Japan and (B) the Philippines. Table 1. Sampling sites of Monetaria annulus Sea surface Latitude Longitude Sampling date Area Sampling site and station temperature (㱥) (North) (East) (yyyy.mm) Range Mean Temperate Hanase Station 1 31°11' 130°30' a16.8-27.8 a21.9 c2010.06-2011.06 Kyushu Island Hanase Station 2 31°11' 130°30' 2011.06 Hanase Station 3 31°11' 130°30' 2011.08 Yanagihara 30°47' 131°04' Iseki 30°46' 131°04' Tanegashima Ushino 30°26' 130°51' b19.5-28.4 b23.7 2011.02 Island Kamitateshi 30°24' 130°51' Shimoneshime 30⁰21' 130°51' Sub-tropical Amami Island Hienhama 28°18' 129°23' a19.3-28.1 a23.3 2012.07 Kanami 27°52' 128°58' Tokunoshima Shikaura 27°41' 128°54' no data no data 2013.02 Island Motokawa 27°41' 128°59' Tropical Sulangan Island Sulangan Island 10°56' 125°49' b27.5-29.8 b28.8 2013.08 (Guiuan) Nogas Island Nogas Island 10°25' 121°55' 2012.11 b26.9-30.0 b28.6 (Antique) Nogas Island 10°25' 121°55' 2013.08 Sta. Rosa 10°16' 124°02' Olango Island Sabang 10°15' 124°03' b26.7-29.5 b28.4 2012.11 (Cebu) Pangan-an 10°13' 124°03' aSource: Kagoshima Prefectural Fisheries Technology and Development Center bSource: http://www.seatemperature.org cSampling was done every two months. 276 S. Villamor and T. Yamamoto measured. At Amami (62 quadrats) and from Hanase Station 1 (Villamor and Yamamoto Tokunoshima (5-32 quadrats) islands in Japan 2015). and Sulangan Island (20 quadrats) in the Philippines, 50 × 50 cm2 quadrats were set in Results the area where M. annulus was found, and all individuals were counted and measured. Densities of M. annulus in the Philippines and Two to four persons conducted the survey southern Japan at each sampling site within 1-2 h during the In the tropical area, Sulangan Island (8.4 ± low spring tide. Cowries were counted, and the 0.3 mean ± SD ind./m2, n = 42) showed the shell size (length, width, and height) of each highest mean density, followed by Nogas Island live gastropod was measured using digital cal- (4.4 ± 10.6 ind./m2, n = 111), while Olango ipers. The developmental stages of M. annulus Island (0.01 ± 0.003 ind./m2, n = 3) had the were also recorded and categorized as adult lowest mean density (Table 2).
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