Bulletin of the Society of Bull. Soc. Sea Water Sci. Jpn., 57, 481-490 (2003) Sea Water Science,

Special Issue "Harmonic Development and Sustainable Utilization of Coastal Marine Area" Original Paper

Ichthyofauna in Estuaries of the Okinawa, Miyako, Ishigaki and Iriomote Islands during August from 2000 to 2002

Katsunori TACHIHARA*1,Kohei NAKAO*1, Keishi TOKUNAGA*1,Yuko TSUHAKO*2 Mikumi TAKADA*2and Tumid SHIMOSE*2

The temporal and spatial patterns of species composition and the abundance of fish in the mangrove estuaries of the Gesashi River on , the Shimajiri River on Miyako Island, the Nagura River on and the on Iriomote Island were studied during August, from 2000 to 2002. Fish samples were collected by cast nets, hand nets, and angling. In total, 5,747 individuals representing 13 orders, 47 families, 104 genera and 155 species were recorded from four mangrove estuaries. The number of species was found to increase from north to south. In terms of individual numbers, several species represented dominant key species, which comprised over 50 % of the total number of individuals collected in each estuary. In terms of the number of species per family, the most dominant family was the Gobiidae in each river and accounted for 25.5 % of the total number of species that appeared in the Gesashi River, 30.2 % in the Shimajiri River, 40.7 % in the Nagura River, and 38.1 % in the Urauchi River. The diversity of fish species found in the Okinawan mangrove estuaries was considered to be similar to or greater than those in other tropical regions.

Key Words: Mangrove estuary, Ichthyofauma, Okinawa

However, studies of fish assemblages in 1. Introduction mangrove areas in the have been River mouth areas in tropical and subtropical limited to date. For example, several freshwater regions are dominated by mangrove forests and ichthyofauna species of the middle Ryukyu generally consist of Kandelia candel, Bruguiera Archipelago were reported by Hayashi et al.,m as gymnorrhiza, and Rhizophora stylosa as examples)). well as by Shinomiya and Ike14) on Amami-Ohshima Mangrove forests are a dominant feature of tropical Island and by Shokita et al.12) and Uehara") on and sub-tropical coasts, but are presently subject to Okinawa Island. As for the freshwater ichthyofauna many types of pressure resulting from industrial of the southern Ryukyu Archipelago, studies have development2,3). These mangrove areas have mainly focused on the Gobiidae"24). developed brackish water bodies called "Mangrove The goal of the present study was to compare the swamps" which are influenced by tidal waters. mangrove ichthyofauna among four rivers on Mangrove swamps are considered to be important different islands in the middle and southern Ryukyu "cradles" for many juvenile fish , including species archipelago in the summer season and to clarify the of commercial importance4-11). Furthermore, the fish assemblage characteristics in this area. The complex structure of mangrove roots underwater is present paper provides a list of fish collected from thought to be important as a shelter from predators mangrove estuaries in the Okinawan area of Japan. and to be a good feeding area for many fish 2. Materials and Methods species12).

*1 Laboratory of Fisheries Biology & Coral Reef Studies , Department of Chemistry, Biology and Marine Science, Faculty of Science, University of the Ryukyus, Okinawa 903-0213, Japan *2 Department of Marine and Environmental Science , Graduate School of Engineering and Science, University of the Ryukyus, Okinawa 903-0213, Japan

481 482 Bull. Soc. Sea Water Sci. Jpn. Vol.57 No.6 (2003)

2.1 The study site Mugil cephalus cephalus 8.7%, Chelonodon patoca The study sites were as follows: the Gesashi 6.1 % and Kraemeria cunicularia 5.1%. These five River with 5 stations, which is located at the species accounted for 65.7% of the total number of northeastern part of Okinawa Island (26•‹35' 49"N, individuals and the remaining 34.3% consisted of 128•‹8' 33" E at the river mouth); the Shimajiri other 50 species (Fig. 2A). River with 4 stations, which is in the southern part 3.2 The Shimajiri River of Miyako Island (24•‹52' 40" N, 125•‹17' 13"E); the A total of 1,119 individuals representing 10 Nagura River with 4 stations, which is at the orders, 27 families, 46 genera and 63 species were northwestern part of Ishigaki Island (24•‹23' 50"N, collected. The community was dominated 124•‹8' 26"E); and the Urauchi River with 5 stations numerically by three species. Chelon macrolepis at the northern side of Iriomote Island (24•‹24' was the most abundant, making up 35.6% of the 50"N, 123•‹46' 28"E). The length of the Gesashi, total number of individuals, followed by Nematalosa Shimajiri, Nagura and Urauchi Rivers is 5.8 km, come 27.6 % and Caranx ignobilis 6.9 %. These 1.8 km, 8.0 km and 18.8 km, respectively. The three species accounted for 70.1 % of the total localities and sampling stations on the four rivers number of individuals and the remaining 29.9 % are shown in Fig. 1. consisted of other 60 species (Fig. 2B). 2.2 Sampling dates and gear 3.3 The Nagura River Samplings were conducted on 27 and 29 August A total of 1,330 individuals representing 10 2000 on the Shimajiri River, 6 and 24 August 2001 orders, 26 families, 59 genera and 82 species were on the Gesashi River, 29 August 2001 on the collected. The community was dominated by nine Nagura River, and 28 and 29 August 2002 on the species. Gerres oyena was the most numerous, Urauchi River. Fish samples were collected by cast making up 7.5% of the total number of individuals, nets (20 throws per station; mesh size: 11.5 and followed by Rhinogobius giurinus 7.3 %, Mugil 14.3 mm), hand nets (diameter: 35 cm, mesh size: cephalus cephalus 6.8%, Nematalosa come 6.8%, 1.5 or 2.5 mm), and angling was only used at station Chelon melinopterus 5.4%, Papillogobius reichei 3 in the Urauchi River. Surveys were conducted 5.3%, Yongeichthys criniger 4.9%, Chelonodon mainly at low tide and the sampling time at each patoca 4.9 %, Oreochromis mossambicus 4.3 %. station was about one hour using 3 or 4 persons. All These nine species comprised 53.2% of the total samples were fixed with a 10 % formaldehyde number of individuals and the remaining 46.8% solution as soon as possible and placed in a cooler consisted of other 73 species (Fig. 2C). box with ice. Samples were then brought back to 3.4 The Urauchi River the laboratory of the University of the Ryukyus and A total of 2,008 individuals representing 10 identified according to Nakabo"). orders, 34 families, 70 genera and 97 species were collected. The community was dominated by five 3. Results species. Atherinomorus lacunosus was the most A list of fish species caught in the Gesashi, common, making up 19.8% of the total number of Shimajiri, Nagura, and Urauchi Rivers is given in individuals, followed by Apogon amboinensis 11.7% Table 1. Papillogobius reichei 6.6 %, Yongeichthys criniger 3.1 The Gesashi River 6.1%, and Gerres oyena 5.9%. These five species A total of 1,290 individuals representing 7 orders, accounted for 50.1% of the total number of 27 families, 46 genera and 55 species were individuals and the remaining 49.9% consisted of collected. The community was dominated other 92 species (Fig. 2D). numerically by five species. Chelon macrolepis was 3.5 Total the most numerous, making up 27.5% of the total In total, 5,863 individuals representing 13 orders, catch, followed by Leiognathus equulus 18.3 %, 47 families, 104 genera and 155 species were TACHIHARA,NAKAO, TOKUNAGA, TSUHAKO, TAKADA, SHIM OSE: Ichthyofaunainmangrove estuaries ofthe okinawa, miyako, ishigaki and iriomote islands during august from 2000 to 2002 483 484 Bull. Soc. Sea Water Sci. Jpn. Vol.57 No.6 (2003)

Fig. 2 Composition in percentage of number for dominant fish species collected at the Gesashi River (A), the Shimajiri River (B), the Nagura River (C) and the Urauchi River (D). Cma: Chelon macrolepis, Le: Leiognathus equulus, Mc: Mugil cephalus cephalus, Cp: Chelonodon patoca, Kc: Kraemeria cunicularia, Nc: Nematalosa come, Ci: Caranx ignobilis, Go: Gerres oyena, Rg: Rhinogobius giurinus, Cme: Chelon melinopterus, Pr: Papillogobius reichei, Yc: Yongeichthys criniger, Om: Oreochromis mossambicus, Al: Atherinomorus lacunosus, Aa: Apogon amboinensis

recorded at four mangrove estuaries during this study. The fish assemblages recorded in this study contained ca. 45 species of commercial importance (ca. 30 % of total species), such as Nematalosa come, Caranx sexfasciatus, Lutjanus fulviflamma, Gerres oyena, Pomadasys argenteus, Acanthopagrus sivicolus, Lethrinus nebulosus and Siganus guttatus as examples. In terms of the number of species per family, the Gobiidae was by far the most diverse in each river. The total number of species of Gobiidae collected in the Gesashi, Shimajiri, Nagura and Urauchi Rivers were 14 (25.5% in total species), 19 (30.2%), 33 (40.7%) and 37 (38.1%), respectively. In total, the number of species of Gobiidae reached 50 (32.3 %). Other commonly occurring families were the Mugilidae (11 species, 7.1 %), Eleotridae (8 species, 5.2% ), Lutjanidae (6 species, 3.9% ) and Carangidae (5 species, 3.2%). Fig. 3 Appearance patterns of fish in four mangrove estuaries on Okinawa, Miyako, Ishigaki and The pattern of appearance of fish species among Iriomote Islands the four rivers on different islands is shown in Fig. 3 and Table 1. Fish appearing in all four rivers (Type A) comprised 20 species, including, for example, Nematalosa come and Mugil cephalus cephalus. On amboinensis were only present in the Nagura River the other hand, 12 species such as Omobranchus (Type N), and 32 species such as Carcharhinus loxozonus and Kraemeria cunicularia only appeared leucas and Cestraeus sp. were only found in the in the Gesashi River (Type H), 11 species such as Urauchi River. Lethrinus harak and Cristatogobius lophius were only 4. Discussion found in the Shimajiri Mangrove (Type L), 19 species such as Plectorhinchus gibbosus and Butis Comparing the four fish assemblages in this TACHIHARA,NAKAO, TOKUNAGA, TSUHAKO, TAKADA, SHIMOSE: Ichthyofauna in mangrove estuaries of the okinawa, miyako, ishigaki and Howie islandsduring august from 2000 to 2002 485

Table 1 A list of fish species collected in the Gesashi River, Shimajiri River, Nagura River and Urauchi River. Distribution patterns are represented in Fig. 2

(Continued) 486 Bull. Soc. Sea Water Sci. Jun. Vol.57 No.6 (2003)

(Table 1; Continued)

(Continued) TACHIHARA,NAKAO, TOKUNAGA, TSUHAKO, TAKADA, SHIMOSE Ichthyofauna inmangrove estuaries of the okinawa, miyako, ishigaki and iriomote islands during august from 2000 to 2002 487

(Table 1; Continued) 488 Bull. Soc. Sea Water Sci. Jpn. Vol.57 No.6 (2003) study, the number of species was found to increase width, is similar to or greater than those of other from north to south (55 species in the Gesashi regions such as Africa, Australia and South East River, 63 in the Shimajiri River, 83 in the Nagura Asia, which have huge mangrove foresth. River and 97 in the Urauchi River), and species that Yoshino et al.28)reported 1,211 species of fresh appeared in only one locality were regarded as and seawater fish around the Okinawan regions. It having the same tendency (12 species in the shows that, in terms of abundance, this area is one Gesashi River, 11 in the Shimajiri River, 19 in the of the prominent regions for fish species in the Nagura River and 32 in the Urauchi River). In total, world. The abundance of the Okinawan mangrove 155 species were listed from four rivers of fish assemblages in the present study is thought to mangrove estuaries during this survey. reflect the diversity of the Okinawan ichthyofauna. Fish assemblages in mangrove areas in this study On the other hand, in terms of the number of were compared to those of other regions as follows; individuals, several dominant species occupied 50 to 232 species were recorded when gill nets were used 80% of the total number collected. This is one of during a 5-year study in South Africa4), 204 species the most important characteristics of fish were collected by rotenone in Papua New Guinea5), assemblages in mangrove estuaries27,29-31). 203 species were recorded using gill nets and seine Regarding the number of species per family, the nets over 13 months in Queensland7), 262 species most dominant family was the Gobiidae (25.5% in were listed after using small bag nets in New the Gesashi River, 30.2 % in the Shimajiri River, Caledonia" and 135 species were listed after using 40.7 % in the Nagura River, and 38.1 % in the towed seine nets and a bag net over a 2.5-year Urauchi River), which is similar to findings in period in Thailand"). Thailand (28 spp., 20.7% in the total species)"). The species' abundance in the mangrove estuary Estimation of the standing crop of mangrove fish depends mainly upon the size of the river system, in varied according to such factors as fishing methods, addition to the condition of mangrove forests and gear, and survey periods. For example, small fish the diversity of the habitat"). Despite the short like the goby are difficult to collect and estimate survey period in this study, we believe our findings quantitatively. Establishment of methods to quantify show that the species' abundance of fish fish assemblages in is one of the most assemblages in Okinawan mangrove estuaries is important goals for further global study. The need similar to those in other regions. This is highlighted for conservation of mangrove fish as well as for by the fact that fish assemblages in the Urauchi management of the resources in these areas is of River resulted in 97 species being recorded after vital concern. only a two-day survey and showed remarkable diversity in this area. In the case of the Gesashi Acknowledgments River, although 143 species were recorded during a year-long survey from September 2000 to We wish to express our particular appreciation to September 200126),55 species were collected during Dr. Shigemitsu Shokita, Professor of the Faculty of August 2001. The total number of species observed Sciences, University of the Ryukyus, for his kind throughout the year in the Gesashi River was 2.6 support. Thanks are also due to students of the times that collected in August. This finding Laboratory of Fisheries Biology & Coral Reef suggests that if a year-round survey were to be Studies, Faculty of Sciences, University of the conducted in the Urauchi River, there is a Ryukyus, for assistance in fish collection and for possibility that the estimated number of fish species providing valuable information. This study was in the river may be more than ca. 250 (97 x 2.6). supported in part by Grants-in-Aid for the Mangrove The abundance of fish species in the Okinawan Survey Project, from the Research Institute for mangrove estuaries, despite the restricted size and Subtropics. TACHIHARA,NAKAO, TOKUNAGA, TSUHAKO, TAKADA, SHIMOSE: Ichthyofauna inmangrove estuaries ofthe okinawa, miyako, ishigaki and iriomote islands during august from 2000 to2002 489

Okinawa island", Master thesis in Marine Science, References University of the Ryukyus, (1991) 1) T. Nakamura and T. Nakasuga, "Mangrove as a 16) T. Suzuki and H. Senou, "Freshwater fishes in forests in the sea", in "Mangrove Nyumon", pp.9-35, ( I )", The Freshwater Fishes, 6, pp. Mekon Inc., Tokyo, (1998) 54-65 (1980 a) 2) M. D. Fortes, "Mangrove and seagrass beds of East 17) T. Suzuki and H. Senou, "Freshwater fishes in Asia: Habitats under stress", Ambio, 17, pp.207-213 Yaeyama Islands ( )", Nanki-seibutsu, 22, pp.65-70 (1988) (1980 b) 3) J. E, Ong, "The ecology of mangrove conservation 18) T. Suzuki and H. Senou, "Freshwater fishes in and management", Hydrobiologia, 295, pp.343-351 Yaeyama Islands (M)", Nanki-seibutsu, 23, pp.9-15 (1995) (1981 a) 4) J. H. Wallace, "The estuarine fishes of the east coast 19) T. Suzuki and H. Senou, "Freshwater fishes in of South Africa. I . Species composition and length Yaeyama Islands (N)", The Freshwater Fishes, 7, pp. distribution in the estuarine and marine 154-159 (1981 b) environments", Invest. Rep. Oceanogr. Res. Inst, 20) T. Suzuki and H. Senou, "Freshwater fishes in Durban, 40, pp.2-27 (1975) Yaeyama Islands (V)", Nanki-seibutsu, 23, pp.81-86 5) B. B. Collete, "Mangrove fishes of New Guinea", in (1981 c) H. J. Teas (Ed.), "Tasks for vegetation science. 21) T. Suzuki and H. Senou, "Freshwater fishes in Vol.8", pp.91-102, W. Junk, The Hague (1983) Yaeyama Islands (VI)", Nanki-seibutsu, 24, pp.12-18 6) S. J. M. Blaber and D. A. Milton, "Species (1982) composition, community structure and 22) T. Suzuki and H. Senou, "Freshwater fishes in zoogeography of fishes of mangrove estuaries in the Yaeyama Islands (VII)",Nanki-seibutsu, 25, pp.49-54 Solomon Island", Mar. Biol., 105, pp.259-267 (1990) (1983) 7) A. I. Robertoson and N. C. Duke, "Mangrove fish 23) T. Suzuki and H. Senou, "Freshwater fishes in communities in tropical Queensland, Australia: Yaeyama Islands (VIII)",Nanki-seibutsu, 26, pp.31-38 Spatial and temporal patterns in densities, biomass (1984) and community structure", Mar. Biol., 104, pp.369- 24) M. Hayashi and T. Itoh, "Gobioid Fishes of Ryukyu 379 (1990) Islands, Southern Japan", Sci. Rept. Yokosuka City, 8) M. Louis, C. Bouchon and Y. Bouchon-Navaro, 24, pp.59-82 (1978) "Spatial and temporal variations of mangrove fish 25) T. Nakabo (Ed.), "Fishes of Japan with Pictorial assemblages in Martinique (French West India)", Keyes to The Species, Second edition", Tokai Univ. Hydrobiologia, 295, pp.275-284 (1995) Press, Tokyo (2000) 9) I. A. Halliday and W. R. Young, "Density, Biomass 26) K Tachihara, "Ichthyofauna in mangrove estuary", and Species Composition of Fish in a Subtropical Mangrove Survey Project, pp.21-22, Research Rhizophora stylosa Mangrove Forest", Mar. Institute for Subtropics, Naha (2003) Freshwater Res., 47, pp.609-615 (1996) 27) P.Tongnunui, K. Ikejima, T. Yamane, M. 10) E. N. Kimani, G. K. Mwatha, E. 0. Wakwabi, J. M. Horinouchi, T. Medej, M. Sano, H. Kurokura, and T. Ntiba, and B. K. Okoth, "Fishes of a Shallow Taniuchi, "Fish fauna of the Sikao Creek mangrove Tropical Mangrove Estuary, Gazi, Kenya", Mar. estuary, Trang, Thailand", Fish. Sci., 68, pp.10-17 Freshwater Res., 47, pp.857-868 (1996) (2002) 28) T. Yoshino, S. Nishijima, and S. Shinohara, 11) P. Thollot, "A list of Fishes Inhabiting Mangrove "Catalogue of Fishes of the Ryukyu Islands" from the South-West lagoon of New Caledonia", , Bull. Micronesia, 29, pp.1-19 (1996) Sciences & Engineering Div., Univ. of the Ryukyus, 12) S. Shokita, T. Ameku, H. Yoshida and H. 20, pp.61-118 (1975) Morishima, "Mangal fishes and their food habits in 29) J. D. Bell, D. A. Pollard, J. J. Burchmore, B. C. Okinawa, the Ryukyu Islands", in T. Marumo (ed.), Pease, and M. J. Middleton, "Structure of a Fish "Fundamental Study on the Dynamics and Community in a Temperate Tidal Mangrove Creek Conservation for the Mangrove Ecosystem", pp.61- in Botany Bay, New South Wales", Mar. Freshwater 76, Monbusho, Tokyo (1988) Res., 35, pp.33-46 (1984) 13) M. Hayashi, T. Itoh, H. Hayashi, K. Hagiwara and K 30) N. J. Quinn and B. L. Kojis, "Annual Variation in the Kimura, "Inland-water fish fauna and Nocturnal Nekton Assemblages of a Tropical zoogeographical features in Amami Island, southern Estuary", Estuarine, Coastal and Shelf Science, 22, Japan", Sci. Rept. Yokosuka City Mus., 40, pp.45-63 pp.63-90 (1986) 31) M. C. Little, P. J. Reay, and S. J. Grove, "The fish (1992) 14) A. Shinomiya and T. Ike, "Fish Fauna of Rivers in community of an East African mangrove creek", J. Amamioshima Island", Mem. Fac. Fish. Kagoshima Fish Biol., 32, (1988) Univ., 41, pp.77-86 (1992) 15) A. Uehara, "Seasonal Fluctuation of Mangrove Fish 平 成15年9月29日 受 付,平 成15年10月20日 採 用 決 定 Community in Ooura River Northern Part of (Received Sept. 29, 2003, Accepted Oct. 20, 2003 ) 490 Bull. Soc. Sea Water Sci. Jpn. Vol.57 No.6 (2003)

要旨 沖縄 島,宮 古 島,石 垣 島 お よび西 表 島 の マ ング ロー ブ水 域 にお け る魚 類 相

立 原 一 憲*1,中 尾 耕 平*1,徳 永 桂 史*1, 津 波 古 優 子*2,高 田 未 来 美*2,下 瀬 環*2

2000～2002年8月 に沖縄 島(慶 佐次川),宮 古島(島 尻川),石 垣 島(名 蔵川)お よび西表 島(浦 内川)の マ ングロ ーブ水域で魚類相の調査 を行 った.そ の結果,4水 域合計 で13目47科104属155種,5,747個 体の魚類が採集 された. 種数は北か ら南に向け,周 辺海域の魚類相 を反映して増加す る傾向が認め られた(慶 佐次川:55種,島 尻川:63種, 名蔵川:81種,浦 内川:97種).い ずれの水域 も種数が多いにもかかわ らず,上 位数種の個体数が全体の50～80%を 占め,最 も多様性に富んだ分類群 はハ ゼ科であ った(計50種).沖 縄のマ ングローブ水域 の魚類相は,河 川規模 が比 較的小 さいにもかかわ らず多様性 に富み,ア フリカ,オ ース トラ リア,東 南 アジアな ど熱帯域 のマ ングローブにおけ る魚類群集に匹敵するものであった.―

キーワー ド:マ ングローブ水域,魚 類相,沖 縄

*1 琉球大学理学部海洋 自然科学科(〒903-0213 沖縄県 中頭郡西原町字千原1) *2 琉球大学大学院理工学研 究科(〒903-0213 沖縄県中頭郡西原町字千原1)