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

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Ichthyofauna in Mangrove Estuaries of the Okinawa, Miyako, Ishigaki and Iriomote Islands During August from 2000 to 2002 Bulletin of the Society of Bull. Soc. Sea Water Sci. Jpn., 57, 481-490 (2003) Sea Water Science, Japan Special Issue "Harmonic Development and Sustainable Utilization of Coastal Marine Area" Original Paper Ichthyofauna in Mangrove 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 Okinawa Island, the Shimajiri River on Miyako Island, the Nagura River on Ishigaki Island and the Urauchi River 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 Ryukyu Islands 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.
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