CRUSTACEAN RESEARCH, NO. 41: 27–46, 2012 Factors affecting distribution of freshwater shrimps and prawns in the Hiwasa River, southern central Japan Minoru Saito, Tadashi Yamashiro, Tatsuo Hamano and Kazuyoshi Nakata Abstract.—Distribution of freshwater serving as major food items for some of the shrimps and prawns and its relationship larger predatory fishes (Maeda & Tachihara, with environmental factors were studied in 2004; Baumgartner, 2007). Crabs facilitate the Hiwasa River, Tokushima Prefecture, leaf litter and woody debris break down southern central Japan, to provide information through ingestion (Kobayashi, 2009). needed for conserving or propagating them Freshwater decapods may even be considered more effectively. Eleven species of decapod as umbrella species, since they often have crustaceans consisting of three palaemonids, similar habitat and diet preferences as six atyids, and two crabs were collected, of diadromous fishes and gastropods found in which eight species were diadromous. Results of the same region, in addition to life history canonical correspondence analysis showed that traits. substrate coarseness in addition to conventional Most of the freshwater shrimps found longitudinal variables largely affects overall in Japan are diadromous (Shokita, 1979; decapod distribution. Differences in distribution patterns among amphidromous species were Hamano et al., 2000), i.e. migrating between mainly explained by riverbank vegetation river and sea for breeding (McDowall, 2007). coverage and the two aforementioned variables. Abundances of diadromous shrimps are In contrast, distribution of a non–diadromous primarily determined by the accessibility atyid, Neocaridina denticulata, was suggested to of riverine habitat from the sea where be determined by relative ease for them to resist they undergo larval development (Miya & flood in that habitat, rather than by longitudinal Hamano, 1988; Greathouse et al., 2006) factors. These results insist on importance of and availability of preferred habitat for each coarse boulder bed and riverbank vegetation as species in the river (Iwata et al., 2003). Cross shrimp and prawn habitats at reach scale. The river structures including dams and weirs range of Caridina typus within a river differed have altered distribution of crustaceans, but between the Japanese Archipelago and the the negative impacts of these structures can Ryukyu Archipelago, and may be explained by be lessened with effective use of fishways limited low–temperature tolerance of this species. (e.g. Hamano et al., 2008). Incorporating these results and life history Fauna and distribution patterns under traits of the collected species, we propose a new natural condition are the fundamental classification system of distribution patterns for information to push forward conservation freshwater decapods on the Japanese Archipelago. programs of decapod crustaceans. In Japan, distribution patterns of atyid shrimps within rivers have been well documented in the Introduction context of longitudinal distribution (e.g. Decapod crustaceans are major Shokita, 1979). Differences in distribution components of unstable insular streams patterns among species were attributed to in tropical and temperate zones. Atyid topography of rivers and differences in shrimps facilitate recovery from flooding by migrating capabilities among them (Shokita, removing particulate organic matters that 1979; Suzuki et al., 1993; Usami et al., enhances algal growth (March & Pringle, 2008). These studies succeeded in describing 2002). Palaemonids as well as atyids are who lives where, especially the upper limit SHRIMP DISTRIBUTION IN SOUTHeRN CeNTRAL JAPAN 29 28 28 et al. M. Saito Fig. 1. Map of the Hiwasa River System and the locations of the sampling stations. Arrows indicate the confluences of major tributaries and the main stream. O: Okugata River, K: Kitagawachidani River, Y: Yamagawachidani River. of distribution, and how much, but additional use of two atyid shrimps in French Polynesia Fig. 2. Profile of the Hiwasa River System; a: Hiwasa and Yamagawachidani Rivers; b: Kitagawachidani and information is needed in order to identify using an ordination method. Although ranges Okugata Rivers. Dots represent the sampling stations. Arrows indicate the confluences of major tributaries and the type of habitat best suited for each species of Atyoida pilipes (Newport, 1847) and main stream. Y: Yamagawachidani River, O: Okugata River. K: Kitagawachidani River. of crustacean. For example, Caridina Caridina weberi De Man, 1892 overlapped multidentata Stimmpson, 1860 has high substantially in the studied rivers, they used climbing capability and is abundant in the habitat with different velocity. As shown upper reaches (e.g. Shokita, 1979; Hamano in Richards et al. (1993) and Fossati et al. central Japan, using a multivariate analysis. main stream, Hiwasa River, and three et al., 1995). However, it is still unclear why (2002), ordination techniques are effective Distribution pattern of each species and trend major tributaries, Kitagawachidani, the shrimp prefer upper reach habitat over tools to summarize complex relationships in of body size distribution among reaches Yamagawachidani and Okugata Rivers, lower reach habitat. Lack of such information community with key environmental factors. were compared with other regions in Japan. and flows into the Pacific Ocean at Hiwasa, is one of the major obstacles in identifying Its application to freshwater crustacean For future use in their conservation and Minami Town, Tokushima Prefecture (Fig. the environment essential for conserving community in Japan would yield beneficial habitat restoration programs, we categorized 1; 33°44’ N, 134°32’ e). We chose Hiwasa endangered species or propagating species information for identifying important habitat distribution patterns of freshwater decapod River System as the study site because natural valuable for fisheries. of each crustacean species in a river system crustaceans in rivers on the Japanese distribution patterns of freshwater decapod Aquatic organisms could be protected and for roughly estimating their probable Archipelago that are under influence of the crustaceans are well preserved there, owing more effectively, if we manage to answer this ranges prior to anthropogenic alterations of warm Kuroshio Current. to limited human alterations of river channel question by identifying factors determining channel or watershed. or riparian zone, and absence of carnivorous alien fishes (Hamano et al., 2000). Profile distribution pattern and fundamental criteria We investigated relationship between Materials and Methods for their habitat (Katoh & Takeuchi, 1991; environmental factors and distribution of of the 16.7 km main stream and the three Richards et al., 1993). Fossati et al. (2002) freshwater shrimps and prawns in the Hiwasa Sampling location major tributaries resemble logarithmic curves compared distribution patterns and habitat River, Tokushima Prefecture, southern Hiwasa River System consists of the (Fig. 2) and tidally influenced area extends SHRIMP DISTRIBUTION IN SOUTHeRN CeNTRAL JAPAN 29 28 et al. 29 M. Saito Fig. 1. Map of the Hiwasa River System and the locations of the sampling stations. Arrows indicate the confluences of major tributaries and the main stream. O: Okugata River, K: Kitagawachidani River, Y: Yamagawachidani River. of distribution, and how much, but additional use of two atyid shrimps in French Polynesia Fig. 2. Profile of the Hiwasa River System; a: Hiwasa and Yamagawachidani Rivers; b: Kitagawachidani and information is needed in order to identify using an ordination method. Although ranges Okugata Rivers. Dots represent the sampling stations. Arrows indicate the confluences of major tributaries and the type of habitat best suited for each species of Atyoida pilipes (Newport, 1847) and main stream. Y: Yamagawachidani River, O: Okugata River. K: Kitagawachidani River. of crustacean. For example, Caridina Caridina weberi De Man, 1892 overlapped multidentata Stimmpson, 1860 has high substantially in the studied rivers, they used climbing capability and is abundant in the habitat with different velocity. As shown upper reaches (e.g. Shokita, 1979; Hamano in Richards et al. (1993) and Fossati et al. central Japan, using a multivariate analysis. main stream, Hiwasa River, and three et al., 1995). However, it is still unclear why (2002), ordination techniques are effective Distribution pattern of each species and trend major tributaries, Kitagawachidani, the shrimp prefer upper reach habitat over tools to summarize complex relationships in of body size distribution among reaches Yamagawachidani and Okugata Rivers, lower reach habitat. Lack of such information community with key environmental factors. were compared with other regions in Japan. and flows into the Pacific Ocean at Hiwasa, is one of the major obstacles in identifying Its application to freshwater crustacean For future use in their conservation and Minami Town, Tokushima Prefecture (Fig. the environment essential for conserving community in Japan would yield beneficial habitat restoration programs, we categorized 1; 33°44’ N, 134°32’ e). We chose Hiwasa endangered species or propagating species information for identifying important habitat distribution patterns of freshwater decapod River System as the study site because natural valuable for fisheries. of each crustacean species in a river system crustaceans in rivers on the Japanese distribution patterns of freshwater decapod