The study region is located in the Kubo, Tochikura and Ichinono river systems (38°52′–38°55′ N, 140°56′–141°03′ E; Fig. 1), which are all tributaries of the Iwai River within the Kitakami River drainage that empties into the Pacific Ocean (Ichinoseki City, Iwate Prefecture, northern Japan). It includes the headwaters of these rivers, and headwater areas in smaller valleys (Fig. 1). The Kubo and Tochikura rivers each have a sediment control dam constructed in the lower reaches (Fig. 1). Rural cultivation and the typical ecological networks created by rice paddy ecosystems (traditional secondary nature, “satoyama” landscape: Washitani 2008) are widely established in the region (Ohtani et al. 2013; Fig. 2a).

Figure 1.  

Map of the Kubo, Tochikura, and Ichinono river systems. Black circles and red trapezoids indicate the main survey points where fish sampling was conducted and sediment control dams, respectively.

a

b

c

d

e

f

Figure 2.

Examples of the study sites.

a: The typical landscape of the region.  
b: The irrigation pond where many aquatic plants, including several threatened species, occur.  
c: The irrigation pond that a carp population inhabits.  
d: The upper reach of the Tochikura River.  
e: The middle reach of the Kubo River.  
f: The lower reach of the Ichinono River.  

The potential fish species pool of the study region was determined by a review of existing literature (Kawanabe et al. 2001, Ozawa et al. 2003, Matsuzawa and Senou 2008, Kumagai and Katsushima 2012, Nakabo 2013) as follows: the freshwater fishes with a natural distributional range located entirely or partly within Iwate Prefecture were catalogued, and the subsequent list was refined by considering ecology of the individual species and geography of the study region (i.e., whether they are known to inhabit headwaters and/or upper reaches of Japanese rivers or not). In other words, the fish species included in the potential species pool were determined by literature reports recording the species from the headwaters and/or upper reaches of rivers in Japan. For example, Kawanabe et al. (2001) reported that the Japanese eel, Anguilla japonica, often inhabits the upper reaches of Japanese rivers including Iwate Prefecture, and therefore we included A. japonica in our potential species pool of the region.

The fish fauna was assessed during field surveys using hand nets, minnow traps, cast nets, set nets, and hook-and-line angling. More than 200 irrigation ponds and three sampling sites (upper, middle and lower reaches) in each of the three rivers were sampled from April to October in 2008, 2009 and 2010 (Fig. 1). The substratum of the irrigation ponds consisted mainly of silt and organic litter with aquatic plants (Fig. 2b, c). The substratum of the river sites consisted mainly of cobble and gravel, often with boulders, as evident in the structure of one pool and riffle unit (Fig. 2d, e, f).

Voucher specimens and photographs are deposited in the Kanagawa Prefectural Museum of Natural History, Odawara, Japan (KPM) and the National Museum of Nature and Science, Tsukuba, Japan (NSMT). Unless otherwise stated, the systematic arrangement of families and scientific names follows Eschmeyer (2014), while that of standard Japanese names follows Nakabo (2013).

To evaluate the accuracy of the potential species pool (the predicted ichthyofauna), we made rarefaction curves based on presence/absence data from our field surveys. This allows us to estimate the number of additional species that our surveys may have missed. These analyses were conducted using EstimateS with the bias-corrected formula (Chao et al. 2004, Colwell et al. 2004, Colwell et al. 2012).

The voucher specimens and photographs are deposited and registered as KPM-NI 19440, 19447–19454, 211181–21203, 21217–21227, 21398–21413, 22248–22313, 22429–22432, 23639–23659, 23738–23745, 23933–24000, 24396–24398, 24407–24419, 24466–24476, 24988–24994, 30997–30999, 31003, 31005–31007, 31009, 31011, 31018, 31715–31811, and 35077–35105, KPM-NR 43909–43911, and NSMT-P 90703–90723, 91185–91208, 91638–91652, 92194–92195, 96055–96061, 96828–96833, 96836–96860, 96890–96902, 97045, 97084, and 97109–97111.

The information of these vouchers has been submitted to the Global Information Facility (http://www.gbif.org/) via the museums.