Relationships among tributary length, census population size, and genetic variability of white-spotted charr, Salvelinus leucomaenis, in the Lake Biwa water system

Abstract

The relationships between census population size and tributary length and between haplotype diversity of the mitochondrial DNA and census population size in ten white-spotted charr populations in the Lake Biwa water system and its adjacent basins were investigated. The census population size (number of fish with C100 mm in standard length) significantly increased with the tributary length. In the eastern part of the Lake Biwa water system, haplotype diversity increased with the census population size. On other hand, in the western part of the water system and adjacent basins, haplotype diversity was zero irrespective of the census population size. These results suggest that white-spotted charr populations in the eastern and western part of the Lake Biwa water system have undergone different levels of bottlenecks related to the habitat size in the postglacial warming.

Size at maturity of fluvial white-spotted charr, Salvelinus leucomaenis, around the Lake Biwa water system varies with habitat size

“…We were unable to define the watershed area of each tributary because most tributaries were too small, although this may be the most appropriate index of habitat size (Morita and Yamamoto 2002;Morita et al 2009b). Therefore, as an alternative habitat size, we measured the amount of water discharged (m 3 s -1 ) by the tributaries just above the dams or waterfalls in August- Nakano et al (1996) b Estimated density of individuals 100 mm in SL or longer (Kikko et al 2009) c Standard length values are given as the arithmetic mean and the range of observed lengths September 2009 (Koizumi and Maekawa 2004). All tributaries were small, and the amount of water discharged ranged from 0.004 to 0.231 m 3 s -1 (Table 1).…”

“…Because we had no data on the local stream temperature in the studied populations, a water temperature index given by the equation of Nakano et al (1996) was used as the water temperature (Kikko et al 2008c). Fish density was estimated from the density of individuals 100 mm in SL or longer (and one year or older in age) from a previous study (Kikko et al 2009). Sampling by electrofishing was conducted for 1 or 2 days in each tributary (whole period of sampling: 28 October to 11 November) during the spawning season in 2005.…”

“…Field research was conducted in nine isolated reaches (length 350-3,600 m; width 1.6-3.7 m; Kikko et al 2009) above dams or waterfalls where fluvial white-spotted charr occur as isolated populations with other fish (Fig. 1, Table 1).…”

“…In this article, we studied the size at maturity and environmental characteristics such as the habitat size in nine rivers around the Lake Biwa water system. These rivers encompass a wide range of tributary lengths (a proxy for potential habitat size; Kikko et al 2009), which are expected to be important for growth, survival and reproduction. These data will provide important baseline information for the conservation and restoration management of white-spotted charr populations around the system.…”

Multiple stressors in north temperate streams: lessons from linked forest–stream ecosystems in northern Japan

“…, 2009). Morita & Yamamoto (2002) conducted a comparative study of 82 headwater sites in south‐western Hokkaido (52 with dams, 30 controls), and predicted from their analysis that populations isolated in fragments with 2.3 km 2 watershed area or less would suffer a 50% extinction risk in 50 years (see also Endou, Tsuboi & Iwata, 2006 and Kikko, Kai & Nakayama, 2009 for similar results for white‐spotted charr and masu salmon in central Japan). Moreover, the fish that remained above barriers underwent a drastic life history change and showed lower genetic diversity and increased genetic drift (Morita, Yamamoto & Hoshino, 2000; Yamamoto et al.…”