Habitat use by the Formosan landlocked salmon Oncorhynchus masou formosanus

Abstract

The critically endangered Formosan landlocked salmon Oncorhynchus masou formosanus is one of the southernmost natural salmon populations in the world, which only occurs in Chichiawan Stream and its tributaries in the Wuling basin of subtropical Taiwan. We examined habitat uses by different size classes of the Formosan salmon and the sympatric shovelmouth minnow Varicorhinus barbatulus, and identified the relative importance of environmental variables, biotic components and seasonal effects in explaining the variance in the relative occurrences of fish at the catchment scale. After removing seasonal effects, 74.9% of the variation in the relative occurrence of fish was explained by the measured environmental variables and biotic components. Habitat uses by the Formosan salmon and shovelmouth minnow were distinct. The shovelmouth minnow occurred more frequently at sites with a high concentration of NH 3 -N and high proportions of gravel and riffles, while the Formosan salmon utilized sites at high elevations. Habitat uses by Formosan salmon of different size classes varied slightly. Juvenile and subadult salmon inhabited sites with lower temperatures and current velocities, but adult salmon occurred more frequently with large-grain-sized substratum. Our study showed that variations in the relative occurrence of fish in the Wuling basin were best explained by physicochemical parameters (38.8%), followed by substratum composition (11.4%). The variations exclusively explained by mesohabitat composition, seasonal effects, and biotic components were not significant. This conclusion has important consequences for local managers and conservationists. KEY WORDS: Physicochemical parameter · Substratum · Habitat composition · Biotic component · Chichiawan Stream · TaiwanResale or republication not permitted without written consent of the publisher Aquat Biol 10: 227-239, 2010 depended on fish species and size. Habitats being occupied by different size classes may reflect ontogenetic habitat shifts (Nowak et al. 2004), showing microhabitat segregation of fishes of different sizes (Greenberg et al. 1996, Mäki-Petäys et al. 1997. Many stream fishes also shift habitat use by season (Baltz et al. 1991, Harvey & Stewart 1991, Heggenes et al. 1991, Bonneau & Scarnecchia 1998, Nagayama & Nakamura 2007. Other factors, such as predation and competition, are of great importance in habitat use by stream fishes , Schlosser 1987, Greenberg 1994.Integration of catchment-scale considerations into management and conservation planning has recently gained momentum (Smith et al. 2003). Most of the above-mentioned studies on habitat use by stream fishes focused on attributes at the scale of the microhabitat (i.e. the position of the fish) or mesohabitat (i.e. riffles and pools). For stream management, knowledge of habitat requirements at the micro-or mesohabitat scale is valuable in mitigating the effects of habitat alterations caused by stream regulation and restoring stream habitats for fish conservation. However, habitat prefere...

Trophic model of the subtropical headwater stream habitat of Formosan landlocked salmon Oncorhynchus formosanus

“…Habitat uses by salmon and the sympatric shovelmouth minnow were distinct. Hsu et al (2010) discovered that Formosan salmon used habitats which were subject to lower temperatures and were distributed in reaches at higher elevations than those of shovelmouth minnow. The diet composition matrix also demonstrated that the Formosan salmon is insectivorous, whereas the shovelmouth minnow relies heavily on algae.…”

“…Riffles are the major habitat in Chichiawan Stream and comprise > 80% of the stream area (Lin et al 2006 in the wet season (Hsu et al 2010). Consequently, the streambed consists of a high proportion of pebbles (42%) in the dry season (winter), but is dominated by rubble (26%) and boulders (21%) in the wet season (summer) (Lin et al 2006 inputs on downstream water quality and epilithic algae is significant (Yu & Lin 2009).…”

“…current velocity and water depth, Tsao et al 1998) were emphasized as important factors in the distribution of this fish. Up to 50% of the variation in the abundance of Formosan salmon can be explained by physicochemical parameters and substratum composition (Hsu et al 2010), but the importance of trophic relationships on the abundance of Formosan salmon has received much less attention.…”

The effects of storm-induced events on the seasonal dynamics of epilithic algal biomass in subtropical mountain streams

“…Streambed composition varied seasonally, consisting mainly of 39% pebbles and 27% cobbles in the dry season and 44% boulders in the wet season. The catchment of the KSS is covered by natural forests, and no agricultural activity occurs along the stream (Yu and Lin 2009;Hsu et al 2010). The YSS is located downstream of the CCWS and is 11.4 km long with a mean gradient of 68 m km À1 and a catchment area of 31 km 2 .…”

Complete mitochondrial genome of Oncorhynchus masou formosanus (Jordan & Oshima, 1919) (Pisces, Salmonidae)

“…The landlocked salmon of Taiwan, Oncorhynchus masou formosanus (Jordan & Oshima 1919), was listed as Critically Endangered by the IUCN in 1996 (Kottelat 1996), which only distributed in the upstream of Dajia River (Hsu et al 2010). The total number of O. m. formosanus has increased from 200 to around 3000 through the efforts of repopulation and habitat recovery (Chung et al 2008).…”