Habitat factors affecting the distribution and abundance of the spinous loach Cobitis shikokuensis in southwestern Japan

Abstract

We examined habitat factors related to the distribution and abundance of the spinous loach Cobitis shikokuensis, an endangered benthic fish, in the Shigenobu River system, southwestern Japan. In the study river, the spinous loach was distributed widely along the main stem, from headwater to near the mouth, whereas it was rarely found in tributary streams. Classification tree analysis showed that the presence/absence of spinous loach was explained by a combination of percent pebble and length of river fragment between artificial barriers. Spinous loach incidence was high in sites with abundant pebble ([27.7%), but low in sites with short river fragment (B0.97 km) even if pebbles were abundant. A regression tree model for loach density retained only percent pebble as a single best predictor, with sites with higher percent pebble ([40.4%) having higher density. These results suggest that substrate condition is an important factor determining the distribution and abundance of spinous loach and also that habitat fragmentation by artificial barriers has great potential to threaten the spinous loach population in this river. Considering the highly fragmented situation of the study river and prevention of upstream migration by barriers, we conclude that maintenance of suitable habitats in upper reaches has high priority for conservation of the spinous loach.

Comparison of DNA metabarcoding and morphological identification for stream macroinvertebrate biodiversity assessment and monitoring

“…From the mid-to lower reaches of the river, the channel is braided (bankfull width approximately 300 m maximum), and the flow tends to be intermittent owing to a thick channel layer of alluvial deposits. At present, there are three intermittent reaches in the river (upper: 18–22 km from the mouth; middle: 10–16 km; and lower: 4.9–7.4 km) (Kawanishi et al, 2011). Macroinvertebrate samples were collected from 10 sites longitudinally located from the headwater to the lower reaches of the Shigenobu River (elevation range: 4–405 m; Table 1, and Fig.…”

Effects of sedimentation on an endangered benthic fish, Cobitis shikokuensis: is sediment‐free habitat a requirement or a preference?

“…Indeed, during the field investigation for our previous study (Kawanishi et al. ), we found no C . shikokuensis individuals in tributaries where the catchment had been largely converted to agricultural lands (R. Kawanishi, unpublished data).…”

“…This loach is thought to be affected by habitat degradation caused by human activities and has been designated as endangered by the Ministry of the Environment. Our previous study revealed that among-reach variations in the abundance of C. shikokuensis within a river system were primarily related to substrate conditions (Kawanishi et al 2011). We also reported selective use of sediment-free substrate by this species (Kawanishi et al 2010).…”

“…The excessive input of fine sediment to waterways due to human activities, such as logging, agricultural use and urban development, is a serious problem for this endangered species. Indeed, during the field investigation for our previous study (Kawanishi et al 2011), we found no C. shikokuensis individuals in tributaries where the catchment had been largely converted to agricultural lands (R. Kawanishi, unpublished data). The results of the present study strongly suggest that C. shikokuensis populations are threatened due to increased sedimentation via agriculture and that it is important to examine the detailed relationships among land use, fine sediment deposition and the distribution of C. shikokuensis to promote the conservation of this endangered species.…”

“…shikokuensis within a river system were primarily related to substrate conditions (Kawanishi et al. ). We also reported selective use of sediment‐free substrate by this species (Kawanishi et al.…”