Present status and conservation of the markless forms of stream-resident masu salmon Oncorhynchus masou (the so-called 'iwame') in Japanese mountain streams

Yuichi Kano, Takuya Kondou, Yoshitaka Shimizu

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

As a markless form of stream-resident masu salmon (Oncorhynchus masou), the so-called 'iwame,' which can be distinguished from the sympatric normal form of the salmon by their plain body pattern, has been previously reported among seven local populations (A-G) in Japanese mountain streams. In the present study, all populations but B (where any information is entirely missing) were surveyed in a snorkeling survey (detection rate: 34.7%) in 2005 to elucidate the recent conditions of the markless forms. The ratios of the markless forms were 13.0% (9/69), 0.0% (0/364), 5.6% (68/1,205), 0.8% (1/132), 0.0% (0/1,181) and 64.6% (155/240) in A, C, D, E, F and G, respectively. Markless forms might indeed be already extinct in C and F where the stocking of non-native hatchery individuals has been carried out extensively. The same survey was repeated in D in 2009: the markless ratio had significantly decreased to 2.4% (19/783), although the reason for this was unknown. In D, the ratio of the markless form was higher in the mainstream as opposed to the tributaries in both 2005 and 2009, which might imply that the habitat of the markless form differs from that of the normal form.

Original languageEnglish
Pages (from-to)78-84
Number of pages7
JournalIchthyological Research
Volume57
Issue number1
DOIs
Publication statusPublished - Jan 1 2010

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Oncorhynchus masou
mountain stream
mountains
hatchery
hatcheries
salmon
tributary
habitat
habitats
detection
stocking
rate
plain

All Science Journal Classification (ASJC) codes

  • Ecology, Evolution, Behavior and Systematics

Cite this

Present status and conservation of the markless forms of stream-resident masu salmon Oncorhynchus masou (the so-called 'iwame') in Japanese mountain streams. / Kano, Yuichi; Kondou, Takuya; Shimizu, Yoshitaka.

In: Ichthyological Research, Vol. 57, No. 1, 01.01.2010, p. 78-84.

Research output: Contribution to journalArticle

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