Coastal Cutthroat Spawn and Over-Summer in Intermittent Island Streams

There are more than 30 watersheds in the San Juan Islands ranging from less than a square kilometer to 25 square kilometers in extent, rising from bogs, fens, and vernal pools.  As development encroaches on wetlands and impounds runoff, streamflows have declined, and the duration of low- to zero-flow conditions in summer and fall has increased.  Coastal cutthroat, both sea-run and resident, nevertheless continue to reproduce in at least five intermittent streams where dry season flows are barely 0.1 cfs and glides disappear completely for up to four months.  Island cutthroat ascend streams in fall, dig redds in April to May, and juveniles may occupy small stream pools for six months to a year before outmigrating.  Juvenile survival and activity in shallow stream pools at 14-18 degrees Celsius was video documented over several dry seasons.  Oral history and genotyping of individuals brought to hand suggests that at least one stream population is a distinct native relic not influenced by plantings by state agencies or sports fishers.  There is an urgent need to protect stream sources: one of the five stream populations in the islands was extirpated by a private impoundment during the course of this study.