Year Established: 2011 Start Date: 2011-03-01 End Date: 2012-02-28
Total Federal Funds: $2,000 Total Non-Federal Funds: $850
Principal Investigators: Shane Vatland
Abstract: Multiple anthropogenic activities have contributed to the widespread loss and degradation of fish habitat in Montana streams, relative to pre-European settlement. As a result, stream networks often exhibit periods of low discharge and high summer water temperatures. In fact, stream conditions can limit the distribution and abundance of both native and nonnative stream fish, especially coldwater obligates, thus coldwater thermal refugia are critical for the survival of several fish species in these degraded stream networks. In the upper Big Hole River watershed of southwestern Montana, stream fish habitat is degraded by low summer discharge and summer water temperatures regularly exceeding 25 C. Despite these degraded habitat conditions, this stream network supports the only reproductively viable population of fluvial Arctic grayling remaining in the coterminous United States (representing less than 5% of the historic distribution in Montana); however, the distribution and abundance of this population is declining. The availability and use of coldwater refugia by Arctic grayling may be a critical factor affecting summer survival in this system and, concomitantly, the persistence of the last remaining fluvial Arctic grayling population in Montana. There is also a very popular nonnative salmonid sport fishery in the upper Big Hole River Basin, and in contrast to fluvial Arctic grayling, the distribution of some nonnative salmonids (e.g., brown trout) is expanding. Therefore, it is critical to obtain information concerning the use of coldwater refugia by nonnative salmonids because negative interactions between nonnatives and Arctic grayling could be mediated by the availability and use of critical coldwater habitats.