Water Resources Research Act Program

Details for Project ID 2006MT92B

Impacts of beaver on invasion ecology of brook trout (salvelinus fontinalis)

Institute: Montana
Year Established: 2006 Start Date: 2006-03-01 End Date: 2007-12-31
Total Federal Funds: $30,000 Total Non-Federal Funds: $60,000

Principal Investigators: Lisa Eby, Magnus McCaffery

Project Summary: As a keystone species, beaver promote the creation and maintenance of wetland areas, provide complex habitat for wildlife and fish, improve water quality, and augment late season flows. Beaver ponds create excellent juvenile rearing and overwintering fish habitat resulting in substantial benefits to native fish species (8, 19). Promoting beaver either through natural population expansion or active transplantation for watershed restoration purposes is gaining favor with some landowners and managers, but is a very controversial strategy. Aside from direct human-beaver conflicts such as flooding of agricultural lands and damming of irrigation systems (8), there is also the possibility of negative effects on native fish such as, barrier creation and the potential of beaver ponds to facilitate invasion by exotic fish species. In Montanan streams, brook trout are an exotic species whose invasion often displaces native cutthroat trout through competitive interactions (37). Even though many of Montanas native species often benefit from beaver ponds, it has also been suggested that the more pool-adapted and temperature tolerant brook trout have a competitive edge in beaver ponds over more riffle-adapted colder water species (8, 15). Use of these habitats as source populations may then enable their colonization of colder sink habitats, thus sustaining invasions across a larger range (37, 41). Beaver ponds may therefore (i) be detrimental to natives through the creation of warmer, pool habitat that gives brook trout a competitive advantage, or (ii) act as a buffer, facilitating coexistence of both species by adding habitat size and complexity. The proposed research will examine whether beaver ponds mediate brook westslope cutthroat trout interactions. First, we will begin to mechanistically examine if and how beaver ponds may mediate brook trout invasions across southwestern Montana and influence interactions with westslope cutthroat trout. Seasonal sampling and mark-recapture efforts will allow us to determine whether streams with beaver ponds affect overlap between brook trout and westslope cutthroat trout distributions, alter brook trout and cutthroat trout abundances, and influence juvenile trout growth rates in streams with beaver ponds over those without. Secondly, given the potential importance of temperature as a driving factor, we will examine whether beaver ponds alter stream temperatures. We predict that beaver impoundments will increase temperatures at and below the impoundment. This question will be answered by deploying a series of temperature loggers in streams with and without beaver ponds.