Recipient Organization
UNIVERSITY OF MONTANA
COLLEGE OF FORESTRY AND CONSERVATION
MISSOULA,MT 59812
Performing Department
College of Forestry and Conservation
Non Technical Summary
Many researchers and managers consider interbreeding with non-native species, such as rainbow trout (RBT), to be one of the greatest threats to the continued existence of westslope cutthroat trout (WCT). Current management of cutthroat trout and hybrids (offspring of WCTxRT) throughout the western United States relies on one of two major assumptions: cutthroat trout and hybrids are not different, or cutthroat trout and hybrids are different. This approach to management of a culturally important species is neither informative nor well informed. Taking conservative approaches that only non-hybrids should be considered cutthroat trout for conservation purposes may lead managers to drastic approaches such as barrier placement and eradication of viable populations of fish and potential loss of important fisheries resources. On the other hand, assuming morphological similarity is the same as ecological similarity may lead to irreversible changes in the ecological role of trout if hybridization continues to spread. The results of my research will serve as a first-step toward understanding the ecological consequences of hybridization in a system where rainbow trout are introduced. The research has three major objectives: 1. Understand the fine-scale population structure and distribution of hybrids in Jocko River trout populations; 2. Determine if there are life-history differences between WCT, RBT, and their hybrids related to migration timing, age at maturity, fecundity, and growth rate; 3. Complete computer simulations to explore the demographic consequences of isolating populations with barriers versus the risks of spreading hybridization in systems with open migration corridors. We will work the Confederated Salish and Kootenai tribes to collect tissue samples from fish throughout the watershed, DNA will be extracted and amplified using Polymerase Chain Reaction at multiple polymorphic microsatellite loci, of which several are diagnostic for hybridization between WCT and RBT. Researchers will conduct several tests for significant population structure, including tests for Hardy-Weinberg equilibrium, linkage equilibrium, allele frequency divergence, and population subdivision (Fst). Researchers will also calculate hybrid index scores for each individual fish assayed and complete tests to determine if population samples were collected from population groupings where introgression between WCT and RBT has led to total admixture (a hybrid swarm). Metasim is a program that links demographic and genetic information into a population model. By parameterizing this model to the Jocko, we can simulate the differences in both population growth rates and hybridization associated with different management scenarios. This research will also evaluate different alternatives and provide guidelines for selective passage management for fisheries management. This research will certainly not be the final work that settles the cutthroat hybridization debate, but it will be a crucial next step toward understanding this complex issue.
Animal Health Component
70%
Research Effort Categories
Basic
30%
Applied
70%
Developmental
(N/A)
Goals / Objectives
Many researchers and managers consider introgressive hybridization with non-native species, such as rainbow trout (RBT), to be one of the greatest threats to the continued existence of westslope cutthroat trout (WCT). This is a particularly challenging issue in the Clark Fork River drainage where protection and management of popular native cutthroat fisheries must be considered simultaneously with the management and conservation of world-class fisheries that prominently feature non-native fishes in the catch. Unfortunately, management for these two types of fisheries can come in conflict with each other when they are in the same river system. For example, a viable westslope cutthroat trout fishery should include a fluvial component, but maintenance of a fluvial life history requires suitable migration corridors that may be an open door for hybridizing invasive species. We have only a rudimentary understanding of when, how, and why hybridization spreads among WCT populations. This research in the Jocko River seeks to gain a better understanding of the management, evolutionary, and ecological implications of hybridization between WCT and RBT in one Clark Fork River watershed. The upper Jocko River is considered a stronghold for native WCT. Fish assemblages in lower elevation reaches of the Jocko River and tributaries are currently dominated by non-native fishes, including RBT and WCTxRBT hybrids. The mainstem Jocko River is an important fishery that can produce excellent catches of large migratory fish. The research has three major objectives: 1. Understand the fine-scale population structure and distribution of hybrids in Jocko River trout populations; 2. Determine if there are life-history differences between WCT, RBT, and their hybrids related to migration timing, age at maturity, fecundity, and growth rate; 3. Complete computer simulations to explore the demographic consequences of isolating populations with barriers versus the risks of spreading hybridization in systems with open migration corridors. Timeline: Field collection and lab analyses 2006-2009, dissertation writing 2010. Deliverables include a map of hybridized fish (RTxWCT) for the Jocko River watershed and a report describing the distribution of hybridization and a discussion of the value of specific populations as conservation populations. A dissertation that includes three chapters associated with the objectives. Several scientific presentations and publications at the MT and ID American Fisheries Society Meetings.
Project Methods
Confederated Salish and Kootenai Tribal Department of Natural Resources Fisheries Program researchers have identified the Jocko as a primary watershed of interest where they are going to collect non-lethal tissue samples from trout aggregations that may include WCT, RBT, and their hybrids. Currently this involves over 40 sites for sampling. In addition, the tribal biologists will collect migrating spawning fish at two fish traps along the Jocko for genetic analyses, fecundity, and growth. Fecundity will be determined by volumetrically and growth will be determined by otolith extraction, aging fish, and back-calculating growth rates. Tissue will be analyzed in the Montana Conservation Genetics Laboratory (MCGL) at the University of Montana, Missoula, where DNA will be extracted and amplified using Polymerase Chain Reaction at multiple polymorphic microsatellite loci, of which several are diagnostic for hybridization between WCT and RBT. Researchers will conduct several tests for significant population structure, including tests for Hardy-Weinberg equilibrium, linkage equilibrium, allele frequency divergence, and population subdivision (Fst). Researchers will also calculate hybrid index scores for each individual fish assayed and complete tests to determine if population samples were collected from population groupings where introgression between WCT and RBT has led to total admixture (a hybrid swarm). The simulation of population and genetic consequences to different management actions will be accomplished with the use of rMETASIM. This program is a metapopulation model (Strand 2002) that have a basic matrix population model base but that also follows alleles associated with population processes of mating and dispersal. This model will be parameterized using information collected in the Jocko River in this project and previously in the tribal fisheries program including growth rates, sex ratio, age of maturity, fecundity, dispersal, and size-specific survival rates.