Efficacy of otolith microchemistry to determine natal origin and movement of westslope cutthroat trout and redband trout
July 2012 - September 2013
- US Geological Survey
Project need and justification: Native salmonids have experienced declines in distribution and abundance throughout the western U.S (Behnke 2002). For instance, cutthroat trout Oncorhynchus clarkii have one of the broadest native distributions of any salmonid in North America and are found in a variety of habitats, including small streams, large rivers, and lakes. Unfortunately, cutthroat trout have drastically declined across their distribution. Of the 14 recognized subspecies of cutthroat trout, two subspecies have gone extinct, two subspecies are federally listed as threatened, and several subspecies have been petitioned for listing under the Endangered Species Act. Similar patterns of decline have been experienced by Pacific salmon Oncorhynchus spp., bull trout Salvelinus confluentus, and redband trout O. mykiss (inland form of rainbow trout) across the western U.S. Although Pacific salmon and bull trout are species of high conservation concern in Idaho, westslope cutthroat trout O. clarkii lewisii and redband trout are of considerable interest because they are not only species of conservation concern, but also provide important recreational fisheries. Lake Pend Oreille, located in northern Idaho, is the largest and deepest lake in Idaho. Native salmonids in the system include bull trout and westslope cutthroat trout; however, their numbers have declined due to habitat degradation, interactions with nonnative species, and barriers to movement. Cutthroat trout are further threatened by hybridization with introduced rainbow trout. With regard to cutthroat trout, extensive effort has been expended by the Idaho Department of Fish and Game (IDFG) to monitor the abundance of cutthroat trout in tributaries to Lake Pend Oreille, but little is understood about the origin of fish found outside of tributary habitats (i.e., westslope cutthroat trout in the system are adfluvial). Understanding the natal origin of cutthroat trout in the lake would greatly enhance the ability of managers to evaluate factors influencing recruitment dynamics and help guide conservation actions in the basin. The Kootenai River is located just north of Lake Pend Oreille and has been highly altered due to extractive land use in the watershed (e.g., mining, timber harvest) and water development (i.e., dam construction). In addition to burbot Lota lota and the federally-endangered Kootenai River white sturgeon Acipenser transmontanus, redband trout are a species of interest in the basin. Redband trout serve an important ecological role and also provide an increasingly important sport fishery. Redband trout spawn in small tributaries and then move downstream to the Kootenai River. Much like the situation in Lake Pend Oreille, the origin of fish in the Kootenai River is unknown. Questions associated with residence times and movements between tributaries of redband trout have also hindered management efforts. Because the population is thought to be recruitment limited, identifying tributaries that are contributing to the mainstem population of redband trout and describing movement of fish within the system is a high priority. Describing and quantifying recruitment dynamics is one of the most important yet most difficult tasks faced by fisheries ecologists. A number of techniques have recently emerged that allow scientists to investigate recruitment and movement of fishes (Barnett-Johnson et al. 2005). In particular, chemical signatures in the hard structures (e.g., fin ray, otolith, scales) of fish have been demonstrated as a useful tool for defining the origin and movement of fishes (commonly known as microchemistry techniques; Muhlfield et al. 2012). Unique chemical components of the water are incorporated into hard structures and provide a history of where an individual fish was hatched and lived. However, chemical signatures are influenced by the underlying geology of a region and areas (e.g., tributaries) with similar geology may not lend themselves to microchemistry techniques (Barnett-Johnson et al. 2008). Thus, an initial evaluation of water chemistry and fish signatures is needed before resources are expended on implementing microchemistry techniques to answer research questions. The purpose of this project is to evaluate whether or not microchemistry techniques are useful for determining natal origin and movement of fishes in the Lake Pend Oreille and Kootenai River systems. Expected benefits: The proposed project provides a number of important benefits. Because the research questions and management problems were brought to the PIs by our Cooperators, there is substantial interest in the project. Determining whether or not microchemistry analysis will be a useful tool is critical for moving forward with other research efforts in the region. If the geology and water chemistry are such that the technology “works”, at least two graduate projects will be developed that use the technique to evaluate recruitment and movement. These projects are likely to be funded by IDFG, Avista Utilities, and the Bonneville Power Administration. The proposed project also provides one of the PIs (MCQ) and at least one of his graduate students (Steven Whitlock, MS student at the University of Idaho) experience with an important emerging technology, provides the other PI (SAC) the opportunity to further develop his expertise with microchemistry techniques, and provides an opportunity for inter-Unit collaboration.