Recipient Organization
UNIVERSITY OF NEVADA
(N/A)
RENO,NV 89557
Performing Department
Natural Resources & Environmental Sciences
Non Technical Summary
The historic distribution of the Lahontan cutthroat trout (LCT) was throughout Pleistocene Lake Lahontan, a lake that covered northwestern Nevada and northeastern California. In the past century populations of the fish have been declining, and today, there are pure, self-sustaining populations in only 0.4% of the historic lake habitat and 7% in historic stream habitat, including Summit Lake, Independence Lake, the headwaters of the Humboldt River, and tributaries of the Truckee, Walker, and Carson Rivers (Hodge). The fishery at Summit Lake is well known for supporting the single secure lacustrine population of LCT remaining in its native range (USFWS 1994). LCT were listed as endangered by the USFWS in 1970, and were reclassified in 1975 to facilitate management and allow angling in specific locations. The USFWS Lahontan Cutthroat Trout Recovery Plan (1994) (Recovery Plan) lists several recovery actions for the stabilization of populations and delisting of the species. These actions include securing habitat and managing LCT populations, conducting biological studies and research to validate recovery objectives, and coordinate fisheries management activities to complement LCT conservation. In the description of securing habitat and managing LCT populations, several goals are specific to the Tribe's management of the Summit Lake population of LCT. Goal 15185 is to "manage minnow populations in Summit Lake," with the directive that "interactions between minnows and LCT need to be investigated to determine if minnows significantly reduce the viability of the LCT population" (USFWS 1994). Currently there has been little research or monitoring of the trophic status or bioenergetics of the lake.The last food habit or stomach analysis study of the LCT revealed that they were not utilizing the newly introduced minnows as a food source (USFWS 1977). This relationship may have changed dramatically in the past several decades and an updated study of the food habits of LCT is necessary to facilitate their continued recovery. In addition, the previous study indicates that interspecific interactions and the level and impact of the competition of the minnows with LCT for possible food sources is unknown (USFWS 1977).
Animal Health Component
100%
Research Effort Categories
Basic
(N/A)
Applied
100%
Developmental
(N/A)
Goals / Objectives
The objectives of this project are to understand the fishery and food web energetics of Summit Lake to assist managers in planning future monitoring and management activities. Specifically the goals are to 1) validate whether there is a need for management of minnows in the Summit Lake aquatic ecosystem, 2) Define the trophic status and bioenergetics of the Summit Lake aquatic ecosystem, and 3) Educate tribal members as well as broader stakeholders involved with LCT restoration in the Lahontan basin.
Project Methods
Resource dependencies on benthic versus pelagic habitats will be made for minnows previously thought to compete for food resources with LCT. Gut content methodology represents ingested but not necessarily assimilated food resources. Using mass spectrometry, the ratios of heavy to light isotopes of carbon and nitrogen are measured. These isotopic ratios are expressed relative to predetermined standard materials, providing natural stable isotopic 'signatures', which can be characterized for any tissues that contain these elements. 13C values are the same between predator and prey, but differ among benthic algae and phytoplankton. Thus, it is possible to estimate the degree to which each fish at varying size classes is supported by a benthic vs. pelagic food chain. Delta nitrogen signatures increase predictably up the food chain, thereby reflecting fish trophic height or food chain length. The two approaches used in concert provide complementary and useful information about food web structure (Vander Zanden et al. 1999). Benthic invertebrate samplings for biomass and isotopic signatures are also part of determining the lake food web structure. Two sampling events will occur.Two transects will be sited in the lake, where near shore samplings will be taken at random from up to 5 locations along each transect. In addition, zooplankton samples will be obtained from 8 week samplings collected from a central index sampling station used previously by the Tribe for the water quality monitoring program. The station will be monitored and the samples collected.The potential energetic of LCT based on their food resource utilization will be calculated using a bioenergetics model. Specifically, they can be used to determine growth rate changes at different age classes of fish resulting from food resource use. Utilizing temperature, habitat, and diet data of LCT from the first year of study, a model of the bioenergetics of Summit Lake will be created. The goal of this task is to determine the potential growth rates for various age classes of LCT, and thus, potential impacts from resource competition for food resources in Summit Lake can be determined for specific age classes in the lake. Special attention will be paid to LCT size at age where ontogenetic feeding shifts occur. Comparisons between predicted and observed growth rates determined from opercule annuli counts will be made for each age class. The Tribe will work with us to develop a curriculum for understanding natural resource issues.The workshop will be held in conjunction with the annual Tribal meeting. This workshop will be focused on showing Tribal members how the research has been conducted during the past summer, alerting them to why this research is important, and how the LCT that they fish are linked with the food web of the entire lake ecosystem. Advertisement will take place both in conjunction with and independently of the advertisement of the annual meeting, and the target audience will be Tribal members. The curriculum will be developed jointly by UNR and Tribal researchers based on the research and data collection of the previous summer, and will be administered by Tribal employees.