Food Web Interactions in Pyramid Lake, Nevada: Factors Influencing Lahontan Cutthroat Trout Growth and Production

Lahontan cutthroat trout, Oncorhynchus clarkii henshawi (LCT), currently occupy 0.4% of their native lacustrine habitat and are listed as threatened under the ESA.  In Pyramid Lake, Nevada, this species provides subsistence for the Pyramid Lake Paiute Tribe, is a popular sport fish, and is the top predator in the aquatic food web.  The primary focus of this study is to investigate food web interactions that may limit LCT growth or survival.  Since extirpation of naturally-reproducing individuals in 1942, LCT in Pyramid Lake have been maintained through stocking programs; however, these hatchery LCT fail to reach pre-extirpation sizes and their survival rates are unknown.  We hypothesized that: 1) LCT are food limited, and 2) compete with Sacramento perch (Archoplites interruptus) for both vertebrate and invertebrate prey.  We assessed food web structure and inter-specific interactions by comparing species distribution, diet, and stable isotope data.  We observed strong evidence for competition between LCT and Sacramento perch.  Netting data indicated that tui chub (Gila bicolor) and Sacramento perch generally occupied littoral habitat while LCT were more widely dispersed during the summer sampling period.  These observations suggest that LCT may be limited by thermal constraints and prey availability during some seasons.