title: Seasonal and age-based aspects of diet of the introduced redside shiner (Richardsonius balteatus) in Ross Lake, Washington
Creators: name: Welch, Carmen Ann
Publisher: name: Western Washington University
Year: 2012

description: <p>This study investigates the introduced population of the Redside Shiner (Richardsonius balteatus) in Ross Lake, Washington. The Redside Shiner was introduced to Ross Lake around 2000 and in the summer months, can be found in densities of hundreds per cubic meter in the shallow areas of Ross Lake. Ross Lake is a protected thirty-five and a half kilometer long reservoir in North Cascades National Park with cold, clear water of exceptional quality. Fish native to Ross Lake include: Bull Trout, Dolly Varden and Rainbow Trout. It is a commonly held belief that the introduced Redside Shiner have no negative effect on the native fish in Ross Lake and that they benefit the native fish as a source of prey. However, previous studies in other lakes have reported reduced growth and survival of juvenile Rainbow Trout as a result of the introduction of the Redside Shiner. Considering the conflict about the potential effects of the introduced Redside Shiner in Ross Lake, the two main goals of this study were to determine what the Redside Shiner in Ross Lake consumes and to evaluate the potential threat of long-term impacts to the native fish in Ross Lake. Samples were collected from three different locations in the lake across all seasons. Age was determined for 178 Redside Shiners and the stomach contents of 271 Redside Shiners were evaluated. Samples were collected to represent northern, middle and southern areas of Ross Lake. Collection occurred in the winter, spring, summer and fall. Age determination showed the samples consisted of Redside Shiners ages 0 to 6. Regardless of location, season and age, zooplankton and insects are the most important diet categories to the Redside Shiner in Ross Lake both in terms of frequency of occurrence and percent volume of total diet. They also consume oligochaetes, cestodes, algae and other unidentifiable incidental items such as wood, sediment and what appears to be plastics, however none are of much importance. Based on my findings, the Redside Shiner likely competes with the native fish in Ross Lake for food. The competitive juvenile bottleneck theory explains the potential for a predator to be negatively impacted from its prey due to competition with its juveniles. Like the Redside Shiner in Ross Lake, the juvenile native fish may also depend primarily on aquatic insects and zooplankton. Unless food resources are partitioned spatially and seasonally, the competitive juvenile bottle neck theory holds merit in Ross Lake and direct competition between the introduced Redside Shiner and the native fish seems likely. Based on back-calculated ages of the Redside Shiner in Ross Lake, this population seems to be stable with the potential to persist in high numbers into the future, forecasting that the risk for competition may also persist into the future. Considering the potential for competition now and into the future, further research is required to generate information about the dietary habits of the juvenile native fish, their spatial distribution and how they use the different habitats in Ross Lake.</p>