Document Type

Thesis - Open Access

Award Date

2018

Degree Name

Master of Science (MS)

Department

Natural Resource Management

First Advisor

Steven R. Chipps

Abstract

Density-dependent growth is often observed in stream-dwelling Brown Trout Salmo trutta populations. In Spearfish Creek, South Dakota, biomass of adult Brown Trout (>200 mm) is about three times greater than that reported for similar Black Hills streams while mean length of adult fish is about 30% less. Here, we evaluate large-scale density reduction as a management tool for improving growth rate of stream-dwelling Brown Trout. We compared age-specific growth of wild Brown Trout in stream sections receiving 50% reductions in fish abundance. We also assessed the effect of fish density manipulation on Brown Trout movement patterns and home range size. We compared gross movement, net movement and home range size of Brown Trout between stream sections with targeted fish removals to sections with natural fish densities. Annual growth in length and weight of older Brown Trout (> age 2) generally increased following fish removals; we observed significantly greater growth for age 3 and 4 fish (162 to 258 %, g/y) in stream sections receiving density reductions. Bioenergetics modeling revealed that total, annual consumption by smaller Brown Trout (ages 1 and 2) was dominated by aquatic invertebrates (91 %) with terrestrial invertebrates comprising only (9%). In contrast, larger Brown Trout (ages 3-6) consumed more terrestrial prey (35%) in order to meet annual energy requirements. In most cases, consumption of aquatic invertebrates by

large Brown Trout was insufficient to meet annual maintenance requirements. As a result, we postulate that growth rate of larger fish is more responsive to density reduction, owing to constrains imposed by availability of aquatic invertebrates. Additionally, we found no evidence that movement patterns or home range size of stream-dwelling Brown Trout differed between sections with natural densities and those where fish density was reduced. There was no relationship between fish density and fish movement parameters or home range size. Brown Trout in Spearfish Creek exhibited limited movement and home range sizes following reductions in fish density. Brown Trout tracked during fallwinter months were observed exhibiting larger gross movement and home range size presumably related to fall spawning activities, although net movement was similar to spring/summer periods – indicating strong site fidelity. A small proportion of radiotagged (6%) trout exhibited extended movements (> 0.6 km), typical of straying behavior in salmonids. Many factors have been shown to effect variability of movement of streamdwelling Brown Trout, however, it does not appear that density or large-scale density reduction is among them. Improved growth rate and reductions in intraspecific competition during our study (~1 year) coupled with negligible immigration from natural high-density sections are promising for large-scale density reductions as a management technique to improve the growth of stream-dwelling Brown Trout.

Library of Congress Subject Headings

Brown trout -- South Dakota -- Growth.
Brown trout -- South Dakota -- Geographical distribution.
Fishery management -- South Dakota.
Fish populations -- South Dakota.

Description

Includes bibliographical references

Format

application/pdf

Number of Pages

107

Publisher

South Dakota State University

Rights

p>In Copyright - Non-Commercial Use Permitted
http://rightsstatements.org/vocab/InC-NC/1.0/

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