Native Trout Fly Fishing: Chewaucan Basin Redband Trout

Chewaucan Basin Redband

Oncorhynchus mykiss newberrii

A Chewaucan basin redband from an Oregon desert stream

Introduction

Chewaucan basin redbands are native to streams flowing into Lake Albert and Summer Lake in south-central Oregon. These fish are thought to be most closely related to the redbands of Goose Lake and the Warner Valley and are currently classified as part of the subspecies Oncorhynchus mykiss newberrii (Behnke 2002).

Life History Information

During the Pleistocene period the Chewaucan basin was filled with a large lake, today Summer Lake and Lake Albert are all that remain of this ancient lake. These two lakes highly alkaline and as such are barren of fish (Behnke 1992). There are currently four streams in the basin that contain populations of native redbands, one flowing into Summer Lake and three flowing to Lake Albert (ODFW 2005). The most common life histories exhibited by the trout in the basin are fluvial and stream resident. The fluvial population spawns in the upper reaches of the watershed, than migrates to the lower reaches of the river where they feed and overwinter. Historically adfluvial fish also occurred in the basin, but the draining of the Chewaucan Marsh and construction of weirs which blocked migration eliminated this life history (ODFW 2005). In 1994 the Rivers End Reservoir was constructed near the mouth of the Chewaucan River and since then large migratory fish have been spotted in several streams since indicating that this life history (ODFW 2005).

Status

The Oregon Department of Fish and Wildlife (ODFW) considers the redbands native to the Chewaucan basin to be potentially at risk of extinction, with degraded habitat conditions and barriers to migration presenting the greatest threats to these fish. The Chewaucan Marsh was historically an important feeding and overwintering habitat for these redbands, but it was diked, channelized and drained for agricultural purposes (ODFW 2005). Migration to the Chewaucan Marsh and Rivers End Reservoir was also blocked by several irrigation weirs, but in 2006 fish ladders were constructed at the weirs to restore access to spawning habitat found in the upper reaches of the basin (ODFW 2005). The destruction of riparian vegetation, erosion and headcuts caused by livestock has also been an issue throughout the basin. Non-native fish present another threat to Chewaucan basin redband population, through hybridization, competition and predation. Hatchery rainbow trout were stocked throughout much of the basin up until 1998, and Behnke (1992) showed that there was at least some hybrid influence present in fish from the Chewaucan River drainage. The main threats today come from competition and predation from introduced largemouth bass and brown bullheads which are found in the lower reaches of the river and brook trout in the upper parts of the watershed (ODFW 2005).

Description

The coloration of these fish is olive or bronze on the back and transitions to a greenish-yellow or yellowish color across the body. These redbands have a pink to brick red stripe along their lateral line, and their gill plates are a rosy color. The spotting pattern consists of small irregular shaped spots that are distributed primarily above the lateral line, but may occur below the lateral line on some fish. Spots are also found on the caudal and dorsal fins. Purplish colored elliptical shaped parr marks are often retained into maturity in stream resident fish, but may fade away in larger migratory individuals. The fins are orange, with the caudal fin being forked. The dorsal fin may be tipped with either white or orange and the lower fins are tipped with white.