Kern River Rainbow Trout

Oncorhynchus mykiss gilberti

Native Trout Fly Fishing

A darkly colored Kern River rainbow trout from a small stream in southern California.

Introduction

The Kern River rainbow trout inhabits the mainstem of the Kern River and several of its tributaries above Lake Isabella. This fish is thought to be an intermediate form between golden trout and rainbow trout, which are thought to have gained periodic access to the basin during the Pleistocene epoch (Behnke 2002). The colorations of these fish is more subdued than that of the two golden trout subspecies, but is more brilliant than that of coastal rainbow trout.

Life History Information

As the native range of the Kern River rainbow trout includes the main Kern River and its tributaries these fish exhibit both stream resident and fluvial life history strategies. Like other varieties of rainbow trout the Kern River rainbow trout are generalists. This means that they will opportunistically feed on what is available and as such aquatic and terrestrial invertebrates make up the majority of their diet. Due to the larger size of the Kern River and greater availability of food, fluvial fish in the Kern River have been known to reach sizes up to 28 inches and 8 pounds, while small stream resident fish usually have a maximum size of about 12 inches. According to Behnke (2002) these fish typically spawn in April and May, with the first spawning occurring at an age of two to four year old.

Status

Very little is known on the overall status of the Kern River rainbow trout and it is currently unknown how many, if any pure populations remain today. Hybridization with introduced rainbow and golden trout is thought to be the biggest threat to these fish (Moyle et al. 2008). Hatchery rainbow trout have been continually stocked in the Kern River and its tributaries for more than 90 years and the fish found in the Kern River show evidence of hybridization (Behnke 2002). Beyond hybridization, non-native brook, brown and rainbow trout compete with and prey on the Kern River rainbow trout further jeopardizing their continued existence. Typical causes of habitat degradation, such as grazing and recreational use of the area also suppress Kern River rainbow trout populations. When I fished for these trout in 2007, cattle were grazing right up to the banks of stream and cave-ins and other issues associated with grazing were common. As such I found the population of Kern River rainbows in this stream to be quite depressed and had a difficult time finding any trout.

Description

The Kern River rainbow trout is much more brilliantly colored than the typical rainbow trout. The coloration of the backs on these is ranges from a greenish-olive to a bronze color. The side of the body is a golden yellow color, but is much more subdued than on the other to golden trout subspecies and can be quite dull in some fish. Their bellies are typically an orange color, but once again are much more subdued than the other golden trout subspecies. The spots on the Kern River rainbow trout are smaller, more irregular shaped and more profusely distributed than on the two golden trout subspecies and are typically found across the entire body, instead of being isolated above the lateral line. Juvenile or small stream fish typically display around ten purplish colored parr marks along the lateral line. A crimson colored stripe is found along the lateral line, and a similar color is found on the gill plates. The fins are a yellow or orange color and the pelvic, anal and dorsal fins are darkly bordered and tipped with white.

Native Range

Native Trout Fly Fishing

A map of the native range of the Kern River rainbow trout. Data Source: Behnke (2002).