By Paul Divine and Dave Lenz
Anglers from near and far have long enjoyed fishing for the large rainbow trout that is endemic to Eagle Lake, northwest of Susanville in Lassen County. Eagle Lake is the second largest natural lake that is entirely located in California. The lake is found within the larger Lahontan basin of western Nevada. Because of its location in a closed basin, the lake concentrates dissolved materials and has high alkalinity and pH conditions (pH 8.4-9.6). These conditions are too harsh for other rainbow trout species and may have caused the elimination of all introduced non-native fish species in the lake. Besides the Eagle Lake rainbow trout, the lake supports four native Lahontan fish species: Tahoe sucker, Eagle Lake tui chub, speckled dace and Lahontan redsides. One non-native species, brook trout, does exist in the Pine Creek headwaters – over 20 miles upstream from Eagle Lake.
Since the late 1950’s Eagle Lake rainbow trout have needed to be sustained by a hatchery program. Deteriorated habitat conditions prevent self-sustaining reproduction in Pine Creek, Eagle Lake’s only tributary capable of supporting spawning and rearing. The goal for restoration at Eagle Lake is to improve habitat conditions so that these large trout can successfully migrate to suitable spawning areas in Pine Creek, spawn in natural conditions, and have young trout return to the lake.
It is likely that natural conditions (precipitation, stream flow, and fish migration passage) in this arid location frequently prevented successful migration, spawning and rearing from occurring due to insufficient water volume in the water course. Eagle Lake rainbow trout may have adapted to these conditions with a long life span strategy, living as many as eleven years – which helps improve the odds of surviving through periods of poor conditions to times when conditions favor successful spawning and rearing of young. One of the chief obstacles for Eagle Lake rainbow to successfully reproduce in the Pine Creek headwaters is the presence of brook trout. These non-native trout were introduced many decades ago and compete for limited habitat and may prey on the young Eagle Lake rainbow trout.
As part of the SWAP update, conservation strategies are being developed to improve stream conditions to support spawning and rearing in Pine Creek as well as migration of both adult and young Eagle Lake rainbow trout to and from Eagle Lake and Pine Creek. These strategies are focused on improving fish habitat through: repairing degraded stream channel and reducing erosion due to past and present land management practices, better use of the limited water supply to improve stream flow, removal of existing migration barriers to improve fish access to available habitats, and removal of non-native brook trout to improve spawning and rearing success. The overarching goal of these strategies is to improve the connectivity between the lake and streams and create habitat conditions so that Eagle Lake rainbow trout regains a self-sustaining population within the watershed, while other native species occurring in this watershed also receive conservation benefits by the implementation of these strategies.