Wildland Fire: An Opportunistic Event for Reintroducing a Native Salmonid

Abstract

The Missionary Ridge Fire (summer 2002) burned approximately 28 520 ha in the San Juan Basin, Colorado. Prior to the fire, no native Colorado River cutthroat trout (Oncorhynchus clarki pleuriticus) had been observed in the San Juan Basin for over 100 yr due to over-fishing, introduction of non-native fishes, and habitat alteration. Mud and ash flows into the Florida River in fall 2002 and spring 2003 resulted in a complete fish kill of non-native rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta). Between 2003 and 2007, the Colorado Division of Wildlife released 138 728 Colorado River cutthroat trout ranging from 5 cm to 35 cm in length within a 22.5 km reach of the Florida River. Two barriers, a reservoir dam and an irrigation diversion dam, prevented non-native fish from entering this reach. Each fall from 2003 through 2007, we surveyed two locations on the Florida River and estimated population size. Heavy silt deposits and extremely high river flows (3.8 m3 s-1) precluded us from making population estimates during 2003 to 2005. The catch of Colorado River cutthroat trout decreased from 76% in 2006 to only 44% in 2007. Interspecific competition and predation by rainbow and brown trout, whirling disease (Myxobolus cerebralis), and extreme fluctuations in regulated river flows in 2007 may have contributed to the observed decline in cutthroat trout. It is still too early to conclude whether reintroduction efforts of Colorado River cutthroat trout have been successful, but early indications suggest non-native trout are beginning to re-colonize this section of the Florida River at the expense of the cutthroat trout.