Response of coastal stream habitat and juvenile steelhead to the Honeydew Fire in Humboldt County, California

Graduation Date

2012

Document Type

Thesis

Program

Other

Program

Thesis (M.S.)--Humboldt State University, Natural Resources: Fisheries, 2012

Committee Chair Name

Walter G. Duffy

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

Juvenile steelhead, Fish ecology, Salmonidae, Large woody debris, Humboldt State University -- Theses -- Fisheries, Pacific Northwest landscape, Water temperature, Effects of wildfires

Abstract

Fire plays an important role in shaping the Pacific Northwest landscape, including riparian areas. Riparian areas provide important habitat for many species of the family Salmonidae, including steelhead (Oncorhynchus mykiss). Over the last century, fire suppression has resulted in forests becoming denser and more prone to intense and catastrophic wildfires. Global climate change is expected to increase the frequency and severity of wildfires. With the general decline of salmonids throughout the Pacific Northwest, understanding the role that wildfire plays in fish ecology is of increased importance. To determine the effects of wildfire on steelhead, two burned streams (Kinsey Creek and Big Flat Creek) and one unburned stream (Spanish Creek), located in the King Range National Conservation Area, California were chosen. Each study stream had one to two years of pre-fire data. The study streams were monitored during the summer and early fall months over a three-year period post-fire to determine potential changes in fish habitat (pool depth, water temperature, large woody debris abundance and volume) or fish response (abundance, condition, mean size, and density). A lack of extensive pre-fire data prevented this study from reaching any conclusions about fire effects. However, I found a variety of apparent responses to fire. These apparent responses may be due to fire or could be a result of natural variation; I did not have the dataset needed to distinguish between them. There was some evidence of a post-fire reduction in pool depth in Big Flat Creek, particularly the first year post-fire, but not in Kinsey Creek. The maximum depth of pools in Spanish Creek varied little among years. Daily mean and maximum water temperature was lower the first year post-fire than it was pre-fire in both Kinsey and Big Flat creeks, both the burned streams. Daily mean and maximum water temperature was higher than it was pre-fire the second and third years' post-fire in Kinsey Creek while remaining lower the third year post-fire in Big Flat Creek. The observed increase in the mean of the daily mean and maximum temperature in Kinsey Creek was less than 1˚C. Post-fire temperatures in the study streams were in the preferred range of juvenile steelhead. Number of large woody debris pieces per 100 m increased post-fire in Big Flat Creek and volume of large woody debris per 100 m was greater three years post-fire than it was pre-fire. However, there was only one year of pre-fire LWD data in Big Flat Creek and LWD in Kinsey Creek did not appear to respond to fire, which both prevent the conclusion of a fire effect. In addition, LWD volume per 100 m in Spanish Creek was greater in the post-fire period than in the pre-fire period. Juvenile steelhead abundance in Big Flat Creek was significantly greater three years after fire (12,157 ± 2,854) than the year of the fire (7,461 ± 359), but the average post-fire abundance (7,343) was very similar to the pre-fire abundance (7,461). Like in Big Flat Creek, the highest observed abundance of juvenile steelhead in Kinsey Creek was three years post-fire (1932 ± 284) but it was not significantly different than the pre-fire value (1509 ± 342). Abundance of juvenile steelhead in Spanish Creek varied from 730 ± 160 to 3887 ± 695. Fire appeared to negatively affect the summer body condition of age 0+ juvenile steelhead in Big Flat Creek the first year post-fire. Fire did not affect summer body condition of juvenile steelhead in Kinsey Creek. Summer body condition varied little among years in Spanish Creek. Fire appeared to have a positive effect on fork length of juvenile steelhead; average fork length of 0+ and 1+ juvenile steelhead increased significantly post-fire in the burned streams but not in the unburned stream. However, when the pre- and post-fire mean fork length of age 0+ and age 1+ juvenile steelhead in the study streams are compared in a balanced dataset, it appears that fire had a positive effect on the mean fork length of age 0+ juvenile steelhead but did not affect the mean fork length of age 1+ juvenile steelhead. Conclusive evidence of fire effects in this study were not possible due to the limited extent of pre-fire data but overall, juvenile steelhead were able to persist if not thrive after fire disturbance.

https://scholarworks.calstate.edu/concern/theses/5425kc85v

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