The removal of riparian cover during clear-cut logging can increase the amount of solar ultraviolet radiation (UVR) impinging on streams. Studies in British Columbia have documented increases in UVR of 300-500% following logging (Clare 2000). UVR can be harmful to fish and recent studies at the Pacific Biological Station in Nanaimo, BC have shown that exposure to high levels of natural solar UVR can have deleterious effects on juvenile coho ranging from fin erosion to incipient cataract formation. While these effects are potentially harmful to development they are difficult to quantify. However, coho exposed to UVR also show increased skin pigmentation, and this characteristic is more easily quantified. Since juvenile coho are known to behaviourally avoid high levels of UVR, it?s unclear how much UVR they are actually exposed to when watersheds are logged. In this project we are developing a bioassay for UV exposure of juvenile coho based on the amount of UV-absorbing pigmentation in their skin. The bioassay will be used to assess the efficacy of various logging practices in protecting coho from exposure to UVR and to better understand the relationship between logging and UVR exposure of stream biota. UV exposure trials at the Rosewall Creek Hatchery have quantified the amount of UV-absorbing substances in juvenile coho skin as a function of the cumulative exposure of the fish to UVR. While UVR plays the dominant role in development of the pigment, visible light is also involved. Experiments also established the long-term stability of the pigment.
Max L. Bothwell and Donovan R. Lynch.
Bothwell, Max L., Lynch, Donovan R.. 2005. Does logging elevated ultraviolet radiation exposure of streams impact juvenile coho?: 2004-2005 completion report for the BC Forest Science Program. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2005MR010