One inescapable consequence of the removal of riparian cover during logging of timberland watersheds is the increased exposure of small and mid-sized streams to solar radiation. In British Columbia, the removal of riparian cover during clear-cut logging can increase solar radiation exposure of streams by 8-fold (Clare 2000). While some of the ecological impacts associated with elevated sunlight, such as higher water temperatures and stimulated algal production are well known, the effects of enhanced exposure to the ultraviolet portion of the solar spectrum remain unclear. Numerous studies have shown the potential for solar ultraviolet radiation (UVR) to cause deleterious effects on multiple trophic levels in shallow water ecosystems. UVR can also directly harm fish. Studies at the Pacific Biological Station in Nanaimo, BC have shown that exposure to high levels of solar UVR can have direct effects on juvenile coho salmon including fin erosion, incipient cataract formation and altered body morphology. This charismatic fish species is ubiquitous in coastal and interior streams of British Columbia. Of all Pacific salmon, coho are probably the most susceptible to UVR because they spend a full year in shallow freshwater streams under potentially high UVR levels. However, coho are also known to avoid high levels of light and have been shown specifically to avoid high UVR exposure (Kelly and Bothwell 2002). It is unknown how effective this behaviour might be in protecting juveniles from excessive radiation in natural streams. Currently, there is no way to determine if stream-rearing coho are exposed to deleterious levels of UVR during or after logging operations. The goal of this project is to develop and implement a bioassay procedure that will enable logging practitioners and environmental workers to quantify the amount of UVR that juvenile coho are exposed to in natural stream environments. The implications for management of logging operations are clear. If this project is successful in developing a scientifically valid bioassay for determining UVR exposure of juvenile coho, we will be able to determine with confidence whether or not juvenile coho are exposed to excessive UVR following logging.
Max L. Bothwell and Donovan R. Lynch.
Bothwell, Max L.. 2006. Does logging elevated ultraviolet radiation exposure of streams impact juvenile coho?. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2006MR295