Shasta River. Photo by Mike Weir
Not all streams are created equal, at least in their ability to produce salmonids. For example, the Shasta River, a spring-fed river, historically accounted for greater than half the lower Klamath Chinook Salmon run, despite contributing approximately one percent of mean annual flow to the Klamath River. While it’s impossible to go back in time and understand all of the potential mechanisms contributing to such prolific production, current research in the Shasta River basin and elsewhere in the greater Mt. Shasta area has produced some intriguing results related to the value of spring-fed rivers and their importance for trout and salmon.
A recent paper by Jeffres et al. (in review) found that juvenile steelhead trout on the Shasta River exhibited growth rates six-fold greater (mass) than the same age class of steelhead on the Scott River, another tributary to the Lower Klamath River but one that is dominated by snowmelt runoff. Analysis suggested that steelhead in the spring-fed Shasta River emerged as fry from gravel, on average, 60 days earlier than those in the Scott River (a function of water temperature), which, in turn, provided a significant head start on growth. The analysis also showed that Shasta River juvenile steelhead exhibited daily growth rates that were approximately 14% greater than those in the Scott River. Daily growth rate differences were attributed to warmer water temperature and enhanced food resources associated with the Shasta. Growth and size of juvenile fish is important because research has shown that fish entering the ocean at larger sizes generally have a better chance for survival and eventual adult return. So, it appears that both stable environmental conditions (water temperature, but also flow) and improved food resources likely played an important role in producing large numbers of Chinook Salmon in the Shasta River, among other factors.
Spring-Fed Rivers and their importance for trout and salmon
and food webs on the Eel River