This truth is revealed quite clearly, as is the wonderful recovery of salmon habitat near Shasta, in this story from the California Water Blog.
On the Shasta River, a lifeline for Siskiyou County cattle ranchers, more than 18,000 fall-run Chinook salmon returned from the ocean. That’s more than double the return from the previous fall. More importantly, average returns during the past four years have quadrupled.
No one knows for sure why salmon are surging in the Shasta; many factors affect salmon population dynamics. However, one of those factors — the condition of freshwater habitats — dramatically improved following the exclusion of cattle from Big Springs Creek in 2009.
Historically, the Shasta River tributary had been a poster child for salmon habitat. Its water originates from springs fed from the snow-capped Mount Shasta, elevation 14,162 feet. As snow melts, it flows underground through porous volcanic rock, rather than running off in streams. Water eventually bubbles up, forming the creek, at about 55 degrees (12 degrees C) — just right for salmon and steelhead trout.
Enriched with nitrogen and phosphorous from volcanic and sedimentary rock, the spring water nourishes an abundance of aquatic plants that teem with insects. The plants provide good cover from fish-eating birds and a respite from high-velocity currents. Fish can eat bugs at their leisure. They grow exceptionally fast and big, increasing their chances of survival when they leave for the ocean and return to the creek to spawn.
All 2.2 miles of the creek flows through a cattle ranch that has been operating for more than 100 years. During that time, the luxurious habitat gradually deteriorated. Cows trampled banks and spawning beds and stripped streamside vegetation. And they devoured the aquatic plants, making the creek shallower and inhospitably warm in the summer.
The Nature Conservancy had long eyed the Shasta Basin because of its potential to provide high quality habitat for native salmon and steelhead — particularly coho salmon, which are federally designated as “threatened” with extinction. Historically, the 60-mile-long Shasta River was one of the most productive salmon streams in California. As a tributary to the Klamath River, the Shasta contributed only 1 percent of the flow but supported 50 percent of the Chinook salmon (NRCS 2004).
Retrieved January 20, 2015 from http://californiawaterblog.com/2015/01/20/a-salmon-success-story-during-the-california-drought/