Four scientists, who have all worked at the University of California-Berkeley’s Angelo Coast Range Reserve, introduced the topic of “ecohydroatmogeomorphology,” the interconnection of water, atmosphere, and geology, and how this affects fisheries.
The Angelo Coast Range Reserve is on Elder Creek, a tributary of the South Fork Eel River high in its watershed west of Laytonville, a long way from the confluence of the South Fork with the main stem Eel at Dyerville, but the interplay of impacts on fish is felt throughout the system.
River incision, the carving of the landscape by the river, drives evolution of fish species because it determines fish barriers and habitats, said Bill Dietrich. He described the mapping of the upper South Fork, including the incision of the river, topography, water temperature, soil and vegetation types, and how each of these factors affects the others.
Biologist Mary Powers talked about the food web in the upper South Fork, which she and a team of her students have studied extensively.
Those long green strands of the algae Cladophora, which most people find ugly but which Powers describes as “beautiful green Rapunzel’s hair,” harbor food for young salmonids in the form of microscopic silica-encased diatoms and the insects that feed on them. Even when the algae turn yellow and eventually rusty as the water warms in summer, it remains a food source for fish.
Diatoms are full of polyunsaturated fatty acids, Powers said, the same nutrient that makes wild salmon so healthful for humans.
Cladophora algae becomes toxic only when the bloom is so dense and heavy that it sinks, causing anaerobic (without oxygen) conditions in the water. Some other species of algae are more toxic, or may become toxic more readily, Powers said.
Powers introduced Sarah Kupferberg, a field biologist who has extensively studied the Foothill Yellow-legged Frog, which lives in many California rivers. Kupferberg has been comparing populations of the frogs living in free-flowing streams with those living in dam-restricted streams, including the Eel River.
Eight hundred dams exist in the frogs’ entire range, and studies show that the frogs are absent more often in dam-restricted streams, and that the height of the dam correlates to the scarcity of frogs.
Frogs need consistent water flows, and because the tadpoles are small and fragile, they need slow-moving water so that they can swim against the current to hide from predators.
Unlike young salmonids, tadpoles and “metamorphs” (tadpoles whose front legs have emerged but who have not yet matured as frogs) prefer warm water to cool water. On the main stem Eel, frog populations have declined near the base of Scott Dam because the needle valve releasing water from Lake Pillsbury into the river draws cold water from the bottom of the reservoir.
Bill Trush, described as a leader in the applied science of river restoration and management, spoke about methods for determining cumulative impacts, particularly as applied to salmonid species.
He began with a quote from Voltaire, the 18th century philosopher who said, “No snowflake in an avalanche ever feels responsible.” Trush continued by presenting a step-by-step process of analyzing causes and effects, using a chain of simple graphs with each conclusion leading to the next graph. In the end the larger connection between the original cause and the final effect is established.
In his example, Trush demonstrated how increases in turbidity so small that the human eye can’t detect them can lead to decline in fish population because turbidity interferes with light in water.
For more information about the Angelo Coast Range Reserve, visit the website www.angelo.berkeley.edu. The reserve is open to visitors.
With so many speakers and topics, the symposium went into overtime. For those who missed it, more information can be found on FOER’s website, www.eelriver.org, or by calling them at 822-3342.