Posted on November 13, 2014 by UC Davis Center for Watershed Sciences
Recent studies on spring-fed streams challenges this mindset. The findings strongly suggest these streams should play a larger role in the recovery and management of sensitive cold-water species, particularly salmonids.
Researchers at the UC Davis Center for Watershed Sciences found that trout in spring streams grow faster than those reared in streams fed by snowmelt and rainfall runoff, such as those in California’s redwood forests.
Surprisingly, they suggest that trout benefit not only from the stable flow and temperature regimes of spring streams but also from another dominant – yet much underappreciated – habitat feature: aquatic plants.
Known as macrophytes, these rooted vascular plants provide similar benefits as pools, and large woody debris.
As fish habitat, this debris provides structure, velocity heterogeneity and refuge from predators . It also has been shown to increase habitat area and reduce competition between fish . Similarly, biologists have long recognized pools as superior salmonid habitat for providing predator and thermal refuge, velocity heterogeneity and improved food resources .
Macrophytes grow in many spring streams and are largely a product of naturally occurring nutrients, stable flow and temperature, open canopy and low gradient. These plants provide many of the same benefits to trout and salmon of the more classic redwood streams type habitat.
On the Shasta River, a large spring-fed tributary to the Lower Klamath River, the UC Davis researchers conducted an experiment to understand the potential benefits of macrophyte habitat on juvenile steelhead trout.
Presented with multiple habitat types, the steelhead overwhelmingly selected macrophyte habitat during spring and summer foraging. The researchers found that macrophyte habitat provided abundant food – the plants also are important for invertebrates – and refuge from high-velocity currents. The trout gorged on seemingly unlimited food while exerting minimal energy.
These broader benefits may be particularly important for salmonid populations in California during late summer and early fall, when flows in runoff streams typically decline and water temperatures rise.
Pacific salmon recovery efforts in the Lower Klamath River drainage often focus on spring systems such as the Shasta River because of they provide flow stability and optimal thermal habitat for rearing salmonids.
While many factors contribute to fish production, macrophyte habitat has received far less attention for its beneficial effects on trout and salmon. Fully understanding such species-to-species interactions as those between plants and fish is important and will assist salmonid conservation planning and recovery.
Robert Lusardi, a doctoral candidate in ecology at the UC Davis Center for Watershed Sciences, researches stream ecology and food web dynamics of volcanic spring-fed ecosystems in Northern California. Ann Willis, an engineer who coordinates research programs at the Center, has done extensive fieldwork in monitoring the restoration of Big Springs Creek.
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