Santa Cruz Steelhead
Monitoring Juvenile Density & Habitat Quality in Santa Cruz County, California
Steelhead (Oncorhynchus mykiss) are a species of salmon found in cold-water tributaries of the Pacific Ocean.
A juvenile steelhead
Like other salmonids, steelhead are anadromous — they use both oceanic and freshwater habitats throughout their life cycle.
Unlike other salmon species, some steelhead can live their entire lives in freshwater, never going to sea. These freshwater-only steelhead are called rainbow trout.
Steelhead Life Cycle
During winter, adult steelhead swim from the ocean into freshwater streams to spawn. They lay their eggs in nests, called redds, that they dig into gravelly stream beds. After spawning, steelhead return to the ocean and can potentially repeat their migration again another year.
Background: two adult steelhead, female (left) and male (right). Photo Credit: Morgan Bond
Young steelhead, called juveniles, live in freshwater for one to two years. They need to grow to at least 150mm (fork length) to have the best chance of survival in the ocean. Their growth rate depends on stream temperature and availability of food – mainly stream drift (insects and other tiny creatures floating in the streamflow). They also need hiding places, called escape cover, to evade predators and avoid dangerous winter storm flows.
Background photo: a juvenile steelhead
A Threatened Species
For more than a century, steelhead have suffered widespread habitat destruction from both human-induced and natural environmental changes. This has contributed to a drastic decline in steelhead populations, putting the species at risk of becoming extinct if trends continue. In 2006, steelhead were listed as threatened under the federal Endangered Species Act (ESA).
In 2006, Steelhead were listed as threatened under the federal Endangered Species Act.
In Santa Cruz County, steelhead face several constraints to population growth, including:
• Low stream flows from prolonged drought or excessive water withdrawal. Low stream flow limits steelhead growth and reduces escape cover. • Reduced habitat complexity, typically from human development. Channel straightening (often for flood protection) and removal of stream wood reduces habitat variety and utility for steelhead. • Excessive sedimentation, caused by erosion of silt and sand into stream beds. This degrades spawning habitat and diminishes food availability.
Monitoring Program
The County of Santa Cruz, in partnership with local water agencies, conducts an annual monitoring program to better understand steelhead population and identify local conservation priorities in the region.
The Juvenile Steelhead & Stream Habitat Monitoring Program (JSSH) assesses stream habitat conditions and measures steelhead population density across four major watersheds in Santa Cruz county.
Santa Cruz County
Watersheds
The monitoring program focuses on watersheds where human development has impacted steelhead the most.
The North Coast region (actually the western portion of the County) is sparsely populated and outside the scope of this monitoring program.
However, the North Coast is studied by the National Marine Fisheries Service, California Department of Fish and Wildlife, City of Santa Cruz, and others.
Reaches
Within the studied watersheds, streams are categorized into reaches based on similar characteristics such as: gradient, channel width, substrate composition, and habitat types.
Segments
Within each reach, 1/2-mile stream segments are assessed for habitat quality.
This involves identifying specific habitat types (riffles, runs, or pools), measuring stream depth and width, and assessing substrate and cover.
Sites
After stream segments have been assessed, sampling sites are chosen based on average habitat quality within each segment (with a focus on pool length, depth, and cover).
A typical sampling site consists of two pools and any adjacent runs and riffles.
Sampling
The sampling process requires catching, measuring, and releasing steelhead at sites such as this one.
Block Nets
The first step is to install block nets. These nets isolate the site so that fish cannot move in or out during the sampling process.
Electrofishing
With block nets installed, electrofishing begins. This technique uses electricity to briefly stun fish so they can be captured with hand nets. The sampling team makes three passes through each site, attempting to catch as many fish as they can.
Two captured steelhead temporarily held in a mesh basket
Count & Measure
Each steelhead is measured and then released back into the stream. Two measurements are taken: from the tip of the snout to the base of the vertebrae (Standard Length - SL) and to the middle of the tail fork (Fork Length - FL).
Measuring a juvenile steelhead (Photo credit: Lois Robin)
If any other species are captured or observed at the site, their presence is recorded too.
A pacific giant salamander
Metrics
Density
Sampling sites differ in length due to the unique composition of habitat types in each stream. To compare steelhead populations across sites, the monitoring program reports steelhead density: the total number of steelhead per 100 feet of stream.
Density is the total number of steelhead per 100 feet of stream.
The steelhead densities include both the counted (captured) steelhead and an estimate of any steelhead that may have evaded capture. The number of escaped fish are estimated with a formula based on the depletion rate from each of the three stream passes during the electrofishing process.
Size
The monitoring program measures steelhead in autumn and assumes that fish longer than 75mm (SL) will be big enough by spring to migrate to the ocean.
Fish that are smaller than 75mm (SL) in autumn will likely need an additional year in freshwater to grow before migration.
A 75mm long juvenile steelhead. It will likely be able to migrate in the spring.
Because size is such an important indicator of migration potential, density is reported for both the total steelhead population and for steelhead 75mm or longer.
Juvenile Steelhead Density Timelapse
This map shows juvenile steelhead densities from 2006 to present.
You can use the time controls to pause the animation or view a specific year.
(Map not displaying? Click here )
Conservation
While monitoring programs such as this one can help inform conservation efforts, future steelhead success is still uncertain.
Luckily, there are many ways in which we can aid these amazing animals.
Protect Dry-Season Streamflows
Local water supply comes from stream diversions or groundwater pumping. Help maintain adequate dry-season stream levels through water conservation and by supporting sustainable management practices.
Increase Habitat Complexity
Leave fallen trees and wood in streams. Woody material that remains in streams helps fish by scouring pools, sorting sediment, and providing protection from predators. Protect and enhance riparian areas by limiting stream-side development. Stream-side trees and vegetation provide overhanging cover habitat for steelhead and help stabilize banks, reducing erosion.
Reduce Stream Sediment
Prevent erosion. Control storm runoff from your property by providing adequate drainage, especially along unpaved roads. Maintain natural vegetation or landscape with native plants to help hold soil in place.
Ultimately steelhead recovery is up to all of us.
For more information about this program, visit Santa Cruz County Environmental Health
Funding for this program is provided by:
