Science Behind the Scenery: Coho Salmon and Steelhead Trout

Point Reyes National Seashore


[water flowing in a stream]

[Brannon Ketcham] The watersheds of coastal Marin County have supported coho salmon and steelhead trout for thousands of years. In the last 50 years, throughout the California coast, we have witnessed a dramatic decline in fish populations. This decline coincides with impacts to the watersheds in which these fish survive

[water flowing in a stream]

In 1996, the National Marine Fisheries Service listed coho salmon as threatened. The Park Service started a project to find out how many fish they had and how they were doing within the...the watersheds within the parks.

[water flowing in a stream]

As things went on, we learned more and more about the fish and, sort of, all the habitats that they used. And a lot of the work that we've come up with has shown that these populations in, uh, coastal Marin County are, sort of, the southern-most stable populations of coho in their range.

[water flowing in a stream]

Coho salmon have always been thought of as being weak because there are fewer of them around and they're harder to find. But, really, what we found watching them is that they're the more aggressive, the more dominant fish when you have steelhead and coho together.

[water flowing in a stream]

Coho salmon have a, uh, pretty stringent three-year-lifecycle. Um, starting from the adult phase, um, November, December, January the period of time where the adults come up into the freshwater streams to spawn. Um, for the adults, they've spent about six to 18 months out in the ocean and they've got about three weeks to enter the freshwater, find a place to spawn and, um, do that before they pass away.

But, if they spawn successfully, the eggs will stay in the gravel for about six weeks before they hatch. And then, another six weeks, the alevin, or egg sac fry, will stay in the gravels before emerging to the water column. And, so, it's normally February, late February, early March that we start seeing the, um, young of year juveniles come out of the gravel and they populate the pools. And they'll spend a full year in the fresh water, so, March–April through the next March–April, before they head out to the ocean.

[water flowing in a stream]

Steelhead trout they can live anywhere from one to three years in fresh water, sometimes four or five, before going out to the ocean. They don't need to go to the ocean. The other thing about steelhead trout is if they're ocean run, they can come back and spawn and go back out to the ocean. So, they're...are some of the fish that actually can spawn multiple years. They're able to adjust to changes in the, uh, weather conditions. If you have a really bad year, you might lose a lot of the fish in that watershed. But that's okay, because maybe some of them will come back and reproduce next year, as well. Whereas coho salmon, they're pretty much...they have one chance to reproduce and that's it.

[water flowing in a stream]

The redd is a, uh, the egg nest, r e d d, really consists of multiple pockets of eggs. The female will lay their eggs and the...the male will, um, kind of, broadcast, um, his milt over the eggs. And then, the female will go ahead and bury those eggs. And if she buries those eggs, she digs a new pit where she can lay more eggs. So, a redd is anywhere...sometimes two to four meters long, two to four meters wide, so it's a big area where the fish will work the gravel. And, basically, within that zone, there are multiple pockets of eggs.

The typical location for a redd would be, sort of, in this pool tail out section where you have a transition from, um, kind of, flat water into a riffle zone. And the ideal, or the advantage to that is that the water is accelerating, and not just on the surface, but it's accelerating through the gravels. So, it's a very good way of delivering oxygen to the eggs, um, while they're in the gravel.

[water flowing in a stream]

When we started this work, we were really focused in on...on, uh, coho salmon and steelhead, but we found, everywhere we looked, we'd find steelhead and...and coho were few and far between. So, we really keyed in on their, uh, their conditions.

[water flowing in a stream]

John West Fork is the largest tributary of Olema Creek and, in 1997, we...started...looking at that watershed and saying, "Gosh, this has lots of potential."

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There was a culvert along Highway 1 that was really difficult for fish to get through, in terms of adult migration.

[water flowing in a stream]

So, we're on the John West Fork of Olema Creek. And this is a riparian exclusion zone that we constructed in 1997, in cooperation with, uh, the local rancher. Um, prior to the fence being constructed, the creek bed, itself, looked much like the...the area over here, to the left, where we have, um, regular livestock access. In cooperation with the rancher, we were able protect the riparian zone. Um, but what we need to do is provide, uh, access to other pastures that the, uh, cattle use. The cattle have access to the grazing lands. We have a riparian zone that we've been working on since '97, including a great deal of willow planting and some small-scale, um, streambank stabilization structures.

One of the interesting things is: why are we protecting a dry creek bed? And when you're out here in the wintertime and there's a great deal of flow coming down this stream channel and you see fish swimming up it and spawning, you''ll know why.

[water flowing in a stream]

Here at Point Reyes National Seashore, we monitor and study coho salmon and steelhead trout as indicators of watershed health. The survival of these fish is the survival of California watersheds.

[water flowing in a stream fades away]


The seventh part of the ten-part Science Behind the Scenery documentary featuring hydrologist Brannon Ketcham talking about coho salmon and steelhead trout and efforts to protect their riparian habitat at Point Reyes National Seashore.


6 minutes, 34 seconds


Pacific Coast Science and Learning Center

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