On this day, two teams of 2 walked both forks of Matilija Creek - the main stem from above the Matilija Dam reservoir to the Forest Service trailhead, and North Fork Matilija Creek from the confluence to Wheeler Gorge Campground. Other reaches of the river, from the rivermouth up, are surveyed on different days of the week, and the whole process is repeated two weeks later. Depending on conditions it takes about 5 hours to wade upstream in the creek looking for 'redds,' so this is no small undertaking.
This is an example of a fresh 'redd,' or steelhead nest, in Matilija Creek. The redds are noticeable as a clear patch of gravel in a riverbed which is otherwise often covered in algae and/or silt. The female fish spends hours fanning the streambed with her tail to create a clean pile of gravel in which to lay her eggs. The eggs are fertilized by a male as she lays them, and assuming clear water flows through the redd for the next few weeks, a single redd may produce thousands of alevin which in turn may mature into hundreds of steelhead smolt.
|Steelhead redd in Matilija Creek|
On close inspection the redd may be divided into a 'pit' and a 'tailspill' which are measured and recorded. The size of the redd is an indication of the general size class of the spawning fish.
|NOAA Steelhead spawning survey protocol|
|Measuring a steelhead redd in Matilija Creek|
These types of field surveys are critical to advancing the knowledge of this endangered species, both specific to our watershed, and more generally in the drought-and-flood environment of Southern California.
|Steelhead redd in Matilija Creek - looking across the flow|
note depth of 'pit' to the left, and size of gravel
|Steelhead redd in Matilija Creek - looking downstream|
note clean gravel and cobble in pit and tailspill