Wednesday, March 14, 2012

Steelhead spawning surveys

Last week I volunteered to help NOAA Fisheries biologists conduct a steelhead spawning survey on the Ventura River.  NOAA has been conducting these surveys every two weeks during the spring spawning season for the past two years.  These field surveys help build the knowledge of which parts of the river system are important to steelhead reproduction, and compliment the Population and Habitat surveys that are conducted during the summer months.  (The Matilija Coalition has also sponsored occasional spring surveys.)

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 
Unlike its more famous family member, the king or chinook salmon, steelhead do not die upon spawning and are capable of returning more than once to spawn or reproduce.  Steelhead may also remain resident, as proven by these redds above Matilija Dam, which blocks passage to and from the ocean.  Removal of Matilija Dam would re-establish an ocean run of steelhead, as is a critical part of the long term Steelhead Recovery Plan released last year by NOAA.

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