Field Notes
U.S. Fish & Wildlife Service
Field Notes Entry   
RED BLUFF FWO: Green Sturgeon Study LikenedtoSearching forNeedles in an Underwater Haystack
California-Nevada Offices , August 1, 2008
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USFWS crew deploying artificial substrate mats to sample green sturgeon eggs on the Sacramento River, CA.  Photo courtesy of University of California, Davis.  2008.
USFWS crew deploying artificial substrate mats to sample green sturgeon eggs on the Sacramento River, CA. Photo courtesy of University of California, Davis. 2008. - Photo Credit: n/a
Green sturgeon egg sampled in 2008.  Photo courtesy of University of California, Davis.
Green sturgeon egg sampled in 2008. Photo courtesy of University of California, Davis. - Photo Credit: n/a

by Will Poytress, Red Bluff FWO
In the spring of 2008, the Service's Red Bluff Fish and Wildlife Office (FWO) began a three year study to evaluate the effects of operating the seasonal Red Bluff Diversion Dam (RBDD) managed by the US Bureau of Reclamation on the Southern Distinct Population Segment of green sturgeon.  This genetically distinct population was listed in 2006 as threatened under the federal Endangered Species Act (ESA) and is currently only thought to spawn in the Sacramento River near Red Bluff, California. 

 In 2001, the Red Bluff FWO obtained some evidence that spawning was occurring in close proximity to the dam by sampling two green sturgeon eggs from devices known as artificial substrate samplers.  These samplers, commonly known as egg mats, are simple steel-framed devices with furnace filter material sandwiched between supports.  This type of passive sampling device, when placed in or near sturgeon spawning habitat at the river bottom, has been successful in sampling newly deposited eggs from a variety of sturgeon species throughout the nation including white, lake, and Gulf sturgeon.  The problem with this concept for green sturgeon is that no one knew precisely where the natural spawning habitat of this benthic species was in the Sacramento River.  The two eggs found in 2001 were found in close proximity to the RBDD which appears to be a common finding for sturgeon species impacted by man-made fish passage barriers.  The eggs are only about 4.0 mm in diameter or about the size of a pencil eraser and thought to be found in water depths greater than 16 feet in a natural setting.  We were tasked with finding these green sturgeon eggs (the "needles")) in one of the largest river systems in California (the "haystack.")

To aid in finding some underwater haystacks (i.e., spawning habitat), the Red Bluff FWO worked with partners including the Bureau of Reclamation and the University of California, Davis.  These researchers are using acoustic telemetry technology to track the migration and movements of acoustically tagged adult green sturgeon.  The Red Bluff FWO was able to use our partners’ real-time data to assist in egg mat placement.  We located two large pools where fish were holding for extended periods of time.  We sampled the river bottom upstream, within, and at the tail portion of these pools.  We were not certain if the green sturgeon moved upstream out of the pools, stayed within the deep portions of the pools, or dropped back to the pool tail to spawn.  So we sampled all three areas.  Within a week of fine tuning our placement of egg mats using more telemetry data, we captured our first green sturgeon eggs.  We then caught some at our other sample location, and then again multiple times at each natural location.  We found a total of 42 needles (green sturgeon eggs) throughout a six week period from the two natural sites with one egg found directly below the dam.  All confirmed green sturgeon eggs were found on the egg mats sampling within the deep portions of the natural pools; except the one at the dam.  This would indicate that fish are holding and spawning directly within these deep pool areas.  More data will be needed to confirm this theory as eggs may have drifted into the deep areas from upstream of the pools.  Throughout the season we were able to sample eleven eggs several miles above the seasonal dam from sturgeon that were able to get upstream before the dam gates closed in May, one at the dam after the gates closed, and thirty several miles downstream of the dam before and after the gates were closed. 

Needless to say it can be very difficult to find a needle in a haystack, but finding a needle in an underwater haystack without knowing the location of the haystack is even more challenging.  The Red Bluff FWO with its partners was able to locate some underwater haystacks and find some needles thereby gaining valuable life-history information on a pre-historic ESA listed fish species.  Information gained from this first year of study will help direct our efforts for the next two years and will ultimately benefit the conservation of a threatened native fish species which relates directly to the Red BLuff FWO's mission of providing biological expertise and assistance to entities seeking to conserve and protect the eco-systems of North-Central California.

Contact Info: William Poytress, 530 527 3043, bill_poytress@fws.gov
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