'River Jedi'

'River Jedi': Biologists Lyla Pirkola, left, Chad Praetorius and Lenny Cheskiewicz, right, prepare for another night on the water. The crew conducts survey trawls to study the migration of green sturgeon in the upper Sacramento River.  Credit: Steve Martarano/USFWS

Red Bluff Fish & Wildlife Office biologists break new ground in Sacramento River juvenile green sturgeon migration research

By Steve Martarano
June 14, 2018

On a cold, dark, moonless night last December, the U.S. Fish and Wildlife boat stealthily cruised along the upper Sacramento River near Corning, California on its nightly mission to find green sturgeon.

Except for the sound of the boat engine signaling a change of location, and an occasional coyote howl heard off in the distance, most of the four-hour trip on this frigid night took place in workmanlike silence.

The upper Sacramento River at dusk the evening of Dec. 7, 2017. After taking off from a county park boat ramp in Corning, the crew uses an underwater missile-shaped hydrophone receiver to detect if there are any previously tagged green sturgeon in the area. Credit: Steve Martarano/USFWS

Even now, in June and amidst the scorching heat of another northern California summer, the chill of that winter evening remains fresh, as the crew diligently worked its unique assignment: a regular winter nighttime fish survey.

“Nighttime trawls are really rare,” said crew chief Chad Praetorius. “You have to know the river and where you’re going. You basically have to be a River Jedi.”

The survey -- officially known as the Juvenile Green Sturgeon Outmigration Investigation -- was just one of 39 weekday trips conducted in 2017 by the Red Bluff Fish and Wildlife Office, all led by Praetorius.

As the survey gears up for September and its third year of tagging, once again the goal is to capture, tag, release and then track 50 green sturgeon, a number that was reached by mid-December last year, following the 21 that were captured and tagged with UC Davis assistance during the initial 2016 survey.

“Nighttime trawls are really rare. You have to know the river and where you’re going. You basically have to be a River Jedi.”

– Chad Praetorius, fish biologist

We’re out there from September to December, four days a week, 10 hours a day – sometimes more – averaging between six and 15 trawls a night,” said Praetorius, who has been the crew lead since the project’s pilot launch back in 2015. His two assisting crew members rotated among nine others.

“Those nets and weighted boards are heavy. This work can be very difficult and technical, especially during the late evening hours and under inclement weather conditions.”

This night, along with Praetorius, the crew consisted of biologists Lenny Cheskiewicz and Lyla Pirkola, enthusiastically going about their tasks knowing they’re breaking new ground in green sturgeon research.

Throughout the year, other crew members included Bill Poytress, Josh Gruber, Casey Collins, Robert Larson, Samantha Adams, David Ryan and Scott Voss.

Biologist Lenny Cheskiewicz checks his data as night falls on the upper Sacramento River. Credit: Steve Martarano/USFWS

The crew does its work with methodical precision, with no natural lighting except what is generated by headlamps and the boat.

Crew lead Chad Praetorius fixes a net that developed a snag in the middle of a survey trawl on Dec. 7, 2017. Credit: Steve Martarano/USFWS

After taking off from a county park boat ramp in Corning, the crew makes its way along the river, using an underwater missile-shaped hydrophone receiver to detect if there are any previously tagged green sturgeon in the area that might be potentially recaptured.

With each night resulting in up to 15 separate trawls, crews successfully completed 337 total trawls during the 2017 survey, Praetorius said.

For each trawl, the net is dragged downstream in the water between seven and 15 minutes with the boat lights off to eliminate detection by the fish. The onboard Sonar unit tracks the boats progression through the sampling reach.

This information is later uploaded into a GIS layering system, which provides a visual breakdown of the habitat sampled for each individual trawl in terms of water velocities, depths, and temperature.


By the numbers

Green sturgeon, listed by NOAA Fisheries as threatened under the Endangered Species Act in 2006, are regularly found in the upper Sacramento and Feather rivers. Last fall, for the first time, one was verified in the Stanislaus River.

The prehistoric-looking greens are different from other bony fish in that their skeleton is made of cartilage, producing a sponge-like feel, and they possess large bony plates, called scutes, instead of scales. They can live 70 years, weigh up to 350 pounds and have a maximum length of more than 8 feet.

One of the four juvenile green sturgeon that were captured by the 'River Jedi' crew, Dec. 7, 2017. Credit: Steve Martarano/USFWS

In its two years in existence, the outmigration survey has collected new information to determine how long the juveniles occupy the upper Sacramento River after leaving hatching areas near the Red Bluff Diversion Dam before entering the Bay-Delta Estuary near downtown Sacramento, 160 river miles away. Tracking is accomplished after captured juveniles are surgically implanted with micro-acoustic telemetry tags that “ping” at intervals up to 10 seconds.

The fish are then tracked using an elaborate set of receivers in the water that are also utilized by other agencies such as NOAA Fisheries, U.S. Army Corps of Engineers and California Department of Fish and Wildlife.

Two types of acoustic receiver tags that are implanted into the captured green sturgeon juveniles before they are released back into the river. Credit: Steve Martarano/USFWS

The implanted tags can last from 100 to 184 days, depending on the size of the fish and ping rates of the device, said Poytress, a fish biologist in Red Bluff who heads up the project.

“The collaboration with other agencies and researchers has been exceptional,” Poytress noted. “There are many different agencies interested in what this species is doing and where it is and at what time of the year.”

“Knowing more about this species can allow regulatory biologists to work with project proponents to provide such things as work windows where impacts to fish and their populations can be minimized or, in some cases, eliminated,” Poytress continued. “This knowledge is also very helpful for managers of California's water resources and their end users.”

Data from 2017 has been coming in this spring and is being analyzed now, said Poytress. That data shows that 20 of 55 tagged fish made it to the legal Delta boundary, with 54 of the 55 fish getting detections. Almost 70 percent of those were detected by three or more acoustic receivers (five were tagged in 2018 prior to the March storms and included). In the prior year, data showed up to 95 percent detections.

“Interestingly, 69 percent were last detected during storm events as river flows and turbidity increased,” Poytress said. He said that flow and turbidity appear to cue migration where some fish moved significantly during flow events, a pattern seen both in 2016 and 2017.

Chad Praetorius clips the fin of a captured green sturgeon before inserting an acoustic tag. Credit: Steve MartaranoUSFWS

Biologist Lyla Pirkola logs information gathered on fish collected during the nightly trawls. Credit: Steve Martarano/USFWS

The third season of the survey starts in September depending on when the larvae show up in the Red Bluff Diversion Dam traps, which is an indication spawning has occurred. One change will be an additional number of detection receivers.

“This year we will still be interested in Delta entry timing and cues, but we also want to take a look at having more receivers covering the upper river in a two-dimensional array to obtain finer-scale habitat use movements prior to outmigration” Praetorius said.

Poytress added that the hope for the 2018 surveys and beyond will be to obtain habitat data that will quantify juvenile green sturgeon rearing habitat in the Sacramento River.

The data will be compared with winter-run Chinook juvenile habitat to see how much area exists and overlaps from a water temperature perspective.


Back on the water

Finally, when a half-dozen net trawls that December night failed to produce a green sturgeon, the crew decided to try a new sampling location upstream. Quickly over the next three trawls, a total of four juveniles were caught.

For the last 90 minutes of the trip, after declaring “it’s time for surgery,” Praetorius successfully implanted tiny acoustic receiver tags into each sturgeon, then released them back into the river. The night’s catch meant they were surprisingly just a few fish shy of the survey’s limit of 50, a number few on the team thought they’d reach.

“In 2016, we got 21 and had to work really hard for that,” Praetorius said. “But no one’s done this before and we are learning as we go, continuing to learn from our experiences and refining our methods along the way.”

At the end of the night, the crew – Lenny Cheskiewicz, Chad Praetorius and Lyla Pirkola – show the four captured and successfully tagged green sturgeon that are ready to be released back into the upper Sacramento River. Credit: Steve Martarano/USFWS

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Steve Martarano

About the writer...

Steve Martarano is currently a public affairs specialist in the San Francisco Bay-Delta Fish and Wildlife Office located in Sacramento, California.

He has spent almost 30 years in both state and federal government public affairs after a 10-year stint at a daily newspaper in Sacramento.

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