Background

The southern distinct population segment (DPS) North American green sturgeon is one of two sympatric sturgeon species found in Central Valley rivers. The southern DPS or Sacramento River population was listed as threatened on 7 April 2006 by the National Marine Fisheries Service (NMFS). The majority of recent studies have focused on adult green sturgeon with most research focused toward understanding the behaviors, habitat preferences, identification of spawning sites, and population dynamics of adult southern DPS green sturgeon within the main-stem Sacramento River, Sacramento-San Joaquin Delta, and San Francisco Bay. Significant data gaps remain regarding the movements and emigration patterns of young-of-year and yearling southern DPS green sturgeon from their spawning grounds in the Sacramento and Feather Rivers (Brown 2007, Poytress et. al. 2013, Seesholtz et. al. 2014). Juvenile southern DPS green sturgeon are thought to rear for up to three years throughout the lower Sacramento River, Sacramento/San Joaquin Delta and San Francisco Bay the before emigrating to the Pacific Ocean (Moyle 2002). However; there is virtually no information on size, age, or environmental cues contributing to downstream emigration and subsequent residence time within each habitat. Even less is known regarding microhabitat preference and utilization within the lower Sacramento River, Sacramento/San Joaquin Delta and San Francisco Bay. Information on timing, survival, and transition rates through the bay/delta region are necessary for understanding and managing potential risks to juvenile southern DPS green sturgeon.

Read more about Green Sturgeon (Acipenser medirostris. )

Methods

We are proposing to capture, measure, and tag 100 juvenile green and white sturgeons per year. Study objectives include:

1. Develop capture methods for monitoring of juvenile green and white sturgeon in the lower Sacramento River and Sacramento/San Joaquin Delta,

2. Describe spatial and temporal movements during emigration from the lower Sacramento River to the tidally influenced reaches of the upper delta using biotelemetry,

3. Assess the seasonal migration and survival past/through engineered flood plains (e.g., the Yolo Bypass) and

4. Describe spatial/temporal use of the Sacramento/San Joaquin Delta and behavior and emigration timing to San Francisco Bay.

Currently approved methods for capture of juvenile southern DPS green sturgeon authorized by National Marine Fisheries Service Authorizations and Permits for Protected Species (NMFS APPS) Permit 17551 include the use of gill or trammel nets in the Sacramento-San Joaquin Delta and the use of modified D-nets or fyke traps in the Sacramento River. Gill nets have been shown to be an effective method for capturing juvenile southern DPS green sturgeon in the Sacramento-San Joaquin Delta (Radke 1966). Factors influencing sample site selection included depth, substrate, current velocity, and submerged or drifting aquatic vegetation. Sampling in the Delta is conducted by deploying 100-ft long 2-inch square mesh gill nets. The nets are anchored with 30 to 40 lb weights to prevent the nets from drifting. Net soak times range from one to four hours and are dictated by temperature and dissolved oxygen levels. Captured juvenile sturgeon are surgically implanted with 69 kHz acoustic transmitters (tags) and released near the point of capture. Arrays of 69 kHz acoustic receivers deployed throughout the lower Sacramento River and Sacramento-San Joaquin Delta, and San Francisco Bay collect detection data for tagged juvenile sturgeon. The detection range of the receivers is dependent on factors such as turbidity, wave action, and tidal phase (water depth), but typically ranges from 200 to 1,000 meters. The receivers are downloaded quarterly and the detection data is uploaded to a database for subsequent analysis. Detections are then mapped to show detection dates at receiver locations. In addition to the receiver arrays, a portable receiver is deployed during sampling to provide real-time monitoring for the presence of recently tagged juvenile sturgeon at sampling sites. Analysis of the data will provide an understanding of spatial and temporal movements by juvenile sturgeon that can be ultimately be used by fisheries and water operations managers to develop a framework for population recovery.

Results

References

Brown, K. 2007. Evidence of spawning by green sturgeon, Acipenser medirostris, in the upper Sacramento River, California. Environmental Biology of Fishes 79:297-303.

Moyle, P. B. 2002. Inland fishes of California, 2nd edition. University of California Press, Berkeley.

Poytress, W. R., J. J. Gruber, C. E., Praetorius, and J. P. Van Eenennaam. 2013. 2012 Upper Sacramento River Green Sturgeon Spawning Habitat and Young of the Year Migration Surveys. Annual Report of U.S. Fish and Wildlife Service to U.S. Bureau of Reclamation, Red Bluff, CA.

Poytress, W. R., J. J. Gruber, and J. P. Van Eenennaam. 2012. 2011 upper Sacramento River Green Sturgeon spawning habitat and larval migration surveys. Final Annual Report to U.S. Bureau of Reclamation, U.S. Fish and Wildlife Service, Red Bluff, California.

Radtke, L. D. 1966. Distribution of smelt, juvenile sturgeon and starry flounder in the Sacramento – San Joaquin Delta. Pp. 115-119 in Turner, S.L. and D.W. Kelley (Eds.), Ecological Studies of the Sacramento - San Joaquin Delta, Part II. California Department of Fish & Game, Fish Bulletin, 136.

Seesholtz, A., M. Manuel and J. Van Eenennaam. 2014 First documented spawning and associated habitat conditions for green sturgeon in the Feather River, California Environmental Biology of Fishes DOI 10.1007/s10641-014-0325-9.

Marc Beccio
Environmental Scientist
North Central Region Anadromous Fisheries
California Department of Fish and Wildlife
1701 Nimbus Road, Rancho Cordova CA 95670

Marc.Beccio@wildlife.ca.gov