Project: Movements of green sturgeon in the San Francisco Estuary and Sacramento River System

Introduction:

The green sturgeon (Acipenser medirostris) is a long-lived, iteroparous (e.g. spawns many times througout its life), anadromous, native fish that occurs in low numbers in the San Francisco Estuary. Adults spawn in freshwater rivers in Oregon and California including the Sacramento River. Larvae develop within these freshwater systems, and remain in the estuaries for between one and four years before migrating to the ocean. Mature adults move into estuaries in the spring, and spawning adults continue into natal rivers in late spring/early summer. Post spawning adults return to the estuary before migrating back to the ocean in late fall. Sub-adult fish also are thought to enter estuaries during summer and fall months.

Objectives:

Fig. 1. F/V Intrepid

There is very little information about green sturgeon distribution and movements within the San Francisco Estuary and Sacramento River in comparison to the better known white sturgeon (Acipenser transmontanus - Click here for a more detailed comparison between the two species). Basic knowledge of this kind is required for a better understanding of green sturgeon in California, and for improved natural resource management and protection of this rare species. We seek to fill in some of the many blanks, such as what parameters (e.g. temperature, dissolved oxygen (DO), salinity, bathymetry, currents) influence movements within the estuary, where are adult fish moving within the river, where are the fish spawning, what is the preferred spawning environment, what is the residence time within the river and estuary, and what is the interval between spawning runs?

This project is comprised of several phases. Phase I will elucidate fine scale movements of individual fish within the San Francisco Estuary over periods of hours, days, and weeks. Phase II will focus on large scale movements of fish throughout the entire river system over periods of months and years.

Methods:

Green sturgeon were captured in San Pablo Bay, CA, by trammel and gill netting as well as hook and line fishing. In 2000-2001, fish were provided to us under permit by the captains and crew of the R/V Striper II operated by the California Department of Fish and Game, Bay-Delta Branch. In later years, fish were captured for us in San Franscisco Bay by Captains Mike Holm and Mike Fontes aboard the F/V Intrepid (Fig. 1.) and in the Sacramento River by hook and line fishing.

Fig. 3. Manual tracking system in operation aboard R/V Turtle

In Phase I, fish were surgically implanted with depth sensing ultrasonic transmitters (Vemco V22XP, Fig. 2). These tags are high power transmitters that permit relocation of fish from substantial distances. Maximum tag life was 10-14 days. Tagged fish were manually tracked (Fig. 3) for 2-16 hours a day over periods ranging from 1-12 days. At hourly intervals during each track, the salinity, temperature, and DO profiles of the water column were sampled to a maximum depth of 25 m with a Hydrolab Surveyor II. Collected data were entered into ArcView along with spatial data sets for analysis.

In Phase II, fish were surgically implanted with small ultrasonic tags (Vemco V16). Tag life was >4 years. The ultrasonic tags permitted long term monitoring of tagged fish with automated listening stations (Vemco VR2) in both salt and fresh water (Fig. 4.). These monitors were deployed throughout the Sacramento River system and remained in place year-round.

Fig. 4. Vemco VR2 automated listening station attached to mooring prior to deployment in Sacramento River

Progress:

Phase 1: Five sub-adult and one adult fish (genders unknown) were tracked in the San Francisco Estuary during the fall months of 2001 and 2002. Green sturgeon made use of much of the San Francisco Estuary, and occasionally made significant large scale movements throughout the region. At the start of the project, it was assumed that these movements would be influenced by physical parameters such as temperature, salinity, and DO with the fish seeking preferred conditions. However, the estuary is vertically well-mixed and there is no apparent pattern to sturgeon preferences. Different results may be found in a more stratified system.

Green sturgeon movements in the bay are not random. They shift between highly directional movements over long distances and localized non-directional movements consistent with foraging. Reasons for directional movements likely vary with both maturity of the fish and time of year. Movements by sub-adults and pre and post spawn adults may be related to ranging between resources, while late season movements by adults are likely the initiation of migratory behavior. When moving directionally, green sturgeon either move on the bottom or on very near the surface of the water column.  Movements on the bottom typically occur in shallow, slow-flowing regions of the bay and are not oriented with respect to water currents.  In contrast, movements near the surface occurred over deeper water in swift-flowing regions of the bay.  These movements were closely associated with tidal currents, with the fish orienting in the direction of the water, using the flow to aid in transport.  Fish moving in this manner can realize significant energetic savings.  The results from this study are currently either in press or have been submitted to peer review.

Phase II: Field work began in April 2004 and continued through March 2006. A total of 212 green sturgeon were captured, of which 96 met the tag-size criteria and were tagged and released.   An array of 50 automated listening stations was deployed in the Sacramento River and San Francisco Bay between the A.C.I.D. Dam in Redding, CA and the Golden Gate Bridge. Monitors were checked and the data downloaded at regular intervals. In addition to detecting fish tagged in this project, detections have been recorded of chinook salmon and steelhead tagged by other programs and agencies.  This monitor framework formed the basis for the array now operated by the Central Valley Fish Tracking Consortium. Sixty tagged green sturgeon were later detected within the monitor array.  Of these, we observed three separate annual “spawning migrations”  involving 15 individuals.  Most fish that migrated into the river entered the bay in March and April.  Sturgeon entering later in the season often failed pass Red Bluff Diversion Dam (RBDD) prior to the annual installation of the water control gates on May 15.  We noted two different patterns of migration and emigration.  Six green sturgeon are thought to have spawned in the river near Redding, CA, then moved out after the summer with the onset of the first fall high flow.  This pattern is similar to that observed in the species in northern rivers.  However, nine sturgeon exited the river early, before the end of August, not correlated to any changes in temperature or flow.  Of these fish, five passed under the RBDD gates during emigration.  The results of this study are in press.

These phases of research on green sturgeon movements are no longer active at this time; however, the Biotelemetry Lab remains actively involved in green sturgeon research (click here see active projects).

Personnel:

John T. Kelly, Ph.D. (co-lead)

A. Peter Klimley, Ph.D.
Department of Wildlife, Fish, & Conservation Biology, University of California, Davis

 
Joseph C. Heublein (co-lead)

Carlos E. Crocker, Ph.D.
Western University of Health Sciences

Acknowledgements:

We greatly appreciate the efforts of N. Kogut, R. Schaffter, D. Kohlhorst, M. Silva, and the field staff of the CDFG Bay/Delta Branch. Thanks also to B. Kihslinger and all those that volunteered their time on the water. This research is funded by a grant from the Anadromous Fish Restoration Project (a cooperative US Fish and Wildlife Service and US Bureau of Reclamation program) and CALFED.