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, current regime) 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.

Fig. 2. Vemco V22 transmitter

Methods:

Green sturgeon are 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. Currently, fish are captured for us by Captains Mike Holm and Mike Fontes aboard the F/V Intrepid (Fig. 1.).

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

In Phase I, fish are 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 is 10-14 days. Tagged fish are 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 are sampled to a maximum depth of 25 m with a Hydrolab Surveyor II. Collected data are entered into ArcView along with spatial data sets for analysis.

In Phase II, fish will be surgically implanted with small ultrasonic tags (Vemco V16). Tag life is expected to be >4 years. The ultrasonic tags permit long term monitoring of tagged fish with automated listening stations (Vemco VR2) in both salt and fresh water (Fig. 4.). These monitors will be deployed throughout the Sacramento River system and will remain in place year-round. Data recorded in this manner will both elucidate the timing of green sturgeon movements and identify which reaches of river are most important for spawning and holding. When critical reaches are identified, we will be able to describe the habitats and quantify the physical parameters in those locations.

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) have been tracked thus far in the San Francisco Estuary during the fall months of 2001 and 2002 (Fig. 5). Green sturgeon make use of much of the San Francisco Estuary, and occasionally make 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 localized non-directional movements consistent with foraging, to large scale, highly directional movements. 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. Detailed analyses of the recorded movements of these fish are underway, and peer reviewed publications are in preparation.

Phase II: Field work began in April 2004. Fifty eight sturgeon were tagged and released in the Spring and Fall 2004 field seasons. We hope to tag as many as 50 more fish in the Spring 2005 season currently under way.

Fig. 6. Locations of VR2 listening stations in the Sacramento River area (click for 579kb higher resolution image)

An array of 38 automated listening stations is now deployed on the Sacramento River between the Rio Vista Bridge at the entrance to the river delta and the A.C.I.D. Dam in Redding, CA (Fig. 6). Monitors are 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.

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.

Department of Biology, San Francisco State University

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.