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San Francisco Estuary Invasive Spartina Project
Drift Card Study

Overview | Locations | FAQs


This study is intended to mimic the dispersal patterns of non-native Spartina seed by releasing floating ‘drift cards’ at selected locations within the Bay and tracking where the cards are found. This will help us to better understand where Spartina might crop up in the future.

Spartina dies down the ground each fall/early winter. The stems break off and form large mats (called wrack), which float with the tides on the water surface. Wrack may carry Spartina seed – which can survive in wet, cold, salty conditions (like those found in Bay waters) for periods of one year. If we can find the “hot spots” for where seed is drifting, we will be able to identify high-risk areas where we want to concentrate our future monitoring work.

The first round of drift cards involved three releases at each of seven sites in spring and summer 2007. The letters (A-G) identify the sites and the numbers (1-3) indicate which release date. For example, at Site A, there were three separate releases of 50 cards each, so the identifying group code would be A-1 for the first release, A-2 for the second and A-3 for the third.

To gather additional information, a second round of drift card releases commenced in December 2007. As before, letters (H-N) identify the locations and the numbers mark whether the card came from the first, second or third batch of cards dispersed at that site. (See below for exact release dates.)

It has now been several years since the first two rounds of drift card releases and there has been significant progress on the eradication of invasive Spartina from San Francisco Bay. The baywide infestation has been reduced by over 90% from the peak acreage of 2006, and a large number of sites are approaching eradication. However, there are a small number of sites that still contain a substantial infestation of invasive cordgrass and ISP is seeking more information about how those sites may influence the eradication around the Bay as treatment progresses.

Information from a third round of drift card releases from these sites in late 2011 and early 2012 will help to inform future monitoring efforts, will provide additional data on currents to enhance the lessons learned from the first two rounds, and will provide an educational tool for discussions with permitting agencies as well as shoreline landowners.

The cards are released individually at each marsh site — flung, dropped, or tossed into the open water, taking advantage of outgoing tides.

Public volunteers who report the locations where they find the cards are a critical part of our drift card study. Your efforts directly enhance the effectiveness of ISP’s Control Program.

From the information gathered in this study, staff is developing a database and map of the distribution of cards throughout the Bay. Several cards released from Creekside Park, Corte Madera Creek traveled many miles to the outer coast. Many of the cards released at the West Bay sites of Colma Creek and Bair Island traveled southeast, crossing the entire Bay. One interesting deposition spot from multiple release sites was the USFWS Don Edwards National Wildlife Refuge near the Dumbarton Bridge.


If your card has the letter: It was released from:
Round 1  

The mouth of the Alameda Flood Control Channel in Fremont

B Bair/Greco Island Complex, San Mateo County
C Elsie Roemer Bird Sanctuary, Alameda
D San Lorenzo Creek Mouth, San Leandro
E Colma Creek, South San Francisco
F Cogswell Marsh, Hayward
G Creekside Park, Corte Madera Creek, Corte Madera
Round 2  
H Stevens Creek Tidal Marsh, Mountainview
I MLK New Marsh, San Leandro Bay
J Rheem Creek Point, Richmond
K Knapp Tract on Alviso Slough, Santa Clara County
L SamTrans Peninsula, Colma Creek, South San Francisco
M San Leandro Marina
N Napa River at Sears Point Bridge, Vallejo
Round 3  
O Bair Island at Steinberger Slough, Redwood Shores
P Alviso Slough at Calaveras Marsh, Santa Clara County
Q Cooley Landing, East Palo Alto
R Corte Madera Creek Mouth, Larkspur
S San Pablo Marsh, Richmond
T Arrowhead Marsh/ MLK Restoration Marsh, Oakland
U North Marsh, San Leandro


Frequently Asked Questions

1) What should I do with the card(s)?

After you have shared the location where you found the card, please feel free to either throw the cards away or to keep them.

  • ! Please do NOT throw them back into the Bay!
  • ! Please do NOT place them back on the beach!– where they could wash back into the Bay. (This would confound our findings!)

2) When was my card released?


The number following the release location letter on your card indicates the release date of your particular card. For example, the first cards were released in March 2007.

The second set of releases (with cards numbered 2) occurred in April.

The third and last set was dispersed at various dates from late May to mid-August 2007.


The first batch of cards from each location was released in December 2007-January 2008. The specific dates are:

Dec. 19 – I-1
Jan. 18 – H-1, J-1, K-1
Jan. 23 – L-1, M-1, N-1

The second release of cards from these sites occurred in February and March. The specific dates are:

Feb. 18 – H-2, K-2
March 4 – I-2, L-2, M-2
March 5 – J-2, N-2


The first batch of cards was released for each location in late November 2011.

3) How long is this study?

The first two rounds of drift card releases began in March 2007 and continued throughout 2008. A third round of card releases began in November 2011 and will extend into early 2012. People may be finding cards up to a year after the initial release. So, please contact us with any additional cards you find at (510) 548-2461 or www.Spartina.org

4) Aren’t you contributing trash to the Bay?

While these drift cards are man-made objects, they are fully biodegradable and constructed to degrade within a short period of time. They are made of sustainably farmed mahogany plywood and coated with non-toxic, lead-free paint and ink. The cards are considered a very low-impact way to study surface currents in oceans around the world. This method of study has helped to model potential oil spill scenarios, collection points for garbage, and now, the potential spread of invasive species.

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