Eelgrass Survey PARADISE CAY BELVEDERE, MARIN COUNTY CALIFORNIA. Prepared For:

Transcription

1 Eelgrass Survey PARADISE CAY BELVEDERE, MARIN COUNTY CALIFORNIA Prepared For: Radford (Skid) Hall, Ph.D. Land Planning and Permitting Consultant 500 Airport Blvd., Suite 350 Burlingame, CA (650) WRA Contact: Justin Semion Amy Parravano Date: August 31, 2006

2 TABLE OF CONTENTS 1.0 INTRODUCTION BACKGROUND Eelgrass Ecology Eelgrass Regulatory Policy STUDY AREA DESCRIPTION PROJECT DESCRIPTION RESULTS CONCLUSION REFERENCES...6 LIST OF FIGURES Figure 1. Project Location Map....2 Figure 2. Project Area....4

3 1.0 INTRODUCTION The purpose of this study was to survey and map of the distribution of eelgrass (Zostera marina) within existing channels proposed for maintenance dredging at Paradise Cay, a residential community built on the waters of the San Francisco Bay (Bay) in Tiburon, Marin County, California (Figure 1). The Study Area for the eelgrass survey included two existing access channels to Paradise Cay, one at the northern end of the residential area, and one at the southern end. The survey was conducted at the request of the Dredged Material Management Office (DMMO) as part of their review of an addendum to the previously issued maintenance dredging permit. The survey was conducted on August 24, Eelgrass Ecology 2.0 BACKGROUND Eelgrass (Zostera marina) is a sea grass with dark green, long, narrow, ribbon shaped leaves cm in length (exceptionally up to 2 m long) with rounded tips. Leaves shoot from a creeping rhizome that binds bottom sediments. An individual rhizome may have many shoots; however, most shoots tend to be towards the growing end of the rhizome. Leaves and rhizomes contain air spaces, called lacunae, that aid buoyancy. Numerous flowers occur on a reproductive shoot similar to those of terrestrial grasses. The flowers float near the surface, are pollinated by floating pollen and produce seeds that sink to the bottom and germinate the following year. Eelgrass is common throughout the northern Pacific and Atlantic Oceans. It is a known spawning habitat for Pacific herring (Clupea pallasii) and provides habitat for many other species of fish, mammals, and invertebrates. In San Francisco Bay, the first study on the baywide distribution of eelgrass indicated that it covered upwards of 300 acres (Wyllie-Echeverria and Rutten 1989). More recent studies suggest it is more widespread within the Bay, covering approximately 2,880 acres (Merkel and Associates, 2003). Eelgrass in the Bay is restricted to a narrow intertidal range between approximately +1 ft MLLW and -6 ft MLLW. Its depth range at a particular site is dependent primarily on water turbidity as plant growth is light limited (Zimmerman et al. 1991). Sediment type, currents, bottom shear, and water temperature also affect its distribution. Although eelgrass is typically a perennial species that dies back to a persistent underground rhizome during the winter, there is mounting evidence that it also occurs as an annual species in many parts of the Bay (Fonseca et al., 1998, 2003; Merkel and Associates, 2003). These studies noted a high annual overturn for some beds, especially those in warm and turbid environments. The number of individual plants can, therefore, fluctuate and show more of an annual growth pattern in some areas, as opposed to typical perennial growth shown in other areas of the Bay and coastlines around the world. Eelgrass on the Tiburon peninsula tends to grow in sheltered coves away from the strong currents that can occur in the area. Studies in Kiel Cove, south of the Study Area on the Tiburon peninsula, measured turbidity as among the lowest recorded in the Bay, allowing eelgrass to grow to depths of -6 ft MLLW (Zimmerman, et al. 1991, 1995). Patchy distributions of eelgrass have been mapped in the cove directly south of Paradise Cay as part of the San Francisco Bay Eelgrass Inventory (Merkel and Associates, 2003). 1

4 To San Rafael Study Area Location 101 To San Francisco Figure 1. Paradise Cay Location Map. Tiburon, California Miles Date September 2005 Basemap: U SGS DRG Sausalito Quad Map By: Justin Semion Filepath: l:\acad 2000\16000\16123\gis\ArcMap\Figure1 location.mxd

5 2.2 Eelgrass Regulatory Policy Eelgrass itself is not listed as threatened or endangered. However, because eelgrass is spawning ground for Pacific herring and is important habitat for other aquatic wildlife, eelgrass beds are regulated as Essential Fish Habitat (EFH) by the National Marine Fisheries Service (NMFS), and by the California Department of Fish and Game (CDFG) through the California Environmental Quality Act (CEQA) review process. As a responsible agency under CEQA, CDFG can comment on any proposed project that may affect eelgrass habitat, and approve mitigation measures for any impacts. Protection of EFH is mandated through changes implemented in 1996 to the Magnuson-Stevens Fishery Conservation and Management Act (Magnuson-Stevens Act) to protect the loss of habitat necessary to maintain sustainable fisheries in the United States. The Mangnuson-Stevens Act defines EFH as "those waters and substrate necessary to fish for spawning, breeding, feeding, or growth to maturity" (16 U.S.C. 1802(10)). Under regulatory guidelines issued by NMFS, any federal agency that authorizes, funds, or undertakes action that may affect EFH is required to consult with NMFS (50 CFR ). The first official regulatory policy regarding eelgrass protection on the west coast was the Southern California Eelgrass Mitigation Policy, issued by NMFS in 1991, developed by NMFS, CDFG, and the U.S. Navy. Although there is no official regulatory policy for eelgrass in San Francisco Bay, the Southern California Eelgrass Mitigation Policy is used as guidance for subtidal work that may affect eelgrass in the Bay. However, final approval for projects that may impact eelgrass are determined by NMFS and CDFG on a project by project basis. 3.0 STUDY AREA DESCRIPTION The Study Area included subtidal areas within two entrance channels to Paradise Cay harbor. Elevations in the entrance channels range from approximately -3.4 feet Mean Lower Low Water (MLLW) to feet MLLW. The entrance channels have been dredged consistently in the past to provide boat access to residences in Paradise Cay, and are used regularly by boat traffic into and out of Paradise Cay. 4.0 PROJECT DESCRIPTION The proposed project consists of maintenance dredging within two entrance channels to Paradise Cay (Figure 2). The entrance channels will be dredged to a depth of approximately -8 feet MLLW to allow for residential boat access to the Cay. Each channel will be dredged for a sufficient distance for dredged depths to reach equivalent existing depths in the Bay. Dredging in the north channel will extend approximately 650 feet from the entrance to the Cay. The south channel will be dredged to a distance of approximately 1000 feet from the harbor entrance. Each channel will be approximately 25 feet wide, with 3:1 side slopes. 5.0 SURVEY METHODS The eelgrass survey was performed at low tide on August 24, The Study Area was traversed by boat along transects running parallel to the shoreline to determine presence or absence of eelgrass. A sub-meter accuracy Global Positioning System (GPS) unit was on hand 3

6 Legend Dredge Project Area Study Area Figure 2. Project Area and Study Area Location SCALE Feet 1 inch equals 400 feet 1:4,800 Map By: Justin Semion Basemap: USGS UrbanAreas 2004 Filepath: l:\acad2000\15119\gis\arcmap\ Figure 2 Project.mxd

7 for use to map any eelgrass patches and eelgrass beds that were present. Eelgrass patches are defined as those areas smaller than 0.01 acres and containing fewer than 10 individuals. Eelgrass beds are defined as areas larger than 0.01 acres and containing more than 10 individuals. Areas where eelgrass occur as patches smaller than 15 feet in diameter are typically mapped as GPS points. The perimeters of eelgrass beds (areas greater than 0.01 acres) are mapped as a polygons by tracing the perimeter of the eelgrass. If observed, the number of shoots present and the approximate diameter of each eelgrass patch are recorded. The approximate cover by eelgrass shoots within the eelgrass beds is estimated visually using m quadrats. 6.0 RESULTS No eelgrass was observed within the Study Area. A few small patches were observed within the northern portion of the Paradise Cay harbor, more than 140 feet from edge of the 3:1 slopes in the proposed dredge area. Eelgrass in this area occurred at elevations shallower than approximately -1 foot MLLW, with the majority of the eelgrass occurring in mudflat areas along the shoreline. Eelgrass was observed growing in a similar pattern and at similar depths in the cove just south of the Study Area, where it had been mapped during the San Francisco Bay Eelgrass Inventory. Overall, turbidity in the Study Area and adjacent areas of the Bay appeared to be very high, likely contributing to the limited depths at which eelgrass was able to survive. In addition, current and wind shear in the entrance channels observed during boat navigation appeared to be higher than those in areas of the Bay known to support eelgrass. 7.0 CONCLUSION No eelgrass was observed within the Study Area, which included the north and south entrance channels extending from the Paradise Cay harbor to the eastern edge of the proposed dredge area. Turbidity, wind shear, and current in the entrance channels appeared higher than in other areas of the Bay known to support eelgrass. These environmental factors, combined with the frequent use of the entrance channels by boaters, result in habitat conditions in the Study Area that are not suitable for eelgrass growth. Although a few eelgrass patches were observed close to the shoreline in the northern portion of the harbor, these areas will not be affected by the dredging. The edge of the 3:1 side slopes in the dredged area is more than 140 feet from the eelgrass patches. Elevations within the dredge area are 2 feet or more deeper than the elevations where eelgrass was observed in the area. In addition, existing turbidity in the area in and around Paradise Cay is high, so any increase in turbidity that may occur due to dredging is likely to have a negligible effect on eelgrass. Dredging is also scheduled to occur during the time of year when eelgrass dies back in the Bay, further ensuring that the dredging will not affect the few eelgrass patches present near the Study Area. No impacts to eelgrass are expected as a result of this project. 5

8 8.0 REFERENCES Fonseca, M.S., W.J. Kenworthy, and G.W. Thayer Guidelines for the conservation and restoration of seagrasses in the United States and Adjacent Waters. US Dept Commerce/NOAA Coastal Ocean Analysis Series. No. 12. Merkel and Associates, Inc San Francisco Bay Eelgrass Inventory. Submitted to CalTrans and NOAA Fisheries. June - October Wyllie-Echeverria, S. and P. Rutten Inventory of eelgrass (Zostera marina) in San Francisco Bay/San Pablo Bay. NMFS/NOAA Administrative Report SWR Terminal Island, CA October Zimmerman, R.C., J.L. Reguzzoni, S. Wyllie-Echeverria, M. Josselyn, and R.S. Alberte Assessment of Environmental suitability for growth of Zostera marina (eelgrass) in San Francisco Bay. Aquatic Botany 39: Zimmerman, R.C., J.L. Reguzzoni and R.S. Alberte Eelgrass (Zostera marina L.) Transplants in San Francisco Bay: Role of light availability on metabolism, growth and survival. Aquatic Botany 51: