Save Drakes Bay Coalition
working to protect and preserve the ecology, wildlife, and wilderness status of Drakes Estero in Point Reyes National Seashore
Drakes Estero: A Crown Jewel of the Ecosystem
See below for information and resources regarding Drakes Estero's wildlife, habitat, and the threats to them
See below for information and resources regarding Drakes Estero's wildlife, habitat, and the threats to them
Disturbance of the larger fauna by commercial oyster farming has been documented at Drakes Estero and elsewhere. Harbor seals have been affected by oyster operations because of direct disturbance to seals resting onshore and displacement by oyster bags where seals rest and nurse their young (see photo of bags on right).
Oyster operation structures directly impair eelgrass habitat by reducing the quantity of light necessary for eelgrass growth. Oyster operation motorboat propellers also chop up eelgrass foliage. The NPS has documented approximately 50 acres of eelgrass being affected by these propellers (see photo in the next column). A study of oyster operations in Tomales Bay showed that oyster racks reduced shorebird use of tidal flats as well.
As filter feeders, oysters and clams are known for their ability to improve water quality by removing excess phytoplankton and harmful pollutants. However, Drakes Estero is open and shallow and the twice-daily tide flushes out the entire estero, so it doesn’t carry significant excess phytoplankton or pollutants.
Any “cleaning” that takes place is actually the result of the oysters devouring organisms that would otherwise be available for native fish, clams and other native species. The losers are the native species that depend upon a healthy, food-filled estuary. Dense racks of non-native oysters feed voraciously on phytoplankton and other nutrients that would otherwise support the natural food chain including the larvae of fish and other invertebrates. One oyster can filter 50 gallons of water per day, so imagine what millions of exotic oysters are doing to reduce food for native species (currently, there are 9 million oyster being grown in Drakes Estero).
NPS now has provided a 2010 follow up (click here) to its initial
concern presented in May 2007 to the Marin Supervisors about recent oyster
impacts to a single pupping subsite in Drakes Estero. That 2007
presentation was followed by the Becker 2009 presentation to the National
Academy that expanded the concern to all the three pupping sites in the Estero
over an 11-year period. The Becker 2010 presentation to the Marine Mammal
Commission (MMC) now expands the concern to both colony and regional level impacts over
a 21-year period. All three presentations reach the same
conclusion, namely that there is reason to be concerned regarding impacts of oyster
harvest on seal use within Drakes Estero. The oyster company is
cooperating by providing additional data and the MMC will review both the data
and the analysis to insure a high degree of confidence in the
conclusion.
Oyster operation structures directly impair eelgrass habitat by reducing the quantity of light necessary for eelgrass growth. Oyster operation motorboat propellers also chop up eelgrass foliage. The NPS has documented approximately 50 acres of eelgrass being affected by these propellers (see photo in the next column). A study of oyster operations in Tomales Bay showed that oyster racks reduced shorebird use of tidal flats as well.
As filter feeders, oysters and clams are known for their ability to improve water quality by removing excess phytoplankton and harmful pollutants. However, Drakes Estero is open and shallow and the twice-daily tide flushes out the entire estero, so it doesn’t carry significant excess phytoplankton or pollutants.
Any “cleaning” that takes place is actually the result of the oysters devouring organisms that would otherwise be available for native fish, clams and other native species. The losers are the native species that depend upon a healthy, food-filled estuary. Dense racks of non-native oysters feed voraciously on phytoplankton and other nutrients that would otherwise support the natural food chain including the larvae of fish and other invertebrates. One oyster can filter 50 gallons of water per day, so imagine what millions of exotic oysters are doing to reduce food for native species (currently, there are 9 million oyster being grown in Drakes Estero).
Wildlife and Habitat Significance
In North America, one third of our waterbird species are in decline; worldwide, 90% of all the fish species have been depleted. More than 60% of our coastal waters are moderately to severely degraded. Despite commendable efforts to conserve land resources, only .01 % of the ocean is effectively protected. Eelgrass beds are critical to ecosystem health and fisheries because they provide cover, food, and a nursery for fish and invertebrates. Unfortunately, they are found in only a few estuaries in California.
Drakes Estero’s eelgrass beds comprise as much as 7% of the state’s total. Blessed with such vegetative richness, Drakes Estero is a linchpin component of the regional ecosystem, a resource for many animals, including Dungeness crab, lingcod, rockfish, English sole, steelhead, waterbirds, and seals. Many of the approximately 60 fish species that use the Estero depend on its plankton for food and eelgrass for habitat, including the federally listed steelhead trout and Pacific herring, which spawn there in the tributaries and the eelgrass beds. It is also a seasonal home for threatened bird populations, including thousands of federally listed brown pelicans, and black brant geese, an Audubon watch list species.
The harbor seal population in Drakes Estero is one of the largest concentrations in California, in the past, reaching a maximum of nearly 2,000 seals during the breeding season and annually producing between 300 and 500 pups. The Drakes Estero colony had been growing significantly from the mid 1990s until a few years ago, largely because the level of oyster operations was reduced during that time, according to the National Park Service.
The estuary was recently designated a Western Hemisphere Shorebird Reserve Network (WHSRN), a site of Regional Importance in the U.S. Shorebird Conservation Plan because it is important to a great diversity and abundance of shorebirds. The maximum population of all shorebirds combined was estimated at between 10,000 and 100,000. A similar designation is pending for waterbirds.
Point Reyes Bird Observatory Conservation Science identified over 100 species of birds during winter surveys, including several listed species or species of special concern such as Osprey, White Pelican, Brown Pelican, Snowy Plover, Peregrine Falcon, Black Brant, and Marbled Murrelet. The estuary is very important to wintering Black Brant that only migrate to a few places along the Pacific Flyway. Hundreds to thousands of Brown Pelicans congregate there, feeding on large schooling fish such as anchovies, herring and smelt, and resting on tidal mudflats. Snowy Egrets, Great Egrets, and Great Blue Herons formed a nesting colony along the shores of the estero in the last 15 years.
In North America, one third of our waterbird species are in decline; worldwide, 90% of all the fish species have been depleted. More than 60% of our coastal waters are moderately to severely degraded. Despite commendable efforts to conserve land resources, only .01 % of the ocean is effectively protected. Eelgrass beds are critical to ecosystem health and fisheries because they provide cover, food, and a nursery for fish and invertebrates. Unfortunately, they are found in only a few estuaries in California.
Drakes Estero’s eelgrass beds comprise as much as 7% of the state’s total. Blessed with such vegetative richness, Drakes Estero is a linchpin component of the regional ecosystem, a resource for many animals, including Dungeness crab, lingcod, rockfish, English sole, steelhead, waterbirds, and seals. Many of the approximately 60 fish species that use the Estero depend on its plankton for food and eelgrass for habitat, including the federally listed steelhead trout and Pacific herring, which spawn there in the tributaries and the eelgrass beds. It is also a seasonal home for threatened bird populations, including thousands of federally listed brown pelicans, and black brant geese, an Audubon watch list species.
The harbor seal population in Drakes Estero is one of the largest concentrations in California, in the past, reaching a maximum of nearly 2,000 seals during the breeding season and annually producing between 300 and 500 pups. The Drakes Estero colony had been growing significantly from the mid 1990s until a few years ago, largely because the level of oyster operations was reduced during that time, according to the National Park Service.
The estuary was recently designated a Western Hemisphere Shorebird Reserve Network (WHSRN), a site of Regional Importance in the U.S. Shorebird Conservation Plan because it is important to a great diversity and abundance of shorebirds. The maximum population of all shorebirds combined was estimated at between 10,000 and 100,000. A similar designation is pending for waterbirds.
Point Reyes Bird Observatory Conservation Science identified over 100 species of birds during winter surveys, including several listed species or species of special concern such as Osprey, White Pelican, Brown Pelican, Snowy Plover, Peregrine Falcon, Black Brant, and Marbled Murrelet. The estuary is very important to wintering Black Brant that only migrate to a few places along the Pacific Flyway. Hundreds to thousands of Brown Pelicans congregate there, feeding on large schooling fish such as anchovies, herring and smelt, and resting on tidal mudflats. Snowy Egrets, Great Egrets, and Great Blue Herons formed a nesting colony along the shores of the estero in the last 15 years.
Resources and Documents:
Extensive propeller cuts in eelgrass from oyster operation boats (click to enlarge)
Oyster bag debris in Drakes Estero. These types of bags have been documented on seal pupping grounds (click to enlarge)
A particularly invasive species found on oyster structures in Drakes Estero is the colonial tunicate (Didemnum spp) (click to enlarge)
Learn more about seal ecology at the Marine Mammal Center
Harbor Seal maps
Harbor Seal Disturbance photo (large file). Caption: Nov 9, 2007: "white outbd motor boat just behind site UEN...Seals - 47 - gave head alerts and flush water....during oystermen's presence..." (photo credit withheld at the request of the photographer).
