Oyster Sanctuary Program
North Carolina's effort to restore subtidal oyster populations with protected artificial reefs
Overview
In North Carolina, the eastern oyster (Crassostrea virginica) was once an abundant and economically important species. However, around the world subtidal oyster reefs have declined drastically as a result of overfishing, harvest gear impacts, pollution, disease, and decreasing habitat quality [1,2,3,4] .
In 1996 the Division of Marine Fisheries began the Oyster Sanctuary Program with the aim to restore the state's subtidal oyster population.
Today, North Carolina's oyster sanctuary program extends over 789 acres of protected subtidal habitat across 17 sites.
Impressive right? But you may be wondering...
What is an Oyster Sanctuary?
An oyster sanctuary is an area where the harvest of oysters is prohibited.
DMF's Habitat & Enhancement Section builds these large artificial reefs in Pamlico Sound with the aim to promote thriving subtidal oyster populations.
These reefs range anywhere from 10 to 80 acres in size. That's up to 60 football fields!
Sanctuaries are protected so that oysters may grow and survive to adulthood.
Large, healthy adult oysters act as a brood stock, providing larvae for cultch and natural reefs. A single adult oyster spawns millions of eggs every year.
1 out of every 4 larvae settling on commercially harvested oyster reefs come from a Sanctuary [5] .
Larvae are carried by currents and tides throughout Pamlico Sound as they try to find a place to settle.
After "swimming" for up to two weeks, the larvae attach to an oyster shell or rock on a natural reef, a cultch site, or another sanctuary.
Once settled, baby oysters (also called "spat") will grow into adults.
The Oyster Sanctuaries supplement the larval supply of Pamlico Sound.
They help to restore natural subtidal reefs and help cultch reefs grow, enhancing commercial opportunities for the fishery.
But they also have a few other benefits...
Habitat Benefits
Over time, Oyster Sanctuaries provide several benefits in the form of ecosystem services, by improving water quality and providing opportunity to the people of North Carolina.
In fact, for every dollar invested in North Carolina's oyster sanctuaries, there is a $4 return in the form of economic opportunity & ecosystem services [6] .
Read below to learn more about what sanctuaries and oyster reefs can do!
Water Filtration
Perhaps the most well known benefit of oysters is their ability to filter water. As filter feeders, oysters survive by filtering out small organic matter from the water column.
Lucky for us, a single oyster can filter up to 12.5 gallons a day in the wild [7] . This helps to keep the water clean from harmful bacteria.
Take a look at the video to see the oyster's super power in action! [8]
Reef Builders
Much like tropical coral reefs, oyster reefs provide habitat for many species in estuaries.
Shell-bottom formed by several generations of oysters provide hiding places for diverse assemblages of many small fishes and invertebrates.
Oyster reefs act as nurseries and refuge for small fishes and invertebrates. But they also provide safe forage space for others.
Recreational Opportunity
While the sanctuaries are closed to oyster fishing they are open to hook-and-line anglers, making oyster sanctuaries popular and productive sport-fishing spots.
Some species commonly found on oyster sanctuaries include: sheepshead, oyster toadfish, and North Carolina's state fish, red drum!
From restoring the ecology of subtidal oyster reefs of Pamlico Sound to the socioeconomic benefits, there are many great reasons for building Sanctuaries!
But you may be wondering: "How are they made?"
Scroll down to look into the process!
Construction
Over 28 years, North Carolina's approach to building sanctuaries has gone through various stages, refined with each project through adaptive management.
A variety of materials have been used, including limestone marl, granite, consolidated concrete, concrete pipe, reef balls, and recycled shell. In total, over 280,000 tons of aggregate material have been deployed across the state's 17 oyster sanctuaries.
Building an oyster sanctuary is a little more complicated than simply throwing some rock into the water...for starters, you need A LOT of rocks!
Site Selection
Many factors are considered when building an oyster sanctuary, including salinity, dissolved oxygen, depth, sedimentation, substrate type, and wind patterns to name a few.
These data go into a habitat suitability index (HSI) model (right). This helps determine which areas might have the best conditions for a productive oyster sanctuary [9] .
Managers select a new sanctuary site based on biological and logistic variables as they begin the permitting and planning process.
Material Stockpiling
Moving thousands of tons of rock into the middle of Pamlico Sound doesn't just happen overnight.
Our team coordinates with contractors on material deliveries, maintains stockpile yards, and consolidates the rock with loaders, all while planning the next stages of construction.
To the right we have nearly 18,000 tons of marl limestone piled high! (That's like 180 blue whales!) This material was used to build about 20 acres of protected habitat.
Material Deployment
During the spring and summer, when the water is calm, a tug boat pushes a 200 foot barge packed with 700-800 tons of material to the new site. Onboard, two excavators are ready to lay down the rock.
Over the course of four hours, the deployment team will build two parallel ridges, each approximately 200 feet long and 40 feet wide. The new reef line stands 4-6 feet off the bottom, ideal for water and nutrient flow to the aquatic species that will eventually colonize it.
It will be at least a year before oysters attach and grow on the new material, and within 3 years they will reach adulthood. By then, the first generation of oysters on the sanctuary will begin supplying larvae to the rest of the Sound.
You can see how a new sanctuary is planned below!
OS16 - Cedar Island
This 75 acre site is the most recently completed oyster sanctuary. Over three years, approximately 52,000 tons of marl limestone and recycled crushed-concrete have been deployed to create 132 high profile ridges.
Each ridge is about 180 feet long by 35 feet wide and up to 8 feet tall.
Slide the viewer to see how well the ridges line up with the original blueprint!
Where are the Oyster Sanctuaries?
Interested in recreational hook and line fishing? Want to scuba dive on a protected oyster reef? Use the map below to find the closest Sanctuary to you & plan a visit!
Zoom in & click on a sanctuary to learn more about the various materials used to construct the reef.
Oyster Sanctuaries August 2023
Each year, DMF Biologists and Technicians set out to get eyes in the water and survey the sanctuaries.
Keep scrolling to dive into the monitoring process!
Monitoring
Annual monitoring efforts provide valuable data on the performance of each sanctuary. These data are then used when considering where to place a new site, which materials to use, even the structural design of a new reef.
If you find yourself fishing at an Oyster Sanctuary during the summer, there's a chance you'll see our dive team conducting annual monitoring efforts!
Scientific Dive Team
Biologists and Technicians put on their scuba gear each summer to gather data on each of the 17 sanctuaries.
Our dive team is well trained to dive in low visibility waters while they carry equipment, record data, and excavate samples.
Typical conditions mean divers can't see more than 5 feet in front of them, and other conditions might make it especially challenging. Sometimes there might be swarms of jellyfish getting tangled up in sampling gear or strong currents.
Sample Collection
Divers will visit over 150 randomly selected spots across all 17 sanctuaries in a single year.
They bring a quadrat to keep data collection consistent. Here divers are excavating marl limestone with oysters growing on it. They pack the rocks into a basket and bring back to the surface, where they count and measure the sample.
Over the course of a summer, our team will measure over 20,000 oysters that were found on sanctuaries.
That's a lot of oysters! And data!
Sanctuary Performance
With all those data, we get an idea of how the population at each sanctuary has changed over time.
Check out the graph of Raccoon Island. Watch how the oyster population changes over the course of 4 years.
First, there is a boom of small oysters. In the following years, the population stabilizes as it reaches carrying capacity. By 2024 there were more larger oysters that survived to adulthood.
In 2024, sanctuaries had on average 1,581 oysters per square meter. Many of these were spat or sublegal individuals. On average, the sanctuaries had 169 adult oysters per square meter.
Data Analysis
With a variety of materials used to build the sanctuaries over the last 28 years, knowing how these materials persist over time is important for future oyster restoration efforts.
Monitoring surveys allows scientists to analyze trends in performance with respect to how many adult oysters live on aging material. In the graph on the right, you can analyze the relationship of material age and oyster density.
Analyzing monitoring data provides useful insights for which materials to use, where to build, and how to design a sanctuary reef. If you would like to do a deeper dive into exploring the long-term dataset, check out this visualization tool!
Ongoing Projects
In 2023, the North Carolina Coastal Federation received $14.9 million in grant funding from NOAA through the Transformational Habitat Restoration and Coastal Resilience Grants program.
Through their proposal NCCF will continue its collaborative efforts with DMF to build additional oyster sanctuaries, specifically the construction of the two largest sites within the program. These new sites will be at Maw Point (OS-18) and Brant Island (OS-19), which will combine for 130 acres of protected oyster habitat that will be built through 2026.
Additionally, the proposal will also provide funding for graduate and undergraduate research opportunities to students North Carolina State University’s Center for Marine Sciences & Technology and North Carolina Central University.
The Senator Jean Preston Oyster Sanctuary Network will consist of 17 sanctuaries and encompass 789 acres of permitted, protected habitat.
Sanctuary Collaborators
Over the past 27 years, DMF has partnered with several organizations to develop the extensive network of sanctuaries that exist today. From providing funding to coordinating contractors, these partners have assisted in DMF's efforts to rebuild Pamlico Sound's subtidal oyster reefs.
