TO GROW AN OYSTER

Oyster Hatchery Building
Close-up of spat on shell.
Contractors use high-pressure seawater hoses to blow cultch material off of a barge while making a new cultch plant near Breton Sound.
FRL staff removing SOS shell bags from setting tanks and stacking them on pallets (50 shell bags per pallet) for loading into refrigerated trucks and transport to deployment location near Breton Sound.
D-stage larvae 24 hours post-fertilization. This larvae is from a brood produced March 28, 2017.
Map of SE LA showing locations of NRDA funded cultch plants and MCV Oyster Hatchery.

How a partnership between LDWF and LA Sea Grant is guiding the Louisiana oyster into the future

story by Brett Falterman & Erin Olson, LDWF Grand Isle Fisheries Research Lab

 

How did LDWF get into the Hatchery Business?

The link between oysters and oil spills may not be an obvious one, but it was the Deepwater Horizon oil spill in April 2010 that brought the Louisiana Department of Wildlife and Fisheries (LDWF) into the oyster hatchery business. LDWF faced the difficult challenge of preemptively exploring solutions in the occasion the oil spill damaged Louisiana’s oyster resource. Following a commitment of roughly $14 million from BP early restoration funds, LDWF began planning an oyster restoration strategy based on both supplemental cultch planting (see sidebar) and the development of a state-of the-art oyster hatchery capable of producing 1 billion oyster larvae per year. With a construction budget of just over $2 million, the Michael C. Voisin (MCV) Oyster Hatchery opened in August 2015, and oyster production began that same year.

 

The idea of an oyster hatchery in Louisiana wasn’t a new one. LSU and LA Sea Grant Professor Dr. John Supan began scaling up the idea back when he first began working in Grand Isle in 1990. His plans included beginning with a small hatchery, eventually evolving into the joint LDWF and LA Sea Grant facility that exists today. The two organizations joined forces in 2008 when LA Sea Grant began plans to co-locate their existing oyster hatchery at the new LDWF Fisheries Research Lab on Grand Isle.

 

“The partnership between LA Sea Grant and LDWF represents a tremendous return on investment from university research and extension working with the mission of a state agency to support the natural resources that coastal industries of Louisiana rely upon for sustainability,” according to Dr. Robert Twilley, Executive Director of the Louisiana Sea Grant College Program.

 

The final Programmatic Damage Assessment and Restoration Plan, released in 2016, indicated oysters in Louisiana were significantly damaged by the Deepwater Horizon oil spill. While the mandate for hatchery-based oyster restoration has been met, LDWF continues to pursue oyster restoration as well as to identify other roles for hatchery operations. The current joint operation mission tasks LDWF with production of oyster larvae for industry and restoration needs and LA Sea Grant with extension and research.

 

What does it take to Grow an Oyster?

Producing oysters in a hatchery setting along coastal Louisiana is quite challenging due to water quality needs, feeding requirements, and life cycle of the oyster. Salinity is an essential water quality parameter that presents a challenge to both oyster hatchery operations and oyster survival as a whole in Louisiana. The hatchery’s coastal location allows access to higher salinity water (10 ppt and higher, with 12-18 ppt optimal), but hatchery operations are additionally adjacent to North America’s largest freshwater river, causing wild fluctuations in salinity. The hatchery is designed to run on both bay water from the lower Barataria Bay, but can also run on ‘recirculation mode,’ where the same water is filtered and reused until bay salinities return to optimal levels. ‘Recirculation mode’ is enabled by a 24,000-gallon seawater storage tank system.

 

Temperature is another critical water quality parameter, and the hatchery has equipment in place to manipulate water temperature to enhance production. In the wild, oysters spawn in spring and fall, but the hatchery includes a boiler system capable of heating or cooling broodstock conditioning systems, so larvae can be produced outside their natural spawning season for nine to 10 months out of the year.

 

Since oysters are filter feeders, production of food is necessary; therefore, a successful hatchery needs both oyster and algae specialists. The hatchery is designed to harvest 2000 liters of algae per day, composed of a mixture of four different species and strains. The cultures begin in small flasks (“Algal Cultures” in flow chart on page 26). The cultures are transferred into 13-gallon hanging bags for the rearing period (“Algal Production” in flow chart). The algal bags system is continuous, with 144 hanging bags at any given point. Filtered seawater continuously flows into the bags. The harvest rate matches the seawater flow, so if the culture stays healthy, harvest continues from the same bag for several months.

 

Oyster hatcheries are designed to accommodate all life stages of the oyster, including the mobile larval stage and a sessile (sedentary) adult phase. Spawning oysters starts with the broodstock, which are adult oysters kept in a ‘farm’ and managed for spawning needs. Oysters are protandric hermaphrodites, meaning they are male when they are young and become females later in life. LA Sea Grant manages the broodstock (“Broodstock” in flow chart), including different age classes, ploidy (the number of sets of chromosomes), genetic lines, and geographic origin. The hatchery has both diploid and tetraploid lines in its broodstock farm. A diploid is the ‘wild’ variation and has two sets of chromosomes. A tetraploid has four sets of chromosomes. Additionally, LA Sea Grant’s breeding program produces triploid oysters by fertilizing diploid eggs with tetraploid sperm. Triploids are preferred for oyster culture because they are incapable of reproduction and stay in market condition (fatty) all year.

 

The oyster larval cycle begins with external fertilization, with gametes mixing and fertilization occurring in the water column. The eggs hatch in less than a day and become ‘D-stage’ larvae, named for their shape at this early developmental stage, at about 48 hours. The larvae are raised in the hatchery for roughly 10 to 20 days until they reach their final larval phase known as a ‘pedivelier’ (i.e. a ‘footed’ larvae; “Pediveligers” in flow chart). They use this foot to attach to a hard surface or cultch material, preferably calcium carbonate materials such as oyster shell. Hatchery biologists then harvest the pediveligers from the tanks. If left in the tanks, they would attach to the walls (“Larval Sale” in flow chart). Once set, the larvae go through metamorphosis and become young oysters, referred to as ‘spat.’ The type of material pediveliger attaches to ultimately determines how it can be utilized down the road.

 

Where do LDWF Hatchery Products go?

One of the department’s goals for the hatchery is to provide support for the fledging off-bottom oyster industry and for oyster restoration projects. LDWF sells pediveliger larvae and oyster seed. ‘Pediveliger’ are oysters in the developmental stage, while oyster seed refers to a small oyster, less than 1 inch in size, that has already set. The greatest demand is for triploid larvae, which are designated for commercial oyster farms. These triploid larvae are sold for $400 per million, with the department selling over 194 million in 2018. There is also a demand for triploid seed. Seed is produced by setting on finely ground oyster shell, smaller than a grain of sand. This takes place in a setting tank. Larval survival and setting success varies greatly. Triploid seed costs $13.50 per 1,000, and LDWF sold almost 800,000 triploid seeds in 2018. The production season typically begins in late March and lasts through November. Oyster larvae and seed orders can be placed though the department’s commercial sales site at www.wlf.louisiana.gov/fishing/oyster-larvae-order-form. Most triploid products end up on the oyster half-shell market.

 

The hatchery also produces diploid larvae for statewide restoration projects. Rather than using single seed oysters, setting diploid larvae on whole shell is preferred for restoration projects. Interestingly, oyster shell is not that easy to come by, even in Louisiana. But thanks to a partnership between LDWF and the Coalition to Restore Coastal Louisiana, LDWF is able to use recycled oyster shell from local restaurants for restoration projects. The shell is loaded into mesh shell bags (“Spat on Shell Bags” in flow chart) and placed in 2,000-liter setting tanks (“Spat on Shell Setting Tanks” in flow chart), where diploid larvae are set on the recycled shell. The larvae are set in static (no flow) tanks for 48 to 72 hours. The product is then referred to as ‘spat-on-shell’ or ‘SOS.’

 

The current restoration intention for SOS produced at the hatchery is to create oyster broodstock reefs. LDWF identifies locations where wild Louisiana oysters are in need of spawning assistance, and SOS is deployed and monitored in these locations. These areas are closed to commercial harvest with the hope the SOS grows into a successful oyster reef, and young from these reefs enhance the surrounding area. So far this year, LDWF has enhanced four such areas, including locations near Breton Sound and Barataria Bay (“Spat on Shell Deployment” in flow chart).

 

 

Oyster Cultch

The term ‘cultch’ refers to any substrate material to which oyster larvae may set. Oyster shells and crushed limestone are the most common cultch types. Both commercial oyster fishermen and LDWF use cutch material to enhance potential oyster habitat. LDWF has established oyster cultch plants across the state. BP Early Restoration Funds were used to establish seven cultch plants statewide at a price tag of almost $11 million.

 

 

Oyster Sales Proceeds

When LDWF sells oyster larvae or seed to oyster growers who order them from the MCV Hatchery, sales proceeds first go towards paying the royalties LDWF has to pay to the private company that owns the tetraploid oyster line used in the LDWF hatchery to spawn triploid oysters.  Triploids are made by crossing a diploid female oyster (two sets of chromosomes) and tetraploid male (four sets of chromosomes). Once royalties are paid, remaining funds go into the Public Oyster Seed Ground Development Account and support enhancement of the oyster resources in Louisiana waters.

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