Oysters.us - Remote Setting 2

Remote Setting (Part 2)
John W. McCabe

Remote Setting Tanks (C. gigas)

Some type of open, large vat or pool, hereafter called a tank, is essential in remote setting. Remote setting tanks, simply called setting tanks by growers, come in various sizes, shapes and designs. Numerous materials have been used in their construction. Fiberglass, stainless steel and concrete tanks are the most common. Whatever the material used in tank construction, it is imperative that it does not emit toxins when remote setting is attempted. The same applies to any accessories (e.g. PVC aeration pipes, hoses) that come in contact with the water in the setting tanks. Hidden toxin sources are certain sealants that retain "superior flexibility" and, worse yet, are "mildew resistant". Instead, any sealant in contact with the water of such a cultivation environment should be "aquarium safe". It is common knowledge in the shellfish industry that even minute toxin amounts can negatively affect larval setting. As such, newly constructed fiberglass and concrete tanks and accessories must first thoroughly "cure" before use. In some cases, this can take several months. Some stainless alloys can also be problematic.
Ironically, as annoying as later scrubbing countless renegade spat off the sidewalls of a setting tank is, it is an endorsement of its functionality.
Most setting tanks are operated outside. Some tanks are insulated.

While there is no such thing as a "standard setting tank", they all have features in common. An oyster grower that employs remote setting will typically own one or more setting tanks that work well with the cultivation method he or she employs (e.g. ground/bottom cultivation, longline cultivation). It must hold a sufficient amount of weathered oyster shells (cultch) in a way that is conducive for larvae to distribute and affix themselves as evenly in quantity as possible to the individual shells provided.
The saltwater in setting tanks usually originates from a marine environment close-by, typically the grower's leased or owned tideland. To aid the distribution of larvae, the water in the setting tanks is agitated, often by bubbling with oil-less compressed air through perforated PVC pipes. In most cases, the water is heated and maintained at about 20 to 25° C (68 to 77° F). Seawater in setting tanks can be heated in numerous ways (e.g. electric, oil, propane, natural gas heaters or passive solar heating). All setting tanks must be thoroughly cleaned after use. This includes scrubbing off spat that has glued itself to side-walls instead of the offered cultch. Some growers use stainless steel wool to aid in tank-cleanup.

Depending on the size and number of tanks and methodology employed, the remote setting process can last about one to two weeks (excluding any additional marine preconditioning of cleaned cultch). Cleaning of the setting tanks and accessories before and after is essential. Some growers add microalgae to their tanks before, during, and/or after the setting. How much remote setting a grower engages in is usually based on that grower's projected oyster production in coming years. It need not be done all at once. In the course several months, the same tanks may be used repeatedly to produce more spatted cultch. In the North-American Pacific Northwest, remote setting commonly starts in early spring and, in some cases, may continue at intervals until early summer.

The word cultch (also culch) describes a wide variety of objects, naturally occurring or manmade, that are utilized for their appeal to larval or post-larval bivalves as attachment and early grow-out surfaces. In some cases, the alternate term spat collector(s) is preferred. In oyster cultivation, weathered oyster shells are traditionally the preferred type of cultch.

Inset image: Large transporter dumping oyster shells from shucking facilities for natural weathering.

Oyster growers have long known that oyster larvae love to cement themselves to oyster shells. Many oyster growers on the North-American West Coast and in Asia process Pacific/Japanese oysters for their meat only (called shucking), meaning that these oyster are not destined for the half-shell market (i.e. where oysters are slurped raw off the half-shell). Once the meat is extracted, the growers save the shells. Oyster growers then allow them to weather in huge piles on land for later use. These mounds of fresh shells from a shucking facility are of great interest to birds, bugs and bacteria. They immediately start stripping every last bit of oyster meat left on the shells. The sun and wind gradually desiccate the shells. The freshwater from rain gently erodes the calcium carbonate. The organic matrix of the shells also gradually dries, thus reducing structural impact resilience. About two years later, the oyster shells are lighter and have structurally weakened. At this point, they can be considered cultch. Lighter shell weight presents a little advantage in their transport. More importantly, however, years later, when spat on these shells has grown and turned each one into a massive clusters of live oysters, the somewhat weakened old shells help in the process of breaking the oyster clusters apart (called culling).

Before usage, the cultch is often fed through a trommel (from the German word Trommel, meaning drum). The trommel separates debris (small shell fragments, soil, leaves etc) from the shells. The shells are then typically washed with pressurized water and packed into synthetic mesh bags or other, similarly webbed containers.

Inset image: A 40 ft (~ 12 m) commercial flatbed trailer loaded with a shipment of clean cultch, parked at the Coast Seafoods hatchery in Quilcene, Washington State. Clean cultch is commonly packed in polyethylene mesh sacks (e.g. Vexar) which can be stacked like 4 ft logs for transport. Click image for a closer look.

Inset image: Example of a crisscross stack. In remote setting, polyethylene mesh sacks can effectively be stacked in a crisscross fashion, akin to the way logs can be stacked when building a campfire. Stacking cultch in this manner allows good water circulation and optimizes shell surface exposure for the attachment of oyster larvae.

In preparation for remote setting, some growers further condition the clean cultch by temporary submersion in bay water. Doing so will thinly coat the shells with so called biofilm, a rather nondescript word that describes a slippery, organic coating that usually includes bacteria. It is believed that a measured amount of biofilm can be attractive to oyster larvae that are ready to attach themselves and may possibly be of nutritional significance. Other growers do not further condition their cultch in this manner. Instead, the clean cultch is directly offered to the larvae. Although both methods can work well, neither guarantees a "good set" because various other factors come into play (e.g. water circulation, temperature, water quality, larval condition). It is to be expected as normal that many of the oyster larvae will die before ever attaching themselves to the shells. Many more will die during metamorphosis and still more will die soon thereafter. In practice this means that only a small fraction of the larvae in the aforementioned pouches will reach a marketable oyster size.

Once the shells are populated with spat, they are called spatted cultch.

Set and Spatcount
The noun set describes visible evidence on marine surfaces, especially cultch, of an aggregation of oysters or other bivalves that have very recently completed metamorphosis.
Oyster growers rate sets (e.g. very good, good, light, poor or no set) on the basis of the average spat population found on surfaces in a given area, typically the surfaces of oyster shells (i.e. the spat found on a flat or cupped valve). For example, after remote setting, averaging the numbers of spat found on 50 to 100 shells sampled from various areas of a setting tank will yield the spatcount.

Inset image: The shell portion on the left (approx. 10 cm or 4") shows early post-larval Pacific oysters at about three weeks from setting. In remote setting, the set on this shell is excessive (so called spray paint). As these oysters grow, they will compete for space while continuously building their shell. Many will have stunted or malformed shells. Most will not survive. Click image for enlargement.

In remote setting of oysters, a "very good set" typically describes an average of 15 to 30 firmly cemented post-larval oysters (i.e. the spatcount) that are distributed fairly evenly per oyster shell. Some growers and hatcheries prefer 20 to 40. A shell with just six to ten spat, evenly distributed, is a "light set" that can ultimately still yield a very nice return after the oysters have grown. A "poor set" in remote setting are shells that average less than five spat per shell. Although it seems reasonable to conclude that hundreds of spat per shell would be cause for celebration in remote setting, many oyster growers would instead be quite displeased. Hundreds of spat per shell is called called spray paint. Crowded spat on shells leads to mass mortality and tangled, dense clusters of oysters of varying size, many with malformed shells. When faced with such abundant sets, some growers have tediously broken the spatted shells into smaller pieces to later give the growing oysters more room to develop their shells more freely.

Assessments of sets in remote setting differ from assessments in "wild sets". The aforementioned "spray paint" can actually be welcome among bottom cultivating growers that depend on bountiful wild sets on the cultch they have tediously spread on their cultivation grounds. In North-America, the Pacific (or Japanese) oyster used to be principally valued as a cooking oyster, not as a raw, half-shell oyster. As such, it was the meat that mattered, not the shape of the shell. Big, gnarly clusters of oddly shaped, fat oysters thus spelled profit. This has changed in recent decades. Although Pacific oysters are still in demand as meat oysters, they are now also prized as half-shell oysters. In the lucrative half-shell trade, the shell size and shape matters greatly.

"No set" indicates that all the money, time and work invested in offering cultch to wild larvae was for naught. Even if a few wild spat turn up (which is commonly the case), it is still deemed "no set", because so few spat are not nearly enough to support a grower's business. The daunting uncertainty associated with wild sets has plagued oyster growers worldwide for many centuries. It is the underlying reason for today's existence of remote setting.

Inset image: Photo of heavily spatted shells on the cover of the State of Washington Dept. of Fisheries Biological Report No. 43A, 1943. This rare report furnishes details on Washington State's 1942 spawning and setting of the Japanese oyster, renamed as the "Pacific oyster" (then still scientifically known as Ostrea gigas). The image is titled Pacific Oyster Spat on Pacific Oyster Shell Cultch. Each shell features well over one hundred wild spat. They were the result of natural oyster spawning events at an unspecified location in western Washington. The great quantity of wild spat per shell qualified as a "very good set". 1942 was a special year for the oyster industry on the North American West Coast. It was the first year in decades that saw no Japanese oyster seed shipments (spatted cultch) as both Canada and the United States were at war with Japan. Fortunately, Pacific oysters successfully spawned at a never before seen rate during the war years. The absence of Japanese seed supply was thus easily bridged with greatly improved, local seed production. At the same time, Japanese-American oyster growers and their families were sent to internment camps and usually lost their livelihoods.

Example of Remote Setting in a Large Setting Tank
The inset image shows a fiberglass setting tank, one of three, located at the Olympia Oyster Company (click image to enlarge). With a capacity of 28,350 liters (7,500 gallons) it qualifies as a large setting tank. Larger setting tanks exist. The setting tanks at this grower's facility are not insulated. The pictured tank is about 12 years old. Despite repeated, seasonal usage and year-round outdoor exposure, the tanks appear as sturdy today as the day they were built. The size, rectangular design and support framing suggests that any one of these tanks could, if needed, be moved elsewhere with moderate preparation. Sturdy planking surrounds each tank. It provides good footing when working at waist-height anywhere along the upper, inside edge of the tanks in a standing position. A heavy gauge, steel frame rises above each tank. On the frame, a strong, steel overhead rail can be seen, centered and running lengthwise above the tank. When in use, the rail is extended to two more steel supports mounted on a heavy timber bulkhead at the edge of the bay. This rail serves to facilitate mechanical lowering and hoisting of heavy cultch containers in and out of the tank and, after remote setting, moving the cultch containers onto a barge at high tide. All the setting tanks have industrial lighting fixtures for night-time work. Seawater from the adjacent bay is pumped into the tank(s) and then warmed by diesel oil boiler heat-pipes.

The pictured view of the inside of the setting tank shows the heat pipes and two long, white PVC pipe grates resting on the tank's edge. The PVC pipes are perforated. During remote setting, these grates lie flat on the bottom of the tank with the cultch on top. During operation, compressed air from an oil-less electric blower motor is pumped through the perforated pipes. Subsequent bubbling vigorously agitates the tank water.

Remote setting at this grower's facility is repetitive. It may commence sometime in April and continue until June.
For example, this grower gradually fills the clean setting tanks with bay water on a Monday and starts warming and agitating the water with compressed air on Tuesday and Wednesday. Historically, much like many other oyster growing regions, the Puget Sound region has also had occasional seawater conditions that proved detrimental to the setting of oyster larvae and survival of spat (e.g. blooms of certain algal species, heavy siltation). Some growers thus filter the seawater they use for remote setting. This grower does not. Instead, Tim McMillin, a second generation oysterman and the longtime general manager of the Olympia Oyster Company, visually inspects the bay's water condition for appropriate clarity near the setting tanks before pumping the water in. Occasionally, further inspection with a microscope is necessary. He has worked this bay since early childhood and knows it intimately - including its highly variable water conditions.

On Thursday, containers filled with clean cultch are added. Several small, meshed testing bags with cultch are also added in various areas of each tank. The clean cultch is not preconditioned in the bay prior to use (i.e. no light biofilm is provided). On Friday, remote setting is initiated by adding the larvae to the warmed, agitated water in the setting tank. No microalgae feed is added to the water at any point. On the following Monday, the small, meshed bags with cultch are pulled for examination. Microscopic inspection of numerous shells provides an approximate spatcount and also shows the condition of the spat. Ideally, the shell of each spat should appear flat and well affixed to the cultch (i.e. the spat's shell should not be angled). On Tuesday, the spatted cultch in the containers is pulled from the tanks and moved to an intertidal location. Here, the spat will continue to grow. Some growers cover their spatted cultch out on their tideland with tarps to protect it from various environmental threats (e.g. heat, birds). This grower does not. After each remote setting session, the tanks are scrubbed clean. Typically, some spat has stubbornly set on the sidewalls of the tanks and pipes. It is scrubbed off with stainless steel wool.

The Olympia Oyster Company used to operate five large setting tanks. When I took some of the above pictures, they operated three. At the time of this writing, they only operate two large setting tanks and have disposed of the rest. This is because the shellfish business changes as time goes on and all shellfish growers must adjust accordingly. The Olympia Oyster Company used to continuously shuck a large volume of oysters for meat (both Pacific oysters and petite Olympia oysters, Ostrea lurida). Much remote setting was necessary to produce sufficient amounts of Pacifc oysters for meat processing. In recent years, this company has greatly reduced its shucking and instead shifted some of its resources into producing more Pacific oyster shell stock for resale (sizes extra small to large) and expanding tumbler cultivation of their very popular boutique oysters called Kobachii - and all the while still maintaining their classic Olympia oyster cultivation (no longer shucked because Olympia oysters are in high demand as half-shell oysters). Due to increasing demand, the Olympia Oyster Company also expanded its Manila and native littleneck clam cultivation.

The unusually tasty shellfish this company consistently produces has not been a well kept secret. It has been my impression over the course of many years that their wholesale business is consistently brisk.

Details on the Cultch Containers
In remote setting, the Olympia Oyster Company does not use polyethylene mesh sacks filled with cultch. Instead, they use large, specially designed cultch containers that are shaped like a cube with meshing on all sides and also chambered with mesh on the inside (click image to enlarge). This insures good flow-through of water. Moreover, the design prevents restrictive compacting of the shells and, a few months later, allows for easy dumping of the more matured spatted cultch directly onto tideland. These cultch containers will be moved twice. Firstly, they are used for the remote setting process by lowering them into the water filled setting tanks on top of the perforated PVC pipe grates used for water agitation by aeration. A few days thereafter, the containers are pulled and placed on a barge to then be deposited on tideland in a chosen area in the intertidal zone. A few months later, depending on the rate of further development of the spat, these containers are moved again to another section of the company's tideland, typically of lower intertidal elevation, for further grow-out. The design of the containers allows removal of sections to prevent the shells from binding-up when spreading the spatted cultch directly onto the tideland.
Each cultch container is lifted by polyethylene rope secured on top at all four corners.

Details on Pitching the Larvae
I like to refer to the adding of the oyster larvae to setting tanks as "pitching the larvae" because it reminds me of "pitching the yeast" when I make wine and beer. We now return to the aforementioned "tennis balls" that each hold six million oyster larvae. The first step is to open such a pouch full of larvae and inspect its contents. It should not smell "fishy". The larvae ball can easily be broken in half. The inside should appear moist, not dried out. Half of the ball, give or take, is placed into a small bucket that is filled about half-way with warmed water from the setting tank. When gently swishing the larval clump around in the bucket, it readily dissolves into what looks a bit like clear bouillon soup.
This "larval soup" is then carefully and evenly poured onto the surface of one half of the setting tank. This procedure is repeated with the remainder of the larvae in the pouch on the other half of the setting tank. Just a few days from this moment, microscopically small specs, the spat, will be evident on the cultch.

Inset image: Oyster larvae being evenly "pitched" during remote setting. Please note the now extended top rail above the setting tank leading to a heavy timber bulkhead at the edge of the bay. Please also note the exposed tideland (low tide) beyond the bulkhead. When the remote setting process is completed, a barge can conveniently load the cultch containers at the bulkhead at high tide.

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William Firth Wells, Growing Oysters Artificially, The Conservationist, 1920, 3(10), pp 151 -154
Herbert F. Prytherch, Experiments in the Artificial Propagation of Oysters, Dept. of Commerce, Bureau of Fisheries, Doc. No. 961, 1924
Herbert F. Prytherch, The Cultivation of Lamellibranch Larvae, found in 1959 reprint by Dover Publications of Culture Methods for Invertebrate Animals (1937, Comstock Publishing Co.), pp. 539 - 542
William K. Brooks, The Oyster, The Johns Hopkins Press, Baltimore, 1891
Paul Simon Galtsoff, The American Oyster Crassostrea Virginica, United States Dept. of the Interior, Fish and Wildlife Service, Bureau of Commercial Fisheries, Fishery Bulletin, Volume 64, printed by the United States Government Printing Office, Washington, 1964
Victor L. Loosanoff & Harry C. Davis, Rearing of Bivalve Mollusks, U.S. Bureau of Commercial Fisheries, 1963
Jerry E. Clark & R. Donald Langmo, Oyster Seed Hatcheries on the U.S. West Coast: An Overview, Oregon State University, Sea Grant College Program, 1979
Herbert Hidu, Samuel R. Chapman and David Dean,
Oyster Mariculture in Subboreal (Maine, United States of America) Waters: Cultchless Setting and Nursery Culture of European and American Oysters 1, JOURNAL OF SHELLFISH RESEARCH, June 1981, Vol. 1, No. 1, pp. 57-67

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Health advisory: There is a risk associated with consuming raw oysters or any raw animal protein. If you have chronic illness of the liver, stomach, or blood or have immune disorders, you are at greatest risk of illness from raw oysters and should eat oysters fully cooked. If you are unsure of your risk, you should consult your physician.

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© 2014 John W. McCabe