In The Wild
by Bob Thomas

Oysters are among the defining elements of the culture of the lower Lake Pontchartrain Basin, predominantly in the area known as the Biloxi marsh. They are a component of an enormous interconnected economy, essential to the world renowned cuisine of New Orleans and the rest of south Louisiana, and their reefs are essential to the biodiversity of the Basin’s waters, especially those nearest the Gulf of Mexico.

The most common commercially important species in the United States and the sole species harvested in the northern Gulf of Mexico and on the eastern seaboard is Crassostrea virginia. For commercial oyster production, Louisiana waters are number one in America. Louisiana now produces 12-14 million lbs of meat/year ($30-33 million in dockside value). In any given year, prior to hurricanes Katrina and Rita, anywhere from 30-40% of all the oysters consumed in the United States come from Louisiana (source National Marine Fisheries Statistics). Rest assured that Louisiana’s oyster production will bounce back to pre-Katrina status in the coming years.

There are three basic ways that Louisianians harvest oysters:

1. Harvesting wild oysters by hand. This can be done by hand-picking clutches of oysters growing on the bottom or working a real oyster reef. Locals may simply wade about in shallow water and pick up clusters of oysters, placing them in a pirogue. We call this practice “cooning” since it mimics the way raccoon’s are believed to feed on the crabs and other marine life associated with oyster reefs in the shallow intertidal zone at low tide. This means by physically going underwater and picking up the oysters by hand. If a Louisiana citizen wants to do this, he/she may hand-harvest, on public areas, up to two sacks of oysters per day. An oyster sack is measured by volume and is equal to 1.5 U.S. bushels. A fishing license is required.
2. Harvesting wild oysters with tongs. Long ago, Croatian oystermen developed oyster tongs. These are very long “tweezers” that allow a very strong person to stand on the deck of a shallow draft oyster skiff and pick up oysters from the bottom in areas too deep to wade and pick up by hand. This is still done by a few recreational fishers, by oystermen who want to spot check their reefs, and in the western end of the state by commercial oystermen on the public grounds in Calcasieu Lake, although small oyster rakes (also known as dredges) became legal in Calcasieu this past year. Tonging is becoming a rare part of the commercial scene because of the tremendous effort and time it takes to harvest a sack of oysters.. For an extra $4 added to a fishing license one can get a recreational tonging license. Again, as in harvesting by hand, the limit is two sacks per person per day.
3. Harvesting wild oysters off the public reefs and cultivated oysters off the private reefs using an oyster rake (also known as an oyster dredge). This is the most common form of harvest in subtidal waters from the deck of large 30-70ft fishing vessels called oyster luggers. The oyster rake was developed in 1905, and is simply a three to four foot wide device with metal teeth along a bar and a mesh back toward the rear. It is dragged along the bottom, the net fills with oysters, and it is hoisted on deck by mechanical winches and emptied. Sounds easy, but it is very hard work.

Oysters naturally grow in clumps or reefs in brackish water. In the old days, people just harvested oysters where they naturally occurred. Today, oysters are farmed (cultivated). This is traditionally done by simply leasing from the state the bottom of a body of water and covering the area with something hard – called cultch - as a substrate for oyster growth. In the past, Rangia clam shell was the aggregate of choice. Since their harvest was stopped in the Basin, oyster fishers use oyster shells, crushed concrete, or limestone rocks. They shovel them overboard to form a layer across the bottom, and return later to harvest oysters that have grown to maturity. How does this work? Oysters each lay about a zillion (actually "only" 70-170 million) eggs that they spewed into the water column. These are fertilized after they leave the female by sperm suspended in the water column and begin their larval development as they float about. Soon, their shells begin to grow and, when they become too heavy to float, they sink to the bottom. If they land on a hard surface (clam shells, rocks, another oyster), they cement themselves down and begin to grow; if they land on a soft surface, such as the muddy bottom, they usually die, or at least put more energy into shell growth than into soft tissue, so they are not good for human food. For a short while, they can actually move about, and will search for the perfect site to cement themselves. When an oyster larva finally settles and attaches to the bottom it is very small, measuring less than 1/50 of an inch in length. These tiny oysters are then called “spat” until they reach one inch in length, then “seed” until three inches, then “market oysters” from then on.

So the theory is that the water is full of larval oysters, and, by ensuring a hard surface by depositing a hard layer on the bottom, a healthy crop may grow where it never did before.

Oystering is not an easy livelihood. Farming today may involve not only placing shells and limestone in open water areas, but farmers may have to pick them up once spat have formed and move them to a different salinity in order to get the best growth. In some instances, the farmer may have to move them more than once. It is still somewhat common to find oyster fishers moving their product to saltier water for a brief period in order to stimulate last minute growth and to give them a saltier taste. This amount of energy going into oyster farming will have two impacts on the product: 1) it should enhance the quality and quantity of the meat; 2) it will increase the cost of the product.

Oysters are filter feeders, having little hair-like structures called cilia around their gills whose wiggling motion move water into their respiratory chambers. As the water passes through, food particles are removed; the average oyster circulates about 150 gallons of water per day through its system.

Since they are filter feeders, oysters are susceptible to accumulating harmful products if pathogens exist in the water. Heath officials are constantly monitoring water and measuring fecal coliform contamination. For the oyster harvest, the harvest line is changed quarterly depending on fecal coliform counts.

In Louisiana, the coast is sectioned into 30 oyster harvest zones. The Louisiana Department of Health and Hospitals can close zones (based on contamination, salinity, and/or temperatures), while leaving healthy zones open. Sacks of oysters are required to be tagged with the zone number where they were harvested, and that is the technique used to insure the health quality of the oysters we consume. The oysters on the market today are some of the safest ever because of the diligence of oystermen and health officials.

As in all critters that produce huge numbers of eggs, only a few oysters survive to reproduce. Some fisheries biologists believe the magic number is one egg in four million, the rest either dying or, more probably, becoming assimilated into the tissue of a consumer! Sexes are separate, but they can change after spawning - usually from male to female. The oysters become sexually mature in one month at less than one inch long. They usually grow to two inches in the first year.

Spawning is temperature and salinity related and occurs in nearly all months but the coldest, with two peaks being in May/June and again in September/October. They prefer temperatures above 72ºF and salinities above 6 parts per thousand (ppt; by comparison, freshwater is 0-1 ppt, and Gulf water is 35 ppt), though they can survive brief periods of freshwater inundation. Though several weeks below 10 ppt is lethal to adults in hot summer waters, one population is known to have survived for four weeks in 1 ppt during cold weather. Larvae can die in large numbers when salinity stays below 8 ppt in hot summer waters. Permanent colonies are almost always in water ranging 10-35+ ppt, but 5-15 ppt seems to be best due to a lack of predators in water of this range.

Some of the most aggressive consumers of oysters (aside from people) are Black Drum (Ponogias cromis), stone crabs (Menippe mereenaris), blue crabs (Callinectes sapidus), and oyster drills (Stramonita haemastoma). Blue crabs can open live spat oysters quicker than a shucker at Felix's Restaurant and Oyster Bar!

Oyster drills (a type of marine snail) are a special case. Oyster drills feed on oysters by drilling a hole directly through the oyster's shell, using a chemical soup composed of hydrochloric acid, enzymes, and other substances, that is produced by the drill’s accessory boring organ, or ABO (don’t you just love scientific jargon?). The purpose of the ABO fluid is to soften the shell, followed by removal of the softened shell by its rasp-like radula. Once the hole is bored through the shell (this usually takes hours), the oyster drill inserts its proboscis into the oyster shell cavity and the radula scrapes flesh off the oyster’s body until the drill is sated.

Oyster drills require high salinities above 15 ppt salinity and warmer waters. Oyster reefs are generally safe if salinities remain below 15 ppt. If salinities increase, the drills invade and can literally wipe out a reef in a matter of weeks.

Older oysters in their second year of life may fall prey to a parasite named Perkinsus marinus. Perkinsus is often called “Dermo” because it was first discovered in the early 1950s and so named because it was thought to be a fungus, but later identified as belonging to the Kingdom Protista and the name was changed. Young spat oysters may also fall victim to a flatworm predator known as Stylochus inimnicus. Stylochus is often called the “oyster leach,” but is not a leach at all. Stylochus is usually not a very big problem on an oyster reef because small fish love to eat them.

Due to the opening of the Bonnet Carré Spillway and high waters from the Pearl River, oyster production in Lake Borgne has dropped by >90%. Not only does the opening of the spillway cause a drop in salinity, but the average temperatures increased, as well. When the introduction of freshwater does not get out-of-hand, there are three possible positive effects from its presence:

1. it controls pathogens
2. it introduces new nutrients
3. it retards salinity encroachment

All residents of America’s WETLAND know the many values of oysters to our way of life. With all the conditions required to sustain the large harvest required by the popularity of oysters in our cuisine, one must be even further amazed at the ability of the Lake Pontchartrain Basin and the rest of America’s WETLAND to provide this incredible resource.

For further information, contact Patrick Banks at 225.765.2370, or visit http://www.wlf.louisiana.gov. Dr. Earl Melancon, Nicholls State University, is one of our leading experts on Louisiana oysters.

Published in In The Wild, Louisiana Levnt Magazine, February 1, 2007.