Harvesting oysters in New England goes back to way before colonial times. Although today oysters are harvested mainly for food, back in the 1700’s they were collected for their shells. Limestone, vital to the production of masonry mortar, was scarce in the northeast. So oysters and other mollusks were captured and added to kilns to take advantage of the calcium carbonate in their shells.
In 1734, the Colonial Assembly saw that this was a waste of a natural resource and banned the practice unless the meat of the oysters were used for food. The assembly also mandated that oysters could only be collected by tongs (rather than picked up by hand) and couldn’t be collected during spawning season. To me, this is a pretty stunning example of fisheries management going back nearly 275 years.
In fact, the “Oyster Act” of 1844, which allowed states to lease oyster beds to individuals, is considered to be the first Supreme Court decision affecting commercial fisheries. In other words, historically oysters are important.
As important as oyster fishing was during the early part of our country’s history, the fishery went into a serious decline during the mid 1900’s, only becoming revitalized today due to extensive aquaculture efforts. In 1900 - 1910 nearly 5 million oysters per year were harvested from Narragansett Bay, in Rhode Island, alone.
Oysters live in brackish water, usually the mouths of rivers where fresh water and salt water meet. It’s not because they need brackish water to survive, but because oysters living in full salt water are eaten by the myriad predators that can devastate a population of non-moving, non-burrowing bivalve. Those larvae that settle in full salt water are eaten within days or weeks of growing their shell by crabs, starfish, oyster drill snails and other predators that simply latch onto the shell and either yank it open or drill right through it.
Oyster spat (young, just-settled juvenile oysters) that happen to settle in brackish water will survive because those predators mentioned above are unable to tolerate anything but a full salt water environment. But the oysters can.
The oyster industry collapsed during the middle part of the century for several reasons. One was The Great Depression made the purchase of oysters unaffordable to the average family. Other causes included the massive accumulation of toxic runoff since the industrial revolution devastated the oyster beds, manual labor was lost because of war recruitment, and the destruction of oyster beds due to the 1938 hurricane.
Oysters have made a huge comeback in popularity as well as population. Native stocks have ballooned due to both clean water regulations and from the escapees of aquaculture farms. Pretty much no oysters are harvested from wild stocks anymore, since the farming of them is now so easy. It’s a perfect example of harvesting a wild species by allowing it’s natural habitat to do the work for you. Albeit with a few tweaks.
There are three types of oyster cultivation, but all start with what is called a “spat”. The spat is the stage in an oyster's life where it ceases to be a free-floating larvae in the planktonosphere, and actually settles down and cements itself to a hard object such as a rock, or more usefully, another oyster shell.
In one scenario, the spat, which can actually be purchased over the internet, is simply released onto an existing oyster colony to increase their numbers. These will then be harvested by hand, just like collecting oysters in the traditional way.
Another method is to release the spat into floating bags, cages or racks, to ensure the young oysters have a place to settle that is not only convenient, but also safe. Virtually all of an oyster’s predators are bottom feeders. Starfish, crabs and oyster drill snails are unable to swim. So by suspending the artificial oyster colony above the bottom, we avoid these animals. It is also the oyster farmer’s job to inspect the cages periodically, since the larval stages of these predators can settle on the suspended colony and do serious damage as they grow.
The third method is more high-tech, and involves growing the oysters indoors in culture tanks. Optimal temperatures and nutrients for shell growth and reproduction, including adding calcite and aragonite (the two most important elements needed for shell production) to the water. Although the resulting mollusks are free from both poaching (which is a serious problem) and predation, I think it’s a cop-out.
You’ll notice I left pearls out of this essay completely. You can learn about them here, and I can guarantee that the way I describe how pearls are formed is nothing like you’ve been taught.
Other diaries in this series can be found here.