Before such things were better understood, the oysterman never knew when, or if, the oysters would spawn at all. Often they might not spawn for a few years and then suddenly there might be a seemingly spontaneous eruption of breeding, unseen well out to sea or at night. Then there was the question of where these young larvae might end up after a fortnight being battered and carried up and down on the ebb tide. The oysterman might have been farming in one area; and then suddenly found another reef growing in a different place.
The Washington oysterman E N Steele excitedly describes the first time he witnessed the event as thousands of oysters suddenly started spawning together in Samish Bay in the 1930s:
“One day we were standing on a sink float in which adult oysters had been put. It was a very hot day and the water, warmed by coming over the beach, was just flooding over the oysters. Suddenly Dr. Kincaid became quite excited.
"They are spawning. They are spawning," he exclaimed. As he pointed I looked. A stringy white substance was oozing out from many of the ‘The males!’
"Spermatozoid. Just watch a moment," he said.
And as he spoke I saw a jet of white substance was forced by an oyster into the water with much dexterity; then another and another until the water running over the oysters became white as milk.
"See, the females are now spawning" Then he explained how the sperm of the male, when running over the female oysters, had a sex appeal, causing them to do their part in propagation of its kind.
He ran and got a pail and filled it with water containing both elements. This was put in a large glass container and kept warm. At first nothing was visible, although we
examined a drop under the microscope. It was alive with minute objects. The eggs were much larger than the sperm.
The sperm by some force of nature was drawn to the eggs. Sometimes several of them would be attached to one egg. Apparently there was but one entry to the point of fertilization, and there was a struggle between them to get there
first. But the instant fertilization took place the others disappeared.
In a few hours those in the large glass container (now called larvae) became visible when looking through it toward a bright light. As the hours went by they came to life. They first developed a number of cilia, or hairlike processes, which they used to propel themselves. They danced around in a lively fashion, reminding one of some of these modern dances. And well they might enjoy themselves, for it would last such a short time. If they were to mature into oysters they would in about sixteen days develop a thin shell and settle to the bottom. There they would attach
themselves to a shell or some other clean surface with a little glue…”
Huge numbers of egg and sperm will drift off hopelessly to become part of the estuary plankton, while even those that successfully fertilise into larva will be eaten by predators before they can attach themselves to a stationary home. The tiny larvae are just like any other plankton type being swept up in the currents and offered up to passing predators of all sizes from jellyfish or the smaller comb-jellies for dinner.
Korean scientists estimate a female oyster may release 100,000 eggs at a time and the male even more sperm. An American paper suggests one female might release half a billion eggs in a good season. In Barnstaple, Massachusetts scientists calculate they need 14 million competent eyed larvae laid out on 1,000 shell bags to produce 250,000, oysters a year. As ever with oysters, the numbers are mind testingly elastic.