Timing is critical for the placement of "collectors". Oysters spawn once the water reaches a certain temperature - usually in July or August. Hence the myth of not eating oysters during months without "R". Oysters about to spawn do become "laiteuse" (milky) when they're full of eggs, but they are still edible.
Once the eggs are released and fertilized they become free-swimming larvae for about two weeks. At the end of those two weeks of freedom, they must find something to attach to in order to grow a shell and survive. This is a critical period for oyster farmers - to recognize when the oysters have spawned and then to place collectors to provide a point of attachment for the oyster larvae.
The most common kind of collectors in the Arcachon basin are ceramic tiles (kind of like roofing tiles) which must be dipped into a chalk+sand+seawater bath and allowed to dry. This is another laborious step as it is done by hand. Here's what the tiles look like after they've been dipped and are ready to go:
They will be placed in the bay in a special bed out of reach of winter storms and will be left there over the winter. In the spring time - if all goes well - the tiles will be covered with baby oysters about the size of a quarter. Then the tiles will be picked up, brought back to port, and the baby oysters scraped off of the tiles by hand. Some producers use machines for this process, but the Dubourg family does things the traditional and time-consuming way resulting in less damage to the delicate oyster babies.
Following this step, the small oysters are then distributed or sometimes placed in bags to protect them during the first year. Even if Frédéric uses sacks for a short time as a protection from predators, he still retrieves and liberates the oysters to spend their second and third years directly on the bottom of the oyster park.
Sometimes, the oysters don't attach and several weeks of work are lost. This happened earlier this summer when Frédéric placed the collectors at a time he thought was right but none of the oysters attached. Was it the temperature? The algae or lack of algae? Every season teaches new lessons. And at the end of the day "la nature reprend ses droits" or "nature always wins". Only one in 100,000 larvae ever reaches adulthood.