Some (not all) of the matter in suspension may actually be correlated to the washing process. I have been made aware of some techniques that collect most of the dirt even in open sea environment, the reason being that the farmer is environmentally oriented and knows that in the end whatever ill-conceived scheme will result in terms of low production. This said whatever fallen ?debris? would eventually be decomposed and used by the ecosystem, or at least thus would it be in a normal ecosystem.
There is no dirt, really. The strings don't normally contact the bottom. The debris consists mainly of algae, shells and the fleshy remains of organisms. Many of which reproduce by asexual separation. Unless you filter below 100 microns and apply chemicals or thermal control, it's all but impossible to stop the proliferation of these species. Violet Tunicates and Pisasters are particularily troublesome here in Canada since the onset of the suspended growing method of oysters. Farmers are no longer allowed to power wash on site and shells relayed to other areas cannot be stored in the water, nor can their offal be discharged without treatment.
My point being, these are handling methods. Handling inventory costs time and money. When allowed to farm with wreckless abandon, sure, power washing is a cheap and easy fix, but farming in regulated areas, requires innovation by statute, not choice. My lines are 1/3 the length of oyster strings or intertidal, afterall... sunlight is the best disinfectant. Likewise, it's better to provide an environment for the critters instead of eradicating or relocating them.
I've never been keen on the use of some terms, eco-friendly or green because in many cases they are just buzzwords intended to overlook something not so genuine. I prefer terms like "mitigation" and "areas suitable or not suitable" because of "environmental sensitivities"
The volume of debris may now be a concern as observed in salmon / trout production in the 90?s when the abusive feeding of high density cages induced higher level of nitrate contamination, mostly because the bottom feeders couldn?t cope with the volume of food and feces.
It continues to be a problem here, to this day. Fish farmers don't view the environment throught the same eyes as shellfish growers. While we both have similar concerns with weather, that's where the relationship ends. Sediment density has been addressed for the mostpart, because fish are fed much more systematically by measured volumes over time depending on the metabolism of the age group by underwater cameras. Incidentally, they take these measures not necessarily because it reduces pollution, but because it minimizes the cost of feed.
With the exception of sea lice, farmed fish are implicated in infecting wild fish near their home streams,
when really the opposite is true. Wild fish carry a whole host of pathogens and virii from birth, but whether they become affected is another issue. Again, overcrowding, poor husbandry, plankton blooms and predators cause stresses upon which diseases can thrive. Pollution and nutrient loading in the water column from fish farms can be measured in terms of thousands of tonnes annually, whereas even the largest pearl farms can't even begin to hold a candle to those numbers.
Interestingly enough, there are no known diseases in most shellfish. They have parasites, predators and can be contaminated by sewage, pollution or red tides but cases of mass mortality from systemic or metabolic causes are extremely rare.
Pearl farmers don't feed their growout inventory, but shell stocks still generate feces or pseudo-feces. It's not a problem if you provide adequate space, but crowding can cause issues, not necessarily to the inventory itself, but to the local environment.
Big changes happen in the ocean all the time. El Nino, Red tides, storms, stray currents, hot summers and cold winters all have huge impacts on the marine environment, especially in the temperate zones. Salinity data is all over the charts, reaching high and low extremes often for no apparent reason. Even major disasters like oil spills can be rectified over time by natural processes whether by dynamic action or petroleum ingesting bacteria. Freshwater resources are not so resilient, as we'll discuss in a moment.
As for the conditioning (weakening if you may) also called Yokusei, it is not a form of torture but used only for the shell whose condition index is high (high level of glycogen) and the duration may be adjusted as to bring the shell to a normal state prior to operation.
Weakening for grafting is a long debated topic. Some do it, some don't. Most farmers perform some kind of pre-treatment, but to what degree is a social or ethical issue, not necessariy environmental. My understanding of it is to induce the animal to spawn. Personally. I don't feel the need to run the risk of starving my inventory for any reason. Fine mesh gets fouled quickly and you can lose inventory if bad weather sets in and you are unable to reach them in a timely manner. Mussels have gonads unlike conventional pearl oysters and spawn pretty much all year round, so conditioning them to spawn is just another expense in handling that I don't need. During peak spawns, I'll either wait a few weeks or merely sink the inventory into the deeper, cold water for a few hours and they instinctively spawn immediately.
Let's get back to the question posted by you on the other thread:
I would be interested to see if any conclusion has been drawn on the environmental effect of the pearl farm, such as matter in suspension, nitrate level, bicarbonate level, dissolved oxygen and carbon dioxide (that are eventually affected by the seawater temperature).
The freshwater industry in Japan is all but done in most areas. Global warming and pollution have affected it perhaps moreso than farming affected the environment itself, but stands as an example of what can happen. China ought to stand up and take notice, but taking the long view on environmental issues is not their strong point.
Nowadays, I don't think there are enough farms on the globe to even begin to put a dent into the already widely fluctuating elemental composition of our oceans. I don't doubt there might be local issues (not necessarily environmental), but by and large... pearl farmers are symbiotic with their molluscs and generally uphold the ecology that surrounds them.
One significant impact does come to mind though. For and years, shucked shells have been heaped in enormous middens on the shore, wasteful. If anything, they should probably go back into the ocean immediately after harvest. Their decomposition in a small way, acts as buffering base to regionalized acidification.
, but it would be very efficient to clean the oysters right there! Thanks for sharing the photos and video 
