The short answer is that it depends on the environment you're in. It also depends on the amount of organic matter that has accumulated underneath the nets. But certainly the farm benthic environments can recover in anywhere from months to years, depending on the amount of material, as I say.
Most of the operations in Canada are on some type of production cycle that does allow for a break between production cycles to allow the benthic environment to recover. That break can be anywhere from three months to a year, depending on the environment and the jurisdiction.