Before getting a license the applicant must completed an Aquaculture Fish Farm Development Plan. The development plan involves questions regarding physical location and layout of the farm. This goes back to that issue of protection from waves and storms, water quality of the site, etc. It doesn't make sense to put a bunch of fish in toxic water. Site specific predator abundance and how the farm plans to reduce negative effects of predators, bottom profile, proposed anchoring methods, and proximity to other farms or release sights are all pretty self explanatory and if you have some common sense you can figure it out.
Aquaculture dates back well into history.
What is important to keep in mind is that those operations weren't producing 500,000 mt. The evolution of high intensity pen and cage culture has rapidly evolved over the past several decades. Since the inception of aquaculture, ecologists, farmers, scientists, and governments have identified disease, genetic, and health concerns. Many if not all of the concerns are related to escaping or non-returning fish. Research has shown that escaped fish represent such a small number compared to the wild population that there is little chance for a great impact on the natural environment.