Even so, it could take 20 years or so before new ponds will represent most of the area in production. BMPs change over time. For example, when the industry was beginning 20-30 years ago, shrimp farmers were advised to build on former mangrove areas. Today, it is known that this should never happen. This is the worst possible place to build.
Ponds built on former mangroves have shorter life expectancies.
This means that the investment is amortized over a shorter time. This is a considerable investment. Consequently most investors want to see the ponds last as long as possible. Simply put, they are not as profitable to operate. While building above the high tide creates higher pumping costs, it also closes the ponds off from the ocean and can thus reduce other inputs and management costs and increase net profits.