Cage aquaculture in the Persian Gulf: A cautionary tale for Iran and the world

Around the world, coral reefs are in decline. Recent interest has focussed on the impacts of global warming/climate change, but the decline started long before the influence of climate change became apparent, driven by anthropogenic factors such as sedimentation, nutrient increase, and overfishing. These continue with no real signs of abatement, as does concomitant reef damage. The Persian Gulf supports widespread coral growth, especially on the Iranian side. Responding to issues of food security, the Iranian government has proposed large-scale aquaculture (open-net fish pens) along their coastline, with an eventual production of 200,000 t/year. Nutrient discharge will be a major issue. We developed a hydrodynamic circulation model for the Persian Gulf which allows us to follow the path of dissolved material. We estimated the amount of nitrogen that would be produced by the projected farms and modelled nitrogen distribution over time, using production rates of 44kgN released/t of fish. In a model run simulating one year at full operation of the proposed number of fish farms, we estimate that most of the reefs on the Iranian side will be bathed in waters with nutrient levels higher than will allow for reef survival. We used a trigger value of 20 μg/l total N. Mangroves will also be affected. There is significant trans-border movement of nutrients, to the waters of neighbouring countries. In fact, withing a few years the entire Gulf will be affected. These planned aquaculture projects have the potential to damage the mangroves and kill every reef in the Persian Gulf in a very short period of time. There is a high probability of affecting fisheries resources in neighbouring countries-a situation to be avoided in politically volatile regions. There seem only two solutions: 1. either run the fish farms so that nutrient discharge is kept to acceptable levels, using an ironclad monitoring system, or 2. bring the operations on land by establishing recirculating aquaculture systems.