Environmental impacts of fish cage cultures in the southern Caspian Sea

In the last two decades, cage culture industries have developed in Iranian seas, supplying a portion of the needed protein and contributing to food security. In this paper, environmental impacts of cage culture are investigated, focusing on the physical, hydrodynamical, chemical, geological, and biological oceanographic aspects at the Abbas Abad fish farm in the southern Caspian Sea. Multidisciplinary field measurements were conducted from fall 2018 to late summer 2019 in different oceanographic aspects. Results showed that the cages have not significantly affected the hydrodynamics and physical parameters of the aroundwater, and have actually caused a slight decrease in current speed within a few 10 m of the cage. The maximum levels of inorganic phosphates, total phosphorus, total organic phosphorus, nitrite, nitrate, ammonium, total nitrogen, silicate, BOD₅ and COD were 22 ppb, 34.91 ppb, 26.92 ppb, 6 ppb, 103.69 ppb, 69.5 ppb, 1423.99 ppb, 679.06 ppb, 1.9 mg/l, 80 mg/l respectively. The water quality is considered safe and not concerning based on levels of phosphate, nitrite, nitrate, ammonium, BOD₅, and COD. Also, planltonic (phyto and zooplankton) and benthic communities and benthic around the cages were the same with sourounding waters. This paper presented comprehensive information about the effects of cage culture farms on the surrounding waters of the Caspian Sea.