Preliminary studies on environmental impact of cage aquaculture in Canary Islands

Abstract

More than 50% of the present marine finfish aquaculture production in the CanaryIslands (800 Mt for 1999) is carried out in off-shore cage farms, being thepredominant technology involved in all new commercial projects in the Archipelago.This economical sector has experienced a significant growth in recent years at aRegional level, with excellent prospects for expansion due to different geographicand climatic advantages. However, this is giving rise to an increasing social concernabout environmental implications, being frequently used as an argument to restrainthis activity. The present work aimed to develop a protocol for environmentalimpact assessment of these farms, by identifying those physical, chemical, andbiological parameters more sensitive to the operation of this type of facilities. Acomprehensive sampling program was carried out since 1994 at a cage farmproducing 500 metric tons per year of gilthead seabream (Sparus auratd) andseabass (Dicentrarchus labrax), located at the East Coast of Gran Canaria Island.The studies included water quality, retention and discharge of nitrogen andphosphorus by cultured fish, sediments, hydrology, fouling, and biologicalassessment of benthic ecosystems.As a whole, none of the studied parameters showed negative effects on thesurrounding ecosystems, the results suggesting that both local currents regime andcarrying capacity of this particular Bay seem enough to disperse solid organic wastedeposits and to transform ammonia excreted by cultured fish. The presence offouling organisms resulted in appositive biofilter effect.