We are pleased that Black et al. (1996) have found our article ''The cost of eutrophication from salmon farming: implications for policy (Folke et al., 1994)'' interesting enough to write a commentary. We understand that the article may be provocative to the aquaculture sector and for scientists involved in its development. We apologise if our following the instructions to authors for the Journal of Environmental Management in writing also for people outside the academic ivory tower, has amazed Black et al. Even so, the true motivation behind the aggressive tone of Black et al. remains hidden to us. Needless to say we do not agree with their criticisms, for reasons detailed below.
We note that Black et al. admit that waste from intensive fish farming represents a potential risk for eutrophication. However, throughout their critique they argue that this is not a problem, mainly because nutrients from fish farms are different from those in sewage, and that the farms are located in areas of sufficient water exchange that will flush out the nutrients before algal blooms are formed. We will show that this is not valid from the ecosystem perspective. We will also argue that since it is widely accepted that the waters surrounding Sweden are eutrophicated, and an already existing major problem in our coastal ecosystems, any activity (e.g. agriculture, transportation, or aquaculture) that adds further nutrients to this environment should bear its share of the cost of nutrient abatement.
Our reply is divided into two parts. In the first part we respond to the critique of Black et al. and show it to be invalid from the ecosystem and ecological economics perspectives, which we represent. In the second part we elaborate on the invitation of Black et al. to place aquaculture in an integrated coastal zone management framework.
1. Fish farm, urban wastes and eutrophication
Salmon in farms are fed pellets containing fish meal, fats, binders, vitamins etc. Only about 30% of the nutrients added to the farm are incorporated in fish biomass and removed at harvest (Gowen et al., 1991;Holby and Hall, 1991;Hall et al., 1992). Thus, a fish farm producing 100 tons of salmon releases about 900 kg of total-phosphorous and 5200 kg of total-nitrogen in the form of metabolic waste, faeces and uneaten feed