Co-authored with John Volpe, University of Victoria, Canada
The quick guide to Aquaculture by Lucas  recently published in the international journal Current Biology provides a decidedly positive and one-sided view where the myriad of negative impacts associated with the industry are ignored. Introduction of exotic species or genotypes [2-9], amplification and transmission of diseases [10-13] and parasites [14-18]. Indeed the very nature of industrial-scale aquaculture serves to not only accelerate and intensify these impacts  but generates whole new problems when mitigation is attempted [20, 21]. For instance the drug teflbenzuron targets sea lice, a crustacean farm pest, but teflbenzuron is an indiscriminate killer of all crustaceans, equally effective against crab and lobster too. Teflbenzuron levels in the few surviving crustaceans around salmon cages are high enough to trigger human health concerns . The benthic environments around net pens are typically anoxic reflecting the vast biological load of faeces and uneaten feed from farms leading to bioaccumulation of mercury in few wild species left to feed on the deposits .
The commodification of farmed seafood products like salmon and shrimp have created a race to the bottom among producers. Those generating the most product for the least investment gain the market advantage in the modern aquaculture world where consumers base purchasing decisions on price alone. Therefore maximizing economies of scale and offloading costs are fundamental to remaining competitive. Thus, overlooked corollary is that environmental issues such as those above in addition to carcinogenic product [24-26], predator control, feed sustainability, and ecosystem alteration among others are the physical manifestation of “cheap” seafood – the magnitude of these issues being directly related to the scale of ever increasing production [27, 28]. Consider the proposed Marine Harvest farm that was being considered for Galway Bay (Ireland) with a capacity of 15 000 tonnes (~3 million 4-5 kg fish). The native Galway Bay salmon number in the 10s of thousands. A single significant escape event, which is all but guaranteed , could eliminate this native population both demographically and genetically. All this appears to matter little, as industrial aquaculture is so prosperous that it now buys the support of former critics like the WWF .
As demonstrably poor as the international salmon farming industry is, its environmental performance is superior to all other major marine finfish aquaculture products globally . In other words, as bad as it is, it’s as good as it gets. As we turn from fish to tropical shrimp farms the story becomes even darker. Irresponsible development in mangrove areas have eradicated large areas of irreplaceable coastal ecosystems which act as repositories for biodiversity, resources for local indigenous populations, natural coastal defences and sovereignty of local populations [31, 32]. Absence of regulatory oversight dramatically threatens both ecological viability  and human health [34, 35].
The underlying business model of all industrial scale fish and crustacean aquaculture is to convert inexpensive inputs to higher value outputs. This means converting vast quantities of edible but low value fish such as sardines, and anchovies into much reduced volumes of salmon, shrimp, grouper and sea bass etc. – a net global loss of edible protein but big profits for producers. Profits peak when regulations (or lack thereof) facilitate maximum consumption of “natural subsidies” such as permitting factory farm waste products to be “washed away” by tides free of charge, penalty-free escape events and transmission of pathogens to wild fauna or wholesale conversion of biophysical parameters in and around the production zone. We contend that such farms should pay the state fair market value for the natural capital their operations consume. The alternative is to internalize these costs through transition to self-contained recirculating aquaculture systems (RAS) that can be placed anywhere on land greatly reducing the impact on the environment.
Magnus Johnson is a Senior Lecturer in Environmental Marine Biology based at the University of Hull. His views presented here are his own, not his employers.
One slide/phrase from the Slow Fish Manifesto presented at UNESCO in Bergen
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