In 2000, the Worldwide Fund for Nature estimated that Scotland's salmon farms produced the same amount of nitrogen as the sewage of 3.2 million people. Phosphorous deposits were equivalent to the sewage of 9.4 million people.
"If you extend that to cod you get a handle on the potential problem," Staniford added.
Sea cages can also act as reservoirs for parasitic lice, disease such as infectious salmon anaemia, and chemicals used in feed, he added.
There is evidence to support such claims in a region where wild salmonid stocks have collapsed in recent decades. For instance, rod catches of sea trout in Loch Maree in Wester Ross have fallen 90 percent since salmon farming started nearby in the 1980s.
Anglers blame fatal levels of sea lice infestation for the demise of what was once a world-famous fishing destination.
Fisheries Research Services scientists confirmed last fall that salmon farms can generate unnaturally high numbers of these parasites which then infect wild salmonids as they migrate between rivers and their ocean feeding grounds.
These and other concerns are highlighted in an article about Atlantic salmon and fish farming in this month's [July] National Geographic magazine.
Responding to the concerns, Scottish Quality Salmon says recent initiatives such as the Strategic Framework for Scottish Aquaculture build on industry efforts to protect the marine environment.
Brian Simpson, chief executive of the industry's main umbrella organization, said Scottish Quality Salmon's quality standards, whilst non-statutory, were "independently inspected, certified, and accredited to international standards."
However, Staniford points out that in the past year the Scottish Environment Protection Agency (SEPA) recorded 13 fish farm pollution incidentsdouble the usual figure. They included an outbreak of sewage fungus in the Sound of Mull which infected the River Rannoch and the discovery of decaying farm salmon floating in a loch on the Isle of Lewis.
Staniford said: "The fundamental flaws inherent in salmon farming can only be replicated if we go down the same path with cod."
Such concerns are echoed by Robin Malcolm, riparian owner of the River Add in Argyll. One of Scotland's first large-scale commercial cod farms has been given the go-ahead at a site close to the river.
He said: "It's the only remaining salmon river on the west coast of mid Argyll and they've chosen to put the cod farm in the mouth of the estuary. I fear all the gunge will extend across the estuary like a curtain and have a disorientating effect on migratory salmonids. I've received no assurance that this will not be the case."
Alan Kettlewhite, biologist for the Argyll Fisheries Trust, added: "I think the decision is incredibly stupid. We don't know the full consequences of cod farming yet. It's going to be a learning curve, just like there's been with salmon farming."
But Derek Robertson, chief executive of the nearby cod hatchery which will supply fish to the new farm, denies it poses any threat.
He said: "There is a major difference between cod and salmon. The cod is an animal that doesn't migrate, doesn't go up salmon rivers and is all around the Scottish coastline, so I really puzzle why salmon river owners would have a concern about it. They have been farmed in Norway for over 50 years, including areas containing famous salmon rivers, and there haven't been any problems."
Robertson says cod farmers are subject to the same controls as salmon farmers and that new operations will be closely monitored by SEPA.
These assurances don't convince Staniford. He believes there's only one way for farmed and wild fish to coexist in northwest Scotland. And that's for the aquaculture industry to adopt closed-contained marine or land-based farms which prevent waste getting into the environment.
Such technology already exists, though it's more costly to install and operate than open-sea cages. Given the negative publicity currently surrounding the fish farming industry, such costs could become worth weighing up.
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