A Christmas carp about salmon

Sales of smoked salmon rocket over the holidays. If you’re buying Scottish smoked salmon, it’s become a shadow of its former self, so make the most of each slice. Wild Scottish salmon have lost up to one-third of their body weight in the last 10 years. This means you’ll need more to cover the cream cheese mounded on that brunch bagel.

Scientists at St. Andrews, Scotland's oldest university, have found the weight of wild salmon returning to freshwater spawning grounds from the sea has dropped by 15 percent since 1997. The female grilse salmon -- fish that have only spent one year out in the ocean and weigh an average of 4 pounds -- have lost one-quarter of their fat content. And the number of fish returning to spawn is believed to have dropped by half since the 1970s.

Global warming and rising sea temperatures driving plankton into cooler waters and starving salmon of their food supply may be to blame. But we’re also being encouraged for our health to eat far more of all fish than we used to.

With natural supplies becoming harder to sustain, fish farming is on the rise, accounting for almost half the seafood consumed globally. Commerce Secretary Carlos Gutierrez has called for doubling the U.S. aquaculture industry over the next decades by allowing it to operate up to 200 miles out to sea.

Consumers, however, are increasingly concerned about the impact of conventional fish farming on the environment. They’re putting pressure on supplies of farmed fish organically.

The difference between the two methods, though, seems tenuous. A conventional farming cage can contain up to 70,000 fish. An organic farming cage as much as 30,000. Fish with limited mobility attract parasitic sea lice. Organic fish farms are allowed to use the same chemicals as used by conventional fish farms to keep disease at bay -- but only twice in the 30-month life cycle of an organic salmon. If necessary, fish may be dosed with three courses of appropriate medicines over the period.

Organically farmed fish are also allowed to be fattened on feed that may include fish oil and matter from fish that might not necessarily have been raised themselves on an organic diet. In both conventional and organic fish farming, feed and feces fall through cages onto the ocean bed.

So far there’s no U.S. Department of Agriculture certification behind the “wild caught” label. But if you want an organic “wild caught” salmon or smoked salmon, go for an Alaskan fish. That state is still free of fish farms. So any salmon from it is currently believed sustainable and being wild-caught is organic.  Which is more than you can say of its Scottish cousin.