Fish farms are in danger of losing any ground they may have gained over the past few years to becoming a sustainable industry, according to Rebecca Goldburg, a senior scientist with Environmental Defense in New York.
While aquaculture is proving less wasteful now than in the late 1990s, it is using up more resources than ever before. And recent US policies could be set to make things worse.
Environmental Defense is concerned about the sustainability of aquaculture primarily because farmed fish are frequently fed on meal made from wild-caught fish. In 2000, Goldburg co-authored a paper revealing that 1.9 kilograms of wild fish were on average required to produce every 1 kg of fish farmed in 19971.
Goldburg has now recalculated these figures with more recent data, and has come up with some good news. In 2001, each kilo of farmed fish consumed only 1.36 kg of wild-caught fish.
This increase in efficiency is due in large part to an expansion of freshwater aquaculture in China, says Goldburg. Fish farmers there tend to raise carp or tilapia, which are vegetarians, and so don't consume any wild fish stocks.
Efforts are also being made to coax carnivorous fish, such as salmon, into eating feed based on vegetable protein2. "They're going to have to figure out how to use less fishmeal in the long run," says Claude Boyd, an expert on aquaculture at Auburn University in Alabama.
But it's not all good news. The expansion of aquaculture has meant that the total catch going towards fish food has continued to increase, from 10 million tonnes in 1997 to 12 million tonnes in 2001. As aquaculture continues to boom, it will exact a growing toll on species such as sardines and herring, Goldburg says.
The situation could be made worse by a new policy from the US National Oceanic and Atmospheric Administration (NOAA), which aims to promote offshore farming of species such as red snapper and cod. By growing these fish in cages held almost 5 kilometres off the coast, NOAA wants to expand the worth of the US aquaculture industry from $1 billion to $5 billion per year.
The problem is that these fish are carnivores, which could reverse the trend to use feed containing a lower proportion of fishmeal. "An explosion in growing carnivorous fish can easily override these efficiency gains," says Goldburg.
References
Naylor, R. L. et al. Effect of aquaculture on world fish supplies. Nature, 405, 1017 - 1024, doi:10.1038/35016500 (2000).
Powell, K.. Fish farming: eat your veg. Nature, 426, 378 - 379 , doi:10.1038/426378a (2003).