Oct 6, 2009
Aquaculture: friend or foe?
Aquaculture has boomed in recent years and it's set to supply half the fish and shellfish consumed by humans in 2009. But does the industry protect the oceans' fish stocks or is it leading to their depletion to produce fish oil and fishmeal for consumption by the farmed fish?
"Aquaculture feed technologies have improved considerably over the years; however, the growing volume of fish produced means that feed demand for fish meal and fish oil remains high," Alice Chiu of Stanford University, US, told environmentalresearchweb. "In order for aquaculture to continue growing, the aquaculture industry will need to reduce its reliance on forage fish for feed and instead increase use of other feed ingredients, such as algal meals and oils, plant proteins and oils, and seafood and animal processing byproducts."
To date, the aquaculture industry has improved feed conversion ratios – the amount of food required to increase body mass – for piscivorous (fish-eating) fish; increased the proportion of nonfish ingredients in formulated feeds; and replaced some piscivorous species with omnivorous ones.
What's more, between 1995 and 2007 the ratio of wild fish input to farmed fish output (except for filter feeders) fell from 1.04 to 0.63 for the aquaculture sector as a whole, although the ratio remains as high as 5.0 for Atlantic salmon. But farmed production of fish and shellfish nearly tripled over the same period, so that the industry's demand for fish inputs increased.
Aquaculture's share of global fishmeal and fish oil consumption has more than doubled in the past ten years, to 68% and 88% respectively, as a result of rapid expansion of aquaculture and a reduction of fishmeal use in the livestock industry due to rising prices.
Chiu and colleagues from the US, Canada, Norway and Australia studied trends in fish oil and fishmeal use in industrial aquafeeds between 1995 and 2007. The team found that the use of fish oil in aquaculture feeds has a much higher impact on forage fisheries than the use of fishmeal.
Forage fish, such as herrings, sardines, menhaden, sprats and anchovies, are often a vital part of oceanic food webs, supporting a number of predators, such as larger fish, marine mammals and seabirds, so that their removal from the food web for aquaculture can have a large impact on oceanic ecosystems. To make matters worse, most such fisheries are fully exploited, overexploited or recovering from overexploitation.
Feed costs are typically an aquaculture provider's largest variable cost, so it could be in the providers' interest, as well as the ocean's, to reduce their fish product usage in feed. Global production of fishmeal and fish oil have been relatively steady over the last few decades, at around 5–7 million metric tons of fishmeal and 0.8–1.5 million metric tons of fish oil. Chile and Peru account for around 40% of this production, with more than half of their fishmeal exports now going to China, Japan and Taiwan. Europe uses around half the world's production of fish oil, which is used most heavily in salmon aquaculture.
"As consumers increasingly seek out heart-healthy omega-3 oils, elevated demand for fish oil could cause increased pressure on marine fisheries," said Chiu. Maintaining high omega-3 oil levels in farmed salmon requires a relatively high use of fish oil in their feed, although research into alternatives is underway. Trials of a terrestrial plant oil (stearidonic acid) have been promising; genetic modification of canola and soy plants to produce LC omega-3 oils could be an option; and single-cell oils from microorganisms such as thraustochytrids may also be a suitable replacement.
"Each of the feed ingredients mentioned above – algal meals and oils, plant proteins and oils, and seafood and animal processing byproducts – comes with varying nutritional, economic, ecological, and technological challenges and benefits," said Chiu. "Further research is needed to overcome these challenges."
In the meantime, Chiu says that short-term strategies can be adopted to conserve fishmeal and fish oil resources. These include blending non-fish feed ingredients to satisfy fish nutritional requirements and reserving the use of fish oil for the final feeding stages of the fish lifecycle, so that their health benefits are retained in the final product.
"Our paper draws attention to the need to find ways to minimize the impact aquaculture has on forage fisheries," said Chiu. "I hope that policy measures will be implemented that support responsible feed use, ecosystem-based management of forage fisheries, and research and development initiatives to accelerate the transition toward alternative feed ingredients and reduce aquaculture's reliance on forage fish."
Writing in PNAS, Chiu and colleagues say that by taking action now to implement the right policy interventions, one can only hope that by 2015 the transition toward alternatives will be well underway. "If so, it is likely that a consensus will emerge that aquaculture is aiding the ocean, not depleting it," they add.