Twenty years ago, as farmed salmon and shrimp started spreading
in supermarket freezers, came an influential scientific paper that warned of an
environmental mess: Fish farms were gobbling up wild fish stocks, spreading
disease and causing marine pollution.
اضافة اعلان
Some of the same scientists who published that report issued a
new paper concluding that fish farming, in many parts of the world, at least,
is a whole lot better. The most significant improvement, they said, was that
farmed fish were not being fed as much wild fish. They were being fed more
plants, like soy.
In short, the paper found, farmed fish like salmon and trout had
become mostly vegetarians.
Synthesizing hundreds of research papers carried out over the
last 20 years across the global aquaculture industry, the latest study was
published Wednesday in the journal Nature.
The findings have real-world implications for nutrition, jobs
and biodiversity. Aquaculture is a source of income for millions of small-scale
fishers and revenue for fish-exporting countries. It is also vital if the world’s
7.75 billion people want to keep eating fish and shellfish without draining the
ocean of wild fish stocks and marine biodiversity.
At the same time, there have long been concerns among some
environmentalists about aquaculture’s effects on natural habitats.
The new paper found promising developments, but also lingering
problems. And it didn’t quite inform the average fish-eater what they should
eat more of — or avoid.
The aquaculture industry is too diverse for broad
generalizations, said Rosamond Naylor, a professor of earth systems science at
Stanford University and the lead author of both the 2000 cautionary paper and
the review published Wednesday.
“The aquaculture industry is so diverse (over 425 species farmed
in all sorts of freshwater, brackish water, and marine systems) that it doesn’t
make sense to lump them all together into a “sustainable” or “nonsustainable”
category,” Naylor said in an email. “It has the potential to be sustainable —
so how can we ensure it moves in that direction?”
Global aquaculture production has more than tripled in the last
20 years, producing 112 million metric tons in 2017, the most recent year for
which statistics are cited in the paper. China leads the way, producing more
than half of all farmed fish and shellfish worldwide. Outside of China, Norway
and Chile are big players, producing mostly farmed Atlantic salmon, while Egypt
produces mostly the Nile tilapia. Most fish produced in Asia is consumed in
Asia, meaning that it serves as an important source of protein for citizens of
those countries.
The study also found that the production of farmed seaweed and
bivalves, like oysters and clams, had greatly expanded as well. That is perhaps
the most encouraging news, because neither seaweed nor bivalves need extra food
to reproduce. They filter nutrients from the water and, in turn, produce
nutrition for human consumption.
The study also found that freshwater aquaculture today accounts
for 75 percent of farmed fish directly consumed by humans. Its most striking
finding, though, was about the changes in fish feed, especially for carnivorous
fish like salmon, which were traditionally fed lots of wild fish, like
anchovies. Between 2000 and 2017, the study found, the production of farmed fish
tripled in volume, even as the catch of wild fish used to make fish feed and
fish oil declined.
Martin Smith, an environmental economist at Duke University who
was not involved in the study, said the changes in aquaculture resulted partly
from new regulations in some countries — rules in Norway, for instance, reduced
the spread of sea lice in salmon farms — but mostly because the aquaculture
industry had no reason to buy expensive wild fish feed once they could develop
plant-based alternatives.
“It was always in aquaculture’s interest to reduce their most
expensive ingredient,” said Smith, who teaches a class called “Should I Eat
Fish?”
“The language around aquaculture has been overly negative and
overly pessimistic,” he said. “But also, the industry has gotten a lot better.”
But problems linger, the authors of the latest study point out.
Aquaculture needs better oversight to ensure that
environmentally sustainable practices are followed and rewarded. “Many
aquaculture systems still lack motivation, however, to meet sustainability
criteria,” the authors note, “because their targeted markets do not reward
producers through improved prices or access.”
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