Scientists Say Fish Farming Lessens Fish Supply

Many types of fish farming, or aquaculture, result in a loss of fish, according to an analysis in tomorrow’s issue of the scientific journal Nature. A major reason is that many farmed fish are fed diets containing high levels of fish meal and fish oil made from wild caught fish. The result is that more pounds of wild fish are caught to feed many types of farmed fish than are harvested from farms.

“Many consumers believe that when they purchase farmed fish they are helping to take pressure off of wild fisheries,” said Environmental Defense senior scientist Dr. Rebecca Goldburg, an author of the study. “In fact, for many types of farmed fish, the opposite is true. Purchasing farmed fish isn’t necessarily better for our oceans than purchasing wild caught fish.”

The Nature article found that on balance, worldwide aquaculture production still contributes to global fish supplies largely because traditional carp farming systems in China do not use modern fishmeal based feeds. “In the United States, catfish, crayfish, oysters, mussels, and other mollusks are farmed with little or no inputs of wild fish,” said Goldburg. “In contrast, producing one pound of carnivorous farmed salmon or shrimp requires about three pounds of wild fish in the form of fish meal. Shrimp and salmon are two of the four most popular types of seafood caught in the United States.”

The Nature article also highlights a number of aquaculture practices besides feeding that harm marine fish populations. Examples include conversion of coastal wetlands to fish ponds and discharge of untreated fish wastes.

“The aquaculture industry is growing rapidly,” said Goldburg. “Fish farm production more than doubled between 1987 and 1997, and more than a quarter of fish consumed by people worldwide are now from farms. Much of the expanding aquaculture industry has to change its direction or it will threaten ocean fisheries and itself.”

Recommendations in the Nature article include expanding the production of fish that consume largely vegetarian diets, reducing the use of fishmeal and fish oil in feeds, and adopting environmentally sound aquaculture practices.

Co-authors of the paper include two members of the Environmental Defense Board of Trustees: Dr. Jane Lubchenco of Oregon State University and Dr. Harold Mooney of Stanford University.