The most widely adopted measure for assessing the state of the world's oceans and fisheries led to inaccurate conclusions in nearly half the ecosystems where it was applied according to new analysis by an international team led by a University of Washington fisheries scientist.
"Applied to individual ecosystems it's like flipping a coin, half the time you get the right answer and half the time you get the wrong answer," said Trevor Branch, a UW assistant professor of aquatic and fishery sciences.
In 1998, the journal Science published a groundbreaking paper that was the first to use trends in the trophic levels of fish that were caught to measure the health of world fisheries. The trophic level of an organism shows where it fits in food webs, with microscopic algae at a trophic level of one and large predators such as sharks, halibut and tuna at a trophic level of around four.
The 1998 paper relied on four decades of catch data and averaged the trophic levels of what was caught. The authors determined those averages were declining over time and warned we were "fishing down the food web" by overharvesting fish at the highest trophic levels and then sequentially going after fish farther down the food web.
Twelve years later, newly compiled data has emerged that considers such things as the numbers and types of fish that actually live in these ecosystems, as well as catch data. An analysis in the Nov. 18 issue of Nature reveals weaknesses in assessing ecosystem health from changes in the trophic levels of what is being caught.
"This is important because that measure is the most widely adopted indicator by which to determine the overall health of marine ecosystems," said Branch, lead author of the new analysis in Nature. Those involved with the U.N.'s Convention on Biological Diversity, for instance, chose to use the average trophic level of fish being caught as the main measure of global marine diversity.'/>"/>
|Contact: Sandra Hines|
University of Washington