Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Widely adopted indicator of fisheries health questioned

18.11.2010
Inaccurate conclusions may have been reached in many ecosystems

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.

The new analysis was performed by an international team of fisheries scientists, and is reported in this week's issue of the journal Nature.

"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 University of Washington (UW) aquatic and fisheries scientist.

"Monitoring all the fish in the sea would be an enormous, and impossible, task," said Henry Gholz, program director in the National Science Foundation (NSF)'s Division of Environmental Biology, which co-funded the research with NSF's Division of Ocean Sciences.

"This study makes clear that the most common indicator, average catch trophic level, is a woefully inadequate measure of the status of marine fisheries."

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 around four.

The 1998 paper relied on four decades of catch data and averaged the trophic levels of what was caught.

The authors determined that 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 the numbers and types of fish that actually live in these ecosystems, as well as catch data.

The new analysis 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 Nature paper.

Those involved with the U.N.'s Convention on Biodiversity, for instance, chose to use the average trophic level of fish caught as the main measure of global marine diversity.

An example of the problem with the measure is in the Gulf of Thailand where the average trophic level of what is being caught is rising, which should indicate improving ecosystem health according to proponents of that measure.

Instead, it turns out fish at all levels have declined tenfold since the 1950s because of overharvesting.

"The measure only declines if fisheries aimed for top predators first, but for the Gulf of Thailand the measure fails because fisheries first target mussels and shrimp near the bottom of the food web, before shifting to fish higher up," Branch said.

Including the Gulf of Thailand, Branch found that changes in the average trophic levels of what was being caught, and what was found when fish populations were surveyed, differed in 13 of the 29 trawl surveys from 14 ecosystems.

Trawl surveys, generally done from research vessels, count the kinds and abundance of fish and are repeated over time to reveal trends.

Branch and co-authors are the first to combine many trawl surveys for analysis--no one had combined more than a handful before.

The trawl survey data came from efforts started three years ago by fisheries scientists and ecologists, who gathered at the NSF-supported National Center for Ecological Analysis and Synthesis (NCEAS) in Santa Barbara, Calif.

They brought together world-wide catch data, stock assessments, scientific trawl surveys, small-scale fishery data and modeling results.

What emerged is the most comprehensive set of data yet for fisheries researchers and managers.

It paints a different picture from previous catch data and has revealed another major new finding: on a global scale humans don't appear to be fishing down the food web, Branch said.

"The research shows the importance of synthesis to furthering an understanding of fisheries impacts and management strategies," said Phillip Taylor, section head in NSF's Division of Ocean Sciences.

"For complex ecosystem interactions, answers can only come from repeated scrutiny of data, and comparisons of different scientific methods and systems," said Taylor. "This synthesis points to a path forward to evaluate fisheries influences on ocean ecosystems."

The new catch data reveal that, following declines during the 1970s in the average trophic levels of fish being caught, catches of fish at all trophic levels have generally gone up since the mid-80s.

Included are high-trophic predators such as bigeye tuna, skipjack tuna and blue whiting.

"Globally we're catching more of just about everything," Branch said. "Therefore relying on changes in the average trophic level of fish being caught won't tell us when fishing is sustainable--or if it is leading to collapse."

When harvests of everything increase equally, the average trophic level of what is caught remains steady. The same is true if everything is overfished to collapse. Both scenarios were modeled as part of the analysis.

"The 1998 paper was tremendously influential in gathering together global data on catches and trophic levels, and it warned about fishing impacts on ecosystems," Branch said.

"Our new data from trawl surveys and fisheries assessments now tell us that catches weren't enough. In the future we will need to target limited resources in the best way, focusing on species that are especially vulnerable to fishing and developing indicators that reflect fish abundance, biodiversity and marine ecosystem health.

"Only through such efforts can we reliably assess human impacts on marine ecosystems."

"We conducted the first large-scale test of whether changes in the average trophic levels of what's caught is a good indicator of ecosystem status," said Beth Fulton, co-author of the paper and an ecosystem modeler with the Commonwealth Scientific and Industrial Research Organisation, Australia.

"Catch data might be easiest to get, but that doesn't help if what it tells us is wrong," said Fulton. "Instead we really need to look directly at what the ecosystems are doing."

Co-authors of the paper are Reg Watson and Grace Pablico, University of British Columbia; Simon Jennings, Centre for Environment, Fisheries and Aquaculture Science and University of East Anglia, England; Carey McGilliard, University of Washington; Daniel Ricard, Dalhousie University in Halifax, Nova Scotia; and Sean Tracey, University of Tasmania, Australia.

The research also was supported by the Gordon and Betty Moore Foundation and the UW School of Aquatic and Fishery Sciences.

It used data from a National Center for Ecological Analysis and Synthesis working group; the stock assessment database funded by the Canadian Natural Sciences and Engineering Research Council; the Canadian Foundation for Innovation; and the Sea Around Us project funded by Pew Charitable Trust.

Cheryl Dybas | EurekAlert!
Further information:
http://www.nsf.gov

More articles from Ecology, The Environment and Conservation:

nachricht Safeguarding sustainability through forest certification mapping
27.06.2017 | International Institute for Applied Systems Analysis (IIASA)

nachricht Dune ecosystem modelling
26.06.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: The proton precisely weighted

What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.

To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...

Im Focus: On the way to a biological alternative

A bacterial enzyme enables reactions that open up alternatives to key industrial chemical processes

The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....

Im Focus: The 1 trillion tonne iceberg

Larsen C Ice Shelf rift finally breaks through

A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...

Im Focus: Laser-cooled ions contribute to better understanding of friction

Physics supports biology: Researchers from PTB have developed a model system to investigate friction phenomena with atomic precision

Friction: what you want from car brakes, otherwise rather a nuisance. In any case, it is useful to know as precisely as possible how friction phenomena arise –...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

The technology with a feel for feelings

12.07.2017 | Event News

 
Latest News

NASA looks to solar eclipse to help understand Earth's energy system

21.07.2017 | Earth Sciences

Stanford researchers develop a new type of soft, growing robot

21.07.2017 | Power and Electrical Engineering

Vortex photons from electrons in circular motion

21.07.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>