Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Fishing Throws Targeted Species Off Balance

18.04.2008
Fishing activities can provoke volatile fluctuations in the populations they target, but it's not often clear why. A new study published in the journal Nature by scientists at Scripps Institution of Oceanography at UC San Diego and colleagues has identified the general underlying mechanism.

Research led at Scripps with a distinguished team of government and international experts (including two chief scientific advisors to the United Kingdom) demonstrates that fishing can throw targeted fish populations off kilter.

Fishing can alter the "age pyramid" by lopping off the few large, older fish that make up the top of the pyramid, leaving a broad base of faster-growing small younglings. The team found that this rapidly growing and transitory base is dynamically unstable-a finding having profound implications for the ecosystem and the fishing industries built upon it.

This schematic outlines variability on exploited and unexploited.
"The data show that fished species appear to be significantly more nonlinear and less stable than unfished species," said Professor George Sugihara of Scripps. "We think the mechanism involves systematic alteration of the demographic parameters-and especially increases in growth rates that magnify destabilization in many ways-which can happen as fishing truncates the age structure."

Imagine a container of water with a 500-pound fish. With food, it grows a little bigger. Without food it gets a bit smaller. Imagine the same container with 500 one-pound fish. They eat, reproduce and the resulting thousands of fish boom, quickly outstripping the resources and the population crashes. These many smaller fish-with the same initial "biomass" as the larger fish-can't average out the environmental fluctuations, and in fact amplify them through higher turnover rates that promote boom and bust cycles.

The study that included academic and government scientists from Alaska, Asia and Great Britain is based on data from the California Cooperative Oceanic Fisheries Investigations (CalCOFI), a program based at Scripps that has monitored fish and oceanographic activities of the California Current for more than 50 years. To arrive at their results, the researchers compared the CalCOFI records of larvae, a key indicator of adult populations, of both fished and non-fished species in the California Current.

The schematic outlines variability on exploited and unexploited.Fishing typically extracts the older, larger members of a targeted species and fishing regulations often impose minimum size limits to protect the smaller, younger fishes.

"That type of regulation, which we see in many sport fisheries, is exactly wrong," said Sugihara. "It's not the young ones that should be thrown back, but the larger, older fish that should be spared. Not only do the older fish provide stability and capacitance to the population, they provide more and better quality offspring."

Thus the danger, according to Sugihara, is that current policies that manage according to current biomass targets (without significant forecast skill) while ignoring fish size pose risks that can further destabilize the population. This instability can in principle propagate systemically to the whole ecosystem, much like a stock market crash or a domino effect, and magnify risk for the fishing industry itself as well as those of ecologically related fisheries.

This is especially true when trying to rebuild fish stocks, Sugihara says.

"This may be the most important implication of this work, as we attempt to rehabilitate fisheries," said Sugihara. "Regulations based solely on biomass harvest targets are incomplete. They must also account for age-size structure in the populations," he said. "Current policies and industry pressures that encourage lifting bans on fishing when biomass is rehabilitated-but where maximum age and size are not-contain risk."

This is currently the case with Atlantic swordfish, for which industry pressures to resume fishing are based on the restoration of historic biomass levels, even though the swordfish are clearly undersized.

"In the extreme case, the danger of such unstable dynamics for certain populations for management is that harvest targets may lag the population, potentially making things worse," said Sugihara. "A high harvest target may be set after an especially abundant period when the population may be poised to decline on it's own. Likewise future abundant periods may represent missed opportunities, despite current low abundances. As senior officials of the Canadian Department of Fisheries and Oceans have said, 'we are often a year behind in our stock projections.'"

Sugihara cautioned that nonlinearity is not unique to fished species. Nonequilibrium overshooting and undershooting occurs in unexploited stocks, but to a lower extent. Therefore, classical single-species population models that require equilibrium are unlikely to be very successful in stock forecasts, except perhaps in the very short term.

"Other methods that do not rely on these assumptions may be more promising," suggests Christian Anderson, paper co-author.

In addition to Sugihara and Anderson, the study included Scripps Oceanography Chih-hao Hsieh (now a professor at National Taiwan University); Stuart Sandin of Scripps; Roger Hewitt of the National Marine Fisheries Service, Southwest Fisheries Science Center; Anne Hollowed of the National Marine Fisheries Service, Alaska Fisheries Science Center; Sir John Beddington of Imperial College London (current Chief Science Advisor to the United Kingdom) and Lord Robert May of Oxford (a former Chief Scientific Advisor to the UK).

The research was supported by NOAA Fisheries and the Environment program, The MacQuown Chair of Natural History, The Deutsche Bank - Jameson Complexity Studies Fund, the Sugihara Family Trust and the Kyoto University grant for Biodiversity Research of the 21st Century.

Mario Aguilera | EurekAlert!
Further information:
http://www.ucsd.edu

More articles from Studies and Analyses:

nachricht Drought hits rivers first and more strongly than agriculture
06.09.2018 | Max-Planck-Institut für Biogeochemie

nachricht Landslides triggered by human activity on the rise
23.08.2018 | European Geosciences Union

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

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

Im Focus: Storage & Transport of highly volatile Gases made safer & cheaper by the use of “Kinetic Trapping"

Augsburg chemists present a new technology for compressing, storing and transporting highly volatile gases in porous frameworks/New prospects for gas-powered vehicles

Storage of highly volatile gases has always been a major technological challenge, not least for use in the automotive sector, for, for example, methane or...

Im Focus: Disrupting crystalline order to restore superfluidity

When we put water in a freezer, water molecules crystallize and form ice. This change from one phase of matter to another is called a phase transition. While this transition, and countless others that occur in nature, typically takes place at the same fixed conditions, such as the freezing point, one can ask how it can be influenced in a controlled way.

We are all familiar with such control of the freezing transition, as it is an essential ingredient in the art of making a sorbet or a slushy. To make a cold...

Im Focus: Micro energy harvesters for the Internet of Things

Fraunhofer IWS Dresden scientists print electronic layers with polymer ink

Thin organic layers provide machines and equipment with new functions. They enable, for example, tiny energy recuperators. In future, these will be installed...

Im Focus: Dynamik einzelner Proteine

Neue Messmethode erlaubt es Forschenden, die Bewegung von Molekülen lange und genau zu verfolgen

Das Zusammenspiel aus Struktur und Dynamik bestimmt die Funktion von Proteinen, den molekularen Werkzeugen der Zelle. Durch Fortschritte in der...

Im Focus: Dynamics of individual proteins

New measurement method allows researchers to precisely follow the movement of individual molecules over long periods of time

The function of proteins – the molecular tools of the cell – is governed by the interplay of their structure and dynamics. Advances in electron microscopy have...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

5th International Conference on Cellular Materials (CellMAT), Scientific Programme online

02.10.2018 | Event News

Major Project: The New Silk Road

01.10.2018 | Event News

"Boston calling": TU Berlin and the Weizenbaum Institute organize a conference in USA

21.09.2018 | Event News

 
Latest News

Storage & Transport of highly volatile Gases made safer & cheaper by the use of “Kinetic Trapping"

15.10.2018 | Life Sciences

Graphene shows unique potential to exceed bandwidth demands of future telecommunications

15.10.2018 | Materials Sciences

Goldilocks principle in biology -- fine-tuning the 'just right' signal load

15.10.2018 | Agricultural and Forestry Science

VideoLinks
Science & Research
Overview of more VideoLinks >>>