Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Why are cod stocks collapsing?

23.09.2002


Sudden collapses in many ecological systems are the rule rather than exceptions to the rule.

This is shown by Professor Lennart Persson of Umeå University, Sweden, in the latest issue of the scientific journal Proceedings of the National Academy of Sciences. Among other things, the article provides an explanation for the collapses in cod stocks in different parts of the world. Several models have shown that ecological systems can experience catastrophic collapses. On the other hand, these models have not been able to say how common they are.

Lennart Persson and co-author André M. De Roos of the University of Amsterdam have now shown in a model that two fundamental traits of individuals in many organisms promote the occurrence of catastrophic behaviors in ecological systems. The two traits that the authors have examined are the correlation between growth and the amount of ingested food and the correlation between mortality and body size. In simple terms, animals grow more the more they eat, and the smaller an animal is, the greater the risk that it will be eaten. On this basis, Persson and De Roos have been able to show that collapses in ecological systems are rather the rule than exceptions to the rule.

"The mechanism is actually quite simple, but that`s also what makes it so general," says Lennart Persson. "Considering that more than 85 percent of all species on earth exhibit populations with variations in size, these results should be extremely generalizable.

Paradoxically, the number of available prey can increase with the number of predators. This happens because the competition among the remaining prey diminishes, and these prey also grow more quickly. Increased growth yields greater reproduction, and that in turn leads to increased numbers of the small-sized prey that predators thrive on. If, on the other hand, mortality among predators increases, say as a result of high pressures from fishing, it is a natural consequence for mortality to rise among the prey these predators live on. This in turn means that competition increases among the prey, thereby checking their growth. This leads to a decline in the number of prey of the sizes preferred by predators. This can bring about a collapse in the number of predators.

When a collapse occurs, it comes extremely rapidly, and it is difficult to discover changes in advance. The species that professional fishers capture in their nets, such as cod and full-grown herring, provide no clues to what is under way. On the other hand, the small-sized, sexually immature individuals of the species of prey that are nevertheless too large to be eaten by the predators (sexually immature herring, for instance) and the food that the former live on exhibit differences.

"It is actually these small-sized individuals of the species of prey that need to be monitored, because it is here that you can get a measure of when collapse is imminent," explains Lennart Persson.

These small-sized individuals of the species of prey increase in number when the fishing of predators increases. This occurs since the competition for food increases among the small-sized individuals. They have no possibility of growing larger, so their growth is stunted, and the number of small-sized individuals grows. This means that we must be extremely vigilant.

"If fishing is increased, very little change will be noticed until there is a collapse. In order to promote growth at this juncture, fishing must be cut to extremely low levels. Halving quotas, for example, will not help; total bans on fishing are the only answer then," says Lennart Persson.

This line of reasoning is supported by developments in North Atlantic cod stocks, which have not recovered despite drastically reduced fishing.

Karin Wikman | AlphaGalileo

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 >>>