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 When corals eat plastics
24.05.2018 | Justus-Liebig-Universität Gießen

nachricht Dispersal of Fish Eggs by Water Birds – Just a Myth?
19.02.2018 | Universität Basel

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: Powerful IT security for the car of the future – research alliance develops new approaches

The more electronics steer, accelerate and brake cars, the more important it is to protect them against cyber-attacks. That is why 15 partners from industry and academia will work together over the next three years on new approaches to IT security in self-driving cars. The joint project goes by the name Security For Connected, Autonomous Cars (SecForCARs) and has funding of €7.2 million from the German Federal Ministry of Education and Research. Infineon is leading the project.

Vehicles already offer diverse communication interfaces and more and more automated functions, such as distance and lane-keeping assist systems. At the same...

Im Focus: Molecular switch will facilitate the development of pioneering electro-optical devices

A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.

The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...

Im Focus: LZH showcases laser material processing of tomorrow at the LASYS 2018

At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.

At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...

Im Focus: Self-illuminating pixels for a new display generation

There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?

At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...

Im Focus: Explanation for puzzling quantum oscillations has been found

So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics

Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

In focus: Climate adapted plants

25.05.2018 | Event News

Save the date: Forum European Neuroscience – 07-11 July 2018 in Berlin, Germany

02.05.2018 | Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

 
Latest News

In focus: Climate adapted plants

25.05.2018 | Event News

Flow probes from the 3D printer

25.05.2018 | Machine Engineering

Less is more? Gene switch for healthy aging found

25.05.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>