His method has been to monitor population numbers in relation to river flow in March, when the juvenile fish emerge. He concludes that environmental conditions change each year and modify river flow, positively or negatively affecting survival rates. This information throws light on a long debate within ecological theory about the mechanisms that regulate the size of animal populations.
In 2000, populations of trout (Salmo trutta) in the rivers of north East Spain suffered an alarming decline, but fishing was never banned, and fish numbers fell still further. However, these populations recovered "naturally" within a very short time period. Javier Lobón-Cerviá, lead author of the research study and a researcher at the National Museum of Natural Sciences (CSIC) has the answer, and has published it in the journal Freshwater Biology.
"If we use a small measurement and calculate the amount of water that was flowing in March (when the fish eggs emerge), we can predict how many trout there will be now, how many there will be in two years, how many should be fished, how many females are going to reproduce – in other words, we can monitor the entire population perfectly", the researcher tells SINC.
It has taken him 23 years of study to arrive at this conclusion. Contrary to conventional theories, which hold that populations have endogenous mechanisms to respond to variations, and that these depend upon the density of individuals, Lobón-Cerviá says populations "simply respond to the environmental conditions that exist at the time".
Since 1986, the scientist has been studying the Chaballos river in the basin of the Esva river in Asturias, where environmental conditions have varied widely year-on-year up to 2007. "Information as simple as river flow in the month of March is enough to enable us to predict everything that will happen in the river", stresses Lobón-Cerviá.
Rain and temperature are natural factors that create the ideal conditions for young trout. The number of juveniles is highest when river flow is average, because there is an ideal amount of useable river area for the larvae. "If the amount of water flowing rises, this space is reduced, because water velocity increases too much, which is harmful to the larvae", says the scientist. However, drought is the worst condition for this species, because "river sections dry up".
The river is a vital space for larvae
Rain determines river flow, and creates useable area in rivers for a particular size of trout. "Small larvae live in a certain river area, but when they grow they move to deeper waters. The river's flow determines how much useable area is available for each size group of trout", explains the researcher.
Temperature regulates the so-called "embryonic stream", in other words the two months that fertilised salmonid eggs remain in the river. For this reason, an increase in temperature affects embryonic development. "Temperature also plays a role in the strength of recruitment, the number of juveniles, but there is an inverse relationship between river flow and temperature – when flow is very low, the water heats up more, and in years with much more water the river heats up less", adds the scientist. However, the great changes in temperature each year make it difficult to work out the direct relationship between this aspect and the number of juveniles born.
This research could also be applied to salmon (Salmo). Although they occupy different parts of the river, they have the same population dynamics processes as trout. Lobón-Cerviá is now looking at the possibility of a link between reproduction and reproductive success among populations swimming out into the Cantabrian Sea and those that swim into the Duero. "If this can be demonstrated, this study could be widely applied", the researcher concludes.
Lobón-Cerviá, Javier. "Why, when and how do fish populations decline, collapse and recover? The example of brown trout (Salmo trutta) in Rio Chaballos (northwestern Spain)" Freshwater Biology 54(6): 1149-1162 junio de 2009.
SINC | EurekAlert!
Bare bones: Making bones transparent
27.04.2017 | California Institute of Technology
Link Discovered between Immune System, Brain Structure and Memory
26.04.2017 | Universität Basel
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
27.04.2017 | Life Sciences
27.04.2017 | Physics and Astronomy
27.04.2017 | Earth Sciences