Over a 23-year study, Javier Lobn-Cervi has found the mechanism that controls the number of salmonids found each year in Cantabrian rivers. 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 Lobn-Cervi, 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, Lobn-Cervi 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 en
FECYT - Spanish Foundation for Science and Technology