Creixement i demografia de la perca americana (Micropterus salmoides), el peix sol (Lepomis gibbosus) i la perca de riu (Perca fluviatilis) a l’Estany de Banyoles

Abstract

In Banyoles Lake there are a lot of exotic species, especially there are a lot of exotic fish that have been introduced by human activity over many years. Exotic fish change original communities. These changes are: trophic relationships, hybridization and genetic alteration, introduction of pests and diseases and global changes in the whole lake ecosystem. However, these introductions are also the cause of the extinction of some native species, such as three-spined (Gasterosteus aculeatus), or there are others, which are in a terrible decrease of theirs populations. Basically this project studies three exotic species: largemouth bass (Micropterus salmoides), pumpkinseed (Lepomis gibbosus) and perch (Perca fluviatilis). Nowadays, the first and the second ones are the most abundant in the lake and the third one appears in lower amounts. The growth and the demography will be studied in the Life Project Potamo Fauna through the extraction and the reading of otoliths that are a small structure of calcium carbonate that have all teleost fish inside the inner ear. That one being, the data that we will obtain, will be analyzed by a mathematic model that has always been used, Von Bertalanffy model. From the data obtained in the last Life Project (2010-2013), populations of exotic species are compared and then we know if populations have changed or not. Mortality in juveniles of largemouth bass is progressively increasing by the time being, with the exception of the last winter due to the fact that lately it has been fished less intensively. So, largemouth bass population has rejuvenated there are more juveniles fish (0-2 years) than adults, and their longitude have also increased during these projects. It is necessary to maintain it, because there are the biggest fish, which cause a lot of problems to native species, for its big voracity. However, in pumpkinseed population it remains stable over time because of the decline in big largemouth bass, his potential predator and others, such as Sander lucioperca. But, we cannot affirm anything of its demography, because in the beginning of the previous Life Project, the dates were not clear. The only dates that are clear in pumpkinseed population are the obtained this winter (14-15). The demography of Perca fluviatilis could not be studied because we captured only a few and the results are not significant