Replacement of dominant fish species from Cyprinidae fishes into invasive fishes and the amount of its economic loss in a satellite lake, Katata Naiko, of Lake Biwa

Abstract

To understand the process of decrease in biodiversity of Naikos, seasonal and annual changes in fish fauna were surveyed in Katada Naiko, which is located at the western part of Lake Biwa. Specimens were collected by a casting net sampling for 20 min each night from August 2001 to July 2006. In the first and second years, 3 cyprinid species—Carassius sp., Pseudorasbora parva, and Rhodeus ocellatus ocellatus—were the most abundant. Over the five year study period, the frequency of the three most abundant cyprinid fishes combined dramatically decreased from 83.3%, 84.3%, 68.9%, 18.6%, to 15.5% whereas that of two invasive species—bluegill Lepomis macrochirus and largemouth bass Micropterus salmoides—increased from 3.9%, 4.5%, 16.2%, 68.9%, to 78.1%. The amount of economic loss, calculated by the production method, also increased during the period. The decrease in dominant species was simultaneous with the increase in bluegill and largemouth bass, and induced the potential economic loss. We discuss the requirement of removing the two invasive species, and methods for the reconstruction of the biodiversity.