A field study on using artificial substrate for nesting of introduced pumpkinseed sunfish, Lepomis gibbosus (Linnaeus, 1758).

We experimentally tested the potential use of artificial substrate - plastic bottles for egg deposition of non-native pumpkinseed sunfish, Lepomis gibbosus L. in a former sand-pit lake in western Bulgaria. The lake is situated close to an urban area, and is characterised by high pumpkinseed abundance. The study was carried out for a period of 105 days during the active pumpkinseed breeding season (from May to August). Five sites along the littoral area of the lake, with different habitat characteristics were selected. Each site was divided into two sections - an experimental and a control section. The plastic bottles (cut into two) were fixed to the lake bottom in the area of the experimental sections. Pumpkinseeds actively used the artificial substrate for nesting and the average use of each bottle was 2.3 times. Simultaneously, on the natural substrate of the experimental sections a total of 372 nests were built. The results showed that the choice of artificial substrate was neither associated with the type of bottom substrate, nor the remaining environmental traits that were studied. However, the use of artificial substrate has made a significant contribution to the total number of nests only on sites with "unsuitable" habitat parameters. These results show that waste products can seriously facilitate pumpkinseed's abundance. [ABSTRACT FROM AUTHOR]