Variation of Abundance and Demographic Structure of the Introduced Pumpkinseed, <I>Lepomis Gibbosus</I> (Actinopterygii: Perciformes: Centrarchidae), in Relation to Littoral Habitats and Water Body Use

Abstract

Background. The pumpkinseed, Lepomis gibbosus (L.), is one of 23 introduced fish species in Bulgarian freshwaters. With this study we attempt to contribute to clarifying the factors that effect pumpkinseed abundance and demographic structure in water bodies differing in macro- and microhabitat parameters. Materials and methods. Fish were collected during the breeding period of pumpkinseed (May–June 2010) by minnow traps arranged in 31 sites in the littoral zone of 13 fresh water bodies (former- and active sand-pit lakes, reservoirs, adaptive ponds of refineries). Demographic structure (length and age) and abundance (Catch Per Unit Effort; CPUEN; fish per trap per hour) of pumpkinseeds from different sites were compared to provide information about ecological requirements of this species. Results. L. gibbosus dominated at 24 sites and comprised 86.7% of all fish caught. The mean pumpkinseed abundance was 6.35 ± 7.2 fish per trap per hour (mean ± SD). Pumpkinseeds were most numerous in the littoral zones of the former sand-pit lakes, where pumpkinseed’s CPUEN achieved values of 20 fish per trap per hour. Water body use had a significant effect on pumpkinseed abundance and the statistical analyses revealed that the littoral zones in the active sand-pit lakes were characterized by the lowest number of pumpkinseeds than the other types. Microhabitat parameters such as silt and sand bottom substrate also significantly affected pumpkinseeds abundance, size, and age, while gravel significantly affected body length but not abundance and age. Aquatic vegetation also had a significant impact on the abundance and at sites with dense vegetation pumpkinseeds were more abundant than at the sites with sparse vegetation. At the sites where piscivore fish occurred, the mean length and mean age of pumpkinseed were lower. Conclusion. Human activities facilitate establishment of the pumpkinseed population, mainly by extending suitable breeding places for pumpkinseed and eliminating its natural competitors and predators. Some parameters as sand or silt bottoms in littoral area and dense submerged vegetation may use as indicator of suitable conditions for pumpkinseed.