霞ヶ浦の沖帯における魚類群集の季節変動

抄録

Seasonal dynamics of the profundal zone（3.1-5.8 m depth）fish assemblage in Lake Kasumigaura, a large shallow inland-sea lake（220 km ²）in Ibaraki Prefecture, eastern Japan, were examined by monthly bottom trawl-net（mouth size 5.5 m and mesh size 3 mm）sampling from January 2014 to December 2015. A total of 14,840 individuals（mainly late juvenile and adult stages）representing 30 species in 12 families, including 3 commercially important and 2 threatened species, were collected throughout the study period. The mean number of fish species per haul varied from 6.7 to 12.7, with no apparent seasonal tendencies. Considerable seasonal fluctuations in mean numbers of individuals were found in each year（peak abundances > 400 ind. ⁄ haul in summer and winter seasons）, with species composition differing significantly between the two seasons. The most abundant species were Tridentiger brevispinis, Salangichthys microdon, Hypomesus nipponensis, Gnathopogon elongatus elongatus, Ictalurus punctatus, Carassius sp., Cyprinus carpio, Pseudorasbora parva, Acanthogobius lactipes, Gymnogobius urotaenia, Rhinogobius sp. and Squalidus chankaensis biwae, accounting for 98.3% of the total number of individuals. Seasonal changes in abundance and body size of each of the above species suggested that the profundal zone of Lake Kasumigaura is inhabited throughout almost the entire life history of some fishes（e.g., S. microdon and H. nipponensis）, being a dispersal area for early life stages from spawning and nursery grounds in littoral and riverine habitats, as well as an overwintering habitat for other species.