Differences in fish assemblage structures between tidal marsh and bare sandy littoral habitats in a brackish water lake, eastern Japan

Fish assemblage structures and environmental properties (e.g., water quality, sediment condition and prey abundance) were compared between tidal marshes, dominated by the common reed Phragmites australis, and bare sandy areas in the brackish-water Lake Hinuma, eastern Japan, by daytime seine net sampling in October 2014, and January, April and July 2015. A total of 4,076 fish individuals from 30 species and 5,431 individuals from 23 species were collected in the tidal marshes and sandy areas, respectively. Higher species richness in the former habitat was due to the restricted occurrence of ten species, including threatened or near threatened, only to that habitat. Species composition and the abundances of several dominant species, such as the commercially important icefish Salangichthys microdon and the goby Acanthogobius lactipes, also differed between the two habitats, although no interhabitat differences in the mean species and individual numbers per haul were found. Moreover, the individual number of small benthic and epiphytic crustacean feeders, including A. lactipes, was greater in the tidal marshes than in the sandy areas, whereas zooplankton feeders, including S. microdon, showed the opposite pattern. Such interhabitat differences in fish assemblage structures may be partly related to food availability, sediment condition and/or the presence or absence of vegetative structures. Because each of the two habitats harbored a unique fish assemblage, conservation efforts for both habitats are important for enhancing overall fish species diversity and sustaining fishery resources in Lake Hinuma.