Comparison of predation risks for small fishes in salt marsh microhabitats in Lake Hinuma, eastern Japan, using tethering experiments

Abstract

To clarify the role of salt marsh creeks as fish refuges, predation risks for two small species (the nektonic Oryzias latipes and benthic Acanthogobius lactipes) were compared among three microhabitats (upper and lower areas of a creek, and marsh edge separate from the creek) in a salt marsh in Lake Hinuma, eastern Japan, in July 2016, using daytime tethering experiments. The survival rate of O. latipes was highest in the upper creek (96%) and lowest at the marsh edge (62%), whereas no significant differences were found among the microhabitats for A. lactipes, with high survival rates (> 90%) in all microhabitats. Individual numbers of larger piscivorous fishes, determined by fyke net sampling, were greatest at the marsh edge, whereas no individuals were recorded in the upper creek, which was characterized by shallower depths and lower dissolved oxygen levels. The results suggested that the upper creek provides potential refugia for O. latipes, which occupied the upper and middle layers of the water column and exhibited hypoxia tolerance. The higher survival rate of benthic A. lactipes at the marsh edge may be due to their cryptic coloration in relation to bottom sediments, which helps them to avoid predation.