Vertical distribution of cold-water fishes skewed toward anoxic bottom layer

The suitable habitat for cold-water fishes require both a low water temperature and sufficient dissolved oxygen concentration (DO), typically reported below 13 degrees Celsius and above 3 mg/L for salmonids. In temperate lakes, prolonged high-water temperatures limit the vertical distribution of the cold-water fishes at the surface layer, while anoxic conditions limits the vertical distribution at the bottom layer, squeezing suitable habitats for the cold-water fishes. Thus, quantifying cold-water fishes vertical distribution dynamics would be vital to assess climate change impact on their populations in such lakes. Here, we surveyed seasonal dynamics of the vertical distribution of cold-water fish populations in a Japanese lake (Max depth = 13 m, Surface area = 12 km²) using acoustic exploration. We examined the relationship of the vertical fish distribution with water depth, temperature, and quality, finding many individuals at depths below 3 mg/L DO, considered unsuitable. Accordingly, the threshold of DO for the fish distribution identified by a statistical analysis from our data was significantly lower (0.46 mg/L) than reported in the literature. In contrast, the water temperature threshold was consistent with the literature's (13 degrees Celsius). This result suggests cold-water fishes respond differently in the field to the threshold of high-water temperatures and dissolved oxygen. Further examination of the underlying mechanisms generating these differences would provide insights into how cold-water fish select habitats and will be impacted under warming conditions.

Primary Presenter: Ryosuke Katayose, National Institute for Environmental Studies (NIES) (shakeyose.0910@gmail.com)

Authors:

Ryosuke Katayose, National Institute for Environmental Studies (NIES)  (shakeyose.0910@gmail.com)

Taku Kadoya, National Institute for Environmental Studies (NIES)  (kadoya@nies.go.jp)