The Yurappu River, which flows through Yakumo Town in southern Hokkaido, is a river where salmon run up and spawn and we can see natural spawning. Let's look at the spawning environment. Let's start with "water temperature".
2. Flow velocity measurement - white salmon eggs
This video explains the flow velocity, water depth, and riverbed sediment (medium gravel) in the spawning environment and fertilized eggs that have been dug up by other spawning pairs and have died and turned white. As explained in this video with dead eggs, live eggs become also hard.
3. Biofilm - Aquatic Insects
Biofilms and aquatic insects are described as being involved in the supply of substances from post-spawning carcasses.
4. Electric shocker
Electric shock fishing gear (electric shocker) is used when collecting salmon and other fish in relatively shallow rivers. A special harvest permit from Hokkaido is required for use.
5. Secondary sex characteristics
In the training, the external morphology of males and females of post-spawning carcasses, especially secondary sexual characteristic-related traits is measured. We compare with the numbers of immature salmon caught in the open ocean.
