[A-CG40] Coastal Ecosystems - 1. Water Cycle and Land-Ocean Interactions

[ACG40-P03] Relationship between Fish Behavior and Wave Height around Suttsu Fishing Port, Hokkaido

*Rumiko Kajihara¹, Sawako Shirai¹, Masanori Nunokawa¹, Kenji Mori¹, Masami Ohashi², Kazushi Miyashita³, Shigeru Montani³ (1.Public Works Research Institute, Civil Engineering Research Institute for Cold Region, 2.Tokai University, 3.Hokkaido University)

Keywords:nursery function, shelter function from high waves, black rockfish, interval photography, biotelemetry

The location where fish go to avoid disturbance of their habitat during high waves and floods is of great interest not only to anglers but also to researchers. It has gradually become clear that coastal facilities such as fishing ports, in addition to their primary functions of assuring a safe landing of catches from fishing vessels, also serve secondary functions of protection and nurturing, such as providing marine organisms shelter from high waves. There is a great need to enhance these protective and nurturing functions around Hokkaido, an important area in terms of fishery production, but there has been little research on the mechanism of protective and nurturing functions in cold waters. There is in particular a lack of knowledge on the effects of wave height on fish behavior observed in the coastal waters, and on the function of fishing ports as shelters from high waves based on wave height. In this study, we investigated the relationship between fish behavior and wave height by conducting wave height observations and wave field analysis, as well as interval photography and biotelemetry surveys of fish around the fishing port of Suttsu, Hokkaido, in cold waters, and evaluated the function of sheltering fish in the port from high waves.
Interval photographs taken at the port mouth over a period of about one year showed that the number and percentage of individual fish appearing there decreased with increasing significant wave height, and no fish were observed when the wave height was above a certain value. Therefore, the wave height threshold at this time was used to evaluate the shelter function of the fishing port from high waves, and it was considered that the shelter function was high at the most inner part of the port where the wave height was below this threshold, even in the presence of the maximum significant wave height during the observation period. This wave height threshold was considered appropriate taking the current velocity converted from the threshold, fish length, and the local environment into account. In addition, individuals of the dominant species of black rockfish (Sebastes schlegelii) were caught in the port and equipped with an ultrasonic transmitter, and signals from these transmitters were confirmed to be received by ultrasonic receivers in- and outside the port for about five months, indicating that the fish remained in and around the port, moving around in the vicinity of the port. Individuals with a higher percentage of receptions outside of fishing ports had a higher percentage of receptions from deeper water. The wave height increased, the percentage of receptions from deeper water increases even more, and receptions from shallower water disappeared. While the waves were high, the percentage of transmissions inside the port increased. Therefore, it was considered that black rockfish moved to deeper water depths or into fishing port while the waves were high.
These results indicate that fish behavior is affected by wave height in the vicinity of fishing ports in cold waters. While the waves are high, black rockfish moves into fishing ports, suggesting that the calm port function as shelters from high waves.