Entrainment of Fish Eggs and Juveniles
Planktonic eggs and juveniles of fishes are entrained into the cooling system of power plant and released to sea together with warmed effluent water. They are subject to heat and other stresses during their passage through the cooling system.
By field surveys at actual power plants, we have found that most of the entrained eggs and juveniles are those produced in the vicinity of the power plant intake, and that their number varies by season and the time of day.
Based on the quantity of entrained eggs and juveniles, we have estimated that in Ishikawa's icefish (Salangichthys ishikawae) and chum salmon, the entrainment has only slight effects on their stocks.
We are studying the entrainment effects on fisheries resources for other fishes in waters of different regional characteristics.

Collecting fish eggs and larvae
at the intake of a power plant

Fish Behaviors towards Warmed Effluent
Are fish expelled by warmed effluent? This is a question people have been asking for a long time.
By tracking the movement of chum salmon tagged with echo transmitters we have confirmed the fact that they return to the mother river, swimming beneath the warmed effluent plume of a power plant in the northern part of Japan.

Tracking the movement of chum salmon
tagged with echo transmitter

We also have observed fish behaviors in front of the discharge outfall of a power plant with scientific fish finders and underwater video cameras. Some fish swarm near the outfall throughout the year, while others aggregate there only in winter months. Some fish are not attracted to warmed effluent although they are present in nearby waters.

Fish (Bigeye trevally) swarming
at the warmed effluent of a power plant

Warmed Effluent and Seaweed Growth
We have been studying effects of temperature and current changes due to warmed discharge upon growth and distribution of seaweeds.
In the vicinity of outfall of a power plant, where warmed effluent continuously predominates and water temperature is 4 to 5°C higher than the ambient, the number of growing algal species has been observed to decrease while some species of green algae, Cladophora and Jania, flourish in summer months. Warmed effluent may have brought about changes in dominant species in the affected area.
Distribution of large brown algae including Sargasso has been surveyed periodically in the outfall area before and after a power plant operation. In a zone below 2 to 3 meter depth that is a main habitat of these algae, no changes in their growth have been observed.

Underwater observation of seaweed