Fish Return Design Support – Tagging Study

Clean Water Act 316(b) requires the design and operation of cooling water intake structures to minimize adverse impacts; this entails reducing impingement mortality and entrainment. Installing and operating fish-friendly traveling screens and a fish return system can reduce impingement mortality of non-fragile species. The proper design of the fish return is as important as the selection of screens. The location of the fish return terminus determines the extent of re-impingement and the potential for thermal or other impacts.

ASA has performed several tagging studies to assess suitability of fish return termini. The design engineer first identifies two or three potential fish return termini, then biologists release a known number of tagged fish from those locations. Tagged fish that return to the intake indicate that their release location may be unsuitable for a fish return terminus. The study needs to be conducted under representative receiving/source waterbody conditions.

When implementing these studies, ASA surgically implants Passive Integrated Transponder (PIT) tags in an appropriate number (approximately 500 per location) representative species of impingement at the facility and releases them at predetermined locations at different times of the day. PIT tags allow for continuous monitoring and identification of individual fish to a particular release location, time and total length. PIT tag active readers are placed within the intake structure to detect impinged tagged fish. Prior to release, fish surgically implanted with
PIT tags are held for a minimum of 12 hours to recover. Tagged fish are then assessed for health and tag retention. Dead fish and fish with rejected tags were removed and the total number of fish released recorded for each location. Re-impingement is monitored for approximately three weeks.

When implementing these studies, ASA surgically implants Passive Integrated Transponder (PIT) tags in an appropriate number (approximately 500 per location) representative species of impingement at the facility and releases them at predetermined locations at different times of the day. PIT tags allow for continuous monitoring and identification of individual fish to a particular release location, time and total length. PIT tag active readers are placed within the intake structure to detect impinged tagged fish. Prior to release, fish surgically implanted with
PIT tags are held for a minimum of 12 hours to recover. Tagged fish are then assessed for health and tag retention. Dead fish and fish with rejected tags were removed and the total number of fish released recorded for each location. Re-impingement is monitored for approximately three weeks.

This work supports CWA 316(b) compliance efforts.