Movement and Injury Rates for Three Life Stages of Spring Chinook Salmon Oncorhynchus Tshawytscha : A Comparison of Submerged Orifices and an Overflow Weir for Fish Bypass in a Modular Rotary Drum Fish Screen : Annual Report 1995.

Abstract

The Pacific Northwest National Laboratory (PNNL) evaluated the effectiveness of 6-in. and 2-in. submerged orifices, and an overflow weir for fish bypass at a rotary drum fish screening facility. A modular drum screen built by the Washington Department of Fish and Wildlife (WDFW) was installed at PNNL`s Aquatic Ecology research laboratory in Richland, Washington. Fry, subyearlings, and smolts of spring chinook salmon (Oncorhynchus tshawyacha) were introduced into the test system, and their movement and injury rates were monitored. A total of 33 tests (100 fish per test) that lasted from 24 to 48 hr were completed from 1994 through 1995. Passage rate depended on both fish size and bypass configuration. For fry/fingerling spring chinook salmon, there was no difference in passage rate through the three bypass configurations (2-in. orifice, 6-in. orifice, or overflow weir). Subyearlings moved sooner when the 6-in. orifice was used, with more than 50% exiting through the fish bypass in the first 8 hr. Smolts exited quickly and preferred the 6-in. orifice, with over 90% of the smolts exiting through the bypass in less than 2 hr. Passage was slightly slower when a weir was used, with 90% of the smolts exiting in about 4 hr. When the 2-in. orifice was used in the bypass, 90% of the smolts did not exit until after 8 hr. In addition, about 7% of the smolts failed to migrate from the forebay within 24 hr, indicating that smolts were significantly delayed when the 2-in. orifice was used. Few significant injuries were detected for any of the life stages. However, light descaling occurred on about 15% of chinook salmon smolts passing through the 2-in. orifice. Although a single passage through the orifice did not appear to cause significant scale loss or other damage, passing through several screening facilities with 2-in. orifices could cause cumulative injuries.