Field-Based Evaluations of Horizontal Flat-Plate Fish Screens

Diversions from streams are often screened to prevent the loss of or injury to fish. Hydraulic criteria meant to protect fish that encounter screens have been developed, but primarily for screens that are vertical to the water flow rather than horizontal. For this reason, we measured selected hydraulic variables and released wild rainbow trout Oncorhynchus mykiss over two types of horizontal flat-plate fish screens in the field. Our goal was to assess the efficacy of these screens under a variety of conditions in the field and provide information that could be used to develop criteria for safe fish passage. We evaluated three different inverted-weir screens over a range of strewn (0.24-1.77 m(3)/s) and diversion flows (0.10-0.31 m(3)/s). Approach velocities (AVs) ranged from 3 to 8 cm/s and sweeping velocities (SVs) from 69 to 143 cm/s. We also evaluated a simple backwatered screen over stream flows of 0.23-0.79 m(3)/s and diversion flows of 0.08-0.32 m(3)/s. The mean SVs for this screen ranged from 15 to 66 cm/s and the mean AVs from 1 to 5 cm/s. The survival rates of fish held for 24 h after passage over these screens exceeded 98%. Overall, the number of fish-screen contacts was low and the injuries related to passage were infrequent and consisted primarily of minor fin injuries. Our results indicate that screens of this type have great potential as safe and effective fish screens for small diversions. Care must be taken, however, to avoid operating conditions that produce shallow or no water over the screen surface, situations of high AVs and low SVs at backwatered screens, and situations producing a localized high AV with spiraling flow.

Within-Season Homing Movements of Displaced Mature Sunapee Trout (Salvelinus Alpinus) in Floods Pond, Maine

Tagging, displacemenat nd recapture, and ultrasonict racking of displaced mature Sunapee trout (Salvelinusa Ipinus) in Floods Pond, Maine, demonstrated that rapid within-season homing occurs in this relict form of Arctic char. Of the trout displaced about 1.8 km from their spawning ground from 1972 to 1975, 9% to 32% were recaptured one to four times within the same spawning season in trap nets set on the spawning ground. Eight of 14 trout tracked ultrasonically in 1975 homed in 2.5 to 10.0 h. Movements of the homing fish were variable; some trout homed paralleling the shoreline, others homed in open water or used a combination of near-shore and open-water movements. Behavior was similar between the sexes and during day and night, although two fish did begin to move just at sundown. Swimming speeds ranged from 15 to 35 cm s- 1 and averaged about 0 .6 body lengths s -1•. Swimming directions were not influenced by wind and wave direction, nor were swimming speeds within individual tracks influenced by cloud cover, wave height, or water depth. Heavy overcast at night m&y have inhibited movement. Sunapee trout are apparently familiar with the entire lake and travel widely within it. Visual features are postulated as orientational cues, though use of such cues is not clearly demonstrated by our experiments.

Use of Electroshock for Euthanizing and Immobilizing Adult Spring Chinook Salmon in a Hatchery

This study evaluated the use of electroshock as in alternative to traditional techniques for immobilizing and euthanizing hatchery fish. We used a commercially available electroanesthesia unit at the U.S. Fish and Wildlife Service's Carson National Fish Hatchery (Carson, Washington) to euthanize adult spring Chinook salmon Oncorhynchus tshawytscha and to son and collect gametes of fish at maturation. During euthanization by electroshock, the response of each fish was observed, Muscular and vertebral hemorrhaging wits quantified, and electrical settings were optimized accordingly. During gamete collection, fish were either electroshocked or exposed to tricaine methanesulfortate (MS-222); hemorrhaging, egg viability. egg size and quantity, and resultant fry quality were examined for each treatment group. Electroshocked fish had a higher likelihood Of injury during gamete collection than did fish exposed to MS-222. On average, each electroshocked fish had less than two hemorrhages oil both fillets examined. The size of each hemorrhage was less than 0.10% of the fillet surface. Fecundity and egg and fry quality were not affected by either immobilization method. Electroshock was a viable and efficient means of euthanizing adult spring Chinook salmon or sorting the fish and collecting their gametes. However, equipment settings must be optimized based on site-specific (e.g., water conductivity) and species-specific (e.g., fish size and seasonal state of maturation) factors.