ill., map; Thesis (M.M.A.)--University of Washington, 1997; Vita; Includes bibliographical references (leaves [35]-38)
University of Washington Abstract MANAGING BULL TROUT: THE ROLE OF ELECTROFISHING INJURY IN STREAMS OF CRATER LAKE NATIONAL PARK by Brian D. Mahoney Chairperson of the Supervisory Committee: Professor Marc L. Miller Department of School of Marine Affairs This thesis couples empirical problem research to resolution of a specific policy issue, i.e. how to collect bull trout in management programs with least harm. The objective of this study is to investigate the incidence and severity of injury to wild trout collected with pulsed direct current (PDC) electrofishing in low conductivity streams and to contribute to the knowledge base required for developing policies and implementing protocols for restoring native fish to Crater Lake National Park (CLNP), Oregon. X-rays and necropsy were used to assess the injury rate of 512 fish. Four hundred fifty two brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta) were collected by electrofishing. Sixty brook trout were collected with a piscicide, antimycin as reference for background injury. Injuries consisted of either internal hemorrhages, spinal misalignment, or both. A total 113 hemorrhages and 86 spinal injuries were identified. Most spinal injuries were located in the area between the dorsal and anal fins. The overall injury rate was significantly different (x2, P < 0.05), between electrofishing methods: 25% for single-pass electrofishing and 63% for multiple-pass electrofishing. For fish collected by single-pass electroshocking, a greater number had hemorrhages than spinal injuries. For fish collected by either multiple-pass electrofishing or antimycin treatment a greater number had spinal injuries than hemorrhages. This high rate in control fish may reflect historic injuries (in the antimycin treated fish) from multiple-pass electroshocking in previous years. Thirty nine percent the fish taken by multiple-pass electroshocking and antimycin had pre-existing spinal injury. The rate of new electrofishing injury was not significantly different (x2, P > 0.05) between electrofishing methods: 23% for single pass electrofishing, 22% for multiple-pass electrofishing. This may reflect the fact that the majority of fish taken by multiple-pass electrofishing were taken within the first two electrofishing passes. Injury rate increased with fish length ranging from 13% for fish < 125 mm fork length (FL) to 64% in fish > 175 mm FL. The overall short-term mortality (72 hours) by single-pass electrofishing was 10% (N = 148). Six of the 8 fish that died showed no signs of injury. Thirty seven (25%) of the fish that survived over 72 hours had internal injuries. The effects of stress and physical injury on long-term survival is unknown. In comparison to continued decline and probable extinction, the rate of electroshock induced-injury projected here, represents an acceptable level of risk to Sun Creek bull trout. Recomendations include methods for further improving electroshock efficiency and reducing injury to bull trout in Sun Creek CLNP, Oregon.
University of Washington Abstract MANAGING BULL TROUT: THE ROLE OF ELECTROFISHING INJURY IN STREAMS OF CRATER LAKE NATIONAL PARK by Brian D. Mahoney Chairperson of the Supervisory Committee: Professor Marc L. Miller Department of School of Marine Affairs This thesis couples empirical problem research to resolution of a specific policy issue, i.e. how to collect bull trout in management programs with least harm. The objective of this study is to investigate the incidence and severity of injury to wild trout collected with pulsed direct current (PDC) electrofishing in low conductivity streams and to contribute to the knowledge base required for developing policies and implementing protocols for restoring native fish to Crater Lake National Park (CLNP), Oregon. X-rays and necropsy were used to assess the injury rate of 512 fish. Four hundred fifty two brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta) were collected by electrofishing. Sixty brook trout were collected with a piscicide, antimycin as reference for background injury. Injuries consisted of either internal hemorrhages, spinal misalignment, or both. A total 113 hemorrhages and 86 spinal injuries were identified. Most spinal injuries were located in the area between the dorsal and anal fins. The overall injury rate was significantly different (x2, P < 0.05), between electrofishing methods: 25% for single-pass electrofishing and 63% for multiple-pass electrofishing. For fish collected by single-pass electroshocking, a greater number had hemorrhages than spinal injuries. For fish collected by either multiple-pass electrofishing or antimycin treatment a greater number had spinal injuries than hemorrhages. This high rate in control fish may reflect historic injuries (in the antimycin treated fish) from multiple-pass electroshocking in previous years. Thirty nine percent the fish taken by multiple-pass electroshocking and antimycin had pre-existing spinal injury. The rate of new electrofishing injury was not significantly different (x2, P > 0.05) between electrofishing methods: 23% for single pass electrofishing, 22% for multiple-pass electrofishing. This may reflect the fact that the majority of fish taken by multiple-pass electrofishing were taken within the first two electrofishing passes. Injury rate increased with fish length ranging from 13% for fish < 125 mm fork length (FL) to 64% in fish > 175 mm FL. The overall short-term mortality (72 hours) by single-pass electrofishing was 10% (N = 148). Six of the 8 fish that died showed no signs of injury. Thirty seven (25%) of the fish that survived over 72 hours had internal injuries. The effects of stress and physical injury on long-term survival is unknown. In comparison to continued decline and probable extinction, the rate of electroshock induced-injury projected here, represents an acceptable level of risk to Sun Creek bull trout. Recomendations include methods for further improving electroshock efficiency and reducing injury to bull trout in Sun Creek CLNP, Oregon.