Physical Injuries in Juvenile Atlantic Salmon, Slimy Sculpin, and Blacknose Dace Attributable to Electrofishing

Abstract

Juvenile Atlantic salmon Salmo salar captured by electrofishing were X-rayed and dissected to determine rates of electrofishing-induced spinal injuries and hemorrhages. This study showed a low incidence of spinal injuries (11%) in electrofished wild parr captured alive and thereafter sacrificed. A negligible hemorrhage rate (2%) was observed. All of the spinal injuries observed were rated class 1 (minor injury), except for a class 2 injury in one parr. Larger, older wild parr (≥age 2) showed a higher incidence of spinal injuries (17%) than age-1 parr (4%). Parr captured with two or more electrofishing sweeps had a spinal injury rate of 20%, compared with 6% when captured with a single electrofishing sweep. Among the mortalities, 8% of the parr had spinal injuries (class 1 except for one class 3) and 5% had hemorrhages. Spinal injury was observed in 6% of the mortalities of slimy sculpin Cottus cognatus and blacknose dace Rhinichthys atratulus; no hemorrhages were observed in these fish. This study showed that electrofishing produced a low incidence of injuries in juvenile Atlantic salmon, slimy sculpin, and blacknose dace. Nonetheless, caution is advised when conducting electrofishing surveys because sublethal effects other than physical injuries remain largely unknown.