Background/Aims
Recent advances in high-power electrofishing units have enabled boat electrofishing to be increasingly considered for monitoring fish communities in highly conductive estuarine waters. However, the biological effects of these emerging systems remain poorly understood. Most electrofishing-injury research has focused on freshwater species, particularly salmonids, and may not apply to Australian estuarine fishes. This study assesses the incidence and severity of external and internal injuries following boat electrofishing and investigates variation among species and size classes.
Methods
Fish were collected during boat-electrofishing surveys in Queensland estuaries. External assessments recorded abrasions, scale loss, lesions, burns and other visible abnormalities. Retained individuals were necropsied to identify internal haemorrhaging, tissue damage and vertebral injuries. To date, approximately 1,480 fish representing 30 species have been externally assessed. The current detailed dataset comprises 86 retained fish, including yellowfin bream, mullet, dusky flathead, whiting, mangrove jack and spotted javelin. Radiography will supplement necropsy assessments for detecting concealed vertebral damage.
Results
Most fish showed no detected injury. Of the 86 retained individuals, 18 (20.9%) were recorded with an external injury and four (4.7%) with an internal injury. External observations were generally minor and included abrasions, scale loss, mouth injuries, superficial lesions and localised reddening. Several were considered pre-existing or potentially associated with capture and handling rather than electrical exposure. Internal observations included localised intramuscular or vertebra-associated haemorrhaging. One internal injury was attributed to a propeller injury, while another occurred following direct anode contact. No obvious vertebral fractures or extensive haemorrhaging were detected during necropsy.
Conclusion
Preliminary findings indicate a low incidence of serious internal injury under the electrofishing conditions examined. External abnormalities were more frequently recorded but were predominantly minor and could not always be attributed to electrofishing. Continued sampling and radiography will clarify species- and size-specific risks and inform safer estuarine electrofishing protocols.