Injury and short term mortality of benthic stream fishes - a comparison ofcollection techniques

Small benthic fish such as darters are frequently collected for stream inve ntory purposes or to document habitat use, with the intent of releasing the fish unharmed following enumeration. The purpose of this study was to exam ine the injury and short term mortality (8 d) of greenside darters captured by live wire pot trapping and electrofishing, using two different settings (80Hz, 6ms and 60Hz, 6ms). Two different electrofishing techniques were us ed, spot electrofishing and sweep electrofishing. Short term mortality was highest for fish collected in live pot traps. Abrasion from the wi:re traps appeared to remove scales and irritate the skin. By the conclusion of the study, 74% of the fish caught in live pot traps were dead from fungal lesio ns. Greenside darters captured by all electrofishing methods exhibited low short term mortality (<10%). The only initial mortality, hemorrhaging and s pinal damage, occurred for fish collected using 80Hz, 6ms sweep technique, although the short term mortality was still far less than that observed amo ng trapped fish. The spot electrofishing technique resulted in no injury, w ith either of the settings. Live trapping produces little initial mortality , and thus may be wrongly viewed as a safe alternative for the collection o f threatened benthic stream fishes, compared to electrofishing. We suggest that researchers studying small fish in warmwater systems use caution when collecting and handling fish for subsequent release.