Lock gates improve passage of small‐bodied fish and crustaceans in a low gradient vertical‐slot fishway

A modified ‘lock’ mode of operation was trialled within a low‐slope (3.1%) vertical‐slot fishway to improve passage of small‐bodied (<60 mm long) native fishes in the Murray River, Australia. Significantly greater numbers of three small‐bodied native fish and two crustacean species ascended the fishway during lock operation than during standard operation. Up to 9700 small‐bodied fish and crustaceans exited during the lock operation in a single 2‐h replicate. A deficiency of the temporary lock conditions was that large‐bodied fish and their young‐of‐the‐year (>50 mm long) did not ascend during the study. Considerable experimental work is required at other sites and at higher fishway slopes before widespread retro‐fitting of lock gates. Nevertheless, these results highlight new options for potentially improving the ecological performance of existing pool‐type fishways and new facilities.