A Novel Wetland Carp Harvesting System to Target and Harvest Migrating Carp

Common carp (Cyprinus carpio L.) cause detrimental changes to aquatic ecosystems outside of their natural range and are a declared pest in several countries. In Australia’s Murray-Darling Basin, carp occupy shallow off-channel habitats from spring through autumn and deep water habitats during winter. Migrations between these habitats occur annually, but pathways can be blocked by barriers, including weirs, culverts and carp exclusion screens. When confronted by barriers, large aggregations often form and carp exhibit an innate desire to jump over or push through the barrier. This study evaluated the use of a novel Wetland Carp Harvesting System (WCHS) which was trialled during an environmental water allocation that commenced in austral winter (June 2010) and continued throughout the known carp spawning period (austral spring). The WCHS was designed to target and harvest migrating carp and aimed to eliminate manual handling requirements and Occupational Health, Safety and Welfare (OHS&W) concerns identified during previous work with an earlier prototype. The WCHS incorporated: 1) novel jumping and pushing trap elements to separate carp ≥ 250 mm TL from native fish, 2) cage cladding designed to permit the unimpeded passage of small and medium sized native fish, while impeding the passage of carp ≥ 250 mm TL, 3) infrastructure to mechanically lift and automatically funnel captured fish into trailer‑mounted fish bins, 4) novel multi-function carp pivot and deflector screens, and 5) compliance with Australian design and OHS&W legislation. A total of 529 carp (mean total length = 607.6 mm ± 8.1 S.E.; mean weight = 4400 g ± 155 S.E) were captured over 13 harvesting events from the 28^th September to 25^th October 2010, equating to approximately 2.3 tonnes. Given the operational success of the WCHS, this approach has the potential to reduce the biomass of adult carp migrating into off-channel habitats in physically constrained river systems.