Murray cod and modern fish screens: influence of water velocity and screen design on the entrainment and impingement of larval and young-of-year fish at water offtakes

Context

Entrainment and removal of fish from aquatic ecosystems can occur at water pump offtakes. Exclusion screens that reduce these impacts are recognised as an important conservation measure.

Aims

Evaluate the effectiveness of the Australian screen design guidelines in protecting larvae and young-of-year age class of a native fish species, Murray cod Maccullochella peelii.

Methods

Entrainment and impingement of postflexion larvae and young-of-year were assessed in a controlled laboratory environment. Tests were conducted under a range of approach velocities (AV) and impingement durations for two screen materials.

Key results

Fish screens reduced larval entrainment by ≤84%. Screens had no significant effect on reducing larval entrainment at AV ≥0.125 m s⁻¹. Impingement of young-of-year was positively associated with AV and mortality increased with impingement duration, irrespective of screen type.

Conclusions

To protect early life-stage Murray cod, it is recommended that water pump offtakes be fitted with 2-mm vertical wedge-wire stainless steel screens and AV be limited to ≤0.1 m s⁻¹.

Implications

This study represents the first assessment of the effectiveness of the Australian screen design guidelines in protecting larvae, providing knowledge to further refine specifications for screen design and support the recovery of native fish populations.