Improving our ability to collect eggs of the threatened Australian grayling, Prototroctes maraena

Successful monitoring of fish eggs or larvae facilitates the assessment of management actions (e.g. environmental flow releases) on spawning success. Paired sets of drift nets (one at the surface and one on the bottom) were used at six sites in the Thomson River to determine whether we can improve our ability to monitor the spawning success of Australian grayling, Prototroctes maraena. Over 900 P. maraena eggs were captured, with 90% being captured in drift nets set on the bottom. All but one of the eggs were captured at two sites, which had faster flow rates and a substrate of small gravel rather than fine sediment. These results indicate that using surface drift net sets for sampling eggs in rivers with low turbulence may be ineffective and that spawning may be more likely in faster-flowing areas with gravel substrates.