Habitat use and movements of Australian grayling (Prototroctes maraena) in a Victorian coastal stream

Riverine fishes are among the most imperilled fauna in the world; however, for many species, there is little or no understanding of their ecological requirements. The Australian grayling (Prototroctes maraena) is a small diadromous fish endemic to rivers in south-eastern Australia that has declined considerably in range and abundance and is listed as threatened nationally. To improve understanding of the species’ movement ecology and to inform the development of conservation management actions, we examined the day-to-day movements and habitat use of Australian grayling (n=7) over 8 weeks by using radio-telemetry. Tagged individuals of Australian grayling typically occupied restricted (i.e. tens to hundreds of metres) reaches of stream, and were mostly located in moderate- to fast-flowing habitats (i.e. glide or run), although, at night, use of slower-flowing habitats (i.e. pools) increased. They also undertook longer-distance downstream movements during a period of increased streamflow. Incorporation of such information into management strategies has the potential to improve our capacity to maintain or re-instate the conditions required to conserve and restore Australian grayling populations.

Provision of environmental flows promotes spawning of a nationally threatened diadromous fish

Detailed understanding of flow-ecology requirements for aquatic biota underpins the use of environmental flows as an effective restoration tool in regulated rivers. However, flow recommendations are often overly simplistic and insufficient to provide the necessary environmental requirements for these biota. This is often due to failure to gain and integrate information on individual species ecology and, by using coarse generalisations, about flow-ecology responses. To inform more effective delivery of environmental flows, we investigated spawning responses of the threatened Australian grayling (Prototroctes maraena) to environmental flows over 2 years in three coastal rivers. Spawning activity was highest during within-channel flow pulses, especially during periods of environmental flow delivery. Peak spawning occurred in late autumn and was positively related to flow duration. This result has important implications for environmental flows management in regions where water is scarce and there is potential conflict among multiple users because, for Australian grayling, it is not necessarily the volume of water released that is important, but how the flow is delivered. Our study demonstrated the importance of quantifying flow-ecology relationships via targeted monitoring and research so as to develop appropriate flow regimes, and should encourage managers to examine more critically the logic behind generalised environmental flow objectives.

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.

Downstream spawning migration by the amphidromous Australian grayling (Prototroctes maraena) in a coastal river in south-eastern Australia

Understanding the reasons and cues for migration is crucial for developing effective conservation and management strategies of diadromous fishes. Spawning and movement patterns of the threatened diadromous Australian grayling (Prototroctes maraena) were investigated in the Bunyip River, Victoria, using drift sampling (2008–2011) and acoustic telemetry (2009–2010) during the autumn–winter spawning period of each year. Fifty-five adult fish (2009: n = 21; 2010: n = 34) were tagged and released in February ~15–30 km upstream of the Bunyip River estuary. Thirteen fish (2009: n = 7; 2010: n = 6) undertook rapid downstream migrations from March to April to reaches immediately upstream of the estuary. Drifting eggs were detected at multiple sites between April and July; however, the majority (78.8%) were collected in the lower reaches within ~0.5 km of the estuary in early–mid-May. Tagged adult fish arrived in this area 1–4 weeks before eggs were detected and usually moved back upstream within 2 weeks following the peak egg abundance. Downstream migration and peak egg abundance were associated with increased river flows. Although the proportion of fish that undertook migrations was low, low rates of tag retention in this species likely account for the failure to detect migration by many of the tagged individuals.