David Morgan

Goldfish (and Koi) are known to exacerbate algal blooms which can lead to increased turbidity and thus ecosystem alteration and function. They achieve this unwanted outcome by resuspending nutrients because of their vigorous bottom feeding, making nutrients available to algae. One study demonstrated that significant growth of blue‐green algae can be stimulated by the passage through Goldfish intestines, where it is thought that this process gives nutrient enrichment to the algae (Kolmakov and Gladyshev 2003). It is likely that Koi infestations cause similar unwanted environmental outcomes…

Three river restoration demonstration sites were created upstream of Bristol Rd in the Harvey River in autumn 2021. The project is a partnership between Harvey River Restoration Taskforce (HRRT), Greening Australia and the Water Corporation. Pre and post restoration ecological assessments were conducted in autumn and spring 2021, respectively. The surveys used the revised version of the DWER South West Index of River Condition (SWIRC) protocols, that specifically focussed on aquatic biota, and in addition depth profiling also occurred. The autumn 2021 surveys demonstrated there was no significant differences in the habitat, depths, fish/crayfish populations or macroinvertebrate communities between the control and restoration sites. The spring 2021 survey found an increase in abundances of several native fishes in both the control and restoration sites compared with the autumn 2021 surveys. It also recorded significantly larger Nightfish at the restoration site compared with the control sites and also Smooth Marron was recorded in the restoration sites, that had not been recorded in this reach during historical monitoring. The current progress report summarises the results of the autumn 2022 ecological survey of the three restoration and three control sites. The methods used replicated those employed in the previous surveys…

This study determined how Black Bream used the fish gate on the Vasse Surge Barrier by tagging them state of the art internal electronic tags. The tags, known as PIT tags, detected fish that passaged upstream and downstream through the fish gate over an 18 month period in 2017 and 2018. The local community helped us tag and release 322 Black Bream. The study revealed that movements through the fish gate were unrelated to spawning activity of this species and supported early work that the Vasse Estuary is not a key breeding site; instead they use the Deadwater to reproduce. Up until May 2018, Bream passaged through the fish gate 440 times (265 downstream and 175 upstream). Black Bream preferred to passage when the water velocity in the fish gate chute were lowest, which occurred when the water levels upstream and downstream of the surge barrier were relatively similar. When the dissolved oxygen upstream of the surge barrier was good, fewer fish passaged downstream to the Wonnerup Inlet although this was a relatively weak effect. However, the dissolved oxygen around the Vasse Suge Barrier during the current analysis period was relatively high compared to other years and therefore we anticipate that the effect of low dissolved oxygen on fish passage would be even stronger in those years. They also preferred to pass downstream through the fish gate during the evening, whereas upstream passages mostly occurred during the dawn and dusk periods. The findings greatly increase our understanding of the conditions that Black Bream require or prefer to use the fish gate on the Vasse Surge Barrier. However, as the PIT tags last for 20 years, additional data analysis is recommended to compare the factors influencing the passage of the species over multiple years of fish gate operation; including those years that experience poor oxygen levels. It is also recommended that additional fish PIT tagging occur, including other species, so that long-term fish passage through the structure may be further quantified.