Marine and Freshwater Research
Volume 73
Number 2 2022
Special Issue
Fish Kills in Freshwaters
This special issue of Marine and Freshwater Research, 'Fish Kills in Freshwaters', presents 11 articles that advance our understanding of how to manage mass fish kill events such as the sudden death in 2018–19 of many millions of native fish in the Darling–Baaka River in Australia. Papers in this issue deal with: ecological impacts and recovery; technologies and approaches for prediction, preparedness and response; and the role of the public in preparing and responding to these catastrophic events.
Guest editors: Craig A. Boys, Simon M. Mitrovic, Katherine E. Doyle and Lee. J. Baumgartner
Mass fish kills capture the world’s attention and their frequency is increasing worldwide. The sudden death of many millions of native fish in the Darling–Baaka River in Australia in 2018–19 was a catalyst for the 11 articles in this special issue. Collectively, they advance our understanding of how to manage these events, dealing with: ecological impacts and recovery; technologies and approaches for prediction, preparedness and response; and the role of the public in preparing and responding to these catastrophic events.
In late 2018 to early 2019 three significant fish death events occurred in the Lower Darling River, Australia, with mortality estimates of over one million fish. We examined the causes of these events and determined that the conditions existing at the time, as well as antecedent conditions, particularly during 2010–17, were significant contributing factors in the fish deaths. Our observations have implications for future river management with the aim of minimising fish death risks into the future.
Millions of native fish died in mass fish kill events from 2018 to 2020 in the Darling–Baaka River, Australia. This study examined the impacts of these fish kills and short-term changes in the fish community after the initial fish deaths. Differences in species abundance, diversity and size composition illustrate the dramatic extent of the effect of the fish kills on the fish community.
Decaying fish are important nutrients in rivers and lakes, but can create water quality issues. The release of cyprinid herpesvirus-3 in Australia will cause carp mortality and may have serious effects on water quality. To evaluate this, dead carp were placed into mesocosms to monitor water quality changes. Our experiment suggests that high carp biomass mortality will affect water quality.
Following three large fish kills near the Menindee lakes in New South Wales, Australia, in the summer of 2018–19, we have created an online tool to predict when stretches of river may be under stress, leading to fish deaths. By combining routinely collected weather and water data, we have been able to develop the Fish Health Risk Indicator tool, which we hope will limit and potentially prevent large-scale fish deaths from happening again.
Fish deaths due to low dissolved oxygen can result when thermally stratified river systems turn over or mix. Different options for mixing and aerating refuge pools were reviewed from the literature. Recommendations are made regarding which chemical and mechanical options may be suitable for reducing the risk of future events or sustaining fish once dissolved oxygen crashes.
This paper examines the efficacy of aerators deployed in the Murray–Darling Basin in response to a series of fish deaths in the Darling River. Aerators deployed in 2019 most likely prevented several fish deaths. However, aerators are, for the most part, expensive to operate and only affect a very small part of a river. Although aerators play a role in emergency responses, other longer-term solutions need to be assessed.
To inform rehabilitation following catastrophic fish kills in the Darling River, otoliths (fish ear stones) were used to understand pre-fish kill population structure, provenance and movement of golden perch. Throughout the Darling River, golden perch recruitment was associated with periods of elevated flow, but there were regional differences in age structure and variation in recruitment source and movement. Mitigating barriers to movement and restoring river flows associated with spawning, recruitment and dispersal are key considerations for population rehabilitation.
Otoliths were used to retrospectively determine lifetime movements of golden perch, Murray cod and silver perch that died in fish kills in the lower Darling River in 2018–19. Movement between the Murray and Darling rivers appears important for population function of golden perch and silver perch, but not Murray cod, emphasising the need for complementary local and regional-scale recovery efforts.
The Darling–Baaka River is a large semi-arid desert river of eastern Australia. In 2015–16 there was a continuous period of zero flows for 524 consecutive days with the first ever environmental flow implemented in late 2016. Based on an ecohydraulic conceptual model, the flow regime matched key Murray cod life history requirements and helped rebuild the fish population. In future, we advocate for a permanent protected lotic flow regime.
During 2018 and 2019, major fish kill events occurred throughout the drought-stricken Murray–Darling Basin in Australia. However, although large fish kills often receive substantial media attention, the significant negative effects that the fish kills have on local communities, particularly Indigenous groups, are rarely documented. We explore the social and cultural aspects of a series of major fish kills on the lower Darling Baaka River in Australia.
Fish kills are increasing and need greater attention. This paper provides 15 recommendations to improve their assessment, evaluation, reporting and future management.
