Early stages of fish life, such as eggs and larvae, are most likely to suffer lethal impacts from dredging-related stress, while adult fish that migrate from fresh water to the sea to spawn (catadromous fishes) are more likely to change behaviour, according to new research.
A team led by University of Queensland postdoctoral researcher Amelia Wenger examined hundreds of studies to determine how dredging related stressors, including suspended sediment, contaminated sediment, hydraulic entrainment (organisms that get sucked up with the sediment) and underwater noise, directly influence the size of the effect and response in fish across all aquatic ecosystems and all life history stages.
The Western Australian Marine Science Institution Dredging Science Node project, found that across all dredging-related stressors, studies that reported fish mortality had significantly higher effect sizes than those that describe physiological responses, though indicators of dredge impacts should aim to detect effects before excessive mortality occurs.
“Both suspended sediment concentration and duration of exposure greatly influenced the type of fish response we observed, with both higher concentrations and longer exposure associated with fish mortality,” Dr Wenger said.
(Figure 1. A schematic diagram of categories of potential effects of dredging on fish. – Wenger AS, Harvey E, Wilson S, et al. A critical analysis of the direct effects of dredging on fish. Fish Fish. 2017;00:1–19. https://doi.org/10.1111/faf.12218)
“It’s well known that some fish avoid turbid waters but moving to a less ideal environment can affect their chances of survival. Increasing exposure to suspended sediment makes it harder for fish to find their food, elevates their stress levels, and causes damage to fish gills affecting growth, development and swimming ability.
“By analysing several studies, we were able to see clear evidence that fish from all aquatic ecosystems were sensitive to turbidity,” Dr Wenger said.
Studies examining the effects of contaminated sediment also had significantly higher effect sizes than studies on clean sediment alone or noise, suggesting combined dredging stressors produce an effect greater than the sum of their individual effects.
“The review highlights the need for in-situ studies on the effects of dredging on fish which consider the interactive effects of multiple dredge stressors and their impact on sensitive species of ecological and fisheries value,” Dr Wenger said.
The findings are expected to improve the management of dredging projects to ultimately minimise their impacts on fish.
Wenger AS, Harvey E, Wilson S, et al. A critical analysis of the direct effects of dredging on fish. Fish Fish. 2017;00:1–19. https://doi.org/10.1111/faf.12218
The WAMSI Dredging Science Node is made possible through $9.5 million invested by Woodside, Chevron and BHP as environmental offsets. A further $9.5 million has been co-invested by the WAMSI Joint Venture partners, adding significantly more value to this initial industry investment. The node is also supported through critical data provided by Chevron, Woodside and Rio Tinto Iron Ore.