Do fish thrive in harmful waters?

24 September, 2021
Erin McCallum
Erin McCallum conducts research at the Department of Wildlife, Fish and Environmental Studies at the Swedish University of Agricultural Sciences in Umeå. Photo: Erin McCallum

Do fish seek out the polluted water near treatment plants? And if so, how are they affected by it in the long run? Researcher Erin McCallum will try to find out over the next four years.

Erin McCallum is a researcher at SLU, and much of her work is focused on how human behavior affects aquatic environments. Now she will be awarded a scholarship for her research on whether fish seek out water released from treatment plants, and how they may be harmed by it.

“This research project builds on much earlier research on the subject. But the research has mostly been done in the laboratory, and we know next to nothing about how the fish are affected by the polluted water in the wild, in their natural environment,” she says.

Ecological traps

McCallum describes a phenomenon called ecological traps, which are at the heart of this project.

“Ecological traps occur when animals and other organisms are attracted to, and seek out an environment that actually impairs their survival and reproduction in the long run,” she explains.

The treatment plants must of course purify the water, but you do not completely get rid of the pollutants. There could be several reasons why the fishermen would go to areas where the water from the treatment plants is discharged. Nutrients such as phosphorus and nitrogen are released into the water, which can cause fish to directly seek out the outlet. But they can also be attracted to these areas because the organisms they eat go there.

The temperature of the water can also make fish happy to stay close to the treatment plants.

“The water that is released has a stable temperature. It is colder than the water around in summer and warmer in winter. If fish live in that water, they don’t have to adapt to temperature changes, McCallum says.

Four years and several methods

The project will last for four years. McCallum will take samples of the water and compare with tissue samples from the fish. She will also use acoustic telemetry, which means that a chip surgically inserted into the fish communicates with recipients underwater. This is done to map the movement patterns of fish in the different areas.

She hopes that the ambitious project will provide increased knowledge about an area that can be difficult to understand.

“It is complicated to understand waste water, because it looks different at each site. It depends on the population and activities nearby. One treatment plant can be located only at homes, one can be located at an industry and another at a hospital where medicines are leaked, she says.

Compare six treatment plants

Erin does not want to name the treatment plants involved in her research project, as she does not want any individual activity to be demonized. But she will focus on six treatment plants in southern Sweden, all of which discharge the water into freshwater rivers inland. There won’t be a focus on any particular species of fish, but there’s a lot of perch and roach being caught, according to McCallum.

On December 8, she was awarded funding from the King Carl XVI Gustaf Foundation’s 50th anniversary fund for science, technology and the environment at the Royal Palace in Stockholm.

“I’m really happy about it! The money will be used for equipment needed for these telemetry surveys that haven’t been done in these areas before,” McCallum said.

Text: Daniel Hedström
Photo: Kimmo Hagman, Erin McCallum, TT/Trons

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