Shrinking rivers affect fish populations

July 5, 2018, University of Canterbury
Reducing a river's size is likely to reduce its capacity to support predatory fish. Underwater view of the Waimakariri River, Canterbury. Credit: Angus McIntosh/University of Canterbury

New research from the University of Canterbury published today has found that a shrinking river is less able to support larger predatory fish, such as the highly-valued sports fish like brown trout or at-risk native fish like galaxiids and eels.

New research from the University of Canterbury published today has found that a shrinking river is less able to support larger predatory fish, such as the highly-valued sports fish like brown trout or at-risk native fish like galaxiids and eels.

Using data from 29 New Zealand rivers, a new research paper by lead author Freshwater Ecology Professor Angus McIntosh of the School of Biological Sciences, UC Science, and co-authored by UC mathematician Associate Professor Michael Plank ,UC biologist Dr. Helen Warburton, and collaborators from NIWA and overseas, has been published in the online journal Science Advances.

The research findings in the paper – "Capacity to support predators scales with habitat size" – show that reducing the size of a habitat undermines its capacity to support larger predators.

This potentially explains why reductions in habitat size are such a powerful driver of loss worldwide, Professor McIntosh says.

"If you make a habitat smaller, for example by taking water out of a river, you shrink the physical dimensions of the space which can reduce the size of predators, such as fish, that live there. When predators are smaller, they are not as efficient in their energy use so the food, such as stream insects, available in the habitat will support fewer and smaller fish," he says.

Capacity to support predators like this brown trout scales with river size. Credit: Angus McIntosh/University of Canterbury
"We show that smaller rivers support fewer fish per unit of prey resource compared to larger rivers and we derive a theory explaining why this happens. The theory is based on how the dimensions of a habitat constrain the body size of individual predators, the fish in our case, and how that affects the efficiency of prey use."

"One of the neat things about this study is that the mathematical theory actually helped us to understand the underlying causes of population declines. This means we can be better informed when making decisions that affect habitats for key species in New Zealand," Associate Professor Plank says.

How much water is taken out of rivers is a hot topic and the subject of great public debate and lengthy court battles. The researchers expect this work will have an important influence on decisions about resource use, particularly regarding the flow in rivers.

"We make many decisions about how to manage natural resources which affect the size of habitats, for example when we take water from rivers. Our work shows that those changes in size affect how food webs work, and that they could have a detrimental effect on the capacity of those habitats to in rivers. Moreover, these effects haven't generally been considered in how we make decisions about natural resource management," Dr. Warburton says.

Explore further: Male guppies grow larger brains in response to predator exposure—but not females

More information: Angus R. McIntosh et al. Capacity to support predators scales with habitat size, Science Advances (2018). DOI: 10.1126/sciadv.aap7523

Related Stories

Fish step up to lead when predators are near

May 3, 2017

Researchers from the University of Bristol have discovered that some fish within a shoal take on the responsibilities of leader when they are under threat from predators.

Six reasons habitat matters to fish, and people too

May 19, 2016

Our oceans and coasts contain a stunning variety of marine habitats—everything from coral reefs to salt marshes, oyster beds to kelp forests. These habitats are essential for maintaining the robust fish populations that ...

Recommended for you

Coffee-based colloids for direct solar absorption

March 22, 2019

Solar energy is one of the most promising resources to help reduce fossil fuel consumption and mitigate greenhouse gas emissions to power a sustainable future. Devices presently in use to convert solar energy into thermal ...

NASA instruments image fireball over Bering Sea

March 22, 2019

On Dec. 18, 2018, a large "fireball—the term used for exceptionally bright meteors that are visible over a wide area—exploded about 16 miles (26 kilometers) above the Bering Sea. The explosion unleashed an estimated 173 ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Jul 05, 2018
Not only them. Crocodiles and Alligators are doing it. We do not need them at all. Similarly, if more than 10,000 Birds are seen, Govt. should trap/kill 1000 of them and move to stores or factories for making Biofuel.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.