Are headwater fish running out of liveable stream habitats?

By Mischa Turschwell

Many freshwater fish populations have declined globally as freshwater habitats have become increasingly fragmented and degraded by climate change and human disturbances.

Image of a stream and forest
One of the study sites

For the successful management and conservation of species living in freshwater habitats, we first need to know what variables affect their distribution. We investigated what environmental variables affect both adults and juveniles of the locally threatened Northern River Blackfish in a headwater system.

We found that the presence of adults and juveniles was negatively affected by extended stream warming events. The impact of warm weather suggests these fish are restricted to their current habitat range by temperature extremes.

We also found that juveniles were much more sensitive to increased temperature compared to adults. This means that juvenile fish could be lost if stream temperatures keep increasing.

graph showing decline in abundance and temperature
Relationships between the abundance of adult and juvenile River Blackfish and the number of days in a row that stream temperature was over 28°C (Event Days), and the total number of days in summer where stream temperature was over 28°C (Frequency Days).

We suggest the rehabilitation of riparian zones to provide shade cover which will buffer stream temperatures against future climate warming.

This work was published in Freshwater Science.

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