Restoring woody habitat in a degraded section of Australia's Murray River has led to a major increase in the populations of two native fish species.
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Restoring → restore → species
In the research carried out over seven years, the number of Murray cod in the restored reach increased threefold, while the population of golden perch increased twofold.
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population → carry → perch
The aim of the study was to examine whether adding large pieces of coarse woody habitat could increase fish populations.
uncertain
adding → examine → populations
The
study was published in Ecological Applications in 2019.
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study → publish → 2019
During the study, researchers put 4,450 pieces of coarse woody habitat back into about 110 km of the Murray River in south-eastern Australia.
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researchers → put → Australia
The timber was placed between 2007 and 2010 in four priority zones.
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timber → place → zones
Most of the pieces weighed more than one tonne and came from natural trees recovered from a large road project.
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Most → weigh → project
Researchers then monitored fish populations over seven years, from 2007 to 2013.
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Researchers → monitor → 2013
The work focused on Murray cod (Maccullochella peelii) and golden perch (Macquaria ambigua), two native freshwater fish that use woody structures for refuge, cover while hunting and spawning sites.
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that → focus → refuge
Both species had declined in abundance and range since European settlement.
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species → decline → settlement
To assess the changes, researchers compared the restored section, called the intervention reach, with three nearby control reaches where the structural restoration was not carried out.
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restoration → assess → reaches
The study was designed to account for the fact that fish do not remain in one section of a river.
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fish → design → river
Researchers used electrofishing, tagging, angler reports and radio telemetry to track fish, their movement and mortality.
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Researchers → use → fish
They also used a Bayesian state-space model to estimate population sizes while accounting for differences in capture rates and movement between the river reaches.
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They → use → reaches
More habitat added
The intervention reach had previously lost much of its woody habitat.
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reach → add → habitat
More than 25,000 large pieces of coarse woody habitat had been removed from the section between 1950 and 1980 to improve water conveyance.
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pieces → remove → conveyance
The reach was described as degraded, with poor riparian and instream habitats and an altered flow regime.
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reach → describe → habitats
Between 2007 and 2010, researchers reintroduced 4,450 large pieces of coarse woody habitat into the reach.
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researchers → reintroduce → reach
The restored section extended for approximately 120 km from Lake Hume to the junction of Lake Mulwala, with the restoration concentrated in four 5,000-metre priority zones between 25 and 100 river kilometres downstream from Lake Hume.
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restoration → restore → Hume
The researchers wanted to find out whether the new habitat would increase the overall fish population or simply cause fish already present in the reach to move into the newly restored areas.
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fish → want → areas
To test this, they sampled sites both inside and outside the resnagging zones.
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they → test → zones
The monitoring continued for seven years, providing a longer record than many smaller river restoration studies.
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monitoring → continue → studies
Fish populations increased
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populations → increase → ?
During the study, researchers captured 7,312 Murray cod and 3,743 golden perch through electrofishing.
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researchers → capture → electrofishing
They tagged 3,839 Murray cod and 3,316 golden perch with PIT and external tags.
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They → tag → tags
They also fitted 689 Murray cod and 466 golden perch with radio tags.
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They → fit → tags
Recreational anglers reported the capture of 1,338 tagged Murray cod and 275 tagged golden perch.
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anglers → report → cod
The population model showed a clear increase in Murray cod in the restored reach.
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model → show → reach
The estimated population of Murray cod larger than 200 mm increased between 2007 and 2013, while a comparable control reach experienced a 40% decrease over the same period.
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reach → estimate → period
The researchers said the increase in the restored reach did not coincide with a decline in the nearby populations that could explain it simply as fish moving from those areas.
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fish → say → areas
Golden perch also increased in the intervention reach.
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perch → increase → reach
The study sites held about 1,000 golden perch larger than 200 mm between 2007 and 2011, with the estimated number rising to around 2,000 over the course of the study.
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number → hold → study
Also, more than six million records were collected from logging stations and reduced to 558 permanent location changes.
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records → collect → changes
More fish moved into the restored population than moved out, with many movements coming upstream from two neighbouring populations.
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movements → move → populations
The researchers found that these nearby populations acted as source populations, supplying adult fish to surrounding areas.
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populations → find → areas
Role of connectivity
The researchers said the restoration worked in combination with connectivity between river populations.
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restoration → say → populations
Fish could move between several of the study reaches, allowing individuals from source populations to reach the restored habitat.
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individuals → move → habitat
Most immigrants came from the closest neighbouring populations where there were no barriers to movement.
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immigrants → come → movement
This means adding habitat alone was not the only factor involved.
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adding → mean → habitat
The restored section was part of a larger connected system in which fish populations interacted.
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populations → restore → which
…and 6 more, not listed.
The Aporia
