Can wild jungle perch populations be restored?

Background

Jungle perch  Kuhlia rupestris are a popular freshwater angling species in tropical north Queensland, where jungle perch reach a maximum size of 5 kg.

Within Australia jungle perch have been recorded from east coastal streams north from the Richmond River in NSW to the tip of Cape York. 

They are normally found in permanent streams and have a preference for riffles, runs and pools below cascades.  

Beyond Australia jungle perch have a wide Indo-Pacific distribution.They have been recorded in New Caledonia, Fiji, Samoa, French Polynesia, Papua New Guinea, Indonesia, Malaysia, Guam, the Philippines, Taiwan, Southern Japan, India, Madagascar, Mauritius, the Seychelles, Reunion, South Africa, Mozambique, Tanzania and Kenya. 

Unfortunately  in Australia jungle perch have become rare or extinct in most river systems south from Mackay.

Why are jungle perch important?

Jungle perch are a natural part of east and north-east coastal river systems and are therefore an important component of the biodiversity of these streams.

The presence of jungle perch is normally a good indicator that the stream is:

• free of barriers;
• has good water quality,
• acceptable flows
• and riparian cover. 

Jungle perch are one of the top predators of medium sized streams.  Loss of a top predator can have flow on effects down the food chain, leading to an altered or out of balance ecosystem.  Loss of jungle perch and other natural predators from a stream could also make the stream more susceptible to invasion by pest fish species.

Jungle perch are also important recreational sportsfish.  Jungle perch are targeted by local, interstate and overseas tourists. With the current bag limit of one fish, and a maximum legal size of 35 cm, the majority of fish are targeted by catch and release anglers.  At a number of clear water locations such as at Eli creek on Fraser Island and at  Mossman Gorge in north Queensland, jungle perch are highly visible and are a viewing attraction for ecotourists.

Why have jungle perch declined?

The decline in jungle perch probably has a variety of contributing factors,  including loss of  riparian (streamside) vegetation, loss of undercut banks following clearing of riparian vegetation, reduced flows and barriers to migration.  The major cause of their decline appears to be barriers to migration. Weirs, barrages, culverts and road crossings all have the potential to be total or partial barriers to migrating jungle perch.  Migration between freshwater and marine waters is essential for the completion of the jungle perch life cycle.

Jungle perch lifecycle

Jungle perch are diadromous fish.  That is they have obligatory movements between freshwater and the sea.  Jungle perch spawn in saline water, but juvenile jungle perch return to freshwater to mature into adults.  Adult jungle perch also return to freshwater after spawning.  Depending on the location of a barrier, barriers can either prevent juvenile and adult jungle perch from entering freshwater or limit the amount of freshwater habitat they can penetrate.  Sometimes a flood may permit the odd jungle perch past a barrier, but the total numbers of fish are greatly reduced compared to an open river system.  Juvenile jungle perch are also easy targets for predators like herons and large fish when their upstream movement is blocked by weirs, culverts and other barriers.  Research by DPI indicates jungle perch rapidly disappear from river systems when barriers are installed low down in the catchment.

Research to date

In the 1980s research on  the jungle perch life history in Queensland was done by DPI fisheries biologist Alf Hogan. Alf Hogan was able to prove the dependence of jungle perch on access to saltwater for spawning. More recently DPI AFFS Fisheries and Aquaculture have done some preliminary work on the captive breeding biology of jungle perch and have investigated the past and present distribution of jungle perch in Queensland and NSW.  This work clearly demonstrated that jungle perch have declined. 

For further details download the report - Restoring jungle perch (Kuhlia rupestris ) recreational fisheries to South-east Queensland ; A Pilot Study ( PDF 95kB)

Research gaps

Research on the population genetics of jungle perch  would be valuable.  This will determine whether or not jungle perch populations in streams on the east and north-east coast are a number of distinct sub-populations or one large, but fragmented population.  Distinct sub-populations are common for species which spend most of their life in freshwater. If jungle perch are made up of a number of genetically distinct sub-populations this will have implications for management of a recovery program.  It will be important to source the appropriate stock for the catchment being targeted for restoration as these fish are likely to be better adapted to that region.  If jungle perch are all one stock, then it will be much easier to run a recovery program, as brood stock could be sourced from some of the more abundant northern populations.

Developing reliable techniques for captive breeding of jungle perch will also benefit any future recovery program. Streams suitable for a jungle perch recovery program should be identified based on their habitat characteristics. Reintroduction of jungle perch into appropriate catchments should be followed by a program that monitors their survival, growth and ultimately natural recruitment of juveniles. Effects of the re-introduction of jungle perch on the ecosystem should also be monitored.

What can be done to restore jungle perch populations?

There are a number of things that can be done to help restore jungle perch populations to their previous range within NSW and Qld and to restore their range within catchments where there distribution has become truncated or patchy.

These include