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Australian endangered species: Murray Cod

The Murray cod (Maccullochella peelii) is the largest native Australian freshwater fish species, and is probably the most iconic. The species’ credentials are impressive: it can live for more than 50 years…

The Murray cod is popular amongst fishers, and also critically endangered - at least according to the IUCN. Flickr/guochai

The Murray cod (Maccullochella peelii) is the largest native Australian freshwater fish species, and is probably the most iconic.

The species’ credentials are impressive: it can live for more than 50 years and has been recorded weighing over 100kg and measuring longer than 1.5m. It can move hundreds of kilometres. It was and is important culturally and as food for Indigenous Australians. Once it formed the basis of an important commercial inland fishery, and it remains one of the most popular recreational fisheries in this country.

The Murray cod is also one of our most beautiful freshwater fishes, with a creamy-white underside, and a green mottling on its body and broad head.

Its natural distribution is within the Murray-Darling Basin, and it can be found, at least historically, from clear upland streams to turbid lowland rivers, but likes cover, especially submerged logs (or “snags”).

The Murray cod matures at about four or five years and breeds predictably between September and December in the main channel of rivers, usually when water temperatures are above 15°C. Breeding isn’t associated with rises in flow as once thought.

Murray cod may spawn more than once per season. Between 10,000 and 90,000 eggs are laid either in hollows in the river bank or on snags either in hollows in the river bank or on or in snags. The male remains to guard the eggs, and he continues to watch the newly hatched larvae until they are about a week old. The young fish then emerge into the river and drift downstream for several days.

Status

Murray cod are listed as critically endangered by the IUCN, and as vulnerable under the Environmental Protection of Biodiversity and Conservation Act, and by the Australian Society for Fish Biology.

The IUCN listing states that numbers of Murray cod have substantially fallen. There is considerable controversy over the status of Murray cod because many recreational fishers consider the species abundant and widespread, not least because it is stocked widely by commercial organisations, fishing clubs and government agencies. Changing ideas of what the “natural” size and age structure is may be contributing to these perceptions.

Threats

Murray cod suffered severely from commercial overfishing from the mid 1800s, and the few records indicate massive declines through the late 1800s and into the 1950s. Commercial fishing has now mostly ceased.

Now Murray cod are threatened by a variety of factors.

Recreational overfishing is still a problem. Many anglers catch and release fish but there is still intense pressure in particular locations. The closed season (1 September-1 December) needs attention considering that fish breed into December in some parts of the rivers.

Habitat, breeding and feeding are affected by the removal of dead trees (desnagging) and loss of riverside vegetation.

Water regulation means there is higher flow during the breeding season, which is a major challenge for Murray cod larvae. Potentially millions of young fish are physically pumped out of the river onto farms during the breeding season.

There are now barriers to fish movement on the river such as weirs and dams, which severely impact on adult fish migrating up and down, and larval fish dispersing downwards.

Dams pose a another threat when water is released into the river. Blackwater events can cause low oxygen levels, causing fish deaths, while cold water impacts on fish larvae and eggs, which do not survive below 13°C.

Invasive species, particularly Redfin (Perca fluviatalis), likely eat the young stages of Murray cod. Intensive aquaculture and introduced species also have the potential to introduce viruses and disease into wild fish.

Widespread stocking may mask the true status of the species, leading to reduced urgency of conservation actions.

Strategy

A recovery plan for Murray cod was prepared in 2010. Its main aim is to have self-sustaining populations throughout the river system. The target is to restore the species to 60% of pre-European numbers in 50 years.

As part of the recovery, a number of actions have been proposed. Gaps in the knowledge of Murray cod biology need to be filled to ensure sustainable management. Distribution and population structure need to determined, as well as the habitat use by different life stages. River flow can then be managed to encourage breeding and survival. Risk of threats, and benefits of recovery actions need to be assessed.

Murray cod is fished recreationally throughout its range and is targeted by almost half of all Victorian fishers. More than one million are stocked each year in the Murray-Darling Basin, and nine million were stocked in NSW and Victoria from 2000-2010. Concerns about the number of fish being removed before reaching maturity has led to the recent minimum legal length being raised from 500 to 600 mm in NSW, Victoria and the ACT.

Conclusion

It is indeed an interesting situation where a species listed variously as critically endangered, threatened or vulnerable forms the basis of such a popular and economically important recreational fishery. But with proper fisheries management, community engagement and conservation, the future may be brighter for Murray cod than it has been for many decades.

The Conversation is running a series on Australian endangered species. See it here

Join the conversation

20 Comments sorted by

  1. Wade Macdonald

    Technician

    Quote..."Recreational overfishing is still a problem. Many anglers catch and release fish but there is still intense pressure in particular locations. The closed season (1 September-1 December) needs attention considering that fish breed into December in some parts of the rivers."

    Fair enough about the closed season for breeding but recreational fishers are the biggest benefit to the existence of murray cod. Our funds and physical effort contirbute to the release of millions of these fish through stocking programs year in year out.

    Plenty of other sectors of society complain but do stuff all to help the situation.

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    1. Andrew Loyd

      Stay at home dad

      In reply to Wade Macdonald

      Indeed

      Cod fingerlings were translocated by the Acclimatisation society into Western Australia on the 1800;s. Unfortunately or fortunately depending on who you speak to, salinity wiped them out.

      I had the chance to cod in dams. On one occasion the water was down. An angler next to me hooked a small 2 kilo fish. As he brought the 2kg fish onto the bank of shallow repose a 15 kilo fish swam straight onto the sand to grab its prey, missing then wriggled backwards into the water.

      They are cannibals in a survival situation. Big fish eat smaller fish to control population according volume of water similar to the Northern Pike.

      We must get structure back into our rivers for the fish to breed. They appear to breed quite well.

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  2. Mat Hardy

    Lecturer in Middle East Studies at Deakin University

    Do they taste any good? I tend to think of old, sluggish fish in muddy water as not being that palatable!

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    1. Peter Ormonde
      Peter Ormonde is a Friend of The Conversation.

      Farmer

      In reply to Mat Hardy

      Damn fantastic Mat ... very sweet with a nutty flavour - not at all muddy - but far too pretty to eat ... served with lashings of guilt and regret.

      There was actually quite a significant effort looking at Murray Cod aquaculture in Victoria (which is where I got mine). Not sure how that ended up but my mates were amazed at how quickly they grew in intensive systems... better than barramundi.

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    2. Tim Connors

      System Administrator / Public Serf

      In reply to Mat Hardy

      About a year ago I rode up to and along the Murray. At an tiny unnamed pub, the bardude was just writing up the night's menu and mentioned they caught a cod that morning and had just finished gutting it. I didn't even think of it being endangered until later on, but it was fantastic. I felt really guilty afterwards.

      I decided to get a smartphone very soon after so I could install an app to tell me whether any given fish was endangered. Turns out the apps are all crap, and I wouldn't have had phone access in said small town, but thems the breaks.

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  3. Colin Creighton

    Chair, Climate adaptation, Marine Biodiversity and Fisheries

    Hmm - to my knowledge there is not one species of Australian freshwater, estuarine or marine fish made extinct from fishing. Sure in the past thee was over fishing, but more importantly is gross habitat destruction. These days fishing both professional and recreational seek to be sustainable and maintain their resources so please lets skip the blame game where its incorrect and get on to the main issues - habitat repair. For example for the Murray Cod, with all the $ spent on R&D and some works we are still not re-creating the deep holes needed for refuge, such as during the low flows that characterise Australian river systems. As to estuarine habitat the same applies, fishing productivity has been trashed because of indiscriminate habitat destruction. Watch the Conversation in the coming months as we build the science detail behind the need for a massive investment in estuarine habitat repair - for the good of all Australians, including fishers.

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    1. Paul Humphries

      Senior lecturer in Ecology at Charles Sturt University

      In reply to Colin Creighton

      Hi Colin, my point was that fishing is one of many threats to Murray cod, and an an inadequate closed season does not help and should be dealt with. Of course modern recreational and commercial fishing 'seek' to be sustainable and that's great. It doesn't mean that they actually are, and changes to size limits is indicative of inadequate regulations in the very recent past. Habitat is just one factor, albeit very important, but the Field of Dreams concept ('give them habitat and they will come back') is, I think, simplistic and is an easy one to resort to when there are much more intractable problems. Thanks for your comment. Paul.

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  4. Nick McKenzie

    Account Manager

    I have to say this is a very thin, poorly researched and out of date article.
    It may have been fairly accurate 15 years ago ( when the recovery plan and the 60% aim was identified - not 2010 )....... To be honest, a 13 year old could have written this for his/her science project by googling Murray Cod...the same old lines have just been trrotted out!
    Regarding threats
    - firstly as pointed out, recreational fishers contribute financially and without them future fish foundation etc would not exist…

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    1. Paul Humphries

      Senior lecturer in Ecology at Charles Sturt University

      In reply to Wade Macdonald

      Nick, thanks for the comment but not the insults. You are right that fishers are increasingly contributing to good conservation and management of recreational fisheries. They/you are important in making the fishery sustainable. There are still concerns, however, that the size limit of 60 cm is not sufficient because of when fish mature, and I am personally concerned after 17 years research, that the closed season is inadequate, given fish typically breed into December in many parts of Victoria…

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    2. Nick McKenzie

      Account Manager

      In reply to Paul Humphries

      Paul,
      Thanks for the reply, apologies for the tone which obviously offended you, in hindsight it was a little caustic. I appreciate your response and I agree we are on the same side with both of us wanting to see the best and most well managed fisheries possible under the circumstances.

      The fact is however that you did paint a picture of desnagging, severe overfishing by morons with little understanding of the species, and weirs and locks being absolute barriers to migration......my assertion…

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    3. Paul Humphries

      Senior lecturer in Ecology at Charles Sturt University

      In reply to Nick McKenzie

      Hi Nick, no worries. The word limit did not allow me to add references, although I wanted to. Here are some scientific papers that might be of interest in you are looking for information on biology and fishery-related stuff. Cheers, Paul
      HUMPHRIES, P. 2005. Spawning time and early life history of Murray cod, Maccullochella peelii peelii (Mitchell) in an Australian river. Environmental Biology of Fishes, 72, 393-407.
      KOEHN, J. D. 2004. The loss of valuable Murray cod in fish kills: a science and…

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    4. Simon Kaminskas

      Desk-Bound Environmental Scientist

      In reply to Nick McKenzie

      Nick, there's no need for such an insulting tone in your response.

      Paul was giving a brief overview -- I can assure you he knows all of the issues.

      Several points:

      1) Your argument that as a rec-fisher you pay for stockings of cod doesn't have much relevance. The contribution of stockings to overall cod stocks is trivial in most places. In some specific rivers or stretches of river, yes, they have contributed, but in most rivers most cod are still from natural breeding. Given the size…

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    5. Nick McKenzie

      Account Manager

      In reply to Simon Kaminskas

      Simon, this is supposed to be "the conversation", if I wanted a brief overview, I'd be still reading the Age or same old outdated info on "fact sheets" you find by searching murray cod on google!

      This is supposed to be informed and rigorous debate. I thought the article was far to thin, and I believe the debate created by my response ( as caustic as it was ) has resulted in far more detailed, specific and up to date facts being brought out.
      I'm appreciative of the references Paul provided and…

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    6. Simon Kaminskas

      Desk-Bound Environmental Scientist

      In reply to Nick McKenzie

      “This is supposed to be informed and rigorous debate. I thought the article was far to thin, and I believe the debate created by my response ( as caustic as it was ) has resulted in far more detailed, specific and up to date facts being brought out. I'm appreciative of the references Paul provided and will read them all in due course.”

      I just don’t think the aggro was necessary.

      “you say re-stocking makes no difference apart from a very few isolated area's, yet Paul says " In many cases stocking…

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    7. Nick McKenzie

      Account Manager

      In reply to Simon Kaminskas

      Thanks Simon,

      the aggro maybe wasn't necessary, but i'm glad it has you so fired up that you are helping educate me and others much more so now than if no-one had questioned Paul's article in the first place.

      It sounds like you agree how bad practices were, you acknowledge the improvement in practices( yet I sense a lot scepticism), yet you still want to bash every fisherman over the head..........this along with your comment "So if a scientist is saying the broader situation with wild Murray…

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    8. Simon Kaminskas

      Desk-Bound Environmental Scientist

      In reply to Nick McKenzie

      “It sounds like you agree how bad practices were, you acknowledge the improvement in practices( yet I sense a lot scepticism), yet you still want to bash every fisherman over the head..........”

      No. That’s an exaggeration on your part. As someone who carefully caught and released 4 wild river Murray cod on Sunday (using lures with single barbless hooks, strong tackle, and best practice catch-and-release techniques), I’m fully aware of how much things have improved in *some* rec-fishing circles…

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  5. rachael watkins

    Nurse

    Oh the poor Murray. So beautiful
    Great getting this topic out there.
    Obviously there are lots of contributing factors.
    Fishing cant be ruled out as a contributor. Many people do not fish legally unfortunately and are just looking for the catch, using drum nets, keeping undersized fish and not keeping to correct seasons etc. It is very hard to police this, as the river is very large.
    Cod is getting harder and harder to catch in the SA side of the river according to people i know who live on its banks and have lived there for generations
    Carp on the other hand.

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    1. Garry Fitzgerald

      logged in via email @sweetwaterfishing.com.au

      In reply to rachael watkins

      Regarding "fishing"..... There is recreational fishing & there is harvesting. Recreational fishing is a legal activity that is regulated by various states.
      The use of cross lines, gill nets, drum nets, set lines is almost always illegal is harvesting.
      As a recreational angler I find it disappointing that educated people choose to group the two and tar all with the same brush. An effective way to alienate allies...

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