Recently I was asked to write a short piece on Murray cod in The  Conversation, since the International Union for the Conservation of Nature list the species as Endangered. This is quite a controversial topic, since the species is one of the most popular inland recreational fisheries in Australia. I list one of the threats as ‘fishing’, which is what the documents state.  And I think it is beholden on all of us to recognise all the potential reasons for the poor status of the species. Sure, as one reader pointed out to me, rehabilitation is happening, and a lot has been done to improve conditions for our native fishes. But I believe that we have a long, long way to go before we can relax. The pressures on Murray cod and other species (people often forget that there are another 30 or so species in the MDB that need consideration too!) from continued flow regulation, instream barriers, introduced species, future water resource development (including advocacy of new dams like for the Ovens River in northern Victoria) and reductions in funding for native fish research, conservation and management, all mean that there is a great risk in letting our guard down. And I couldn’t agree more with one respondent, that fishers are key contributors to the effective conservation of Murray cod. In the end, we all want the  same thing.

I gleaned material for the piece from a range of  sources, including the Murray-Darling Basin Commission’s Native Fish Strategy, the Murray cod Recovery Plan and several other references, which I include below, as there was not space for them in the article.

Hope you find it interesting.

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 management perspective.  Management of Murray cod in the Murray-Darling Basin: Statement, recommendations and supporting papers. Proceedings of a workshop held in Canberra, MDBC 2004. 3-4. KOEHN, J. D. 2009. Multi-scale habitat selection by Murray cod Maccullochella peelii peelii in two lowland rivers. Journal of Fish Biology, 75, 113-129. KOEHN, J. D. & HARRINGTON, D. J. 2006. Environmental conditions and timing for the spawning of Murray cod (Maccullochella peelii peelii) and the endangered trout cod (M. macquariensis) in Southeastern Australian rivers. River Research and Applications, 22, 327-342. KOEHN, J. & TODD, C. 2012. Balancing conservation and recreational fishery objectives for a threatened fish species, the Murray cod, Maccullochella peelii. Fisheries Management and Ecology, 19, 410-425. LINTERMANS, M. 2013. Conservation and Management. In: Humphries, P. & Walker, K.F. (eds). Ecology of Australian Freshwater Fishes, CSIRO Publishing, Collingwood. ROURKE, M. L., MCPARTLAN, H. C., INGRAM, B. A. & TAYLOR, A. C. Biogeography and life history ameliorate the potentially negative genetic effects of stocking on Murray cod (Maccullochella peelii peelii). Marine and Freshwater Research, 61, 918-927. ROWLAND, S. J. 1989. Aspects of the History and fishery of the Murray Cod, Maccullochella peeli (Mitchell) (Percichthyidae). Proc. Linn. Soc. N.S.W., 111, 201-213. TODD, C. R., RYAN, T., NICOL, S. J. & BEARLIN, A. R. 2005. The impact of cold water releases on the critical period of post-spawning survival and its implications for Murray cod (Maccullochella peelii peelii): A case study of the Mitta Mitta River, southeastern Australia. River Research and Applications, 21, 1035-1052.

I am pleased to announce that the Ecology of Australian Freshwater Fishes book, edited by Paul Humphries and Keith Walker, is to be published by CSIRO Publishing in March 2013.  You can pre-order now by clicking here.

Description:

This edited volume reviews our past and present understanding of the ecology of Australian freshwater fishes. It compares patterns and processes in Australia with those on other continents, discusses the local relevance of ecological models from the northern hemisphere and considers how best to manage our species and their habitats in the face of current and future threats.

The chapters are written by some of our foremost researchers and managers, developing themes that underpin our knowledge of the ecology, conservation and management of fish and fish habitats. For each theme, the authors formulate a synthesis of what is known, consider the need for new perspectives and identify gaps and opportunities for research, monitoring and management. The themes have an Australian context but draw upon ideas and principles developed by fish biologists in other parts of the world.

The science of freshwater fish ecology in Australia has grown rapidly from its roots in natural history and taxonomy. This book offers an introduction for students, researchers and managers, one that the authors hope will carry Australian fish biology and resource management to new levels of understanding.

So, you’ve decided to do a PhD in river ecology in Australia.  Good choice! But where is the best place to go?  Should you study in one of the large city universities, or head out into the country and study in one of the smaller regional universities? And how do you find the right supervisor?  There are many universities and departments to choose from and most have excellent postgraduate programs and academics who can supervise your project.  But each department has its own expertise, and it is worth shopping around for the place and the person that would suit you best. In an accompanying page, I have begun to list the universities in Australia that have good research backgrounds in river ecology.  There are quite a few, and it allows a bit of choice. The list will develop over time as I continue my search. The following is the first in several posts that I hope will help you think about how to choose where to go and who to study with. It will also provide links so that you can make contact and get the ball rolling. I will add to the series over the next few weeks to give some more hints about what I think are important considerations when contemplating a PhD in river ecology. Note: these thoughts are mine alone, are not definitive by any means and not officially sanctioned by any institution.  Make sure that you make an informed decision and look around for information and advice from a number of sources.

Where in Australia would you like to study?

Doing post-graduate research is a great way to see the country and learn about how people, animals and plants live in environments that you are not familiar with.  I began my studies at Monash University in Melbourne, went on to do a Masters by research at the University of Tasmania and then to do a PhD at Murdoch University in Perth.  Travel was not my primary aim; in fact my main motivation for moving was to work with really good fish ecologists with good track records of research.  It was quite confronting at times to move to new places where I knew virtually no-one, but I wouldn’t change it for the world, and think that it really enriched my thinking, my research and my life.

There are universities from all around Australia that support PhD studies in river ecology. From the Northern Territory (Charles Darwin University) to Tasmania (University of Tasmania), from Western Australia (e.g. Murdoch University, Edith Cowan University) to Brisbane (e.g. Griffith University), there are universities that have strong cultures of research and teaching in river ecology. Each university tends to focus on the environment and climate in which it sits, of course. So, you will get a pretty good picture of what types of ecosystems you will have open to you by where the university is located. This is not always the case, but it is a pretty good bet.

If you have a hankering for working with tropical species, then clearly you should be looking at one of the more northern Australian universities, like Charles Darwin University, Griffith University or James Cook University, all of which do lots of tropical and sub-tropical river research. Murdoch University in WA also has researchers who routinely do studies in the northern part of that huge state. The University of Adelaide and Griffith University also have good track records for research in central Australia, the Lake Eyre Basin and arid-zone rivers generally. If you want to work in alpine areas, then the University of Tasmania is a great place to go.  But the University of Canberra, Charles Sturt University in Albury and La Trobe campus at Wodonga are all within spitting distance of the alps and are good bases from which to study alpine stream ecosystems.  Most universities have campuses hugging the coast, and so finding a university to study at where you can work on coastal streams is not difficult. Melbourne University, the University of Tasmania, the Warrnambool campus of Deakin University and Griffith University are good choices if you want to work on coastal streams.

City or country?

Are you a city person or do you like the countryside? There are good reasons for wanting to study in cities, because they have so many resources, the univesities tend to be bigger, have more facilities, there are often more postgraduate students, there is public transport etc etc. But the downside is that unless you want to work on urban streams, you have to travel long distances and through city traffic to get to your field sites. That can be a real pain, believe me.

At regional universities or campuses (e.g. Charles Sturt University, Warrnambool campus of Deakin University or the Wodonga campus of La Trobe University) or universities in smaller cities (e.g. University of Tasmania), this is less of an issue. And being close to your field sites can be a great advantage. It means that mistakes are less costly and accommodation may not be an issue. It may mean being able to monitor your river better, because you can nip out at a moment’s notice and still be back in time to watch your favourite TV show. It may also mean being able to live within the catchment of the river which you study. This can give you greater insight into the environmental and social issues associated with your river. It is not to say that you won’t have to travel large distances if you want to work on arid-zone rivers, for example. But you don’t have to if you don’t want to.

What kinds of animals and plants are you interested in?

Generally speaking, the diversity of riverine fauna and flora in Australia is greatest in the tropics and sub-tropics.  So, if you want to work in regions with large numbers of species, and perhaps work on a project in community ecology, universities in the Northern Territory or Queensland are for you.  Research into the structure of river fish assemblages and the environmental factors that influence them, have been the focus of considerable effort at Griffith University. The Murray-Darling Basin would not be a great place to choose to work, for example, if you were after diverse fish assemblages – although there are lots of fish, but not always the ones we like to catch and eat. But temperate regions do support quite diverse groups of animals and plants – certainly enough to keep most PhD students busy and happy. In fact, some of the most diverse macroinvertebrate assemblages can be found in ordinary streams close to Sydney or Melbourne or other temperate zones of Australia. Tasmania also is a hot-spot for fish in the family Galaxiidae, which is one reason why I went there to do my Masters degree.  Temperate regions are also good places to find frogs, platypus and crayfish. Tasmania has a great freshwater crayfish fauna, with the largest freshwater crayfish in the world – Astacopsis gouldi.

If introduced species are your thing, you could just about go anywhere in Australia, although WA has fewer of these than most.  The more populous areas around big cities are prime spots to work on introduced species. The Invasive Animals CRC, for example, has its freshwater centre operating out of Queenscliff not far from Melbourne. If you want to help solve the carp problem, then the Invasive Animal CRC is a good place to start. They have a number of PhD scholarships available each year for projects related to introduced species, including carp. Mind you, carp have relatively recently made their way to Tasmania and occur throughout the Murray-Darling Basin, so take your pick where you’d like to work. In fact, the Murray-Darling Basin is home to many introduced species, so any of the universities in South Australia, Victoria, New South Wales, ACT and southern Queensland will give you access to this large area.  Many universities have links with natural resource management agencies whose job it often is to deal with introduced species. I can assure you, there is no shortage of work to be done on introduced species and we need bright, fresh minds to come up with novel ways to manage and eradicate these pests.

Stay tuned for more on thoughts on where to do a PhD in the next post, including: do you want to be a pioneer and how to find and choose a supervisor.

By Damian Kelly, Masters candidate, School of Environmental Sciences, Charles Sturt University

Fishing and hunting are two of the most common and widespread occupations of indigenous peoples throughout the world since at least the Neolithic (starting about 12,000 years ago). All the world’s peoples have at some stage fished with spears, poisons, hooks, nets and traps.  Australian Aborigines living along the coast, for example, have caught and eaten aquatic animals for many thousands of years. People living in inland Australia have also exploited aquatic animals, probably for as long, but this has received much less attention.

Aboriginal people have fished, hunted and collected food along rivers and in lakes for at least 30,000 years. The best known and oldest of these sites is Lake Mungo, where we know that people fished for Murray cod (Maccullochella peelii) and golden perch (Macquaria ambigua) amongst others (Bowler et.al 2003). There is also ample evidence to show that fishing has been an important and ongoing activity in the Murray-Darling Basin for a similar period of time (Balme and Hope 1990). Not only fish, but also mussels, crustaceans, mammals, birds and aquatic plants were used as food (Humphries 2007).

The types of methods used in fishing by indigenous Australians range from the use of spears, poisoning the water, nets and lines of people in the water to drive fish towards others waiting with nets, and spears and fishing lines with hooks (Gerritson 2001).  But one of the most widely used techniques was that of fish traps (Gilmore 1933). These come in all shapes and sizes, but usually target fish species that have behaviours that make them trappable.  Iconic sites such as Brewarrina in northern New South Wales are frequently cited as representative of fish traps (Dargin 1976). However, the reality is that the technology of fishing varied widely among rivers (Ross 2009).

The ephemeral nature of many fish traps requires the use of indirect evidence, i.e. inferring the existence of such fishing technologies from a variety of data gleaned from archaeology, ecology and historical and ethnographical sources. A possible correlation of traps with midden sites (Gribble 2005), as well as gathering places, needs to be evaluated, because fish traps can provide adequate food for large gatherings of people for various ceremonies, including those at Bora grounds. Based on the data collected about known traps, it may also be possible to predict additional locations where traps may have existed in the past.

Most research so far has been largely descriptive, focussing on where traps have been found and how they were constructed (Welz 2002). To date, little research has been done to link fish traps to river ecology. Many important questions remain to be answered, such as which fish species were trapped, at what time of the year and during what types of flow were the traps effective,  and how long were fish trap technologies used?

 My project aims to investigate the archaeological and ecological significance of the location, structure, contents and context of Aboriginal fish traps of the Murray-Darling Basin. It will: describe the distribution of fish traps in the Murray-Darling Basin, along with riverscape features associated with them, and technologies used in their construction; attempt to work out which species of fish were trapped, precisely how they were caught and at what time of the year or under which river conditions fish were most likely trapped; see if there are links between the locations of fish traps and gathering places, such as Bora or Corroboree grounds; and explore whether it is possible to predict the location of other fish trap sites from the analysis of known trap features.

References: Balme, J. and J.H. & Hope, J., 1990. Radiocarbon dates from midden sites in the lower New South Wales Darling River area of western. Archaeology in Oceania, 25(3), pp.85-101. Bowler, J. M., Johnston, H., Olley, J. M., Prescott, J. R., Roberts, R. G., Shawcross, W., & Spooner, N. A. (2003). New ages for human occupation and climatic change at Lake Mungo, australia. Nature, 421(6925), 837-837. Bowler, J. & Jones, R., 1970. Pleistocene human remains from Australia: a living site and human cremation from Lake Mungo , western New South Wales. World Archaeology, 2(1), pp.39–60. Dortch, C.E., 2012. New perceptions of the chronology of Aboriginal development in south-western Australia. Archaeology, 29(1), pp.15-35. Gerritsen, R., 2001. Aboriginal fish hooks in southern Australia: Evidence, arguments and implications. Australian Archaeology, 52(52), pp.18–28.  Gilmore, M., 1933. Old Days: Old Ways, Sydney: Angus and Robertson. Gribble, J., 2005. The Ocean Baskets: Pre-colonial fish traps on the Cape south coast. Digging Stick, 22(1), pp.1–16. Humphries, P., 2007. Historical Indigenous use of aquatic resources in Australia’s Murray-Darling Basin, and its implications for river management. Ecological Management & Restoration, 8(2), pp.106–113. McNiven, I.J. et al., 2012. Dating Aboriginal stone-walled fishtraps at Lake Condah, southeast Australia. Journal of Archaeological Science, 39(2), pp.268-286. Ulm, S., 2002. The Seven Mile Creek Mound: new evidence for mid-Holocene Aboriginal marine resource exploitation in central Queensland. Proceedings of the Royal Society of Queensland, The, 110, pp.121-126. Walters, I., 1985. The Toorbul Point Aboriginal fish trap. Queensland Archaeological Research, 2, pp.38–49.  Welz, A.I., 2002. Fish Trap Placement: The Environmental and Cultural Influences in Fish Trap Placement Along the Australian Coastline. Flinders University of South Australia, Dept. of Archaeology.

The biota of rivers in Australia, and many other dry parts of the world, have evolved in the context of extremes of flow. The ability of some species of fish, such as the dwarf galaxiid (Galaxiella pusilla), the Queensland lungfish (Neoceratodus forsteri), or the inimitable salamanderfish (Lepidogalaxias salamandroides), to aestivate (the summer equivalent of hibernate and meaning to become dormant, usually in the absence of free water, during dry periods) is one example of a physiological adaptation to frequent, and in many cases predictable, dry periods. The life history of other species of fish, like golden perch (Macquaria ambigua) or silver perch (Bidyanus bidyanus), which produce hundreds of thousands of eggs and can reabsorb these if conditions are not right, is another example of an adaptation to taking advantage of the good times, while biding time during the bad ones. Actually, many species of native fish in the Murray-Darling Basin seem to breed during the drier, warmer months of the year because of good growing conditions at this time, which is contrary to what we thought some years ago and often surprises people used to overseas patterns.

The migration of thousands of pelicans to the vast waters of newly inundated salty Lake Eyre or other water birds to wetlands previously dry, is a further illustration of how animals take advantage and ‘cue-into’ the dry and wet periods for which Australia is so well known. When rivers start flowing, after prolonged dry periods, microinvertebrates, like copepods, cladocerans and rotifers, and some macroinvertebrates, like fairy and shield shrimps, hatch from dormant, desiccation-resistant eggs and appear in their billions. Fish, that have taken refuge in small, isolated water holes, emerge and breed – also in vast numbers – take advantage of the abundant food supply and grow quickly. The fish eat the invertebrates, and the birds in many cases eat the fish.

Of course, not all parts of Australia show such extremes, but all regions, even in the relatively wet south-east have wet and dry periods each year. In fact, many of our rivers would have naturally dried to a series of isolated pools during most summers. The Broken River, that runs through Benalla and meets the Goulburn River at Shepparton, for example, was supposedly named because it did just this: the river ‘broke’ into pools, interspersed with dry riverbed, in most summers. The animals that depend on the water, like fish, would in many cases move downstream to more permanent water, or take refuge in pools. Nowadays, river regulation does not allow most rivers to dry, and we actively managed to keep rivers wet at all times. This is called ‘anti-drought’ by Tom McMahon and Brian Finlayson of the University of Melbourne.

High flows also occur naturally and frequently, of course. In fact, most rivers would normally ‘break their banks’ once every two years, by definition…if allowed. As I have talked about in a previous post, river channels are defined largely by the flow which travels down them. And it seems that the flows which exceed the capacity of what we call the main channel, occur with relatively predictable frequencies. Like drying, we also try to manage rivers so that they don’t flood. We build levees to increase the height of river banks or construct upstream dams to ‘flood-proof’ our rivers and hold back unusually large rainfall events.

Sometimes dry periods are longer than normal and become ‘droughts’. So-called droughts do stress the inhabitants of rivers; there is no doubt. Isolated pools or water holes that gradually dry because of declining groundwater, become more concentrated with solutes, like salt, and often also have lower dissolved oxygen concentrations than flowing water. While most species of native fish, for example, can cope with quite high salinities and low dissolved oxygen levels, there comes a time when these will prevent growth and ultimately cause death. The recent ‘millennium drought’ went on for so long that there were major concerns for fish, river redgums and water birds, much of it warranted. But droughts and drying also allow the build up of organic material, both living and dead, in the dry parts of rivers. This will contribute to the energy of rivers when water returns, although drying will also change the biogeochemical make-up of the sediment. And during this same extended dry period, there appeared to be a resurgence in Murray cod (Maccullochella peelii) numbers in some parts of the Murray-Darling Basin, whereas exactly the opposite was true for carp (Cyprinus carpio). Something interesting was happening, and not all of it bad!

Sometimes wet periods are of greater magnitude than normal and become ‘floods’. So-called floods certainly cause some ‘inconvenience’ for our river fauna and flora. Flooding may displace individuals downstream, because they can’t resist the current. But once the flow has reached bankfull and floods, there is an abundance of inundated habitat that is slow-flowing or still, as the water makes it way slowly across the landscape – now part of the ‘riverscape’. Some riverine animals respond to floods by breeding and/or feeding on the floodplain. Others may take advantage of food that comes back off the floodplain, although this depends on the nature of the connection of the river with the floodplain. Some species of fish, like southern pygmy perch (Nannoperca australis) or flatheaded galaxias (Galaxias rostratus), seem to use floods to move around within the floodplain. Dormant microinvertebrate eggs hatch and plant seeds germinate in response to floods and take advantage of the nutrient-rich waters on the floodplain. And the sediment that is deposited by rivers on to floodplains also promotes much animal and plant growth.

So, to riverine animals and plants, ‘droughts’ and ‘floods’ can be seen as disturbances, but not catastrophes. And, despite some knowledge, we really know so little about the roles of these events and associated processes in riverine ecosystems, that our ‘anti-droughting’ and ‘flood-proofing’ activities are almost certainly to the detriment of the native biota and perhaps beneficial to many introduced species.

I should have added above that in an unmodified landscape and riverscape, ‘droughts’ and ‘floods’ can be seen as disturbances, but not catastrophes. But once we put up barriers to movement, fish in isolated pools, introduce species, prevent drought-breaking rainfall from reaching rivers, change temperature conditions etc, the effects of droughts and floods can take on a different perspective. What were natural events from which riverine animals and plants could previously bounce back (=resilience), now can threaten populations and even species. Much of our biota, as I have described in a few examples above, is inherently resilient, because of the nature of the environment in which it is has evolved. This is not universally the case, but is probably a reasonable generalisation. But because of our modifications to rivers and to the way we interact with rivers, say through fishing, we have in many cases, compromised that resilience.

It has always puzzled me as to why the fish in the Murray-Darling Basin are doing so badly under river regulation, given the fact that they have evolved in such a harsh environment. Surely, with all their wily ways, coping with ‘droughts’ and ‘floods’ as they have for millennia, a bit of regulation here and there wouldn’t bother them. Sure, we have added insult to injury to insult in the way we have modified our rivers, but still, it didn’t quite work for me. Perhaps it is that, like in all ecosystems, the animals and plants get knocked around by disturbances, but recover after a time, and things go on pretty much as before. But now we have largely taken away that ability to bounce back, either because many species are in much smaller numbers than in previous times, or because our activities actively prevent it, and so ‘drought’ and ‘flood’ disturbances become much more significant and potentially catastrophic. Considerable conservation and management programs are now being implemented to allow more resilience in our rivers, and I sincerely hope they work. We are profoundly ignorant, however, at what spatial and time scales recovery from disturbances, like ‘droughts’ and ‘floods’, operate. Indeed, the time and spatial scales that are relevant to relationships between the dynamics of riverine animal and plant populations and the driving forces in rivers – like flow – are largely unknown. Continuing and enhanced research in this area is essential if we are to improve the health of our river ecosystems.

So, in the end, ‘droughts’ and ‘floods’ are not really a problem for riverine animals and plants…as such. They may be affected, in some cases dramatically; but they will recover. However, human activities and modifications to our rivers may have shifted the goal posts to one where recovery is much less certain.

References

Probably the best most recent reference on drought, and one of the few that looks at the ecological effects of drought, would be Sam Lake’s book, Drought and Aquatic Ecosystems: Effects and Responses, John Wiley and Sons.  I also co-edited (with Darren Baldwin) a special issue of Freshwater Biology on drought and the ecology of aquatic ecosystems that came out in 2003 and has lots of good papers in it.

Balcombe SR, Bunn SE, Arthington AH, Fawcett JH, McKenzie-Smith FJ and Wright A (2007) Fish larvae, growth and biomass relationships in an Australian arid zone river: links between floodplains and waterholes. Freshwater Biology 52, 2385-2398. Humphries P and Baldwin DS (2003) Drought and aquatic ecosystems: An introduction. Freshwater Biology 48, 1141-1146. Humphries P, King AJ and Koehn JD (1999) Fish, flows and flood plains: Links between freshwater fishes and their environment in the Murray-Darling River system, Australia. Environmental Biology of Fishes 56, 129-151. Lake PS (2003) Ecological effects of perturbation by drought in flowing waters. Freshwater Biology 48, 1161-1172. McMahon TA and Finlayson BL (2003) Droughts and anti-droughts: the low flow hydrology of Australian rivers. Freshwater Biology 48, 1147-1160. McNeil DG and Closs GP (2007) Behavioural responses of a south-east Australian floodplain fish community to gradual hypoxia. Freshwater Biology 52(3), 412-420. Nielsen DL, Hillman TJ, Smith FJ and Shiel RJ (2002) The influence of seasonality and duration of flooding on zooplankton in experimental billabongs. River Research and Applications 18, 227-237 Tonkin Z, King AJ and Mahoney J (2008) Effects of flooding on recruitment and dispersal of the Southern Pygmy Perch (Nannoperca australis) at a Murray River floodplain wetland. Ecological Management and Restoration 9, 196-201.

“My history on native fish has been published online by the MDBA and can be downloaded in total, as well as individual chapters and booklets.

“The chapter titled ‘species summaries’ reviews all the historical information I collected on each species. The section on Murray cod discusses the record size for murray cod. Basically, I think there is serious doubt on the Walgett cod record. The same person published a number of other letters on giant cod, including another at Walgett weighing 250 lb that was a pet and towed a barge! There is no supporting evidence for the capture of a 250 lb cod at Walgett.

“The best documented example may be a 225 lb fish taken from the Murray in South Australia in 1914. There are a number of news stories on it and the head may have been in the South Australia museum. There are news accounts reporting the capture of a 250 lb fish from the Murray River in 1857, and one of 200 lb from the Murrumbidgee River near Hay in 1913, but they lack details.”

Will also sent me the links to the newspaper articles concerning the South Australian Murray cod records from December 1935 and here.

Thanks very much, Will. 

So, it looks like the Walgett record is dead-in-the-water, if you will excuse the pun.  Which still begs the question why it continues to be used in textbooks.  We should not use any unsubstantiated record, despite the appeal of mega-cod and all the images that they bring up.  Perhaps we should move towards something along the lines of: “There are several unsubstantiated reports of Murray cod in excess of 225 lb, however, extrapolating from verified sizes of this species, it is quite possible that fish of this size could have, and maybe still do, exist.”

I really recommend reading Will’s remarkable histories of Murray-Darling Basin fishes.  He has provided us with a wonderful and rare window into the past.

See below for the actual newspaper clipping.

This particular fish is included in many, many scientific texts as the biggest Murray Cod ever caught and it is possible that Murray cod can actually get that big, if one extrapolates from length-age records in scientific papers (Anderson, J.R., Morison, A.K. and Ray, D.J. 1992, Australian Journal of Marine and Freshwater Research 43(5) 983 – 1013).

Noble was a mounted trooper in the early 1900s in Walgett and I have verified this from newspaper reports at the time.

Being a fish ecologist and interested in history, I have attempted to verify the existence of this monstrous fish by trawling through copies of the Walgett Spectator between 1900 and 1905, but to no avail.  There was no mention that I could find.  There was also no mention of a donation of £20 to the Walgett Hospital from those associated with the fish.  This is despite the hospital acknowledging many much smaller donations during the same period.

I visited Walgett in July 2005 and met with various people, including members of the Historical Society.  They were very helpful and kind, and I would especially like to thank Noreen and Darcy Dunn for their time and patience. Although most people I talked to had heard of the big cod, and some even remember seeing a picture, no one has come up with any hard evidence of the fish having existed.

Did it ever really exist? Or was it an exaggerated memory from a half-century before? It would be great to find out, not least to verify for scientific purposes. Should we be using this record in our textbooks, since it comes from such an unauthenticated source? Surely, unless it can be verified, it should be treated with caution.  Scientists are usually wary of such things, but here, we seem to be ready to accept a letter to a newspaper, based on a memory from 50 years previously, as reliable evidence.

I, for one, would love to believe the story.  It is also interesting because it could tell us something about the potential of this wonderful species to reach truly remarkable sizes.  Where there was one monster, there were bound to be others.  And there may be again….if we just treat our rivers and fish with the respect that they deserve.

If anyone who might know something of the fish (or might have some clue where to look). I can be contacted at the email address at the top of the home page or leave a comment on this blog.

Many species of riverine fish drift, using river currents to sweep them from areas where their parents have spawned, to areas more suitable for growing and maturing.  For some species of riverine fish, broadcast spawning (throwing eggs and sperm into the water column and hoping for the best) results in eggs and newly-hatched young, being swept downstream as a matter of course.  But for others, where eggs are laid or attached to the bottom of rivers, newly hatched (and even older) young move up into the current and drift downstream, seemingly deliberately.  We are, however, mostly talking about fish larvae, or fish in the first few weeks of their lives, and often less than 15 mm in length.  Drift largely is a way of dispersing from a location where there is a concentration of young fish all potentially competing for the same resources or potentially wanting to eat you, to locations where this is less likely to happen.

There has been an ongoing debate for many decades about whether river fish do deliberately drift or are swept into currents unwittingly.  There are, of course, current speeds that fish cannot resist, because they are too strong for them to swim against.  Stacey Kopf, a PhD student at Charles Sturt University (CSU), is currently studying aspects of the swimming ability of several species of river fish from the Murray-Darling Basin.  But for riverine fish, flow is what they do, and even the smallest are amazingly adept at getting out of the current if they have to.  But, when they are in the current, do they have control over the distance they drift and where they end up?

Dmitrii Pavlov and colleagues from the Institute of Ecology and Evolution, Russian Academy of Sciences, have studied drifting fish for many years and have come up with a 3-way classification of drifters.  There are ‘passive drifters’, who drift downstream in an un-orientated sort of way and apparently have little control of how they drift and where they end up.  ‘Active drifters’ swim with the current, facing downstream and apparently can influence how far they drift and for how long.  And finally there are ‘active/passive drifters’ that face upstream, and have some control during their time in the drift.  It is a little bit like driving a car down a hill.  Passive drifting is like having no steering: you will career down the hill and be lucky if you don’t crash – you’ll certainly find it hard to get to where you want to go.  Active drifting is like having the engine on, being able to steer and facing down hill: not only can you steer, but you will actually be able to go faster than just coasting and you should make it down OK and get to where you want to go.  Active/passive drifting is like having brakes, being able to steer, but only being able to face uphill.  You can slow yourself down and have some control, but it’s not easy, and will be touch-and-go if you make it down in one piece.

In the vast majority of cases of drifting young fish, we do not know to which group they belong.  But it is important that we understand these things, because with so many of the world’s rivers regulated and dammed, drifting is not what it used to be.  A nice paper by Dudley and Platania (2007) has highlighted the importance of connectivity, and that dams and associated non-flowing areas upstream in normally free-flowing rivers have likely been responsible for the demise of several species of fish that have drifting eggs and larvae.

Studies of drifting fish larvae in Australia are relatively few and far between, but more are being done each year.  My own work, and that of John Koehn and Alison King from the Department of Sustainability and Environment in Melbourne  (DSE) on the larvae of Murray cod and other species, show that for some of our best-known species, drifting is almost certainly a necessary part of their life cycles.  For others, it may be that some individuals do and some don’t.  A recent Honours study at CSU by Tim Kaminskas showed convincingly, that Murray cod larvae ‘choose’ to drift, and that they do so when they get to a certain stage of development.  Tim’s study also showed that most larvae drifted only at night-time, confirming what we have seen in the wild.  A study by Zeb Tonkin and colleagues at the DSE have shown that the distribution of silver perch eggs is not uniform , they drift towards the shore and near the river bottom and they also tend to be more abundant in the drift at night.

In 2008, I collaborated with Hubert Keckeis and Lissie Schludermann, (University of Vienna) as part of Lissie’s PhD study, when we released 40,000 nase larvae (Chondrostoma nasus) into the River Danube, below Vienna, and collected them as they drifted downstream.  We were interested in working out if they just went with the flow or if they could influence when and where they drifted.  Our results showed conclusively that, despite high current speeds, the larvae did not just drift passively, and some took considerably longer to move through the study reach than predicted from hydrological modelling that had been done by Michael Tritthart (BOKU University). We are now following up on that work and, together with colleagues from the BOKU University, have released more larvae at different locations and at different stages of development.  Ultimately, we want to know what processes are involved in the dispersal and survival of young fish from spawning grounds to where they settle and grow.

What is becoming increasingly clear, is that rather than simply acting as passive particles swept where the current takes them, fish larvae have a lot more control over how fast they move, if they move at all, how long they drift for and where they end up.  However, there is much still unknown about the patterns and processes associated with drifting fish in rivers around the world.  The description above only scratches the surface.  What is certain is that we need to know more about this interesting phenomenon if we are to conserve riverine fish species and manage our rivers effectively.

References

Allan, J. D. (1995). Stream ecology: structure and function of running waters, Kluwer Academic Pub. Brittain, J. E. and T. J. Eikeland (1988). “Invertebrate drift—a review.” Hydrobiologia 166: 77-93. Dudley, R. K. and S. P. Platania (2007). “Flow regulation and fragmentation imperil pelagic-spawning reiverine fishes.” Ecological Applications 17: 2074-2086. Humphries P and Lake PS (2000) Fish larvae and the management of regulated rivers. Regulated Rivers: Research & Management 16, 421-432. 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. Humphries P and King AJ (2004) Drifting fish larvae in Murray-Darling Basin rivers: composition, spatial and temporal patterns and distance drifted. In ‘Downstream movement of fish in the Murray-Darling Basin. Statement, recommendations and supporting papers from a workshop held in Canberra 3-4 June 2003.’ (Eds M Lintermans and B Phillips) pp. 51-58. Murray-Darling Basin Commission, Canberra, Australia. Hynes, H. B. N. (1970). The Ecology of Running Waters. Toronto, University of Toronot Press. Koehn JD and Harrington DJ (2005) Collection and distribution of the early life stages of the Murray cod (Maccullochella peelii peelii) in a regulated river. Australian Journal of Zoology 53, 137-144. Pavlov, D. S., V. N. Mikheev, et al. (2008). “Ecological and behavioural influences on juvenile fish migrations in regulated rivers: A review of experimental and field studies.” Hydrobiologia 609: 125-138.Tonkin Z, King A, Mahoney J and Morrongiello J (2007) Diel and spatial drifting patterns of silver perch Bidyanus bidyanus eggs in an Australian lowland river. Journal of Fish Biology 70, 313-317.

1. to make the research or management we do in streams spatially explicit, because of the loss of information, lack of interpretability and inability to find explanations and make predictions if this is not done (divorcing fish from their habitat template or context is nonsensical but commonplace in stream fish research);

2. we must marry scales at which research and conservation are carried out, both spatially and temporally (in other words, if fish, during a year or during its life, moves hundreds of kilometres, what good is it sampling and monitoring at the reach scale?); and

3. we need to reconcile the hierarchical nature of streams (viz. the HFSHC and the PDC) with the continuous downstream flow or materials and energy (viz. the RCC) and the upstream and downstream linkages that clearly occur via fish movement.

These were – and still are – really tough challenges.

One recent, ambitious attempt to synthesize concepts associated with river function, has been the riverine ecosystem synthesis (RES) of Jim Thorp, Martin Thoms and Mike Delong (2006; 2008). The RES is proposed as merging of eco-geomorphology with a landscape model of hierarchical patch dynamics (Thorp et al. 2006; Thorp et al. 2008). But it does not see the river as a continuum, despite considering the river ecosystem in its entirety. Instead the RES conceptualises rivers as “downstream arrays of large hydrogeomorphic patches (e.g. constricted, braided and floodplain channel areas) formed by catchment geomorphology and climate”. These patches are equivalent to the ‘functional process zones’ mentioned in the previous post and analogous to the ‘process domains’ of Montgomery (1999). The 14 tenets or hypotheses proposed by the RES relate to:

• the distribution of species and species diversity and the factors that influence these; • community (or assemblage) regulation;

• ecosystem and riverscape processes (such as autochthonous and allochthonous production, nutrient spiralling and life history), all largely governed by climate;

• flow and geomorphology.

It is, in effect, a merging of the RCC, FPC, RPM and the various concepts dealing with geomorphic process zone/domains within a nested hierarchical framework. The weakness and strength of the RES are related. As a synthesis, the RES is somewhat lacking for the very fact that it needs to be encapsulated in 14 tenets. The RES seems to involve a high degree of complexity and detail, rather than simplicity and elegance, which would be the ideal outcome. On the other hand, it proposes a one-stop-shop for hypotheses that can be tested and so provides wonderful opportunities for research for decades to come. As for fish in particular, the RES does not say much more than has already been discussed in the individual models above. Its attraction is that the RES brings together aspects of assemblage composition, diversity, feeding and life history of riverine fishes in one conceptual location.

Despite the comprehensiveness of the RES, there is still great potential to find a river ecosystem model that is both simple and elegant. Einstein was convinced, like many physicists and mathematicians, that simplicity, elegance and beauty should in many ways guide our search for fundamental concepts that describe the natural world, or perhaps should be our goal. The premise being that where these are found, truth is most likely to be. I tend to share this view in regard to river functioning. My intuition is that, despite the complexity of river ecosystems, there is a simple, elegant, beautiful truth out there. Perhaps you will find it.

References

Fausch KD, Torgersen CE, Baxter CV and Li HW (2002) Landscapes to riverscapes: Bridging the gap between research and conservation of stream fishes. BioScience 52, 483-498. Montgomery DR (1999) Process domains and the River Continuum. Journal of the American Water Resources Association 35, 397-410. Schlosser IJ (1991) Stream fish ecology: a landscape perspective. BioScience 41, 704-712. Schlosser IJ (1995a) Critical landscape attributes that influence fish population dynamics in headwater streams. Hydrobiologia 303, 71-81. Schlosser IJ (1995b) Dispersal, boundary processes, and trophic-level interactions in streams adjacent to beaver ponds. Ecology 76, 908-925. Schlosser IJ and Kallemeyn LW (2000) Spatial variation in fish assemblages across a beaver-influenced successional landscape. Ecology 81, 1371-1382. Thorp JH, Thoms MC and Delong MD (2006) The riverine ecosystem synthesis: Biocomplexity in river networks across space and time. River Research and Applications 22, 123-147. Thorp JH, Thoms MC and Delong MD (2008) ‘The Riverine Ecosystem Synthesis.’ Elsevier, London.

This third river function model – the Riverine Productivity Model (RPM) – came about largely because Jim Thorp and Mike Delong, US river biologists, did not believe that the contribution of the edge of large rivers to production, especially in the middle and lower reaches, had been given enough weight. They were also dissatisfied with how the RCC and FPC explained the structure of riverine food webs (Thorp and Delong 1994; Thorp et al. 1998).  The RPM proposed that in some river sections, materials and energy are derived mainly through local production of phytoplankton (algae floating in the water column), benthic algae (algae growing on the bottom of rivers) and other aquatic plants, as well as directly from the riparian zone (the edge of rivers) via leaves and other sources of carbon, small particles or dissolved in the water. Thorp and Delong did not, however, reject the RCC or the FPC completely, suggesting instead that these models might be more or less relevant depending on river type or location within the river. Several studies have indicated that carbon in food webs can indeed be derived instream, as proposed by the RPM, but that it is more relevant for high gradient streams, those reaches downstream of dams and within the dams themselves (Thorp et al. 1998; Thorp and Delong 2002; Hoeinghaus et al. 2007).

The RPM initially lacked explicit reference to fish, apart from mentioning the ultimate source of their carbon.  While not downplaying the significance of this process, the FPC explicitly included a number of processes involving fish. The Low Flow Recruitment Hypothesis (LFRH), proposed in 1999 by me, Alison King and John Koehn, to some extent filled this gap. It extended aspects of the RPM to fish, and considered spawning, recruitment and feeding of the young stages of fish (Humphries et al. 1999). From observations in temperate Australian rivers in regions with a Mediterranean climate, we noted that several species breed during the warm, low-flow periods in the year, and suggested that this is because these periods are more predictable than floods and because the production and concentrations of food for larval fish is greatest at this time. These observations have been supported by several studies in Australia and elsewhere (Humphries et al. 2002; King 2004a, b; Zeug and Winemiller 2008), although some have found that fish breed between the transition from floods to low flows (Elron et al. 2006). The Inshore Retention Concept (IRC), developed by Fritz Schiemer and colleagues in large, European rivers, in many ways analogous to the LFRH, proposed that the duration of retention of water in large rivers allows the development of zooplankton, as well as habitat for the young stages of fish, and is significantly affected by river regulation, channel alteration and disconnection from the floodplain (Schiemer et al. 2001a; Schiemer et al. 2001b; Schiemer et al. 2002).

As the concepts of river functioning developed during the last few decades, parallel ideas relating to geomorphology and habitat have also emerged that have helped to underpin and contextualise patterns and processes associated with riverine biota.  The hierarchical framework for stream habitat classification (HFSHC) set out a template upon which fish (and other organisms) could be placed, classifying streams into segment, reach, pool/riffle and microhabitat subsystems, that has proved extremely useful in applied approaches to monitoring, managing and conserving river fishes (Frissell et al. 1986). The process domains concept (PDC) built on the HFSHC to emphasize the influence of geomorphology on disturbance patterns in rivers, and so ecosystem structure  and function (Montgomery 1999).  It argued that ‘process domains’  are “spatially identifiable areas characterized by distinct suites of geomorphic processes” (Montgomery 1999 p. 397) and are themselves nested within ‘lithotopo’ units: areas that have similar topographies and geologies. It effectively reinvigorated the concept of river zones with discrete functions governed geomorphologically; an idea shied away from by the proponents of the RCC, but also taken up by advocates of ‘functional process zones’ (Thoms et al. 2004). This approach has potential for testing hypotheses relating fish to habitat and in the assessment of river health, especially in large rivers (Walters et al. 2003; Boys and Thoms 2006), but in some ways could be considered somewhat of a backward step if the aim of river ecology is ultimately to unite the whole river system.

But the holy grail of one overarching model that describes how rivers function seemed as distant as ever, with at least three models in existence, none of which could explain all observations in all rivers and rivers sections. There was a crying need for synthesis.  And synthesis is the topic of the next instalment of this brief history of ideas of river function.

References

Boys CA and Thoms MC (2006) A large-scale, hierarchical approach for assessing habitat associations of fish assemblages in large dryland rivers. Hydrobiologia. Elron E, Gasith A and Goren M (2006) Reproductive strategy of a small endemic cyprinid, the Yarqon bleak (Acanthobrama telavivensis), in a mediterranean-type stream. Environmental Biology of Fishes 77, 141-155. Frissell CA, Liss WJ, Warren CE and Hurley MD (1986) A hierarchical framework for stream habitat classification. Environmental Management 10, 199-214. Hoeinghaus DJ, Winemiller KO and Agostinho AA (2007) Landscape-scale hydrologic characteristics differentiate patterns of carbon flow in large-river food webs. Ecosystems 10, 1019-1033. Humphries P, King AJ and Koehn JD (1999) Fish, Flows and Flood Plains: Links between Freshwater Fishes and their Environment in the Murray-Darling River System, Australia. Environmental Biology of Fishes 56, 129-151. Humphries P, Serafini LG and King AJ (2002) River regulation and fish larvae: variation through space and time. Freshwater Biology 47, 1307-1331. King AJ (2004a) Density and distribution of potential prey for larval fish in the main channel of a floodplain river: Pelagic versus epibenthic meiofauna. River Research and Applications 20, 883-897. King AJ (2004b) Ontogenetic patterns of habitat use by fishes within the main channel of an Australian floodplain river. Journal of Fish Biology 65, 1582-1603. Montgomery DR (1999) Process domains and the River Continuum. Journal of the American Water Resources Association 35, 397-410. Schiemer F, Keckeis H and Flore L (2001a) Ecotones and hydrology: Key conditions for fish in large rivers. Ecohydrology and Hydrobiology 1, 49-55. Schiemer F, Keckeis H and Kamler E (2002) The early life history stages of riverine fish: Ecophysiological and environmental bottlenecks. Comparative Biochemistry and Physiology – A Molecular and Integrative Physiology 133, 439-449. Schiemer F, Keckeis H, Reckendorfer W and Winkler G (2001b) The “inshore retention concept” and its significance for large rivers. Archive fur Hydrobiologie, Supplement 135, 509-516. Thoms MC, Hill SM, Spry MJ, Chen XY, Mount TJ and Sheldon F (2004) The Geomorphology of the Barwon–Darling Basin. In ‘The Darling.’ (Eds R Breckwodt, R Boden and J Andrew) pp. 68-103. Murray-Darling Basin Commission, Canberra. Thorp JH and Delong MD (1994) The riverine productivity model: an heuristic view of carbon sources and organic processing in large river ecosystems. OIKOS 70, 305-308. Thorp JH and Delong MD (2002) Dominance of autochthonous autotrophic carbon in food webs of heterotrophic rivers. Oikos 96, 543-550. Thorp JH, Delong MD, Greenwood KS and Casper AF (1998) Isotopic analysis of three food web theories in constricted and floodplain regions of a large river. Oecologia 117, 551-563. Walters DM, Leigh DS, Freeman MC, Freeman BJ and Pringle CM (2003) Geomorphology and fish assemblages in a Piedmont river basin, U.S.A. Freshwater Biology 48, 1950-1970. Zeug SC and Winemiller KO (2008) Relationships between hydrology, spatial heterogeneity, and fish recruitment dynamics in a temperate flooodplain river. River Research and Applications 24, 90-102.

The serial discontinuity concept (SDC), proposed by James Ward and Jack Stanford (Ward and Stanford 1983), took the idea of the river continuum and asked what would happen to the patterns and processes, as described in the RCC, if an instream dam or weir (those actually in the river channel, blocking the flow) was placed somewhere in the system. It contends that dams disconnect sections of the river upstream and downstream and displace resource gradients downstream to varying extents. In effect, the dam shifts everything downstream. The SDC does not say much about fish, but does make predictions about the nature of energy and materials that can be translated to fish relatively easily. This concept has been widely cited, but hypotheses coming from it, not well tested, which is somewhat surprising, given how common dams are in rivers. There is, however, general agreement that large instream dams (those actually in the river channel, blocking the flow) do have an influence on longitudinal patterns in fish assemblages. For example, Arajo et al. (2009) found that fish assemblages were affected more by damming and less by season in a large tropical Brazilian river; An and Choi (2003) recorded major changes in fish guild structure following the construction of a dam during a long-term study in Korea; and Reyjol et al. (2001) showed that in unregulated sections of a river in France, temperature determined the transition from the salmonid-dominated region to the cyprinid-dominated region, but that this changed with regulation and the presence of dams. So, the SDC certainly has merit but doesn’t seem to excite people as much as perhaps it should.

The next big idea was the flood pulse concept (FPC), proposed in 1989 by Wolfgang Junk, Peter Bayley and Richard Sparks, working in German and US rivers. It arose from a dissatisfaction with the RCC, based on observations largely derived from tropical floodplain rivers (Junk et al. 1989; Junk and Bayley 2008), although it has been more recently extended to temperate systems (Tockner et al. 2000) and to lakes (Wantzen et al. 2008) as well. The FPC emphasizes the floodplain as an important source of material and energy, inundation of the floodplain by a flood pulse as the catalyst for mobilising that material and energy; and movement of that material and energy from the floodplain into the main channel as the process that fuels food webs in floodplain rivers. The emphasis, therefore, is more on lateral connectivity than a longitudinal continuum. The flood pulse is termed a ‘batch process’, rather than a continuous process – occurring in discrete time periods. The FPC was the first real river model to put up front the significance of a conceptual framework for fish. It emphasized the importance of the floodplain for fish breeding and as a nursery habitat, while also relating fish production in the main channel to nutrients draining back from the floodplain as the flood receded. The main channel, according to the FPC was used only temporarily for migration, spawning, refuge during droughts or freezing and for hibernation. Many examples exist of fish whose life histories or peaks in feeding coincide with predictable flood pulses (e.g. Goulding 1980), Welcomme 1985). Indeed, the timing and duration of flooding has been shown to influence population dynamics (Finger and Stewart 1987; Stassen et al. 2009), growth of species associated with the aquatic/terrestrial transition zone (Gutreuter et al. 1999; Glemet and Rodriguez 2007) and/or production of young (Feyrer et al. 2006; Tonkin et al. 2008; King et al. 2009) in some species of riverine fish. For flatter, low-gradient rivers, it appears that the FPC can predict the source of carbon in food webs (Hoeinghaus et al. 2007).

The flood recruitment model (FRM) developed by John Harris and Peter Gehrke ( NSW Fisheries) for Australian systems, developed the FPC as it related to the recruitment of fish in Australia’s Murray-Darling Basin, arguing that flooding cued some species to spawn and perhaps use the floodplain, whereas others benefited through production of zooplankton derived from the floodplain, but which is washed into the main river channel (Harris and Gehrke 1994). Benefits derived from the flood pulse may be less obvious for some fishes, however. For example, species that normally living on floodplains or only occupying the edges of large rivers may be able to move among floodplain habitats during flooding, contributing to their reproductive success or overall survival (Tonkin et al. 2008). It is apparent, however, that the coupling of temperature and flooding are critical for floodplain use, which is often not the case in temperate systems (King et al. 2003).

These concerns about the coupling or otherwise of the key factors that influence use of the floodplain by fish, especially for breeding purposes, made some scientists question the generality of the FPC and FRM for some river systems. The development of other ideas, especially those related to production within the main channel of rivers, will be the focus of Part 3 of this history of river ecosystem ideas.

References

An KG and Choi SS (2003) An assessment of aquatic ecosystem health in a temperate watershed using the index of biological integrity. Journal of Environmental Science and Health – Part A Toxic/Hazardous Substances and Environmental Engineering 38, 1115-1130. Araújo FG, Pinto BCT and Teixeira TP (2009) Longitudinal patterns of fish assemblages in a large tropical river in southeastern Brazil: Evaluating environmental influences and some concepts in river ecology. Hydrobiologia 618, 89-107. Feyrer F, Sommer T and Harrell W (2006) Managing floodplain inundation for native fish: Production dynamics of age-0 splittail (Pogonichthys macrolepidotus) in California’s Yolo Bypass. Hydrobiologia 573, 213-226. Finger TR and Stewart EM (1987) Response of fishes to flooding regime in lowland hardwood wetlands. In ‘Community and evolutionary ecology of North American stream fishes.’ (Eds WJ Matthews and DC Heins) pp. 86-92. University of Oklahoma Press, Norman. Glemet H and Rodriguez MA (2007) Short-term growth (RNA/DNA ratio) of yellow perch (Perca flavescens) in relation to environmental influences and spatio-temporal variation in a shallow fluvial lake. Canadian Journal of Fisheries and Aquatic Sciences 64, 1646-1655. Goulding M (1980) ‘The fishes and the forest. Explorations in Amazonian natural history.’ University of California Press, Berkeley. Gutreuter S, Bartels AD, Irons K and Sandheinrich MB (1999) Evaluation of the flood-pulse concept based on statistical models of growth of selected fishes of the Upper Mississippi River system. Canadian Journal of Fisheries and Aquatic Sciences 56, 2282-2291. Harris JH and Gehrke PC (1994) Development of predictive models linking fish population recruitment with streamflow. Proceedings of the Australian Society for Fish Biology Workshop. In ‘Population Dynamics for Fisheries Management.’ Ed. DA Hancock) pp. 195-199. Bureau of Rural Resources Proceedings, Canberra. Hoeinghaus DJ, Winemiller KO and Agostinho AA (2007) Landscape-scale hydrologic characteristics differentiate patterns of carbon flow in large-river food webs. Ecosystems 10, 1019-1033. Junk WJ and Bayley PB (2008) The scope of the flood pulse concept regarding riverine fish and fisheries, given geographic and man-made differences among systems. In ‘Reconciling Fisheries with Conservation, Vols I and Ii. Vol. 49.’ (Eds J Nielsen, JJ Dodson, K Friedland, TR Hamon, J Musick and E Verspoor) pp. 1907-1923. Junk WJ, Bayley PB and R.E. S (1989) The flood pulse concept in river-floodplain systems. Can. Spec. Publ. Fish. Aquat. Sci. 106, 110-127. King AJ, Humphries P and Lake PS (2003) Fish recruitment on floodplains: The roles of patterns of flooding and life history characteristics. Canadian Journal of Fisheries and Aquatic Sciences 60, 773-786. King AJ, Tonkin Z and Mahoney J (2009) Environmental flow enhances native fish spawning and recruitment in the Murray River, Australia. River Research and Applications 25, 1205-1218. Reyjol Y, Lim P, Dauba F, Baran P and Belaud A (2001) Role of temperature and flow regulation on the Salmoniform-Cypriniform transition. Archiv fur Hydrobiologie 152, 567-582. Stassen MJM, van de Ven MWPM, van der Heide T, Hiza MAG, van Der Velde G and Smolders AJP (2009) Population dynamics of the migratory fish Prochilodus lineatus in a neotropical river: The relationships with river discharge, flood pulse, El Nino and fluvial megafan behaviour. Neotropical Ichthyology 8, 113-122. Tockner K, Malard F and Ward JV (2000) An extension of the flood pulse concept. Hydrological Processes 14, 2861-2883. Tonkin Z, King AJ and Mahoney J (2008) Effects of flooding on recruitment and dispersal of the Southern Pygmy Perch (Nannoperca australis) at a Murray River floodplain wetland. Ecological Management and Restoration 9, 196-201. Wantzen KM, Junk WJ and Rothhaupt KO (2008) An extension of the floodpulse concept (FPC) for lakes. Hydrobiologia 613, 151-170. Ward JV and Stanford JA (1983) The serial discontinuity concept of lotic ecosystems. Dynamics of lotic ecosystems (book) ed: T.D. Fontane & S.M.Bartell, 29-42.

River ecology is a relatively young science. Until about 1970, rivers and streams were thought of as being a series of zones, largely defined by the dominant fish that lived in them.  In western Europe, there were thought to be four zones – the trout (Salmo), grayling (Thymallus), barbell (Barbus) and bream (Abramis) zones – and these moved successively downstream from the headwaters. In North America, Victor Shelford also proposed that particular fish species occurred in zones near Lake Michigan  and others, like Shelby Gerking in Indiana, had similar ideas. Scientists in other countries described patterns of zonation in river fishes, although they were, of course, specific to each region, which meant that generalisations were a little difficult. The zones typically included other co-occurring fish species, besides the dominant group, and were able to be predicted from stream width, slope and valley shape.

There was some argument in North America over whether fish were ‘replaced’ or ‘added’ as the river progressed downstream.  And in tropical systems, it was argued that fish species were added rather than replaced, unless a waterfall or other barrier to movement occurred.  Other species-based zones were also devised, based on leeches, amphipods (small crustaceans called ‘scuds’), crayfish, mayflies, stoneflies, and many other insect groups. The ‘fish-zone’ classification is still with us today to some extent in some parts of Europe, despite the fact that a review of many European studies concluded that there was little empirical support for discrete fish zones after all.

Illies (cited in Hynes 1970) noted that there were places along the river where assemblages of invertebrate species seemed to dramatically shift to other assemblages, and that these were reasonably well aligned with the fish-based zones. He proposed that these zones had ecological meaning and coined the terms rhithron (upstream, cool, high oxygen concentration, fast and turbulent flow, substratum of rock, stone or gravel, the fauna having narrow temperature tolerances and little plankton) and potamon (more downstream, warmer, oxygen concentration lower at times, flow slower, substratum mostly sand and mud, fauna having broader temperature tolerances and abundant plankton). There were other developments and refinements in terminology which helped to define various types of streams, from springs through to large, floodplain rivers.  I will talk about this terminology in a future post, because it is often a source of confusion for students, River ecologists – like all scientists – love jargon.

River scientists began, after a time, to question the ‘river-zone concept’, recognising its limitations; mainly because, while zones are by definition discrete, they don’t reflect the continuous nature of the movement of water, materials and energy in rivers. This dissatisfaction motivated an attempt to unite the various non-living (abiotic) and living (biotic) components and processes that make up river ecosystems into a continuous, interconnected whole. The River Continuum Concept (RCC) was the first such model, although it had some important precursors, and was to become a hugely influential (and cited) paper by Vannote, Minshall, Cummins, Sedell and Cushing in 1980. Robin Vannote and colleagues, working in North America, emphasized the upstream/downstream linkages and continuous gradients in rivers. They wanted to combine fundamental non-biological factors, like geomorphology (the physical structure of rivers and streams) and hydrology (the flow regime), with biological processes, like feeding and breeding. Their concept stressed the fact that streams – or at least the ones that Vannote and colleagues studied – had much of their organic matter (leaves, sticks, bark and plants) entering at the headwaters and that this organic matter was progressively processed as the river moved downstream, mostly by insects adapted to take advantage of increasingly smaller particles. Shredding and collecting insects dominated upstream, then grazing insects turned up in mid-reaches and were in turn replaced by collectors and zooplankton in the lower reaches.

The RCC says little about very large rivers or about fish and how they fit into the riverine continuum, besides that fish diversity increases as one moves downstream.  Many studies have investigated the RCC in relation to stream fishes, however, often asking if fish assemblage composition changes continuously or in jumps (like the  ‘fish-zone’ concept) from upstream to downstream. Some have found a continuum, whereas others have not. It has been suggested that for many river systems, factors other than the longitudinal transport and processing of organic matter have significant influences on fish assemblage composition. These include habitat diversity, salinity and the duration of the wet season and flooding in tropical regions. Matthews (1998) tested the zone vs. continuum dichotomy for the Strawberry-White River in Akansas and found that there was a “distinct upland region” in which species showed upstream and downstream limits, but that there were no other identifiably distinct zones and that in the lower regions of the river fish had broad distributions and tolerances.

In part 2 of this brief history of ideas related to river ecosystem function, I will describe later developments: some extending the RCC to rivers which have been regulated by dams, and others which found the RCC inadequate for describing what they saw in floodplain rivers, where sources of organic matter were quite different from the sorts of rivers studied by Vannote and colleagues.

General references:

Hynes HBN (1970) ‘The Ecology of Running Waters.’ University of Toronot Press, Toronto.

Matthews WJ (1998) ‘Patterns in Freshwater Fish Ecology.’ Kluwer Academic Publishers, Norewll, Massachusetts.

Welcomme RL (1985) ‘ River Fisheries.’ FAO, Rome.

Fish zone references:

Gerking SD (1945) The distribution of the fishes of Indiana. Investigations of Indiana Lakes and Streams 3, 1-137.

Huet M (1959) Profiles and biology of Western European streams as related to fish management. Transactions of the American Fisheries Society 88, 155-163.

Shelford VE (1911) Ecological Succession. I. Stream Fishes and the Method of Physiographic Analysis. Biological Bulletin 21, 9-35.

River Continuum Concept and some examples of tests of it:

Aarts BGW, Van Den Brink FWB and Nienhuis PH (2004) Habitat loss as the main cause of the slow recovery of fish faunas of regulated large rivers in Europe: The transversal floodplain gradient. River Research and Applications 20, 3-23.

Blachuta J and Witkoswki A (1990) The longitudinal changes of fish community, in the Nysa Klodzka River (Sudety Mountains) in relation to stream order. Polskie Archiwum Hydrobiologii 37, 325-342.

Dauwalter DC, Splinter DK, Fisher WL and Marston RA (2008) Biogeography, ecoregions, and geomorphology affect fish species composition in streams of eastern Oklahoma, USA. Environmental Biology of Fishes 82, 237-249.

Dettmers JM, Wahl DH, Soluk DA and Gutreuter S (2001) Life in the fast lane: Fish and foodweb structure in the main channel of large rivers. Journal of the North American Benthological Society 20, 255-265.

Mazzoni R, Fenerich-Verani N, Caramaschi ÃP and Iglesias-Rios R (2006) Stream-dwelling fish communities from an Atlantic rain forest drainage. Brazilian Archives of Biology and Technology 49, 249-256.

McNeely DL (1986) Longitudinal patterns in the fish assemblages of an Ozark stream. Southwestern Naturalist 31, 375-380.

Oberdorff T, Guilbert E and Lucchetta JC (1993) Patterns of fish species richness in the Seine River basin, France. Hydrobiologia 259, 157-167.

Vannote RL, Minshall GW, Cummins KW, Sedell JR and Cushing CE (1980) The river continuum concept. Canadian Journal of Fisheries and Aquatic Sciences 37, 130-137.

Walters DM, Leigh DS, Freeman MC, Freeman BJ and Pringle CM (2003) Geomorphology and fish assemblages in a Piedmont river basin, U.S.A. Freshwater Biology 48, 1950-1970.

I aim to present scientifically-based material for those interested in how river ecosystems function, the roles of animals and plants in food webs, ecology-flow relationships of these organisms and much more.

The site and blogs aim to be useful to students – mainly at the undergraduate and post-graduate level, conservation and managers.  But there will also be useful links for high school students as well.

I would be pleased to get suggestions about what content might be useful as I continue to construct this site.  Kind regards, Paul Humphries