Australian freshwater fishes have a tough time of it. The thing they most need – water – is regularly in short supply and a lot of people want it. In order to get water, humans have changed the way our inland rivers run beyond measure, and a lot of the things they’ve done have hurt fishes: it’s thought that populations of most species have declined by more than 90% since the 19th century.
Cosmos spoke to John Koehn, principal research scientist in applied aquatic ecology at the Arthur Rylah Institute for Environmental Research, Melbourne, about the just-released Compendium of ecological knowledge for restoration of freshwater fishes in Australia’s Murray–Darling Basin, of which he was lead author.
How long have you been studying freshwater fishes? What got you started?
I’m just about to clock up 40 years as a professional fisheries scientist. Really, I got started as a six year old. I grew up on the Murray River, near Wodonga, and started fishing with my father, mainly catching introduced redfin (Perca fluvialitis). I was always interested in the outdoors and rivers and fish, but particularly the native fish that didn’t seem to exist anymore. So I followed a science career, with a major in biology , then into research on freshwater fishes. When I look at most of my colleagues, like me many of them started off fishing inland rivers.
The compendium drew on 600 publications and more than 25 expert workshops. What period does the source material cover, and how long did it take to work through?
The aim of this work was to support fish populations in the Murray Darling Basin (MDB). The Murray Darling Basin Plan aims to allocate more water to the environment, to the whole river system and to fishes to try to aid population recovery. The questions are things such as: How much water? When do you need it? How can you best apply it to get the best outcomes? So a project was initiated to develop population models to be able to predict those things, and the basis of those models is the very best contemporary, up to date, science on the species’ biology.
We went through everything everyone has ever published – like, forever. About 80% of the scientific papers and reports we looked at, however, had been produced in the last 20 years. So that’s a great basis for the science behind the management decisions. But in order to get an expert assessment, or reality check if you like, we also got experts on each species, and particular regions of the MDB, together with some catchment managers. The managers know what they need, and what questions need to be asked. It was a crazy amount of work, really. But now people can now go to one peer-reviewed publication and get a summary of that information. It wasn’t a continuous workload, but it took us probably five years to pull all this together.
In what areas do we lack knowledge about freshwater fishes? Why?
That’s one of the interesting things we did. We looked at the existing knowledge and then tried to assess where we’re at in terms of being able to make decisions about recovering these populations. It’s estimated that fish populations across the MDB over the past 150 or so years have declined by more than 90%. So, we tried to assess whether we’ve got enough information to actually make sensible management decisions about water and other actions that we need for population recovery. Overall, the knowledge base is good – as I said, a lot of these publications are fairly recent, and we’re building on that quite nicely – but there are gaps.
It’s really the small species that miss out. There’s quite a lot of knowledge about the big, popular angling species like Murray cod (Maccullochella peelii) and golden perch (Macquaria ambigua), but the smaller, unknown species have been much less studied. Also early life stages, which are obviously a bit more difficult and maybe not as sexy to work on, lack study. We need to know more about what happens to eggs and larvae; and then as larvae grow up through the stage we call young-of-year fish, and then beyond that, until they mature. These are really the areas that still need more work. A lot of it is tied to the priorities of managers, which in turn are sometimes tied to the priorities of the general public.
Everyone knows Murray cod. I’ve worked on Murray cod, it’s my favourite fish species. But there’s a lot of other species that need some money spent on them, and people to dedicate their time and work on them.
Is the issue of water and water availability the main issue for freshwater fish in our inland river systems?
Yes, but there are a lot of related things. Freshwater fishes are some of the most threatened vertebrate taxa in the world. They’re sitting in rivers that are subject to whatever happens in their catchments, and also to whatever happens upstream and downstream in their river system. So there’s a range of threats, but most of those threats relate to water extraction, and the associated infrastructure.
We assessed those threats, and water usage was a big part. The amount of water, how it flows, the seasonality of that flow, whether or not it gets out and floods floodplains, and whether or not it provides the cues for spawning and movements are all things needed to get fish to grow through to adults. Cues for movement, so fish can recolonise if a population blinks out. And also all the ecosystem processes: the amount of carbon that goes in; the amount of productivity in the water, and then the number of small invertebrates that become fish food. All those things are supported by water, so it’s the most important thing to fish. It’s really about trying to restore some of the flow components.
There are some big restoration projects in rivers worldwide and to see Australia taking some steps towards this is a great initiative. As well as water, there are a range of other enabling activities that can be undertaken. So there’s been reinstatement of woody habitat in rivers that’s proven to be successful and increase populations. The installation of fishways to allow fish to get over some of the barriers – most of the weirs along the Murray River, for example, have active fishways now, and so fish are able to complete their life cycles.
The compendium identifies nine priority species – can you tell us a bit about some of them, and why they were chosen?
Murray cod is number one, and that’s for a very good reason – to grab people’s attention. Murray cod are the largest freshwater fish species that we have. We still regularly see fish of 40–50 kilos, well over a metre long. They’re still there in our river systems today, living to nearly 50 years of age. They’re a large, long-lived species and really part of Australia megafauna. Then we go to golden perch and other angling species such as silver perch, and then down to some of the smaller, lesser-known species. The nine species – we couldn’t do all 49 species in the basin, we had our work cut out just doing these nine – were the ones that were defined as priorities by the catchment and water managers.
In some ways that reflects what the community want as well. They were also chosen to cover a range of life cycles. So we’ve got some that are purely river specialists, like the Murray cod and golden perch, and we’ve got some like Murray hardyhead that are wetland specialists. And then we’ve got catfish that are sort of in between – they’ll use both these habitats. So we’re trying to cover big and small, fast and slow, river and wetland and other things in amongst this. I think that provides us with a very good basis to actually meet the needs of some of those species, and if we meet their needs we’ll likely meet the needs of some other species as well.
One of the species on the list is the olive perchlet, a fish a few centimetres long that inhabits wetlands. It has population explosions, then comes back to wetlands, then gets flooded and gets distributed out again. It’s received very little study. When we assessed our knowledge of all these species, it was the small species like the olive perchlet that came up with red flags all over the place, simply because they’re hard to study and no-one’s spent the time on them.
If we go beyond the nine species, one of the obvious questions is: how many fish are there in the MDB? You’d think you’d be able to pick out a definitive number, but that’s not the case because they’re still describing new species. Some colleagues of mine have recently described several new species, particularly the smaller taxa. Some of these have only been described in the last couple of years, and there are some that are still some that will be in the scientific literature in the next year or so.
What’s your biggest concern about the long-term survival of Australian native freshwater fishes?
Early last year there was an IUCN workshop at which we assessed every freshwater fish in the country. When you look at MDB fishes, almost half – 47% – of the species have some conservation concern. That’s quite startling. Add that to the fact that overall, there’s probably been a more than 90% drop in native fish populations. We already have one species – the Yarra pygmy perch (Nannoperca obscura) – that appears to have disappeared from the MDB but is still found in some coastal streams in Victoria.
A bigger concern is that we have what we thought were quite widespread and abundant species like silver perch in decline. Particularly in the northern basin, there’s concern that people are just not seeing many of them at all. We get all the silver perch experts together and they say, “When we go out and do surveys, we hardly ever see them now days. So we can’t tell you what’s going on.” So there’s been massive declines. We know what those declines are, and we know roughly how to try and fix those declines. But when you look at the attention they get, in terms of all threatened species, freshwater fish tend to be overlooked, and we need to change that perception. They need to be held up there at least as equals with terrestrial animals. There’s a lot of fishes that are far, far more threatened than many of the terrestrial species that receive funding.
Are the threats to Australian native freshwater fishes being mirrored throughout the world?
Yes; they’re very common, and a lot of those threats have been known for a long time. I’ve worked with a lot of international colleagues, and we have slightly different priorities. In semi-arid regions such as the MDB, water and water extraction and water usage have greater priority, whereas somewhere like Alaska water extraction isn’t really a problem, there are other issues.
It boils down to a relatively small number of threats though. You know good habitat is needed. We’ve discussed water, pretty much. We’ve said that barriers to fish moving up and down rivers are a threat – sometimes fish get injured or worse going through hydro schemes or coming over large dams. Even small weirs can be a problem, causing quite a high mortality if small larvae pass over them. Then there are interactions with alien species; this brings in predation, competition, disease and habitat destruction – carp go into wetlands and destroy a lot of the soft-stemmed aquatic plants that are habitat for many of our small native species.
These are fairly common threats throughout the world, along with removal by fisheries. We had a lot of removal through the commercial Murray cod fishery in the past. Those fisheries no longer exist in Australia, but in many other parts of the world, there’s quite large, freshwater subsistence fisheries, where people are catching for their own table. That’s another difference between Australia and, say, the Mekong River in south-east Asia or freshwater lakes in Africa.