Stocking trout into streams is seen by many recreational anglers as somewhat of a panacea to the the poor trout fishing we had in Victoria last season. As I touched on in this post, last trout season was seen by many as a disaster. One of the things that the DEPI will once again will be trialling, as part of a larger research project into the poor trout fishing in Victoria, is stocking creeks and rivers. While research into fisheries is something I think we need a lot more of, when it comes to trout stockings in rivers and streams, there is a problem; its not likely to work. When you have viable wild populations of trout, trout stockings are often ineffective and can be downright bad. At best they tend to make absolutely no difference and at worst they can actually deplete fish stocks. Why you ask? Well wild trout, are good at what they do. Local adaptation is likely to mean they are going to do a far better job of surviving, finding food and breeding than their stocked brethren. For example, even when stockings have occurred for a long time in places that already sustain wild trout populations, surprisingly little “domesticated” trout DNA enters wild populations. This suggests the fish that are already there are surviving and breeding and that most the stocked trout invariably fail to achieve that. Problems can also arise because stocked fish aren’t neutral. They can actually have a negative impact on wild trout. Putting in a bunch of poorly adapted intruders can upset the social structure of a trout stream, leading to chaos and less trout, stocked and wild overall.
The most famous study from rivers in Monatana in the 1960s and 70s showed just how harmful stocking trout into rivers with populations of wild self sustaining trout can be. In this case, the rivers in Montana were stocked with 5-10 inch fish. The problem was that the stocked fish weren’t surviving all that long, but while they were there, they were chasing the wild fish out of the prime lies and generally causing complete social disorder. The result, less fish, far less fish in fact.When stocking was ceased, fish populations more than tripled in some cases (the biomass of rainbow trout four years after the cessation of stocking increased and incredible 1,016%! in one river). The results showed that stocking catchable sized fish in rivers not only failed to achieve the aim of increasing fish stocks, it in fact made things a hell of a lot worse.
Australia has done similar studies, which have shown similar results. Work done in Victoria during the 70s, 80s and 90s showed that the returns on stocking rivers were invariably poor, leading to the practice being more or less abandoned in the state, at least in rivers that had self-recruiting populations of trout. Studies on the Esk river in Tasmania as far back as the 1950s show the same thing, very poor returns from trout stockings. Together, both the international and local studies show quite clearly that at the very least stocking streams with wild self sustaining trout populations is a best a colossal waster of money and at worst can do considerable harm to overall fish stocks.
The truth of the matter is that fisheries scientists around the globe agree that stocking rivers and streams with wild naturally recruiting trout just doesn’t work all that well. So while it seems logical and like it “should” work, the science clearly shows otherwise. Due to the poor trout season Victoria had last year, once again rivers will be stocked in Victoria. The DEPI will be running a new set of stocking trials over the next three years. Don’t hold your breathe over the results though, the answers are likely to be very similar to results of the many previous studies done in the past. So while stockings are the only way to maintain the wonderful lake fishing we have in Victoria, they are highly unlikely to be the answer to the poor stream fishing that was had last season. If things go badly, they could even potentially make things worse. There are a handful of exceptions to this. Rivers like the Hopkins and Merri are still stocked and produce good returns. The reason for this is that in these particular rivers, there is a low or non-existent self sustaining population of trout. They are more akin to flowing lakes in that regard and in those cases, stocking do work.
So whats the answer? Well, the research being done by the DEPI will likely inform us on that, so for more definitive answers we will likely have to wait three years. The likely answer, where its applicable is stream rehabilitation and habitat improvement. Improving habitat is one thing that has been shown to work wonders when done right. So while stocking trout isn’t likely to work, improving habitat might. In the US remarkable booms in trout stocks have been seen simply by rehabilitating streams. As long as trout are still in the river and still recruiting, focusing on habitat and letting the fish work out the rest is the best way forward. In degraded rivers, rehabilitation boosts the carrying capacity of rivers, which put simply means those streams can sustain more trout (fish), thus vastly improving the fishing opportunities. That may not solve the problem though. One of the leading culprits for last seasons poor trout fishing in Victoria were high stream temperatures. The rivers studied were all streams with good/excellent habitat, stream rehabilitation isn’t going to do much in those cases. So while stream rehabilitation might be able to mitigate high stream temperatures in some cases by providing increased stream cover and shade in places it has been removed, for many of the affected rivers there may not be much that can be done. That is the likely culprit is climate change. The negative effects of climate change on trout in South East streams appear to be two fold, we appear to be seeing lower rainfall as well as increased temperatures. While we may once again have some good years, over the long term, the trends don’t bode well for trout in streams that already experience marginal temperatures. The truth is that with climate change looming large in the future, in the medium to long term, many sections of river that once held trout may not in the future, they will simply start to get too hot too often. Trout are cold water fish and once that cold water disappears, the trout will disappear with it.
If that is the case (and the current climate models suggest that it will be), the best way forward in some marginal trout rivers may be to restore populations of upland natives in habitat that becomes unsuitable for trout due to higher water temperatures. Trout cod and Macquarie perch (even Murray cod) once existed way up into the catchments of many popular trout rivers such as the King, Ovens, Goulburn, Delatite, King parrot creek and many others. Very few population of those fish hold on, almost none in the upper catchments where they once thrived. So while small populations exist in some places, the population of Murray cod in the Delatite above Lake Eildon, the Macquarie perch populations in the Murrindindi river and King parrot creeks for example, in general our native fish have suffered huge declines in abundance and distribution. The declines of those species were multi-faceted, numerous causes playing a role, such as, over-fishing, habitat degradation (siltation etc) and competition with introduced species (e.g. trout).
However, restoring populations of these fish is by no means outside our grasp . With the prospect of climate change making many once good trout regions/rivers poor trout fisheries in the medium term, as anglers, it is hight time that we start looking for a solution beyond trout in the lower sections of those rivers, we need to start thinking about the fisheries we want if climate change pushes trout out. To do that successfully, just like the current situation with trout, we need more research into how we might achieve that. Strong support from anglers for research into improving fisheries is going to be a big part of maintaining/improving our upland fisheries, be they trout or native fisheries. I personally believe our own native fish might provide the answer if climate change does push trout out of many streams and rivers and may be able to “save” future fishing opportunities in many much loved rivers and streams. With slightly higher temperature tolerances our native fish will be able to survive conditions like the ones many low catchment trout streams experienced last season. For the long term future of our fishing options in some of those sections of river, its high time we start to figure out how to restore populations of upland natives.
The are numerous benefits for us as anglers if populations of upland natives are restored in some areas (the success of trout cod stockings in the Ovens shows the potential upland natives fisheries have). Firstly, if stockings are successful they will provide a wonderful fishing resource to us as anglers, and start to restore a resource that was lost to us as anglers more than a generation ago when populations of Macquarie perch and trout cod suffered large declines. They will also provide a greater variety of potential targets in upland environments and will give anglers viable options in rivers where temperatures rise to the heights they did last season on a more regular basis. There are of course also the environmental benefits of restoring populations of native fish, which has value in and of itself outside our desires as anglers. Trout will always be here in Australia, as trout fishermen (of which I am one) we will always be able to target them, but we do need to start thinking about a world where their distribution is Australia is restricted due to changing climatic conditions and what we wan’t replacing them in areas where streams begin to get too hot for trout.
Far too often, the management of fisheries is reactive rather than proactive, only happening once populations collapse. If we want strong upland fisheries, that is something that needs to change, we need to start thinking further ahead. The research by the DEPI into trout is a start, but I think that needs to be expanded in scope in the future, including thinking about other angling options in those waterways if conditions continue to deteriorate for trout into the future. The trout study should only be the beginning of the discussion of how best to maintain vibrant fisheries in our upland rivers and streams. While its easy for this debate to be de-railed by trout vs natives arguments, as anglers we all ultimately want the same thing, vibrant fisheries in our favourite rivers. What matters in my eyes is how we can best to achieve that, how we can improve fishing in upland environments, how we can improve the diversity of angling targets in those environments. I strongly believe that upland natives should be a strong part of that given the potential effects of climate change on trout distributions in Australia. Not only that though, our upland natives are truly unique fish unavailable to anglers anywhere else in the world, selfishly I would love to be able to target them. In the long term it may not even be trout vs natives anyway, but natives vs carp and redfin in many waterways. And if the climate does become more trout friendly, rest assured that trout populations will quickly rebound and re-colonise the areas they have disappeared from. While stockings aren’t likely to help much, if conditions are favourable, trout can breed and re-colonise new areas surprisingly quickly. You only have to look at how quickly they rebounded after the drought of the 2000s or the Victorian bushfires.
While talk about upland natives fisheries may seem like a very long term goal, to me that highlights its importance. Natives are long lived, it will take years to establish viable fisheries. Thats why I think we need to start working towards that sooner rather than later, thinking about ways we might get there. We need to think about a world where trout may not be an option in many lower elevation waterways, just in case they aren’t.