Fish stocking is often hugely popular amongst recreational anglers. It seems obvious, if there aren’t enough fish, put more fish in. Problem solved. However, the reality is much more complex. Stockings can be great and can support and grow important recreational fisheries in the right circumstances. However, there are numerous examples where stocking programs have caused problems for wild fish and even cases where they have caused fish populations to collapse, where they have done much more harm than good. Stocking can also be expensive (up to $36,000 per fish caught in one year for one US stocking program, this is an extreme case but high costs are not uncommon) and used alone fail to solve underlying issues that caused low fish stocks to begin with, potentially obscuring real problems and distracting us from what really needs to be done to have strong resilient fisheries. Some of the most well documented cases of how badly stocking programs can go wrong come from the United States, where there is a long history of salmonoid stockings.
The Montana story is perhaps one of the most well known story about the unintended consequences fish stocking can have on wild populations. Research by Dick Vincent in the late 1960’s and early 1970’s clearly showed that instead of increasing trout populations and the number of “catchable” trout available to anglers, Montana’s trout stocking regime was having the exact opposite effect. Somewhat paradoxically, stocking trout meant you ended up with a lot less trout. Some of the results of that early work are astounding, in one section of creek, three years after trout stocking was ceased, the number of catchable trout (10″ or bigger) went from 1,500 to 4,700 fish per mile. In another section, which had not been stocked, when stocking began the number of trout went from 515 to 280 fish per mile, large fish from 63 to 14 fish per mile. This work lead to Montana abandoning fish stocking in many of its rivers and the results often bordered on incredible, for example in the Gallatin river, the trout population went from 450 to 2500 fish per mile after stocking was discontinued. The great trout fisheries Montana has today are in part thanks to abandoning a practice that on the surface seemed like it should have lead to more fish, not less.
The story of how stocking has affected wild populations of steelhead and salmon on the pacific rim is a more complicated and much more troubling tale. For the last 130 years, pacific coast hatcheries have been producing steelhead and salmon smolts to release into rivers and streams with an aim to boost fish returns and strengthen fisheries. In the beginning, negative effects weren’t obvious. Things seemed to be going ok. In some places hatchery raised smolts seemed to boost fisheries, in others there was no obvious immediate change. However, almost across the board these wins were short lived. In many streams and rivers stocked with hatchery raised fish, returns quickly plateaued and then started to decline, often drastically (there are some success stories). Presently, the plight of many of the USAs famed salmon and steelhead fisheries is bleak, with many populations now sitting at below 10% of their previous abundance. The prospect of losing some of the most iconic anadromous fish populations on the planet, populations immortalised in the fishing literature and folklore is a very real possibility. At the very least, the long history of stocking rivers and streams with hatchery fish has not saved pacific rim salmon and steelhead populations. In fact it is increasingly clear that stockings have played a significant role in the declines of pacific rim salmon and steelhead populations. In the last decade, numerous studies have shown that stocking streams and rivers with hatchery raised fish often harms wild populations and leads to fewer fish overall (a few here, here, here, here, here and here). So despite stocking seemingly being a “good” thing on the surface, much like in Montana, stocking hatchery fish has in fact harmed fisheries and put many wild fish populations at dire risk of disappearing completely. The reasons behind the negative effects of hatchery fish on wild populations are many and complex. They include harmful genetic effects, competition for spawning and rearing habitats, predation and ecological effects. Hatchery programs also distract from solving the real issues facing salmon and steelhead populations such as barriers to migration, water allocation, habitat protection and restoration and the importance of genetic diversity and wild fish. To quote the 2014 HSRG review on the science of hatcheries
“The widespread use of traditional hatchery programs has actually contributed to the overall decline of wild populations.”
Which brings me back to Australia and our own wild fisheries. Stockings of Murray cod, Golden perch, Trout cod, Silver perch, Macquarie perch, Estuary perch, Mulloway and Australian bass are increasingly being used as a tool to boost fish populations for anglers and conservation. Generally, these programs are far better designed than many of their counterparts in the USA, having been informed by some of the failures in the USA. This means that we are likely to avoid most of the big problems like the ones outlined above that have been caused by stockings programs in the USA. For example, most Australian stocking programs use local wild caught brood stock, which are rotated every year or so. This is to avoid domestication effects, which can have negative effects on wild populations and can arise within one generation in a hatchery environment. The science of whether these techniques totally insure against negative effects is still out in the USA, with some studies showing no negative effects on fitness and more fish returning when 100% wild, local, brood stock are used, others showing that negative effects persist even when local wild broodstock are used (this and April Vokey’s podcast with John McMillan make good points about why that may be and the role hatcheries can play). The small chance that even well designed best practice stocking programs could still harm wild populations aside (noting that this is something that needs to be monitored and researched), what do we know about the effectiveness of Australian native fish stocking programs?
The answer is surprisingly little. This is mainly due to the relatively short time stockings programs have been going in Australia. Hatchery techniques were only developed for most native fish in the early 80’s and stocking programs didn’t really take off in a big way until the 1990s. It is only in the last few years that work has been published looking into the effectiveness of Australia’s native fish stocking programs. The results of this work are somewhat mixed. The few studies that have been done have showed that in general, stockings contribute a relatively small proportion of individuals to riverine populations of Murray cod and Golden perch, suggesting that these populations are primarily sustained through wild recruitment. This pattern holds even in rivers recovering from fish kills caused by blackwater events. In impoundments the story is very different, with many populations made up almost entirely of stocked fish (link, link and link). These studies suggest that the way we manage rivers and impoundments should be very different, focussing on habitat and other factors in rivers, while maintaining fish stockings in impoundments to maintain the vibrant fisheries that stockings have created. In many rivers, given the importance of wild fish, we may be far better served spending our time money and effort, not on stocking more fish, but on changing regulations to reduce harvesting and better protect fish during the closed season. For example, given that Murray cod stressed prior to the breeding season have been shown to re-absorb their eggs, it may be prudent to implement full river closures at key times to better protect the fish the fishery relies on.
Added to this stockings play a key role in the conservation of a number of endangered species that have suffered large reductions in abundance, being one of the only tools we have to help restore populations once they have disappeared (the other tool being translocations). The importance of stockings to achieve this aim is demonstrated by the success of trout cod stockings, which have restored populations of trout cod in places such as the Murrumbidgee, Cotter and Ovens rivers. Even here, there may be unintended consequences of fish stockings as illustrated by recent work on the Murrumbidgee near Canberra, showing hybridisation between reintroduced trout cod and Murray cod. This may not be a problem (some hybridisation may have happened historically where murray cod and trout cod cooccurred), but more research is needed to determine why its occurring and whether it is an issue to guard against unintended consequences and ensure future programs are as effective as possible. Given the status of many Australian fish species, the use of fish stockings and relocations to achieve conservation objectives will be ongoing for the foreseeable future and will be one of our best tools for re-establishing populations of threatened fish.
It should be noted, that while these studies answer questions about survival, they don’t answer longer term questions, such as the reproductive fitness of stocked vs wild fish, potential ecological interactions between stocked and wild fish or assess the return on investment of stocking programs compared to other potential management actions such as reducing harvesting or better protecting fish during the breeding season. The small amount of work that has been done, suggest that in places where wild fish are present and self sustaining, regulatory changes are likely to be more effective than stockings (also this). These considerations haves lead to the introduction of a slot limits in NSW and Victoria in recent years, a really positive step in the right direction. Still more research is needed in this area to answer a number of outstanding questions and to continue to improve the way we manage native fish populations.
So as anglers, how should we view native fish stockings? Well it depends. I strongly believe that as anglers we need to move away from seeing fish stockings as a silver bullet and a blanket solution to problems in our fisheries. They aren’t. That as anglers our aim wherever possible should be supporting and establishing wild, self sustaining populations of native fish. In places where wild fish are already present and already self sustaining, our focus should be on wild fisheries management, that is protecting and restoring habitat so that it can support larger, healthier, more resilient populations of wild fish. In places where that isn’t an option (in rivers where wild recruitment is poor and in impoundments) stockings have an extremely important role to play, being a vital tool for the conservation of threatened and endangered species and for creating and maintaining world class impoundment fisheries. As a judiciously used tool, stockings are great. We just need to remember what the ultimate aim should be. Healthy populations of wild fish.
I will leave you with a quote the 2014 HSRG review on the science of hatcheries in the USA
“Today, it is clear that hatchery programs must be seen as just one tool to be used as part of a broader, balanced strategy for meeting watershed or regional resource goals. Such a strategy also incorporates…. actions affecting habitat, harvest rates, water allocation, and other important components of the human environment”
Note: I only scrapped the surface, especially when it comes to steelhead. If you want to know more make sure you follow April Vokey one of the most effective and outspoken campaigners for wild steelhead (pod, FB, Instagram), John McMillan from Trout Unlimited on Instagram, wild steelheaders (and FB page) and wild steelhead coalition and wade in from there.