A little while ago I looked at the effectiveness of trout stockings. One of the things that the research makes clear in the case of trout, is that in many circumstances, stockings are not effective. In fact, under some conditions, they can actually be counterproductive. Rather than helping grow fish stocks, they can significantly hurt stocks, leading to fisheries that are worse than they would have been if they had simply been left alone. Of course, there are times when trout stockings are vital to creating valuable recreational fisheries (i.e. the Victorian trout lake fisheries, which wouldn’t exist without stockings). Today, I’d like to look at stocking native fish and whether a similar pattern holds true and what native fish stocking should look like in Australia.
Life history characteristics between trout and natives are likely to vary considerably. Factors such as growth rates, behaviour, recruitment, longevity and the like may have effects on the success of stockings and how they are best implemented. These factors may also potentially change how we “assess” whether a stocking is “successful” or not, depending on the aim of the stocking. For example, when the goal is to establish self sustaining populations, the long lifespans of some Australian fish (e.g. Estuary perch, Australian bass, Murray cod) may mean that while stockings have established a population of fish, those population may not be recruiting successfully, meaning that the population will not be self sustaining. This could lead to situations where stockings “mask” the “true” health of a fish stock, with large numbers of fish present, but very little chance of a populations survival without assistance.
So to the nitty gritty. How effective are native fish stockings in Australian?
Firstly, lets start with the easy stuff. Dams and impoundments. This is an area where stockings have proved hugely successful, with some of the nations premier native fisheries being stocked impoundments. Often stocked fish can’t breed within these impoundments (e.g. bass, barramundi, estuary perch which are all catadramous species that rely on migrating to salt water to breed), but can however thrive in impoundments, growing quickly and getting to “trophy” sizes in short amounts of time. Good examples of fisheries such as this are the stocked barramundi lakes in Queensland, places such as Tinaroo and Awoonga, where stocking has produced fisheries that produce huge barra consistently. Similar great Australian bass fisheries have been established in places like Glenbawn dam, Lake St Clair, Brogo dam and many others. Another great stocked fishery is Windamere dam, the nations premier golden perch fishery. There is little doubt that stockings have created some truly great native fisheries in this country, for a vast range of species including Barramundi, Murray cod, Golden Perch, Australian bass and others. Of particular interest to Victorians are the relatively recent stockings of Estuary perch in lakes and impoundments. The results of these stockings have been very promising and its likely that in a few years, we will have some absolutely world class perch fisheries on our doorstep thanks to fish stockings.
River stockings are a slightly different beast. This is partly due to the fact that river stockings are usually designed to achieve duel aims, that is, improved recreational fishing and improved fish stocks for conservation objectives. As covered here, the stocks of many of Australia’s native fish are not in good shape. To reclaim “great” native fisheries in our rivers, streams and creeks, stockings (and translocations) are likely to be an important management tool, especially in areas where fish stocks are severely depressed or are now non-existent. The question is how effective are they under different conditions and what part should they play in the overall mix of strategies needed to restore native fish populations. The truth is that the importance of stockings is likely to vary depending on the area, how healthy natural fish stocks are, the carrying capacity of that section of river, the quality of habitat and a raft of other factors. Its likely that stockings will be extremely successful in some areas, produce very poor returns on investment in others.
A success story
An example of how stockings can massively improve fish stocks is the stocking of trout cod in the Ovens river. In this case, trout cod had disappeared from the river entirely by the time the stockings commenced. In situations like this, stocking (combining stocking with translocations may be even more effective) may often be the only way to restore fish stocks in a timely manner. These stockings were carefully designed to avoid the genetic issues that can sometimes be created through fish stockings, i.e. loss of genetic diversity. The trout cod breeding program has strict measures in place to ensure the genetic diversity of stocked fish, meticulously choosing the individuals they use to breed with. Combined with the fact that in all the places trout cod have been stocked there are no remnant trout cod populations, genetic issues relating to remnant populations are not a concern (I will return to genetic issues later). The great success of stockings in the Ovens river was in re-establishing a population of trout cod in the river, a population that had disappeared entirely by the 1980s, a population which has since expanded both up and downstream and into the adjacent King river. This population is now breeding and there is hope that it will be self sustaining and will now grow without human assistance. If that does indeed happen, it will be a true triumph of the power of stocking as a conservation measure and hopefully in the long term it will mean that trout cod can once again be targeted by recreational anglers. This will be a truly great achievement and one Victorian anglers should be incredibly proud of. Stocking programs like this are something we should be pushing for more of. They have the potential to not only improve fishing options, opening up whole new species which can be targeted, but to also vastly improve the conservation of our native fish species. A true win win.
A story of “failure”.
The stockings of Eastern cod were a slightly different story. Stockings took place from the 1984 to 1989 by government and through to the late 1990s by private operators. The stockings were discontinued in the late 1990s due to the low level of genetic diversity in the stocked fish. Given the already high risk of inbreeding depression, stocking large numbers of fish with low levels of genetic diversity carried the danger of not only being ineffective, but over the longer term, potentially contributing the the decline of the species. Recent work has suggested that there was indeed a loss of genetic variation associated with these poorly designed stockings, illustrating the importance of properly designing stocking programs. Stockings can be useful, but if they are designed poorly they can not only fail to achieve their objective, they can be of net detriment to the long term health of populations.
Thankfully most stocking programs in Australia are now more aware of these issues and have addressed them by being more careful when selecting brood stock, ensuring that fingerlings exhibit genetic diversity levels close to that of wild fish. Its important that this keeps happening and that we learn more about the genetic diversity present in wild populations and make sure that stockings don’t negatively impact on this.
Its not only a lack of diversity that can be problematic, but also introducing genetic diversity that shouldn’t be there. That is stocking bioregions with fish from outside those bioregions, fish with completely different genetic makeup. Doing this regularly, could again lead to a net loss of genetic variation across the range of a species or outbreeding depression, leading to a less resilient, less diverse species across its range. An example of this happening comes from Brown trout stockings in Spain. Stocking, instead of producing more fish, resulted in a significant loss of genetic diversity through introgression and the near extinction of the local populations of trout. The trout that replaced them weren’t local, and didn’t possess local adaptions. This meant survival of the stocked trout was poor, requiring stocking each year to maintain populations. In the end, all that was achieved through stockings was the destruction of valuable genetic diversity for little or no benefit, either for conservationists of anglers. It is situations like this that fisheries managers need to avoid.
But back to the effectiveness of river stockings
Sadly there isn’t a huge amount of data available about the effectiveness of river stockings for many native fish. The work that has been done shows varying results between areas. In some areas, stocked fish can make up a significant percentage of the fish present (this may not mean those stockings are “successful” if stocked fish are replacing wild fish, but thats for another post), in other areas, stocked fish all but disappear. For example, recent work by the DEPI in Victoria following up on Golden Perch and Murray cod stockings in the Campaspe, Loddon and lower Goulburn rivers, as well as Lake Eildon and Kow swamp showed that stockings were making up a large percentage of the population in some areas e.g. 54% of Golden perch and 100% of Murray cod caught in the Campaspe river were stocked. On the flip side, stocked Golden perch and Murray cod only accounted for 11% of fish caught in the Lower Goulburn river, suggesting stockings were not effective in this area. The results in Lake Eildon showed that 98% of Murray cod were stocked, indicating that stocking is likely to be the main driver of improved Murray cod fishing in the impoundment (as discussed earlier). (All data is from the report provided in PDF form by the Victorian DEPI, so sorry about the lack of a link.)
Small sample sizes and lack of other data about how stocked fish interact with wild fish, mean its hard to draw hard conclusions from this data, but it does at least suggest stockings may be a great way to boost fish stocks in some areas but not in others. This suggests, that we still have a lot to learn about how best to utilise fish stockings to boost populations. It also illustrates the importance of follow up work when stockings are being carried out. While labour intensive and expensive in the short term, knowing what is most effective will more than pay for itself in the long term. This is why more research in this area is vitally important. Ultimately it will allow us to get a far better return on investment. Stocking, is by its very nature labour intensive and expensive. Knowing when stockings give the absolute best return on investment will be crucial to better targeting stocking programs to provide better returns, for both recreational fishermen and to achieve conservation objectives. Thankfully researchers are working towards better understanding how to best utilise fish stockings (e.g. the work done by the Victorian DEPI referenced above). Recreational fishers can help achieve this by participating in work by organisations such as Recfishing research.
Habitat is still number one.
One thing that it is important to re-iterate is that stockings aren’t going to fix all problems. They aren’t a cure all. They are merely a tool that will allow us to fix some problems faster. In terms of rehabilitating native fish populations the key is still addressing the factors that lead to their original declines. Without doing this, stockings are likely to only provide short term benefit, rather than help restore resilient populations of native fish. To do this, habitat is key. Ultimately the best way to restore native fish populations is to restore habitat and address threats such as the impact of introduced species (for those interested I have written about the history, impacts an future management of carp here). Long term, addressing these concerns is what is going to lead to healthy fish populations. For this, re-snagging, addressing altered river regulation and siltation, carp control programs, providing environmental water at the right times of year, addressing cold water pollution and similar programs are likely to be the best “bang for buck” and be the best thing for native fish and fishers.
There is a risk, that stockings could distract us from what is really important, habitat. Habitat habitat habitat. This is especially so for many native fish which are long lived. As touched on earlier, it may be possible to establish populations of native fish that will survive, but are ultimately doomed if the original threats that lead to their decline aren’t addressed. The long lives of our native fish mean that fish just being there doesn’t mean populations are necessarily healthy. If fish aren’t recruiting adequately, the artificial abundance that can be gained by stockings may mask the fact that populations are still under threat. For anglers and fisheries managers, in the long term we will be far better served by promoting naturally recruiting populations, populations that don’t need expensive stockings to thrive. The wonderful Native fish strategy has gone a long way to determining how to best restore populations of native fish and building on that work is likely to be the best strategy for all involved. Groups such as the Fish habitat network are also doing wonderful work to achieve this aim.
Stockings of natives are a wonderful tool that can be used to create great native fisheries (lakes) and improve fishing in our rivers by restoring populations that have disappeared, as well as potentially boosting low density populations. However, they are unlikely to be a fix all. To have truly great native fisheries, to have truly great fisheries, habitat and addressing the reasons that lead to the original declines still needs to be the major focus. Without great habitat, we wont have great fisheries. Stockings could potentially be a distraction that means we fail to address those factors, which would be to our detriment. Or they could be a tool that allows us to speed up the recovery of our native fish populations, creating wonderful recreational and conservation benefits in the process.
Like most things, stockings are a just tool. To get the most out of them, we have to use them properly. They wont be appropriate in all locations, they wont fix all our problems. Used correctly however, they can be a huge force for good.
Your comments and criticisms are welcome (feedback from fisheries researchers of managers who know a lot more about this than me especially so).
Note: I have barely scratched the surface on this topic for example completely ignoring factors such as disease risk. For those interested in reading more, a more in depth review, detailing the genetic concerns associated with stockings in particular can be found here. More recent work on the genetic effects of stockings on Murray cod can be found here and here. Other reviews looking at the topic can be found here, here, here. The report on the Native fish strategy can be found here and is a must read for anyone interested in native fish. More of the NFS here. Mark Lintermans, the bible on this topic has also written a book chapter that you can read some of here, which also goes into translocations which are a very important management tool but something I haven’t touched on due to lack of space. More on how translocations can be used to help threatened species recover, in this case Macquarie perch can be found here.