Today we had planned to show some more images of the Tongariro River after the flood but the photos would not load. So for today’s report we went to Plan “B”…
An interesting inquiry from an angler to DOC – following up on the 2012 feature article in Target Taupo:
Hello Michel
Issue # 65 of Target Taupo contains an article discussing the experiment aimed at restoring the early run of rainbows in the Tongariro river. I understand from DoC media releases that 5,000 fry with this characteristic were released.
Have the results been noted in any DoC publications or science journals? I would be grateful if you can give me any leads.
DOC’s reply
Sorry for the delay replying to your enquiry.
We didn’t release 5000 fry but 5000 juvenile fish about 10-15cm long. The reason why we released fish of that size was to “maximize” the chance of survival and hence the recapture rate that ultimately would provide an estimation of the success of the operation. However, there is a trade-off: the larger the fish the smaller the mortality but larger fish require longer rearing in hatchery. It is well known that hatchery fish are more “naïve” than their wild counterparts and a longer period in hatchery will make these fish more naïve and therefore less likely to behave the same way as wild fish eventually preventing drawing solid conclusions.
In our experiment virtually no tagged fish were recaptured because of the “naivety” of hatchery fish and/or that we didn’t release enough of them. The total number of juvenile trout in Taupo can be counted in million and 5000 additional fish make only one drop in the bucket.
As you can imagine the results of this experiment were somewhat disappointing and could not provide any explanation about what triggers early v. late run. However, since then we have some very good information from trap data analysis that 67% of the timing of the runs can be explained by the average size of the fish. When fish are large they spawn earlier when small it is the opposite. The reason is the reproduction strategy of trout: they try to grow the larger as possible to produce as much eggs as possible because large fish have more eggs. When they are small they have not been able to grow as large (because of insufficient food abundance). In these situation fish try to hang on as long as possible in the lake to grow but eventually they will have to run.
I have attached a graph showing the relationship between timing of the run and size of fish.
I hope this will help.
Regards
(Taupo and Tongariro anglers still miss the Target Taupo in-depth information and articles such as the following:)
RESTORING THE EARLY RUN
From Target Taupo December 2012 – issue 65 –
By Dr Michel Dedual / Fishery Scientist and Elizabeth Heeg / Ecologist
Stocking trout is not new in New Zealand; in fact, many salmon and trout populations were established through stocking rather than colonization, so there is a long history of liberations in this country. The use of systematic stocking to increase population size stopped when it became apparent that in most waters natural production was sufficient to support a sustainable fishery. Enhancement stocking was undertaken in some Taupō spawning streams to compensate for wild trout eggs taken for hatchery production, but stopped in the late 1970s and in virtually the entire country (except in the Rotorua lakes) shortly after.
However, since the end of the enhancement stocking programme many experimental and accidental fish releases occurred in Taupō waters. We found in the fishery archives records that at least 58 releases, involving 526,167 hatchery trout, had occurred between 1980 and now. Most of these releases were done as a way of conveniently disposing of the surplus of fish that were produced at the Turangi Hatchery, now the Tongariro National Trout Centre. However, some of these releases had scientific purposes mostly targeted at determining the growth rates and the age of adult trout returning to spawn. Taupō trout are difficult to age, but one way to obtain this information is to mark and release fish of a known age reared at the hatchery and then record the date when they are recaptured in traps as they return to spawn.
Another type of experiment was carried out to explore if the progeny of large parents were also growing into large fish. We haven’t found any records documenting the results but we can assume that it wasn’t manifestly successful; otherwise such a programme wouldn’t have stopped. Some other experimental releases were made to look at a very similar issue to the purpose of our research programme. For instance, fish running early in some streams were reared and released in other streams they weren’t known to return to. Unfortunately, here again, we couldn’t find any record on the success of these operations.
In addition to these experimental and ‘convenient’ releases, some accidental releases of hatchery sh also occurred. For example, in February 2004, the hatchery building and children’s pond were flooded and more than 5,000 fingerlings escaped into the Tongariro River system. However, most of these returned within a few weeks back ‘home’ when large numbers of these fish could be seen in front of the viewing chamber at the Trout Centre.
The New Zealand experience is an example of colonial rainbow trout succeeding beyond expectation, despite the potentially negative population effects of introductions and translocations. Unfortunately, many stocking programmes did not keep complete and accurate records, and the effects of stocking were poorly studied until recently. Thus, the history of stocking and its potential outcomes is poorly understood for most New Zealand fisheries.
A four-year long baseline study of the genetics of rainbow trout, undertaken since 2008, has provided strong evidence that Taupō waters have experienced multiple introductions from more than one source. Taupō trout most likely originate from a combination of coastal (like Sonoma Creek) and inland (like McCloud River and/or Lake Almanor) California populations.
Some rainbow trout brought here from California coastal streams were likely to be steelheads (rainbow trout that grow in the sea prior to returning to spawn). Steelhead run at different times of the year but most of them spawn in spring. In the northern hemisphere, ‘summer-run steelheads’ migrate between May and October (equivalent to November–April here). When they run, these fish are ‘green’ and the completion of maturation occurs in the river before the fish spawn the next spring (September here). ‘Winter-run steelheads’, on the other hand, mature fully in the ocean before migrating, between June and October (here), and spawn shortly after.
In the Great Lakes in North America rainbow trout were also introduced from populations of steelheads from several sources. There they have also evolved into distinct fish types running at different times of the year, depending on their origin. Some have evolved into summer-run and some into winter-run but they mostly spawn in spring, although the Michigan Department of Natural Resources reports that more steelhead are beginning to spawn in autumn.
A diverse genetic background from multiple founding populations may also have helped Taupō trout to adapt more successfully to their new habitat with greater genetic resources than their founding populations contain individually. As we mentioned earlier, the original steelheads run from summer to autumn but virtually all of them spawn in spring. In Taupō, something else has occurred. Rainbow trout here evolved into populations that migrated in the rivers and spawned over a very long period stretching from March to November. We are not aware of any other places in New Zealand or around the world where rainbow trout have such an extended spawning period. However, as we explained in previous issues of Target Taupō, during the past 10 years or so the early part of the Tongariro spawning run has been declining with peak spawning now occurring later in the year. The exact causes of this shift in spawning migration timing are not fully understood.
What are the possible causes of the early run decline? Changes in fish populations are generally due to combinations of changes in environmental conditions, in fishing pressure or selectivity, or in predation. A fishery is a balance between mortality and production. When the mortality level is higher than production the population declines and when mortality and production remain equal the population stays stable. Therefore, this requires not only an assessment of the status of existing populations but an appraisal of the environmental conditions that may limit production. These assessments must be based on rm evidence and not hearsay or unsubstantiated complaints.
It is well known in commercial fisheries that fishing may result in genetic changes in sh populations. In addition, deleterious changes in population characteristics, such as life-history traits, behaviour and mortality have also been reported to result from commercial fishing pressure. Fishing selectivity in recreational fisheries has not been as heavily documented due to an absence of long-term monitoring and the lack of knowledge on unfished populations. Nevertheless, more than 20 years ago, research in Europe already suggested that different levels of angler exploitation may alter the genetic potential for growth and aggression in wild trout and that angling tended to select for larger, faster growing, more aggressive individuals.
In light of this, by analysing the genetic make up of fish caught in the lake throughout the year, we investigated if fishing in Lake Taupō is selectively targeting early running trout. We didn’t do this in the river because fishing in the river early in the season will obviously target early running fish. There was no clear indication from this analysis that fishing was selectively removing one particular genetic type. Fish were sampled every month and the proportion of both types of fish didn’t change throughout the year.
| However, as we will see later, this doesn’t mean that fishing has nothing to do with the shift in running timing or the decline in abundance.
Trapping in several Taupō streams indicates that production (the number of trout) and mortality (the number that die) are highly variable from year to Fishing mortality is better correlated with fishing pressure than with trout abundance. However, fishing pressure has consistently declined since 2000 when it reached a peak, suggesting that fishing mortality has also declined. This suggests further that natural conditions are the key drivers of the total adult trout mortality. Angling exploitation in Taupō waters, obtained from diverse tagging experiments, ranges between 25 % and 30 % of the catchable population. However, this may be a minimum exploitation rate, as the figures are obtained only from tags being reported; the inclusion of unreported tags and tag loss could substantially increase the exploitation rate if these factors are significant. Mortality due to fishing pressure can be large when natural mortality is low, without having any visible negative impact on the state of the fishery. However, it can also exacerbate the total mortality when the natural mortality is high. The actual threshold of natural mortality at which fishing pressure can have substantial impact on total mortality is unknown. The estimation of this threshold is currently being assessed by dynamic fish population modelling to better understand what role (if any) fishing pressure might have played in the decline of the early run. WHY IS THE EARLY RUN VALUABLE? Fishing in Taupō rivers traditionally targets fish returning to spawn during winter. Radio-tagging experiments in the Tongariro River indicate that early in the season fish migrate in the river mainly at night with a strong response to freshes (small floods). Each fresh pushes a pulse of fish that stops when the flow conditions return to normal. The next fresh pushes them further up and so on. These fish have spawning migration behaviour similar to summer- run steelheads. They start entering the river as early as the end of March and can spend up to 3 months before actually spawning. Therefore, the early run is what sustains the winter fishing in the region and the livelihood of the community (fishing guides, hoteliers and so on) that relies on it. From a biological angle, it is also very desirable to have the spawning spread over a long period. The success of spawning will largely depend on the incidence of floods, as floods can scour the gravel and remove or crush the buried eggs and flush out the newly hatched alevins. An extended period of spawning is insurance against natural disaster, as any flood will affect only one part of the spawning but not all, thus providing an extra resilience to the fishery. HOW COULD WE PROTECT OR REINSTATE THE EARLY RUN? Those who support stocking argue that the debate about wild sh is purely semantic and irrelevant as fish were introduced in the rst place and if something can be done to improve the fishing, then let’s do it. Those vehemently opposed dispute the release of hatchery stock as they could affect the wild fish. They also tend to suggest instead of stocking, using other management measures like catch-and- release, closed season, reduction in bag limits, slot size, gear bans and so on. These alternative measures are unfortunately unlikely to make any substantial difference on their own. The Taupō Fishery is an open-access fishery meaning that fishing pressure is not controlled because the number of anglers is unlimited. It is possible to close the lake and rivers for a while but if the pressure rockets during the open season then the exploitation of the early run |
(through exploitation of the total Taupō catchment) could still be unsustainable. Catch-and-release only (no kill) and slot limit regulations have the same e ciency limitation if pressure is unlimited. If the catch-and- release procedure is not done properly a substantial proportion of fish will still die, being lost to everybody and the higher the fishing pressure the higher the loss. As any regulations that involve handling fish cause some mortality, the best regulations are those that limit handling to a minimum, but they may not be palatable to many anglers.
Sean Cox, an eminent Canadian fishery scientist, soberly warns:
Regulations in size and catch limits have not been effective at achieving even the simplest management objectives in both commercial and recreational fisheries. Policies based on regulation of individual angler harvest are practically doomed from the start for two reasons. First bag or size limits tend to be unrealistically high and most anglers seldom catch a full bag. The actual limits on both catch and size needed to protect fish populations are so drastic that their implementation is discouraged due to fear of public outcry or perceived loss in total catch. The second cause of failure is an angler effort response to fish abundance. When anglers increase the amount of effort exerted in response to the abundance of fish present, generally a pathology occurs in which “success breeds failure”. Short term increase in abundance due to successful production- or consumption-side programs result in higher effort and potentially higher exploitation until catch rate and angling quality decline to the point where no further effort is attracted.
Because the total mortality of adult Taupō trout is mainly dictated by the highly variable natural conditions in the lake, fishing regulations would need to be particularly stringent, but only when natural conditions are poor. We are actively exploring what makes a good year for environmental conditions but, unfortunately, we are not in a position yet to reliably predict fishery outcomes and performance year-to-year.
This leaves us with restoration stocking as a potential approach to reinstate the early run. The sensitive issues surrounding stocking have aroused some
very emotional responses in fishing magazines and on blogs. While some of the concerns raised are well founded and constructive, many others are based on poor information and/or a lack of understanding. In New Zealand, the introduction of trout was done in water free of native salmonid shes (the scientific family of all trout and salmon), as salmonids are native only to the northern hemisphere. In addition, Taupō trout broodstock were one of the main sources of trout that were introduced throughout New Zealand. By reintroducing other New Zealand trout populations derived from ancestral Taupō trout back in Taupō waters today the risks are far more limited than in America. There, brown and rainbow trout were introduced from Europe and the West Coast of North America respectively into East Coast American waters where they didn’t previously exist, but where other native salmonids were present that they could hybridize with. A similar situation here would be if we were stocking Tasmanian mud fish that could hybridize with Canterbury mud sh – if they interbred then the Canterbury mud fish stock would contain non-native Tasmanian genes, creating a new mix of different genes from two very different species. However, since New Zealand rainbow trout were all introduced from the same American sources 100 years ago, it is essentially just introducing related sh back to other related fish, and remixing genes that were already mixed in relatively recent colonial history.
Based on the genetics study results, it could be argued that the most suitable source of rainbow trout to stock Taupō waters if attempting to reinstate the early run would be to use the initial Californian populations that were released in New Zealand. Unfortunately, it is impossible to source these original populations as the stocking and liberations programmes in California have been so extensive these original sources no longer exist in the same genetic composition that was used for the New Zealand introduction. Over time, geographically separated populations also tend to become more genetically different simply due to random chance, an effect known as genetic drift. This is what we have observed with the Californian populations: now New Zealand rainbow trout are significantly different from all the California populations, including their source populations, due to genetic drift in all populations and the influence of stocking programmes in some areas. So for stocking purposes, the sh now least genetically different from Lake Taupō trout are other New Zealand trout stocks. Therefore, our best option is to use New Zealand populations of wild fish that were introduced from Lake Taupō and that show the desired characteristic of running to spawn early.
WHAT ARE THE RISKS?
The review of the history of fish introductions on all continents of the world indicates that the majority of introductions are often not successful.
So it is wise following the recommendations from Robin Waples who said in 1991 that the rule of supplementation should be: ‘ rst, do no harm’. The most common genetic effect from translocations is the loss of rare alleles, which can be thought of as rare genetic variations. This can have negative effects because these rare variations can be a result of local adaptation; they can also be a result of random chance, though. Indeed, translocations by restoration stocking have been shown in some cases to be able to restore genetic diversity where it has been lost. The long-term ecological effects of stocking are diffcult to monitor because changes in genetic composition and population size tend to occur relatively slowly. One way to increase understanding of the impacts of stocking is to develop models that incorporate demographic and genetic processes between wild and introduced fish. This is exactly the approach that we used to evaluate the risk associated with the release of Tarawera lakes and/or Lake Otamangakau trout – typical early running fish – into the Taupō catchment. The results of the simulations indicate that the introduction of trout from these catchments would not have any significant effect on trout genetics in the Taupō basin.
WOULD THAT WORK?
Predicting whether a stocking exercise is likely to meet its objectives is another important consideration. Just because the risk of negatively affecting Taupō trout is insignificant, doesn’t mean that stocking is likely to be successful. To be fully successful, it is central to consider the time scale of the stocking programme because it needs to be sustainable and a affordable in the long term. The most recent Taupō trout genetics report from Victoria University of Wellington stressed that while the introduction of Lake Otamangakau and/or Tarawera lakes fish may stimulate the early run in the short term, the increase would likely only be of short duration. Once the introduced fish go through a couple of spawning seasons with the previously established fish, the old spawning pattern would likely reoccur because the introduced trouts’ progeny would be outnumbered by the established returning spawners. Even if the introduced trout became established in their new habitat, a proportion of their progeny would be hybrids with the previous residents, and these hybrids might reflect the previous spawning patterns.
Therefore, an ongoing programme of selective stocking would be required to maintain an early run. In order to produce a stock with known traits, a management programme would need to be implemented akin to the Rotorua controlled breeding programme. This would require a much larger expenditure of limited resources that would be possible only through a dramatic increase in revenue (for example, licence cost) and at the expense of the other activities required to properly manage a fishery. Most importantly, without fully understanding the underlying mechanism for the decrease in early spawning trout, it is more risky to attempt solutions that do not fully address that underlying mechanism, and these attempts may end with the same scenario that Lake Taupō populations are currently experiencing.
EXPERIMENTAL APPROACH
As managers of the Taupō Fishery, we have neither downplayed the risks associated with fish introduction nor contemplated embarking on an enhancement stocking programme. But this doesn’t mean we shouldn’t carry out scientific experiments to understand the ecology of trout and to provide objective information to anglers based on scientific results rather than hearsay. The remaining 500 fish were released in Lake Otamangakau to monitor their growth in a highly productive system. These fish can be identified by a fluorescent yellow mark.
An opportunity arose to release a few experimental sh (5,000 juveniles) that were not sufficient to affect the genetic make up of Taupō trout or create further limitation to the production of indigenous trout.
On the other hand, the fate of these fish could provide some precious information.
The experimental fish were reared for several months at the Tongariro National Trout Centre and some of them may return to spawn in the Waihukahuka Stream as they did when they escaped during the flooding in 2004. Therefore, we released some fish in Lake Taupō and some in the Tongariro River upstream of the Waihukahuka Stream where the fish are in olfactory ‘unknown’ water. Some fish
were liberated at the mouth of the Waimarino and Tauranga–Taupō rivers. Conversations with Eastern Fish and Game staff revealed that, in Lake Rotoiti, adult fish return to spawn at exactly the same location along the beaches where they were released as fingerlings. Therefore, it is possible that fingerlings released in the lake may show the same behaviour here in Taupō.
The other reason for the choice of release sites was that the mouths of these rivers are heavily used by anglers. Anglers are big actors in this experiment as they are, or will be, the first to catch and hopefully to report marked fish. The reported captures of tagged fish will signal that the time to crank up surveys in these rivers has arrived. The idea is to recover as many fish as possible by increasing the frequency of surveys of anglers in these waters to provide the best information possible. In Lake Rotoiti, fingerlings return to the beaches where they were released because the lake doesn’t have any significant spawning tributaries and adult trout spawn or try to spawn along the beaches. In Lake Taupō, by contrast, spawning tributaries are abundant and rainbow trout are not known to spawn along the beaches. Therefore, this experiment could provide information that potentially could become extremely relevant if, for some reason, the conditions in rivers are not suitable for spawning over a long period. Having access to fish that can use the lake littoral instead could be very valuable indeed.
The return of the fish and their growth will be monitored as they pass through the Waipa, Waihukahuka or Te Whaiau traps that are operated daily throughout the spawning period. Concomitant creel surveys and spontaneous reports from anglers will provide further information.
This experiment should provide answers to two important unknowns. First, it will allow us to verify if the early running sh from Lake Tarawera that spawn between May and July do in fact return at the same time if released in Lake Taupō and Lake Otamangakau. Secondly, it will allow us to compare the growth rates achieved in the different lakes. Several anglers have suggested releasing fish from Lake Tarawera as they believe that they will do as well in lakes Taupō and Otamangakau and turn into very large fish. The results of that part of the experiment will answer that lingering and recurrent question.
Fisheries management often involves balancing the needs and desires of conflicting user groups within the constraints of the environmental and biological processes that control fish populations. Each action a manager proposes will, if implemented, impact not only on the fish population or community being managed, but also the groups that use the fishery. As scientists and anglers we take our commitment to the Taupō Fishery very seriously, and we aim to use the best scientific tools and techniques at our disposal to make it a resilient, sustainable and productive paradise for anglers far into the future.
Michel is the fishery scientist working for the management of the Taupō Fishery. Elizabeth has just completed a doctorate in ecology and biodiversity at Victoria University of Wellington that examined Lake Taupō rainbow trout population genetics and spawning time.