Angus’s closing thoughts

During this trip, I’ve largely been caught up with translation and logistics, but in the many hours of discussions we’ve had with growers, hatcheries, scientists and grower representatives, I’ve also been trying to draw some conclusions about the way in which the Australian industry should respond and what the short-term priorities should be. In this post, I’ll try to outline some of my thoughts.

Husbandry

In France, as in Australia, there are a limited range of husbandry changes that can be considered to attempt to minimise the impacts of the virus. My understanding of Australian oyster culture is not extensive, but from what I’ve picked up, these include:

• Growing oysters in different depths
• In inter-tidal culture, this influences the period in which they are exposed to the air
• In other systems (floating or deep-water) depth may have other effects, such as limiting exposure to weather (rumbling due to waves), to UV light, temperature effects and possibly virus load
• Stocking oysters at different densities
• Density should be considered with local effects (number of oysters per bag/tray etc), and at a larger scale (number of bags/trays per hectare in a growing area).
• Equipment used
• We’ve seen a pretty wide variety of growing techniques, including bags, baskets, long line, floating, fixed racks, strings, lanterns etc.
• Timing
• Spat can be stocked at different times, so that they are bigger or smaller, older or younger, at times of peak risk (when water temperature is higher). This can be further extrapolated to the age/size of spat that are stocked.
• Transfers
• Stock can be moved between different areas to influence growth rates or to avoid or delay exposure to heavy virus loads and warmer water temperature.
• Selection of spat
• Diploid, triploid, wild-caught or hatchery. For hatchery stock, there is also a choice of hatchery, each of which may be using different approaches and producing spat of different quality
• Grading and handling
• Mechanical graders, hand grading, no grading, and no doubt a whole range of other details of management involving handling / cleaning / processing the oysters.
• Management of survivors
• Oysters that have been previously exposed to the virus but have not died may be treated in different ways:
• some may consider that they have been weakened by the virus and are more susceptible to dying with any later challenge
• others think that they represent a population with some immunity
• yet others think that they are likely to be carriers and therefore risk spreading the disease

There are certainly a large number of other husbandry activities and issues that I have missed, but these are the main ones that have been discussed during our trip. During discussions with both the producers and the scientists, we have heard a range of opinions and conclusions about how each of these factors affect the level of mortality experienced due to OsHV-1 µVar.

There has been a distinct lack of consistency in opinion about the effect most of these factors have on mortalities due to the virus. This could mean that:

• The effects are different in different locations / environments
• There are other more important factors influencing survival that we are not yet aware of
• The factors being considered have little impact on survival, and observed differences are just random variation
• Desperate farmers are clutching at straws, hoping that different ideas may work, but with little support or proof (we have heard of a range of different ideas that sound rather improbable but which some farmers are keen to implement without any evidence that they may actually help).

Despite this there have been a couple of issues that have been a bit more consistent and merit careful consideration.

Temperature

One of the few things that people are pretty confident of is the effect of temperature on triggering the mortalities. If the virus is present, rising temperature triggers the onset of disease. The threshold at which mortalities start to appear varies a little bit, which is what one would expect if a range of other factors are also involved (e.g. other sources of stress, other opportunistic pathogens such as vibrio, age, resistance etc). Most people we have spoken to suggest that the threshold in most of France is around 17° C. IFREMER has also suggested that there is an upper temperature limit to the mortalities, around 24° C, but no similar comments have been made by producers and it is not certain what the practical importance of this would be in France. It may be relevant in Australia, however.

In some parts of France, farmers with multiple leases in different areas take advantage of this temperature effect. Some small areas have lower temperatures than surrounding areas and oysters may be transferred here to avoid the wave of mortalities that accompanies increasing water temperature. In Australia, there is a significant range of water temperatures between different oyster growing areas, but restrictions on interstate movements mean that the opportunities to exploit this type of approach will be rather more limited.

Growth rate

We have regularly heard that rapidly growing oysters are more susceptible. The exact mechanism for this has not been described with any consistency. It may be simply because rapidly dividing cells provide a better opportunity for the virus to replicate itself. Others point to physiological stress in rapidly growing oysters, and others suggest that shell strength plays a role.

A number of strategies appear to have developed in response to the hypothesis of the importance of growth rate, involving speeding up or slowing down growth off different classes of oysters at strategic times.

Age/size

The early observations in France have been that young oysters are more susceptible. This still appears to be the case in most areas, to the point that farmers on the Atlantic coast seem to feel that adults are not at significant risk. They were surprised by the observations from Australia and New Zealand that older oysters also suffered very high mortality rates.  In contrast, in the Mediterranean (and possibly some other areas), adults appear to suffer heavy losses. Based on the hypothesis that genetic resistance is the main determinant of survival, some farmers prefer to have their spat heavily challenged and suffer high levels of mortality, so that the survivors have a lower chance of dying as adults. Losing adults after all the effort of growing them clearly has a very demoralising effect.

What is not clear is the interaction between age, size and growth rate. Definitions of adult and juvenile are generally based on size, but may describe oysters of very different ages, depending on the region of origin. Significant differences in nutrient levels and growth rates , and therefore age/size relationships, are likely to be evident in Australia as well.

Viral load

Another relatively consistent message was the importance of viral load. It appears that oysters exposed to the virus may well continue to carry the virus, even if it is not detectable with PCR tests. It is not known if they excrete the virus in this subclinical state.

One suggestion (that has apparently been patented in the Mediterranean) is to grow mussels between the rows of oysters, based on the theory that they may act as a barrier to the movement of virus, or ‘soak up’ virus from the environment without being affected. There is little information available about the effectiveness of this approach, but one IFREMER study showed that the mortality of oysters grown in a range of different environments (surrounded by mussels, other adults, or spat) were very similar, suggesting that it may not be effective.

On the other hand, the importance of viral load in the environment was demonstrated by an experiment in which spat that tested negative on PCR were grown in a previously unused area that was separated from existing (heavily contaminated) oyster growing areas by land and hydrological barriers, and suffered no mortalities despite having suitable water temperatures. This indicates that it is possible to avoid the disease by using a clean environment and spat that are either free or have infection which is undetectable by PCR.

Spread of the disease

The most effective way of spreading the virus over long distances is within live oysters. Outside the oyster spread is probably limited. Some IFREMER work has indicated that it may be able to spread in the water with currents over about one kilometre (although this is likely to vary significantly in different circumstances). This explains the spread of the disease in infected estuaries. The potential risk of spread on contaminated equipment is uncertain – it is probably less effective than moving live oysters, but still may represent a real risk given the right conditions.

In France, it appears most likely that the virus was spread to virtually all growing areas rapidly in 2007 or 2008 through the extremely high number and transfers. As a result, almost the entire coast was affected before the disease was properly understood. Australia is in a much better position, because a) we know something about the disease so we can be ready for it, b) we have managed to identify it in a localised area and respond, and c) the level of transfers is lower than in France. The three oyster-growing states are relatively separate in terms of movements, with only spat moving between states.

The role of hatcheries in the spread of the disease has been hotly debated in France, and the question is still unclear. Hatcheries claim to be able to produce PCR test negative spat (even if the broodstock have been previously exposed). Also, it is possible to explain the rapid spread of the disease throughout the country without the hatcheries being involved – the transfers of wild-caught spat and of growing oysters between sites can easily account for this.

Long-distance spread of the disease is harder to understand. The question of how it got to Australia and New Zealand has still not been answered, and it is not even clear where it came from (some of the French assumed that they were the source, but this is not at all certain). There is little evidence in either direction, but one hypothesis for the long-distance mode of spread is in infected shellfish on the hulls of shipping. This mechanism seems feasible given the common levels of fouling, the high levels of international shipping, and the fact that the first occurrence in Australia seems to have been in Botany Bay (one of the busiest shipping ports). The disease was probably present in New Zealand for some time before it was confirmed, but its distribution suggests that it is possible that it first arrived with shipping to Aukland.

Information on the origin of the virus and the way that it has spread around the globe may be gleaned from genetic analysis and a comparison of the small genetic differences between viruses in different parts of the world. Initial analysis (using only a small part of the genome), indicated that the viruses from New Zealand, Australia and France were all very closely related, and all quite distinct from the classical herpes virus. However more recent work by IFREMER indicates that there may be greater genetic variation in the μ-var than initially thought. As this work progresses, it may provide a better idea of the ‘family history’ of the virus, and better clues as to how it has spread around the world.

The implications for Australia regarding the way the virus can spread are two-fold:

• Transfers are the best way of spreading the virus. If we want to be serious about prevent the spread we need to ensure that we understand current transfer patterns and are able to stop or change them as required.
• If shipping is a potentially important mechanism for long distance spread, we should identify other parts of Australia that may be at risk of becoming infected through shipping, either from overseas, or from the George’s and Parramatta Rivers, and improve our early detection and response capabilities.

In both these examples, the aim is to be ahead of the game and predict the behaviour of the virus, rather than chasing to catch up (often after it is too late). One possible tool to help with this (particularly for transfers) is spatial network analysis (which I’ll mention again later on).

Breeding programs

There was general agreement amongst the Australian team, and many of the people spoken to in France (with a few exceptions), that breeding programs to select genetically resistant stock represented an important medium- to long-term approach to successfully living with the virus. Reports of the initial success of the Australian program were generally met with interest. The Australian team worked hard to understand the different activities and initiatives in France. These include a number of breeding programs undertaken by private hatcheries, either alone or in a consortium, the use of stock developed under an earlier breeding program as part of the ‘Morest’ (Summer Mortality) research program, and a new publicly funded breeding program (‘SCORE’). This latter program aims to produce enough distinct resistant family lines to ensure continuing genetic variability (the danger of in-breeding was mentioned frequently). The objective is to have 100 resistant lines to achieve this. Using an estimate of the frequency of resistant genes in the population of 5%, the initial number of lines to be used will be about 2000. This enormous program aims to produce results rapidly – initially to produce triploids to immediately address the mortality problems, and then later for the release of diploids into the wild, to increase the prevalence of resistant genes in wild-caught spat.

There is also interest in introducing genetics from Japan (one group already came but the program stopped with the Japanese tsunami), and from South America, although there is some uncertainty as to the logical justification for this.

Given the heavy viral load in infected areas, the challenge when selecting for resistance is very heavy. If (as is likely), resistance is not absolute, but on a sliding scale, it is likely that some ‘relatively’ resistant oysters tested under heavily contaminated conditions may fail to survive. However an entire population of the same oysters may prosper due to the lower levels of contamination. This issue may need to be kept in mind when testing family lines in Australia – survival may be better if large numbers of similarly resistant oysters are stocked together, rather than mixed closely with non-resistant strains. This concept is known as herd immunity, and is seen in human vaccination programs – when most people are vaccinated, the pressure put on the less immune individuals is much less because there is little circulating virus. However when very few people are vaccinated, the challenge may be great enough to cause disease even in those that are vaccinated.

Priorities for Australia

In simple terms, I think Australia’s priorities in dealing with the disease are:

• Know where the virus currently is and where it isn’t
• This was the objective of the national survey
• Stop the virus from spreading
• Banning transfers and movement of equipment out of the George’s and Parramatta Rivers aims to do this. If there are other spread mechanisms (such as shipping or local spread in the water), these measures may not completely prevent spread.
• Detect it as quickly as possible if it does spread to a new area
• There are possible weaknesses in our current capacity for this. If the virus spreads during a period when there is no disease expression, we may not know about it. This is discussed further below.
• Limit the risk of further spread in the absence of clinical disease
• Risk-based pre-emptive disease management
• Be ready for the disease if/when it does appear
• Contingency planning and learning how to live with the disease (this was a large part of what the current study tour was about).
• Know what the options are for maintaining commercial production in an infected area. The most successful operators in France have done this by a combination of massively increasing stocking (to compensate for mortalities), and diversification into other species. These options may not be available to all Australian producers.

Testing

There are currently two main tests to detect the virus:

• Clinical observation of high mortalities
• This is relatively sensitive when the water temperature and other conditions are right – it appears that when the virus is there under the right conditions, lots of oysters will die, and it will be easy to detect (good sensitivity).
• The problems are:
• There are many other diseases that may cause mortality. Therefore the specificity of mortality as a test for OsHV-1 μ-var is not very good.
• When the conditions are not right (cooler water temperatures) oysters will not die, even if the virus is present. This means that the sensitivity is not always good.
• The PCR test
• This tests for small fragments of the viral DNA. Tests currently used either test for oyster herpes viruses in general, or specifically for the μ-var.
• The PCR test can detect very small amounts of DNA. This means that an actively infected oyster will normally give a positive test result. However, the test will also be positive if there are just fragments of DNA an no active virus. This means that a positive test result doesn’t necessarily mean that there is active infection. Dead virus may have been filtered in the water and just present in the gut, without causing disease.
• There is also a question about whether the virus can ‘hide’ in the DNA of the oyster, waiting for the right conditions to reactivate. If this occurs, it could be that the PCR test is negative, even though the oyster could later become clinically diseased and spread the virus. It is not clear whether this is a real or just hypothetical risk.

Other tests exist (histology, in-situ hybridisation, electron microscopy, etc), but these two are the main ones for practical routine use. The conclusion about the tests is that when there is clinical disease, they are pretty good, but when there is no clinical disease (when the conditions are not right for the virus), they are not much use. This has major implications for the surveillance program, and for testing efficiency.

Testing healthy oysters (in the absence of reports of mortality nearby) may not be at all efficient. If they are infected, the viral load may be too low to detect, or the virus may be dormant and undetectable – which means that a negative result can be completely trusted. On the other hand, a positive test result is useful – it shows evidence that the virus is present in some form or other in the environment, but it doesn’t prove that this oyster is currently actively infected.

There was considerable discussion within the group and with scientists that we met about how to overcome the problem of detecting the virus outside the period when the environment is suitable for disease expression. One proposal (that I think is worth investigating closely) involves placing apparently healthy oysters (from cooler water) in tanks and warming the water. There should be a rise of at least 5°C over a few days (temperature shock), and the final temperature should be over 17°C. This approach has been used by IFREMER. Their findings are that unaffected oysters continue to be healthy, but infected oysters express the virus and often die. If necessary, PCR can then be used to confirm the presence of the virus (which is now actively replicating and easy to detect).

The appeal of this approach is that

• It should be relatively inexpensive. Putting oysters in a tank for a few days doesn’t cost much. Virtually all testing in Australia is currently negative, so it would be anticipated that very few oysters would show signs of disease or die using this approach, which means that very few would need the much more expensive PCR test to confirm the presence of the virus.
• It is much more sensitive than just using PCR during the cooler period. This would allow useful surveillance to be carried out all year, allowing detection of the spread of disease to new areas before it causes a problem.

This approach should be explored under Australian conditions to confirm that it achieves better sensitivity and specificity than the PCR alone, and can be implemented at lower cost.

Surveillance

Surveillance can be done for a number of purposes. With the current Australian situation, the first objective was to determine the geographic distribution of the virus. This has already been achieved. The next objective is early detection of spread from the known infected areas.

Surveillance for early detection requires that much of the population is examined frequently. If you are only examining a small part of the population, the disease could get into the part that you aren’t looking at, and you have failed to detect it. If you don’t examine the population frequently, then your detection isn’t early.

The most practical way to test a large proportion of the population is farmer observation of clinical signs. Farmers are looking at their oysters relatively frequently, and if larger numbers die, it is pretty easy to detect. Clinical surveillance is therefore the best routine tool for early detection, when the disease will reliably show clear clinical signs (i.e. during summer). When mortality is detected, obviously this should be followed up with confirmatory testing with PCR to check that the virus is responsible.

However this approach doesn’t work during the cooler period. One option is to only do surveillance in summer, but it is possible that the disease could spread (e.g. with ships), be present and quietly spreading for months, before it is detected when the weather warms up. This would be a failure of early detection. The other option would be to take representative samples of oysters from every bay several times over winter and test them (using the method described above). This is a huge amount of work and would be quite expensive (even if it is cheaper than doing PCR on all the samples).

I suspect a compromise approach may be required. Frequent sampling from all areas may be possible, but it would probably be better to focus available resources on those areas that are at the highest risk. If the disease is going to spread, and if we understand the main mechanisms of spread, we probably have a pretty good idea of where it is likely to spread to first. It would be logical to focus our surveillance effort on these areas.

I would propose three different approaches to identifying risk areas for risk-based surveillance, covering the three different mechanisms of spread:

1)      Local spread through the water

• Areas close to currently infected areas are clearly at higher risk. For early detection of spread though the water (and by using local feral pacific oyster populations as stepping stones), I would suggest focusing surveillance on feral populations along the coast south of Botany Bay, and north of Sydney Harbour. During the summer, volunteer observers may be able to check for mortality on a weekly basis on each of the headlands in these areas (particularly between North Head and Barrenjoey). At other times, monthly samples could be taken from key populations, and tested using the warmed tank approach.

This approach should be able to provide early warning on the movement of the disease up or down the coast towards farmed populations.

2)      Spread via shipping

• Feral populations around areas of heavy shipping activity could be monitored in the same way – frequent clinical observations for mortality during summer and sampling and warming during the rest of the year. Preference should be given in the three oyster producing states to ports with lots of shipping traffic, but in particular to those receiving many ships from Botany Bay or Sydney Harbour.

3)      Spread via transfers

• As there are no transfers out of the currently known infected areas, spread by direct transfer of live oysters from the Georges River is extremely unlikely. However, if the disease got into other areas (either by local spread, shipping, or another unidentified pathway), there is a large risk that it could be further spread to other areas by transfers before it is identified, especially if the infection took place outside summer.

An area that only has transfers out but no transfers in would be at very low risk of receiving the disease, but at high risk of spreading it. In contrast, an area receiving oysters from many different locations but none going out would have a high risk of receiving it, but little risk of spreading it.

Spatial network analysis is a tool that could be used to analyse oyster transfers between bays, and identify those locations that have the highest risk of getting infected, and those that have a high risk of spreading the infection. Based on this type of analysis, it is possible to:

• design surveillance systems to focus on those areas with the highest risk, and
• identify which transfers represent the greatest danger to the industry, and seek approaches to minimising the risk by changing transfer patterns (without banning transfers or causing unnecessary disruption).

Surveillance data

For cost-effective early detection, clinical surveillance (detection and reporting of mortalities) is an important tool. To target surveillance (as well as to rapidly respond to the spread of disease) an accurate understanding of transfer patterns is required. Current systems in Australia for reporting of mortalities and collecting data about transfers are not adequate to effectively protect against and respond to the threat of OsHV-1.

The group discussed approaches to addressing these issues. At the OsHV-1 workshop in Cairns earlier this year, I put forward a proposal for a system to capture and use this type of data. Without going into too much detail (this post is already much too long), the principles of the system are that it should:

• Be industry owned and controlled
• Capture multiple types of relevant information that benefits the industry
• Reports of mortalities
• Data on transfers
• Other data of shared interest to the industry (Production? Toxins?)
• Aim to be comprehensive
• E.g. capture reports on all mortalities (even if they can be explained).
• Be confidential with strict controls on who has access to what data
• Be on-line with real-time reporting and analysis
• Be simple to use and not require transcription or double handling of data
• One option is simple SMS reports that go straight into the database
• Have automated analysis and alerts

Risk analysis and preparedness

It is important that the industry develop contingency or response plans before anything happens. My experience is with veterinary emergency response plans like AUSVETPLAN which contain valuable information about the technical response to a disease emergency. In discussion with the team, it became clear that a response plan needs to be significantly broader and include information on

• possible regulatory response options
• financial options available at the individual farm level and at an industry level including sources of assistance during the recovery phase
• social and other sources of support for producers coping with this sort of problem

Research priorities

This is my personal list of some of the research needs for the Australian industry, in approximate order of priority. Further research issues have been raised in the previous discussions.

• Management options for decreasing mortality
• Researching the relationship between depth, density, growth rate, age and size
• Cheaper, more practical tests for surveillance
• Testing the approach of warming oysters to trigger disease rather than using PCR on healthy oysters
• Development of effective clinical surveillance and transfer data capture systems
• These systems will not only help with OsHV-1 but will provide basic infrastructure to help respond to any other disease problem in the future
• Spatial network analysis
• To understand the risk of spread, both with shipping and transfers.
• Role of other species in spreading the disease
• Some of this work is already planned in France
• Development of an experimental model
• This has been done in France, and may be directly applicable to Australia
• Genomic analysis
• To understand the relationship between different strains, where it came from and how it is spreading over long distances

Thanks

Finally, I’d like to say thanks to Bruce, Rob, Tom and James for making the trip such a success and a pleasure, as well as to Cate for her help in organising, translating, driving, entertaining, charming the French and keeping us all in line. Cate and I set a pretty demanding schedule with very few moments for rest, but, despite jetlag and culture shock (and occasional tummy wobbles) the team stood up well and attacked the task with admirable dedication and good humour. I’d also like to thank the Australian industry as a whole and FRDC for the opportunity to be involved.

Conclusion – James’ thoughts

I am sure the 5 of us could write a 50 page essay on what we have experienced in France but I will keep my report as brief as I can (and leave the scientific experience to Angus & Tom).

I had a preconceived impression of the French oyster industry before I left Australia which I can now say was not what I found or expected. Yes the virus has caused significant damage to the industry as a whole but, as usual with the innovative/survival tactics of most primary producers, there have been many examples of how farmers are changing their businesses to adapt.
Growers have realised they can survive with 40% or less mortality which is becoming possible to achieve by changing growing techniques, better animal husbandry and re structuring their businesses. We have met farmers who have developed area specific farming methods which include lowering their densities, ”hardening” their stock and slowing growth rates before the summer mortality season starts and using translocation (yes, it is still an important tool in France) to minimise extended exposure periods.

One thing that was very obvious to me in all the growing regions we visited is that the more pro active farmers have diversified into other species and other regions which has obviously helped their financial situation. Some may not necessarily grow other species rather they buy in scallops, mussels, snails, abalone, lobster etc to add to their product range and become more of a seafood trader as well as a grower of oysters. A lot of these producers also have farms in more than one area which definitely spreads their risk as the mortality rate varies from year to year and from region to region.
The smaller growers who are locked into one traditional region appear to be the ones who are at the most risk and we have been told many will not survive. I am assuming this is mainly due to their inability to diversify, carry larger amounts of stock/spat and have areas too small to change their growing techniques. There also appears to be an entrenched generational attitude of “this is the way it has always been done!” These smaller growers are normally 1-2 people operations and are probably only surviving thanks to the AU$40 million annual compensation package provided by the government..
These smaller growers could possibly learn a lot and maybe even work with the larger producers. I sense attitude is dictating failure or success in most of the cases we experienced.

The spat supply situation in France is probably of the most concern for me rather than the virus. Dealing with the virus by changing farming practises and diversifying a little is only possible if you can still access stock! In France there are 4 large hatcheries and many smaller ones with another 4 or 5 being established this year, and growers are still struggling to find any spat. We were informed that every year some of the smaller hatcheries collapse due to many reasons which are no doubt due to economy of scale, large financial establishment costs, water management etc which is not helping the situation.
As the wild stock diminishes, the access to wild caught spat has decreased rapidly and farmers are now turning to the hatcheries. We do not have the wild catch option in Australia, and we rely on 2 main hatcheries and 2 smaller ones for all our stock … something which will need some serious thought and planning if the virus spreads in our country! Another critical area which has been identified by growers is the assurance from hatcheries that spat is a) virus free b) have been slower grown (no rapid growth) and c) is generally in good health. This is said to be essential to decrease the percentage of mortality.
Another issue with the hatcheries is that they are requiring payment in advance to ensure the financial security of their hatchery business. With farmers under financial pressure, the hatcheries have to ensure their survival by avoiding bad debt, something which the farmers appear to accept but find difficult to deal with.

When I arrive home, and without pre-empting any reports from this visit and as a farmer, my personal interest will be focused on continuation of good animal husbandry on my farm (through lower density farming, developing handling protocols pre summer, reducing the stress post spawning etc), working with industry in developing genetic programs for disease resistant stock, having a stronger financial security strategy (ie cash reserves) and communicating with government on the industry issues.
After seeing the effects of the virus first hand, if there is any advice I could offer my fellow farmers back in Australia it is definitely the following;
1) Report any mortality events immediately. The French can teach us a few things about managing the virus but the most important message we received is identify the virus as quickly as possible. I am now more confident we could get through and manage any crisis if we communicate and work together.
2) If the virus is ever detected in any growing regions, cease all translocations immediately from all growing areas (within states). Again the French have shown that translocation of stock can still be a useful tool in the right conditions but adopt a sit and watch approach rather than business as usual or worse, panic.
3) Make sure our hatchery stock is virus free. An obvious but important point so that we do not spread any virus to uninfected areas and we have the confidence and security in our spat suppliers.

I would like to thank the team of Rob, Bruce, Tom, and Angus & Cate for a very informative trip. I thought the group worked well together and we all had our areas of strength which filled in most of the gaps. It was fast, and sometimes furious, but it was definitely the hardest working, most informative, and hopefully policy driven study trip I have experienced. I would also like to thank my fellow directors of Tas Prime Oysters Pty Ltd for funding my part in the operation.
If any growers wish to discuss any topics or just a general chat, please feel free to flick me an email at James.Calvert@bigpond.com
Au Revoir

Well done Angus Cameron and Cate McKenzie

On behalf of the Australian industry, I would like to say very well done to Angus and Cate for their fantastic effort to organise our trip to France.

Their organisation, planning and delivery where absolutely fantastic, and to me the success of the trip was achieved very much by their efforts.

We asked a lot of them and they honestly over delivered.

A very big thank you to the rest of the team, all of whom put in without hesitation and inputs were highly valued. Another big thank you to the FRDC for funding this project and believing in us to deliver against our stated aims. Special note that James Calvert funded his own participation, and we genuinely thank him for that highly valued personal commitment

One final thank you the industry bodies in each state for kicking in the extra funding needed to get the project over the line.

 

Density, what is the French Experience

One of the main views of the French industry held by many in Australia is in the regard to  the high densities used in their oyster culture. We had a good go at trying to understand this and what effect it has on the virus. Just like everything else in France, it appears to be a complicated answer, and not completely as it seems to us.

I think the main thing to understand is that density is used to achieve a range of things in France, and it depends on the region. On parts of the Atlantic Coast, it can be used to speed up growth depending on how rough the location is (we heard about some examples of this in the Normandy Region), by having more oysters in the pockets to aid in protection (this was probably not the norm however).

In the Arcachon region and other areas however, it is actually used to slow down growth from what we were told. This seems to alter how the management of the virus is undertaken. One of the key things we were told is that carefully managing your growth over the summer months when the virus is most active is very important. This is why we were repeatedly told to have the spat “close to shore”, which in Australia we would interpret as having your spat more exposed.

So, in areas that are rougher, lowering your densities seems to provide some help, particularly if you can place your young oysters to “rumble” without over doing it. This is where we are hearing that the Australian adjustable long line systems (or similar systems) seem to be helping. However, in areas that aren’t exposed, the Australian style of systems are seen to make the virus worse as they speed up growth due to lower stocking densities, which then brings on higher level of mortality. However, it goes without saying that this approach is a catch 22 as it also increases the viral loading in the water.

Interestingly enough, in the Thau Lagoon on the Mediterranean, their system of what we would possibly interpret as a modified subtidal system with ropes of oysters hanging from “tables” (they actually don’t consider this system subtidal from what I can gather), the rules seem to change again.

This system to me is actually similar to the raft subtidal system used by NSW growers, where trays of oysters are suspended below rafts and then placed on the raft to dry from time to time.

The problem here is that these oysters are grown quicker than other parts of France due to the type of system, and the faster growth plus warmer waters of the Mediterranean over the summer intensify the effect of the mortalities, making this the hardest hit region of France from what we can gather.

The Thau Lagoon is a virtually land locked large lagoon of what that is highly productive but actually has no tide as we know it, hence the development of a system that requires the raising of the oysters to allow exposure. This intensive rapid growth culture technique combined with low overall flushing (therefore higher viral loadings) seems to have created a real hotspot for the virus. There are some small canals linking the lagoon to the Mediterranean, but there would be hardly any real water exchange.

Interestingly enough, there are pacific oysters outside of the lagoon that don’t have the virus. However, these are actually the worst oysters you can put inside the lagoon, as they die very quickly when put in there apparently. We suggested to one grower that they may be interested in trying out the NSW style of subtidal as an experiment, where individual bags of oysters have their own float, and the bags are turned regularly. There is a very similar system in Canada I think call Oystergro, which has a website and is used for their Virginica.

However, the French may find that these style of systems struggles to give the commercial quantaties needed to be commercially viable given the level of production obtained from the tables when things are normal???

Hopes this helps explains some things (or possibly confuses it a bit more)

 

 

 

 

Thursday November 10

The last day and we had the bright idea (all so we thought) before we left home to bound out of bed at 2.30am to go and visit Rungis food markets….
Rungis is the largest “food” market on the planet and covers several square kilometers (I think we must have covered about 6 or 7 kms and would not have seen half of it!!). The seafood section was incredibly clean and did not have the usual scent of other fish markets, in fact it hardly had a scent at all! Every possible species of fish and shellfish available in Europe were presented on show in a very controlled and efficient buying process.
There are laws in France for consuming oysters where all product may only be opened (processed) for a maximum of 24 hours prior to consumption. This obviously means that all fish shops & restaurants have to buy & store the product live and only split/process when about to be consumed. Not sure if our markets could tollerate this back home! It is all part of the great traditions associated with the French oyster industry.

After a quick 2 hour power nap and lunch, it was on to the country’s goverment fisheries department for a meeting with officials. The government representatives gave us a full run down on industry statistics and organisation structures which proved to be a little surprising. Although France may regulate its own industry, when it comes to trade or translocation of product then the European Commission has the final say. This proved to be unfortunate for other countries such as Ireland & England who were worried about the translocation protocols when the disease hit in 2008. The EC has only one rule and that rule is for the whole of Europe, not just particular individuals! When Ireland & England expressed concerns about possibly spreading the virus through spat transfers, this was somewhat ingnored and the final result is that all oyster producing European country’s now have the virus!!

It was interesting to hear that the French government are paying 30 million Euros per year in compensation to the growers for their losses. The figure quoted by the government was 12% of all mortalities/losses were claimable under the anually reviewed scheme.
Other issues discussed were genetic breeding programs, research priorities and their relationships with industry, all information we had previously heard.

So, at 4pm, it was time for some site seeing around Paris … Aussie style! A $30 taxi fare gave us 30 minutes to drive around the Arc de Triomphe (twice!), past the Louvre, down the Champs Elysees and back to the hotel for a 20 minute beer & debrief. Rob, Bruce & Tom then left for the airport to start their long journey home.

Although this is the end of trip, all the team members will be posting their thoughts on the blog site over the coming days so please keep the questions coming!

I am confident in speaking on behalf of the team that this trip would not have been anywhere near the success it has been if it were not for the efforts of Angus & Cate. Through some difficult driving conditions, some intense translation sessions, accommodation & meal planning and putting up with the needs of 4 excited/tired/confused Australians, Angus & Cate provided a very educational, humerous, hectic and thoroughly enjoyable 10 days around France
Thanks Angus & Cate, an exceptional job (Maaaaaate!)

Wednesday November 9

After speeding into Paris on board the 300+km/hr train, the team was guided amazingly well by Angus through the maze of underground train systems to meet up at the head qurters of the CNC

After a tour through the very impresive CNC HQ, President Goulven Brest introduced the CNC office team which included; Communication officer, Environment officer, Financial contoller, Executive officer, Administartion and the President. All of CNC’s expenses (which we estimate at approx $800K+) are covered by the country’s oyster growers.

After a lunch provided by the CNC, the team sat down to discuss the purpose of our trip and a general exchange of information.
One interesting direction the CNC are headed in their fight of the virus is the introduction of stock from Japan. There is a reasonable consensus from growers that because Japan introduced them to the Pacific oyster in the early 1970′s, and due to the micro varient not being found in Japan, seem to beleive it is worth the risk to find resistent brood stock.
The risk is potentially bringing in other viruses that currently do not exist in France. The first batch of tested Japanese stock did have the original herpes virus but not the micro variant (Stress testing was proved inconclusive). The second batch was due to be picked up earlier this year but the tsunami decimated the Japanese industry and a revised trip will most likely occur soon.

Goulven remained positive about the industry and supported the direction of finding the solutions in genetics and animal husbandry. It appears that the industry would settle for 40% (or less) mortality and could operate on a viable basis if this could be achieved.

 Goulven also shared his thoughts on the current market situation in France and research has shown demand has decreased since the mortalitiy event of 2008 and this was due to increased prices. When questioned on whether this trend may continue, Goulven predicted prices may drop if production increases and the industry can supply the market demand. Production has fallen from 140,000 tons (140 million dozen) in 2007 down to 72,000 tons in 2010. It was expected that production would level out at this figure until things improve.   

After 2 big days of travel the team were a bit worn out and had a very early night to prepare for a very early start on Thursday

Tuesday 8th

Monday was a big travelling day: Arcachon to the Thau lagoon. Well driven and navigated Cate and Angus!

On Tuesday we were able to visit two companies operating on the Thau Lagoon – Medithau and Maredoc.

Medithau grows their own oysters and has diversified into processing oysters and mussels from 4 other countries. The owner, Jean-Jaques, reported oyster production in the Lagoon has dropped from 40,000 tonnes (about 40 million dozen) to 6,000 tonnes. A huge drop that is really squeezing those who cannot diversify.

Maredoc employs about 45 people in full production. The Thau Lagoon is almost landlocked and has very little tide. Oysters are grown by attaching them to ropes hung from “tables” out on the water. Each rope is 3-5m long depending on the water depth and the tables we estimate are about 10x30m. In a good year, each table can produce 7-15 tonnes of oysters (deeper water means longer ropes means more oysters).

Ropes are wound up – to bring the oysters out of the water – for about 12 hours a week to imitate tidal movement. Some do this by hand! Medithau uses solar powered motors on some tables – and get a lot of useful marketing attention for doing so.

Mortalities observed by Medithau seem to be lowest near the surface. Jean-Jaques thinks this is related to UV exposure. It could also be due to the oysters being in rougher water and getting bashed around a bit more than deeper ones. This seems to fit with other observations that slower growing oysters survive the virus better than fast growing ones.

While at Medithau we also had opportunity to speak with two IFREMER researchers (I can only recall first names at present – Fabrice and Emmanuelle). This was a very useful conversation and we heard of research just underway or planned that will help shed light on relationships between mortalities, water temperature and virus load. This summer they will also look into the degree to which other species (shellfish and zooplankton) can act as (non-diseased) vectors of the virus and pass it on to oysters.

These folk also reported that they had mortality-age-size results that conflicted with what we’d heard from further north. They are looking into this, but it adds to thoughts that the environment in which the oysters are grown can influence the way this disease manifests.

We heard that PCR testing results will be virtually meaningless while the virus is dormant in oysters, which means we need to consider PCR-based surveillance results very carefully. On pursuing this line of conversation, we heard that the virus can be activated by bringing oysters up above the temperature threshold of 17C or so over a few days. This highlights a potentially cheaper way of testing for the virus than PCR: if you temperature “shock” oysters and they have the dormant virus, then it will activate and they’ll probably die. We think this should be followed up in Australia with parallel PCR testing until we can be confident that a simple temperature stress test will let us know if the virus is present or not.

Next stop was Maredoc – a smaller oyster producing company that also is diversifying into importing and processing shellfish from other countries. Maredoc produces oysters on ropes from tables like Medithau, and has an intermediate step in which they grow smaller stock in lantern cages before gluing them to ropes. They’ve seen no pattern in mortalities between lantern cage culture and rope culture. They think mortalities start earlier in stock near the surface, and that overall mortalities are LOWER near the surface. At least this seems to be consistent.

Maredoc reported that they’ve seen the same stock survive on one farm and die on a nearby one. Environmental and husbandry factors really do seem to be important.

Today (Wednesday) we said an early goodbye to Cate at Montpelier train station and the boys are now heading by fast train to Paris for more meetings (today and tomorrow) with national oyster committee members (hopefully the president) and a visit to the famed fish market before hopping on the plane on Thursday night.

Sunday 6th November

The team headed off early from La Tremblade and arrived at Arcachon late morning.
Arcachon is a large basin/bay with approx 130 growers producing 7,000 tons (7 million dozen) and employing 1,500 FTE and casual staff. we met up with the regional CNC chairman Olivier Laban who gave us a run down of the problems faced in Arcachon.
Olivier and his fellow farmers have been hit hard by the virus with up to 80% mortality last season which is placing a large financial and personal pressure on the farmers.
One of the current associated problems Olivier is facing is the lack of spat supply. With the wild population being decimated, farmers have no choice but to switch from wild caught spat across to hatchery stock but demand has seen farmers paying up front for orders and still waiting for delivery several months later, just another financial burden he did not need.
Olivier explained in detail the structure of the CNC organisation which is based around representatives from the 7 growing regions who each elect a committee of 30 growers to deal with the issues in their particular region. Of these 30 committee members, a chairman and 6 other growers are chosen to sit on the national CNC board which, along whith a few processors, transport reps etc, has a full board of over 50 sitting members. The 50 strong board meet twice a year in Paris.
While sitting down with Olivier over lunch, one could not help but feel a sense of fellowship with the French farmers and I feel extremely sympathetic and saddened when you hear how tough these families are traveling. While we sit back a million miles away in Australia, I cannot help but think how lucky we all are and also how we need to prepare ourselves in case this bloody virus ever spreads accross our country, as it has done in france. Before this trip I initially thought distance would be our saviour back home but with the virus spreading from the south of Spain all the way up north to Ireland & Holland, and accorss temperature ranges of 28+ down to 6 or 7, I think we need to prepare a strategy/response mechnism very soon.

Saturday, 5th November

The group visited the IFREMER research station at La Tremblade in the morning and had the pleasure of Tristan Renault and Isobelle Arzul’s company for the morning.

This was a very informative session for the group, as both of these leading IFREMER scientists have been at the forefront of research into the virus.

We were informed of the new technique for breeding tetraploids directly from diploids, instead of the current method using triploids. IFREMER have patented this new technique throughout the world and are now using it for all their tetraploid production.

IFREMER own all tetraploid broodstock in France, and hatcheries get male tetraploids that are microchipped from them. The dead shells have to be returned.

It would appear that IFREMER have a better understanding of the biodiversity of the virus pre 2008 on an international basis. Interestingly enough, it was felt that the classical virus hasn’t actually disappeared in France. The difference is that it is no longer found in oysters that have suffered mortalities.

Interestingly enough, the PCR will only detect the most prevalent variation of the virus, if there is more than one present. It is felt that it is possible to miss the virus by PCR analysis while the virus isn’t active or dormant. Also, it is possible to miss viral particles by not testing all of the oyster meat.

We also discussed experimental infection models and apparently the models used have been recently published. There appear to be 2, one based on direct injection, the other based on cohabitation. Both Tristan and Isobelle believed that there is no need to develop any more unless there is clear explanation of why it would be needed.

Another area discussed was whether there was a rapid test outside of PCR. Apparently there was some attempt to develop a commercial kit for farmers, but it was found to be too difficult, One interesting point for monitoring was that if the idea of monitoring a bay/estuary was simply to see whether the virus was present, they could not understand why we wouldn’t simply “pool” the samples from a region. Apparently this has been done in Britain.

Another point was in relation to standardising the PCR testing. Tristan has written a chapter within the OIE manual about general standardisation of testing, adopted by the OIE in May, which is a “non binding standard”. It was felt that this standard should be used by all PCR Analysis to test and measure the virus.

In the afternoon, we had the luck to visit what would have to be one of the most advanced hatcheries in the world, which we are still talking about. Eric, the owner of the hatchery discussed aspects of the virus prior to the hatchery tour. It is just well we did it this way around, as we were completely “gobsmacked” when we finished.

One of the very interesting points Eric raised was that he felt the virus attacked the rapidly growing mantle of the oyster when it is active. This would also correlate with growth. He also did not feel that there was “vertical transmission” from broodstock to larvae as such. He felt it was important to not use broodstock showing any signs of the virus.

He also agreed that management of the virus started in the hatchery with good quality spat critical. From discussions with him, it would appear that they have another site for their nursery. This seems to involved a large system almost like an enclosed long trench that is continuously recirculating, where fresh seawater is only added when needed to minimise introduction of the virus.

Eric also runs his own private breeding programme from what we can gather. The current site he is on was recently established, with the old site being used as a hatchery completely dedicated to his breeding program. He currently runs about 200 family lines, with gradual increasing resistance to the virus in some lines (still relatively low at this point in time). He believes he needs to get to about 1000 family lines to achieve what he wants to do.

Rob’s thoughts.

Robs thoughts on husbandry issues to help with management of POMS.

Keeping the growth rates low in the summer time (high risk) for younger oysters. Perhaps manipulate by putting oysters in areas of slower growth or use heights for culture manipulation at high risk times.

Slowing the growth down without stressing the oysters out is important over times when the virus is about to start.

The breeding program is probably going to be our most important tool in Australia. To build a good resistant pacific oyster, diploid and triploid. We should monitor any mortalities with pacific oysters out in the wild north and south of  Botany Bay to help up with a bit more knowledge of how this disease may be spread in NSW.

An emphasis on good husbandry is an overall good management tool for the virus, which starts in the hatchery and nursery before even going to the oyster farmer.