Should we care that a "Mystery Virus" has almost driven a species of turtle to the brink of extinction?? Yeah, Nah, Sort of, Not really?
Overview
So what do we know. It is worth a recap.
1. Over a three week period from mid February 2015, around 500 turtles were recovered dead or displaying external symptoms of a disease and were subsequently euthanased (Spencer 2015)
2. The disease presented symptoms of lesions throughout the body, but particularly around the eyes, making the turtle blind (Britton 2015).
3. 17 turtles were retrieved from the upper reaches of the River as a captive insurance population before the disease had reached these upper catchment populations (ABC News 2015).
4. The disease appeared to be travelling at ~2km per day from downstream to upstream populations (NSW DPI 2015).
5. A press release suggested the disease was a 'Mystery Virus' in September 2015. It was announced by the member for Oxley, Melinda Pavey (Pavey Vimeo 2015). There has been no follow up announcements or scientific publications presenting data to this date.
6. 20 juveniles were collected in limited surveys of the River in November 2015 (Bellingen Courier 2015)
7. A much larger survey in March 2016 confirmed that the remaining turtles in the River are predominantly juveniles (Bellingen Courier 2016).
What does it mean?
Basically, a 'Mystery Virus' has essentially killed the adult population, but largely left juveniles unaffected in the River and no other species has been obviously affected.
The initial announcement from local member of the NSW legislative council, Melinda Pavey.
"It does not mean that there is something wrong with our beautiful River".
There is strong evidence that the turtles were underweight at the time of the disease breakout. Turtles were described as "emaciated" (NSW DPI 2015). Hence it is worth investigating environmental parameters from that area since that time.
It's a Dry Heat
I am now going to get into the data on long and short-term water and temperature data, because "The Epidemiological Triad" suggests that climate-related shifts in pathogen and host ranges can increase exposure to new diseases (reviewed in Smith et al. 2009), as well as, increase stress levels of the host.
Changing climatic conditions can influence the spread of novel viruses and perhaps the chain may have repaired itself if a new pathogen did not proliferate through the population, however, the key to population recovery lies central to understanding the broken parts of the chain and whether turtles can display future resilience. That will rely on understanding ontogenetic changes in their ecology and identifying threats to their survival.
Recovery of the Species?
August 31st 2015 was the date when the press reported that a mystery disease that wiped out the Bellinger River Snapping Turtle- 18 months on, nothing else has been released and we still do not know what caused it and it is possible we will never know.
Going forward, there is no clear plan on whether the species can recover with or without human intervention. So for the species to recover and planning by government agencies and researchers, you would think this small detail would be important to know. But is it?
In this blog, I argue that the virus is largely one of many catastrophic events that could have affected the turtle and in planning for the recovery of the species, we need to treat it that way- just one of many factors that could affect the turtle.
From a logistics perspective (ie. quarantine procedures etc), the virus is importsnt, but from a conservation planning perspective, the virus is likely to be the spectacular culmination of a series of ecological or biological perturbations that affected the turtles well before the outbreak.
Going forward, we need to address issues 'further up the chain', before investing too much into a 'Mystery Virus'. We have all heard the expression "prevention is better than a cure"- We don't need a cure- there are currently no sick turtles alive- so understanding the processes that let a 'Mystery Virus' proliferate is of far greater relevance and importance for planning the recovery of a species that is on the brink of extinction.
So what do we know. It is worth a recap.
1. Over a three week period from mid February 2015, around 500 turtles were recovered dead or displaying external symptoms of a disease and were subsequently euthanased (Spencer 2015)
2. The disease presented symptoms of lesions throughout the body, but particularly around the eyes, making the turtle blind (Britton 2015).
3. 17 turtles were retrieved from the upper reaches of the River as a captive insurance population before the disease had reached these upper catchment populations (ABC News 2015).
4. The disease appeared to be travelling at ~2km per day from downstream to upstream populations (NSW DPI 2015).
5. A press release suggested the disease was a 'Mystery Virus' in September 2015. It was announced by the member for Oxley, Melinda Pavey (Pavey Vimeo 2015). There has been no follow up announcements or scientific publications presenting data to this date.
6. 20 juveniles were collected in limited surveys of the River in November 2015 (Bellingen Courier 2015)
7. A much larger survey in March 2016 confirmed that the remaining turtles in the River are predominantly juveniles (Bellingen Courier 2016).
What does it mean?
Basically, a 'Mystery Virus' has essentially killed the adult population, but largely left juveniles unaffected in the River and no other species has been obviously affected.
The recovery of a species relies primarily on a handful of adult females rescued before they became victims of the disease and a population of juveniles. It is equivalent to leaving the planet to a small number of 5-10 year old humans to eventually repopulate the planet. The likelihood of extinction is very high; the path to recovering the species is complex and has little room for error, but this will be discussed a little later.
The 'Mystery Virus'
Can a disease be that virulent and target-specific to travel upstream at ~2km per day and affect only a portion of the population of single species? If the carrier was traversing upstream and were consumed by adult Snapping turtles only, then possibly.
The 'Mystery Virus'
Can a disease be that virulent and target-specific to travel upstream at ~2km per day and affect only a portion of the population of single species? If the carrier was traversing upstream and were consumed by adult Snapping turtles only, then possibly.
Intraspecific differences in diet are generally related to size with juveniles consuming very little plant material, ephemeropteran larvae and odonate lymphs compared to adult Bellinger River Snapping Turtles (Allanson and Georges 1998). Items like fish, a prime candidate for this type of transmission, are not common food items because short-necked turtles are unable to catch them (Spencer et al. 1998) and probably consume them as carrion.
All turtle species and all size-classes in the River consume fish as carrion. No dead fish were observed during the February/March 2015 emergency surveys. Ephemeropteran or odonate nymphs are also unlikely to be a source for a disease spread through consumption. The closely related species, Emydura macquarii, is a generalist and would have also been consuming similar foods (Spencer et al. 2014).
A suggested hypothesis for the spread of the disease is associated with faster moving eels, as the spread rate during the event occurred upstream at a rate faster than turtles are able to move and eels are one of the few species in that waterway that would routinely move upstream (Moloney et al. 2015). Eels could have spread the disease, but you would still expect turtles other than adult turtles from a single species to be affected. Juveniles are found in the same waterholes as adults, eels, catfish, other species of turtle. The big question is why were only adults from a single species affected if many other organisms had been exposed to the virus, including juveniles of the same species?
The Epidemiological Triad
Identifying the cause of wildlife diseases is difficult because rarely can a single factor be identified as responsible, a concept commonly termed the ‘epidemiological triad’. In addition to immune suppression related to exceeded stress responses and pollutant exposure, environmental change can impinge directly on wildlife health and survival and, consequently, affect the viability of their populations in various intricate ways. For example, climate-related shifts in pathogen and host ranges and pathogen spillover from humans and domestic animals can both increase exposure to new diseases (reviewed in Smith et al. 2009).
A suggested hypothesis for the spread of the disease is associated with faster moving eels, as the spread rate during the event occurred upstream at a rate faster than turtles are able to move and eels are one of the few species in that waterway that would routinely move upstream (Moloney et al. 2015). Eels could have spread the disease, but you would still expect turtles other than adult turtles from a single species to be affected. Juveniles are found in the same waterholes as adults, eels, catfish, other species of turtle. The big question is why were only adults from a single species affected if many other organisms had been exposed to the virus, including juveniles of the same species?
The Epidemiological Triad
Identifying the cause of wildlife diseases is difficult because rarely can a single factor be identified as responsible, a concept commonly termed the ‘epidemiological triad’. In addition to immune suppression related to exceeded stress responses and pollutant exposure, environmental change can impinge directly on wildlife health and survival and, consequently, affect the viability of their populations in various intricate ways. For example, climate-related shifts in pathogen and host ranges and pathogen spillover from humans and domestic animals can both increase exposure to new diseases (reviewed in Smith et al. 2009).
Similarly, changes in habitat size or quality might lead to a reduction in prey population sizes and increased competition for resources (Ryall & Fahrig 2006), which in turn might augment starvation and lead to disease and/or death. Effects will be further complicated if the genetic makeup of the affected populations has been compromised owing to reduced gene flow or inbreeding, as low levels of genetic diversity tend to be correlated with reduced fitness and lowered evolutionary potential (Spielman et al. 2004).
All three aspects of the triad apply here to varying degrees. Given that the epidemiological triad relies on external factors such as environmental parameters, changes in habitat quality and the genetic makeup of the populations, the disease itself becomes irrelevant (to a significant extent). It is relatively unusual for infectious diseases to be the sole cause of endangerment for a species (Smith et al. 2006). Disease can wipe out an entire species. Rats native to Australia's Christmas Island fell prey to "hyperdisease conditions" caused by a pathogen that led to the rodents' extinction. This was classic exposure of a species to a novel pathogen. Ship-jumping black rats carried a protozoan known as Trypanosoma lewisi (ABC News 2008). On this Island population, it appears that the population was driven low enough to become prone to extinction.
"Not every rat would have to be infected," Greenwood explains. "If you push a population down to an unsustainable number then it will collapse. In addition, if a substantial number of reproducing individuals became infected and ill, even if they survived the infection, their reproduction rate may be lowered and lead to a population crash."
The case of the Bellinger River Snapping Turtle is likely to be very different in that the disease has not driven a healthy stable population to the brink of extinction, the turtle population was possibly already in decline and the 'Mystery Virus' proliferated through an immune challenged population. If a virus proliferated through a healthy population, then you would expect the population to be decimated, but the virus would not selectively target any cohort or sex, even if the genetic makeup of the population exhibited low levels of genetic diversity.
All three aspects of the triad apply here to varying degrees. Given that the epidemiological triad relies on external factors such as environmental parameters, changes in habitat quality and the genetic makeup of the populations, the disease itself becomes irrelevant (to a significant extent). It is relatively unusual for infectious diseases to be the sole cause of endangerment for a species (Smith et al. 2006). Disease can wipe out an entire species. Rats native to Australia's Christmas Island fell prey to "hyperdisease conditions" caused by a pathogen that led to the rodents' extinction. This was classic exposure of a species to a novel pathogen. Ship-jumping black rats carried a protozoan known as Trypanosoma lewisi (ABC News 2008). On this Island population, it appears that the population was driven low enough to become prone to extinction.
"Not every rat would have to be infected," Greenwood explains. "If you push a population down to an unsustainable number then it will collapse. In addition, if a substantial number of reproducing individuals became infected and ill, even if they survived the infection, their reproduction rate may be lowered and lead to a population crash."
The case of the Bellinger River Snapping Turtle is likely to be very different in that the disease has not driven a healthy stable population to the brink of extinction, the turtle population was possibly already in decline and the 'Mystery Virus' proliferated through an immune challenged population. If a virus proliferated through a healthy population, then you would expect the population to be decimated, but the virus would not selectively target any cohort or sex, even if the genetic makeup of the population exhibited low levels of genetic diversity.
However, if we look at the population structure between 2007 and the dead turtles collected in 2015, it is clear that the juvenile population escaped the effects of the disease. At first, small turtles may have simply been missed in the collection of sick or dead animals in 2015, but the November 2015 and March 2016 surveys clear demonstrate that turtles less than 100mm plastron length (probably aged 3-5yo) survived the outbreak and those older than that did not. What this means is that <10% of the population remains.
The novel virus hypothesis/low genetic diversity argument is important and may help explain the difference in mortality between the Snapping turtles and the introduced Emydura macquarii, but it does not explain the difference in mortality between adults and juveniles, if anything, juveniles from the same cohort are likely to have lower genetic diversity than the adult population, because the juveniles are likely to have come from a limited number of nests. Remember, these turtles can produce more than 20 eggs per nest (Cann 1998) and if a nest survives, it is a good chance that most of the hatchlings from the same nest would emerge. Similarly, the 2-5yo turtles are coming from mothers and fathers that did not survive the pathogen.
Stop Worrying- Nothing to See Here?
The 'Mystery Virus' is likely to be a spectacular end of a chain that has many broken links and I argue, we need to focus on where the links are broken, rather than concentrate on a 'Mystery Virus', particularly if we want to prevent a die-off of this magnitude occurring in other catchments and to eventually repopulate the River with Bellinger River Snapping Turtles.
Fig. 1. Population changes in body size. Histograms (percentage of animals) of (a) juveniles and females and (b) males captured in 2007 (light grey) and 2015 (dark grey).
The novel virus hypothesis/low genetic diversity argument is important and may help explain the difference in mortality between the Snapping turtles and the introduced Emydura macquarii, but it does not explain the difference in mortality between adults and juveniles, if anything, juveniles from the same cohort are likely to have lower genetic diversity than the adult population, because the juveniles are likely to have come from a limited number of nests. Remember, these turtles can produce more than 20 eggs per nest (Cann 1998) and if a nest survives, it is a good chance that most of the hatchlings from the same nest would emerge. Similarly, the 2-5yo turtles are coming from mothers and fathers that did not survive the pathogen.
Stop Worrying- Nothing to See Here?
The 'Mystery Virus' is likely to be a spectacular end of a chain that has many broken links and I argue, we need to focus on where the links are broken, rather than concentrate on a 'Mystery Virus', particularly if we want to prevent a die-off of this magnitude occurring in other catchments and to eventually repopulate the River with Bellinger River Snapping Turtles.
The 'Mystery Virus' press coverage in August 2016 came over as a great breakthrough, but there was no detail provided. Community communication and consultation is important, but this press release did not relieve community concerns about the state of the River, going by the Bellingen community Facebook site, attending community group meetings, and having well respected members of the community expressing cynicism at the announcement.
It failed in the scientific community too. There has been no data presented to the scientific community about the virus or to recovery teams involved in the conservation and management of this species or the captive breeding population.
The initial announcement from local member of the NSW legislative council, Melinda Pavey.
"It does not mean that there is something wrong with our beautiful River"- this was repeated several times (Pavey Vimeo).
I truly believe that the local member was sincere in her statement because the information in the press release was structured to sound like the cause of death was discovered and that sampling for a contaminant turned up negative results (Bellingen Shire Council).
All this may be true, but none of this data is available. Yes turtles may have died (possibly from a virus); yes limited tests for contamination may have come back negative (so we are told). But from my perspective, we cannot accept that there is nothing wrong with a River based on these two pieces of information, with no data presented. We need to delve a little more forensically into things.
"It does not mean that there is something wrong with our beautiful River".
Let's look at this forensically. Does the discovery of a virus mean that there is nothing wrong with the river? and what does "wrong" actually mean?
Discovery of a novel virus killing turtles certainly does not mean that there is nothing "wrong" with the River. Just go to any country where you cannot drink the tap water to realise that. Surface waters and tap water qualities of both developed and developing countries have continued to deteriorate. Enterovirus bearers are in sewage, sewage sediments, rivers receiving sewage , as well as treated sewage. The sources of enteroviruses may be groundwaters, coastal river waters, coastal marine waters, aerosols emitted from sewage treatment plants and from solid waste landfills, soils and insufficiently treated drinking water (see Kocwa-Haluch 2001).
Discovery of a novel virus killing turtles certainly does not mean that there is nothing "wrong" with the River. Just go to any country where you cannot drink the tap water to realise that. Surface waters and tap water qualities of both developed and developing countries have continued to deteriorate. Enterovirus bearers are in sewage, sewage sediments, rivers receiving sewage , as well as treated sewage. The sources of enteroviruses may be groundwaters, coastal river waters, coastal marine waters, aerosols emitted from sewage treatment plants and from solid waste landfills, soils and insufficiently treated drinking water (see Kocwa-Haluch 2001).
So the discovery of a disease killing turtles should not stop us continuing to question whether there is something "wrong" with the River. If anything, it should make us question it a little more- question why a novel "Mystery Virus" could become so pathogenic so quickly.
"Wrong" is largely defined by what we classify as water quality. For the general public, to which Melinda Pavey was addressing, a turtle virus probably means that there has been no large one off toxic chemical spill. We could deduce that without looking for a virus or even doing a one off test for standard toxins- no other organism seemed affected. But as the Epidemiological Triad suggests above, "In addition to immune suppression related to exceeded stress responses and pollutant exposure, environmental change can impinge directly on wildlife health and survival and, consequently, affect the viability of their populations in various intricate ways." So perhaps we need to broaden the definition of "wrong" to evaluate environmental factors (abiotic and biotic) that may have led to immune suppression in the particular cohorts of turtles affected.
"Wrong" is largely defined by what we classify as water quality. For the general public, to which Melinda Pavey was addressing, a turtle virus probably means that there has been no large one off toxic chemical spill. We could deduce that without looking for a virus or even doing a one off test for standard toxins- no other organism seemed affected. But as the Epidemiological Triad suggests above, "In addition to immune suppression related to exceeded stress responses and pollutant exposure, environmental change can impinge directly on wildlife health and survival and, consequently, affect the viability of their populations in various intricate ways." So perhaps we need to broaden the definition of "wrong" to evaluate environmental factors (abiotic and biotic) that may have led to immune suppression in the particular cohorts of turtles affected.
There is strong evidence that the turtles were underweight at the time of the disease breakout. Turtles were described as "emaciated" (NSW DPI 2015). Hence it is worth investigating environmental parameters from that area since that time.
It's a Dry Heat
I am now going to get into the data on long and short-term water and temperature data, because "The Epidemiological Triad" suggests that climate-related shifts in pathogen and host ranges can increase exposure to new diseases (reviewed in Smith et al. 2009), as well as, increase stress levels of the host.
Average water course levels at Thora were well below average for the last three years (Fig. 2), with water levels almost 30% below average in 2014. Deaths were recorded less than a week after a minor-moderate flood in February 2015 (Fig. 3). Over the 32 year period, average water course height at Thora was ~2m, however from Spring 2011-April 2015, water course levels average ~1.5m (Fig. 3). During this period, only one moderate-major flood occurred in the River until the flood surrounding the disease outbreak in February 2015. It is likely that low River levels negated two minor flood levels in 2013/2014 (Fig. 3).
Fig. 4(a). Cumulative differences from mean daily maximum temperatures over the last five decades and (b) Cumulative differences from mean daily maximum temperatures over the last five years- South West Rocks BOM Site number: 059030 (~60km from Thora).
So What Does It Mean?
Bottom-line. There has been a significant warming event occurring for several decades and this was magnified over the two years prior to the disease outbreak. The water levels in the River have not fully reflected rainfall trends and have been declining since 2012. There was the long period without a flood event in the River. The outbreak of the "Mystery Virus" coincided with significant rain and a minor flood over a three week period. Prior to February 2015, there had not been a flood in the River since 2011/2012, which is a significant period without a flood for the River (Fig. 4).
The region's temperatures are changing and combined with the River's abnormal flow patterns over the last few years- it is a classic pattern of broad-scale environmental patterns interacting (directly or indirectly) with local patterns to create extreme conditions- ie. Climate Change.
Fig. 2. Annual changes from the mean in water course levels from 1983 to 2014 in the Bellinger River at (a) Thora (lat.-30.4259 ,lon. 152.7809) and (b) the Manning River at Killawarra lat:-31.9175 lon: 152.3117)
Fig. 3.Monthly averages of water course levels at Thora from 1982-2015. Solid black line is average levels over the same time period. Dotted lines represent minor (3m), moderate (4.5m) and major (5.8m) flood levels in the River. Deaths we first observed just after a minor-moderate flood in February 2015.
Significant warming has occurred in the region since 1965. Cumulative differences from mean daily maximum temperatures were calculated for each decade and the degree of warming in the region has been 8-9 times greater in the last decade compared to 1965-1974 (Fig. 4a). Mean daily minimum temperatures demonstrated similar trends, with warming occurring even earlier. Looking specifically at the last five years, the degree of heating in the region in 2014 was almost twice as large as compared to 2010.
So What Does It Mean?
Bottom-line. There has been a significant warming event occurring for several decades and this was magnified over the two years prior to the disease outbreak. The water levels in the River have not fully reflected rainfall trends and have been declining since 2012. There was the long period without a flood event in the River. The outbreak of the "Mystery Virus" coincided with significant rain and a minor flood over a three week period. Prior to February 2015, there had not been a flood in the River since 2011/2012, which is a significant period without a flood for the River (Fig. 4).
The region's temperatures are changing and combined with the River's abnormal flow patterns over the last few years- it is a classic pattern of broad-scale environmental patterns interacting (directly or indirectly) with local patterns to create extreme conditions- ie. Climate Change.
This article is not a debate of the validity of human induced climate change, but it does help put data to what people have been saying about the River over the last decade. The Banana farmers in the region will testify to this too. They can no longer compete with NQ growers because of the hotter drier climate experienced in NE NSW and SEQ (Banana Growers Report). Blueberry crops are rapidly taking over the region.
But back to the turtles and the River. There are two possible effects of these sort of climatic changes on the River. Firstly, reduced flow and heating could dramatically change the habitat of the River, a well as it's ecosystem. Flowing parts of the River could become stagnant, further magnifying the heating event- increasing algal growth, reducing clarity and reducing oxygen levels. The Bellinger River Snapping Turtle is a bum breathing clear water specialist- cool, clear and well oxygenated water is very important for it. Heating and drying could also directly impact the timing of breeding for fish and insects, as well as plant growth- common food sources for these turtles.
But back to the turtles and the River. There are two possible effects of these sort of climatic changes on the River. Firstly, reduced flow and heating could dramatically change the habitat of the River, a well as it's ecosystem. Flowing parts of the River could become stagnant, further magnifying the heating event- increasing algal growth, reducing clarity and reducing oxygen levels. The Bellinger River Snapping Turtle is a bum breathing clear water specialist- cool, clear and well oxygenated water is very important for it. Heating and drying could also directly impact the timing of breeding for fish and insects, as well as plant growth- common food sources for these turtles.
These are the links in the chain that I am talking about. All are connected and can be broken at any part. At the end of the chain was the spectacular conclusion- the disease outbreak.
Changing climatic conditions can influence the spread of novel viruses and perhaps the chain may have repaired itself if a new pathogen did not proliferate through the population, however, the key to population recovery lies central to understanding the broken parts of the chain and whether turtles can display future resilience. That will rely on understanding ontogenetic changes in their ecology and identifying threats to their survival.
Recovery of the Species?
Once the species is listed as critically endangered, it will be subject to a Recovery Plan and the guidelines (Department of the Environment) state that
"Recovery plans should state what must be done to protect and restore important populations of threatened species and habitat, as well as how to manage and reduce threatening processes. Recovery plans achieve this aim by providing a planned and logical framework for key interest groups and responsible government agencies to coordinate their work to improve the plight of threatened species and/or ecological communities."
Dissecting it: "Restore", and "Reduce Threatening Processes", are the keywords here.
Restore
In turtles, adult survivorship is the pivotal factor affecting population growth and recovery (see Moll and Moll 2004). Elasticity analysis estimates the proportional change in the population growth rate and can be used to pinpoint those parts of an organism’s life history that should be the focus of management effort, or those that contribute most to fitness. Despite large differences in annual fecundity, survival, and age at maturity, there is considerable congruence of elasticity patterns of freshwater turtles from around the world (Heppel 1998, Spencer and Thompson 2005)- survival of adults, adult females to be specific, has orders of magnitudes greater impact on population stability/growth than any other stage (eg. eggs or juveniles). This is quite easy to visualise. If Bellinger River Snapping Turtle lives for 40-50 years and produces around 20 eggs per year from the age of 10, then one female can produce over 800 eggs during her lifetime. Their longevity and egg producing capabilities are key for population growth.
Under normal circumstances, a population crash would be driven by the remaining adult females in a population. Central to any recovery plan would be protecting adult females and a headstarting program, however, there are few, if any, adults still alive. The adults in the captive insurance population are like gold- the breeding program with them will be critical for any recovery. It is unlikely that they will ever be released, but in time, their offspring might be. However, a recovery program cannot rely on 5-7 adult females in captivity. A proportion of the remaining juveniles will also need to be brought into captivity. Leaving the juveniles in the population (assuming that there are at least 300 in the River) to recover without intervention is doomed to fail. Simple projection matrices with the assumption of an average of 80% survival for these juveniles and applying other life history parameters (eg. 90% nest predation rates, females mature at 10y, 90% of adults survive each years, 20 eggs produced per adult female per year), indicate that after 100 years with no disease or other factors impacting survival, the adult population size will have only climbed to 12 adult females (24 males and females combined) (Fig. 7). The juvenile population will decrease from 300 to 80 (40 females) while we simply wait for them to mature- this is assuming best case scenario!
Minimum Viable Populations (MVP) are difficult to determine and rely on a range of factors. Researchers sometimes assume MVPs of 5,000 in deciding which species need urgent protection. But a study of the North American bog turtle (Glyptemys muhlenbergii) — which lives more than 70 years, and listed as critically endangered by the International Union for Conservation of Nature — found that just 15 breeding females are sufficient for a bog-turtle population to survive the next 100 years (Shoemaker et al. 2013). At this stage, the juvenile snapping turtles cannot be sexed, thus a minimum of another 30-50 juveniles should be considered for another captive insurance population. This should yield 15-25 females. However, female turtles will not reach maturity for another 5-8 years. But given the natural mortality rates of juveniles will see off 60% of the remaining population before they mature, removing far more is justified and would help secure the species. The road to restoration or repopulation is long and the reality is, it may not be able to be achieved. Even with 10 years of headstarting, the adult population size will still only reach a quarter of the size it once was. To my knowledge, the species has not bred previously bred in captivity. Even if hatchlings are produced in captivity, it is not clear whether they could be released.
Reduce Threatening Processes
Unless threatening processes are reduced or removed, headstarting from the insurance populations cannot occur and juveniles currently remaining will be at risk. Headstarting is simply a fancy name for captive raising and releasing of juvenile turtles. It is common in marine turtle conservation and I (my team) have been testing it on the Murray River with Emydura macquarii.
Disclaimer
I have been conducting research into the turtles of the Bellinger River since 2000. I have received several grants to conduct this research, but only in 2000 did I derive any income from the surveys (contract work after I had recently submitted my PhD thesis and was not employed). The institutions that I work for encourage me to seek external grants to conduct research, but I do not derive any income from these surveys- although the institutions do derive on-costs for facilitating research (usually 10-15%). I currently have grants with OEH to maintain the insurance turtle population under quarantine conditions. I am not deriving any income from this grant- any payments to the University for my time are going directly into employing assistants help with turtle research. I also have ARC Linkage and partner grants to investigate declines of Murray River Turtle populations. I have recently appointed a PhD student to the Bellinger River Snapping Turtle recovery program. This is a three year investment worth ~$100K in scholarship and research funds. These funds are independent of any current government agency involved (Australian Postgraduate Award/Western Sydney University).
Kristen Petrov is a new PhD student from Western Sydney University trying to help recover the Bellinger River Snapping Turtle.
The total response has involved NSW Department of Primary Industries, the Office of Environment and Heritage (OEH), National Parks and Wildlife Service (NPWS), Regional Operations Group and Heritage Division (ROGHD), Local Land Services (LLS), the Environment Protection Authority (EPA), NSW Health, the Bellingen Shire Council, Wildlife Health Australia, Taronga Conservation Society Australia, Western Sydney University, University of Canberra, the local community and private veterinarians.
"Recovery plans should state what must be done to protect and restore important populations of threatened species and habitat, as well as how to manage and reduce threatening processes. Recovery plans achieve this aim by providing a planned and logical framework for key interest groups and responsible government agencies to coordinate their work to improve the plight of threatened species and/or ecological communities."
Dissecting it: "Restore", and "Reduce Threatening Processes", are the keywords here.
Restore
In turtles, adult survivorship is the pivotal factor affecting population growth and recovery (see Moll and Moll 2004). Elasticity analysis estimates the proportional change in the population growth rate and can be used to pinpoint those parts of an organism’s life history that should be the focus of management effort, or those that contribute most to fitness. Despite large differences in annual fecundity, survival, and age at maturity, there is considerable congruence of elasticity patterns of freshwater turtles from around the world (Heppel 1998, Spencer and Thompson 2005)- survival of adults, adult females to be specific, has orders of magnitudes greater impact on population stability/growth than any other stage (eg. eggs or juveniles). This is quite easy to visualise. If Bellinger River Snapping Turtle lives for 40-50 years and produces around 20 eggs per year from the age of 10, then one female can produce over 800 eggs during her lifetime. Their longevity and egg producing capabilities are key for population growth.
Under normal circumstances, a population crash would be driven by the remaining adult females in a population. Central to any recovery plan would be protecting adult females and a headstarting program, however, there are few, if any, adults still alive. The adults in the captive insurance population are like gold- the breeding program with them will be critical for any recovery. It is unlikely that they will ever be released, but in time, their offspring might be. However, a recovery program cannot rely on 5-7 adult females in captivity. A proportion of the remaining juveniles will also need to be brought into captivity. Leaving the juveniles in the population (assuming that there are at least 300 in the River) to recover without intervention is doomed to fail. Simple projection matrices with the assumption of an average of 80% survival for these juveniles and applying other life history parameters (eg. 90% nest predation rates, females mature at 10y, 90% of adults survive each years, 20 eggs produced per adult female per year), indicate that after 100 years with no disease or other factors impacting survival, the adult population size will have only climbed to 12 adult females (24 males and females combined) (Fig. 7). The juvenile population will decrease from 300 to 80 (40 females) while we simply wait for them to mature- this is assuming best case scenario!
Fig. 7. Female adult population size projections (a) if juveniles are left in the River to recover the population (purple); (b) if five adult females from the captive insurance population produce 20 eggs each and 50 female juveniles are released each year for ten years (green); (c) if 20 female juveniles are brought into the insurance population. 50 female juveniles are released each year for five years (from the current adults) and eventually 150 female juveniles are released each year from years 5-10 (red). Note that while headstarting for 10 years bringing juveniles into captivity, the adult female population size is still only ~400. Blamires and Spencer (2013) estimated that the population size to be 4500, with over 75% of the population consisting of adults. This means that the projected population size based on 10 years of headstarting is still only 24% of what Blamires and Spencer (2013) estimated.
Minimum Viable Populations (MVP) are difficult to determine and rely on a range of factors. Researchers sometimes assume MVPs of 5,000 in deciding which species need urgent protection. But a study of the North American bog turtle (Glyptemys muhlenbergii) — which lives more than 70 years, and listed as critically endangered by the International Union for Conservation of Nature — found that just 15 breeding females are sufficient for a bog-turtle population to survive the next 100 years (Shoemaker et al. 2013). At this stage, the juvenile snapping turtles cannot be sexed, thus a minimum of another 30-50 juveniles should be considered for another captive insurance population. This should yield 15-25 females. However, female turtles will not reach maturity for another 5-8 years. But given the natural mortality rates of juveniles will see off 60% of the remaining population before they mature, removing far more is justified and would help secure the species. The road to restoration or repopulation is long and the reality is, it may not be able to be achieved. Even with 10 years of headstarting, the adult population size will still only reach a quarter of the size it once was. To my knowledge, the species has not bred previously bred in captivity. Even if hatchlings are produced in captivity, it is not clear whether they could be released.
Reduce Threatening Processes
Unless threatening processes are reduced or removed, headstarting from the insurance populations cannot occur and juveniles currently remaining will be at risk. Headstarting is simply a fancy name for captive raising and releasing of juvenile turtles. It is common in marine turtle conservation and I (my team) have been testing it on the Murray River with Emydura macquarii.
The "Mystery Virus" is certainly a threatening process, but it is simply one of many threatening processes. Disease outbreak is uncommon but not rare in turtles. Ranaviruses (genus Ranavirus) have been observed in disease epidemics and mass mortality events in free-ranging amphibian, turtle, and tortoise populations worldwide. Reports of outbreaks in wild turtles have largely involved box turtles in North America (Devoe et al. 2004; Kimble et al. 2014) Infection is highly fatal in turtles, and the potential impact on endangered populations could be devastating. Hence, unless we can determine if remaining turtles are likely to be susceptible or can be inoculated against the virus, then the type of disease is irrelevant for the recovery of the species. It is a threatening process and once juveniles in the population grow, there is a significant risk that they may also become infected. Long-term monitoring of current population will be important here. It will detect presence of the diseases early, as well as, monitor body condition and survival of the turtles as they grow.
Monitoring body condition and growth rates will also provide evidence of another threatening process- water quality and ecosystem deterioration. A high proportion of the diet of Myuchelys georgesi are insect larvae (Fig. 8), which are greatly affected by water quality. Thus, all factors affecting water quality and their food supply are threatening processes. Aquatic plants are consumed directly by the turtles, but equally as important is that much of their insect prey also rely aquatic macrophytes.
Fig. 8. Proportion of diet that consists of aquatic insects of three short necked species that inhabit clear East Coast River or Lake systems in Australia. Data obtained from Spencer et al. 2014.
The reality is, any threatening process to the aquatic macrophytes in the River is a threatening process to the turtles. Exotic fish, like European Carp; reduced flow and significant warming will increase algal growth and turbidity; increased sediment in the River from a range riparian zone activities will also increase turbidity. The turtles also have cloacal bursae, that is they can extract oxygen directly from the water by drawing it into their bottoms- like fish gills. This is particularly important during their winter hibernation (brumation) period, where their metabolism and oxygen demands are low- it allows them to remain underwater for longer and not use up energy reserves returning to the surface to breathe all the time (Fitzgibbon and Franklin 2010).
Emydura macquarii must also be considered a threatening process. Both the Emydura and Snapping turtle appear to hybridise with each other. That means they are breeding together. In a species with such limited distribution, breeding between the two species actually has the potential to wipe out the Bellinger RIver Snapping Turtle. It is the same concept of a mongrel dog breeding with the best in show- the offspring are potentially worthless. Dingoes have gone through the same process. Stray and wild dogs breed with dingoes and the pure-bred dingo is almost extinct in Australia. So hybridisation with Bellinger River Emydura is a major threatening process. Similarly direct interference competition and predation, as well as, competition for limited food and resources is also a threatening process. What we do with the Emydura is difficult, while not native to the River, they are an Australian native species. Given the lack of adult turtles captured in the recent surveys, the risk of hybridisation is low over the next few years- giving experts, management agencies and the community time to consider the best way forward to reduce the threat from Emydura.
The perennial threat to any freshwater turtle population is from fox predation. It was encouraging to see that the species must have had some relief from fox nest predation in the last 2-5 years. It was probably sheer luck, although there are some indications that nesting grounds with a mosaic of vegetation do experience lower nest predation rates than open areas, like paddocks (Spencer 2015).
Much of the River has been fenced off from cattle over the last decade and this has seen a proliferation of thick vegetation (often weeds) in riparian zones and while this may not have provided preferred nesting habitat for turtles, it may have helped hide the nests in the landscape. Providing preferred nesting habitat amongst a mosaic of habitats is often more effective in reducing nest predation rates than traditional methods like fox baiting or shooting. Captive insurance populations eliminate the threat of nest predation, but planning into riparian nesting habitat design will take up many years to implement and should begin as soon as possible. Identifying historical and current nesting sites (even if they are Emydura) is vital. Please record any historical or current sightings of turtles and nests into TurtleSAT. A range of non-lethal management techniques are also being trialled to reduce nest predation rates and these could be tested and honed specifically for the Bellingen catchment. However, the reality is nest predation by foxes will only become a threatening process once juveniles reach maturity and in the meantime, it may help limit the growth of the Emydura population.
This is what a typical freshwater turtle nest looks like after it has been raided by predators. Please record this into TurtleSAT.
Conclusion
The aim of this publication is to demonstrate that the "Mystery Virus" is nothing more than one of many threatening processes that may drive this species to extinction. I argue that identifying the virus is largely irrelevant for the recovery of the species- it even has limited value for identifying whether species in other catchments are at risk. The species is on a precipice; it cannot rely on the current population for recovery without active intervention. The species will be listed as critically endangered soon and with that a Recovery Plan will need to be formulated. Consultation is part of this process and it will be critical. This document is my scientific opinion, others may have a different opinion. Saving the species requires a critical evaluation of all of these opinions and the science. The threats to the species are real and many of them involve changes to water quality, hence community involvement is essential. If it wasn't a turtle, the species would probably have no hope of recovery, but turtles are resilient- they are survivors, so I am betting on the turtle with a little help from us.
Please visit the Facebook site Save the Bellinger Turtle
The website Savetheturtle.com.au will be up and running soon
I have been conducting research into the turtles of the Bellinger River since 2000. I have received several grants to conduct this research, but only in 2000 did I derive any income from the surveys (contract work after I had recently submitted my PhD thesis and was not employed). The institutions that I work for encourage me to seek external grants to conduct research, but I do not derive any income from these surveys- although the institutions do derive on-costs for facilitating research (usually 10-15%). I currently have grants with OEH to maintain the insurance turtle population under quarantine conditions. I am not deriving any income from this grant- any payments to the University for my time are going directly into employing assistants help with turtle research. I also have ARC Linkage and partner grants to investigate declines of Murray River Turtle populations. I have recently appointed a PhD student to the Bellinger River Snapping Turtle recovery program. This is a three year investment worth ~$100K in scholarship and research funds. These funds are independent of any current government agency involved (Australian Postgraduate Award/Western Sydney University).
Kristen Petrov is a new PhD student from Western Sydney University trying to help recover the Bellinger River Snapping Turtle.
The total response has involved NSW Department of Primary Industries, the Office of Environment and Heritage (OEH), National Parks and Wildlife Service (NPWS), Regional Operations Group and Heritage Division (ROGHD), Local Land Services (LLS), the Environment Protection Authority (EPA), NSW Health, the Bellingen Shire Council, Wildlife Health Australia, Taronga Conservation Society Australia, Western Sydney University, University of Canberra, the local community and private veterinarians.
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