Last week, Bellingen put on a show. The Bellingen Turtle Festival was a symbol for a community concerned about its turtle and a community ready to do something about it. But where are we at since the outbreak of a mystery disease in February 2015. The community shared their theories at the festival, and they were diverse - from meth lab chemicals - to impacts of various agricultural practices - to road construction processes.
Speculation can thrive because it was an August 31st, 2015, press release from the member for Oxley, Melinda Pavey, that reported a mystery disease wiped out the Bellinger River Snapping Turtle. 14 months on, nothing else about this 'Mystery Virus' has been released or subject to scientific peer review, thus we still do not know what caused the die off 18 months ago.
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). Many more decomposing dead turtles were collected and rapidly disposed without counting.
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 (Moloney 2015).
5. A press release suggested the disease was a 'Mystery Virus' in August/September 2015. It was announced by the member for Oxley, Melinda Pavey (Pavey Vimeo 2015), who said that scientists from NSW Department of Primary Industries (DPI) Elizabeth MacArthur Agricultural Institute had recently made a significant breakthrough and detected a new virus, the cause of a mystery illness that killed the turtles.
6. In October 2015, NSW Department of Primary Industries (DPI) Elizabeth MacArthur Agricultural Institute released a report (hosted on the Bellingen Council Website) that described the epidemiology of the disease, but did not name the virus (Moloney 2015). No other public statements, reports or scientific publications have been released since that time.
7. 20 juveniles were collected in limited surveys of the River in November 2015 (Bellingen Courier 2015)
8. A much larger survey in March 2016 confirmed that the remaining turtles in the River are predominantly juveniles (Bellingen Courier 2016). Only two adult female turtles were found in the wild during these surveys and the health of one of these animals was questionable (ARWH Annual Report)
What does it mean?
Basically, a 'Mystery Virus' appears associated with the die off of the adult population, leaving juveniles almost unaffected in the River and no other species has been obviously affected. More than 12 months have passed since the announcement of a 'Mystery Virus', but the identity of the virus has not been released to the public or been subject to scientific peer review.
The recovery of a species will rely 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 young kids to eventually repopulate the planet. The likelihood of extinction is very high without intervention; the path to recovering the species is complex and has little room for error, but this will be discussed in a separate blog.
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 primarily adult Snapping Turtles, then possibly.
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 primarily 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).
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. 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.
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.
"It does not mean that there is something wrong with our beautiful River".
Discovery of a novel virus killing turtles 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).
"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 isolated 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" (Moloney et al. 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.
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. 3).
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.
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.
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
Clearly our climate is changing, but the last 3-4 years in the Bellinger River may have been the tipping point for the turtles. Any cause (or combination of causes) is likely to have been chronic rather than acute. These turtles have survived the last mass extinction, so they are adaptable, but we are driving species like this to the 6th mass extinction?
Next I will explore how we can recover the species. Turtles are survivors, so it is not all doom and gloom.