Snakes on the Brain: Essays on Snakes, Science, and Society. Essay 2. Hide and Sea Snakes: The Rediscovery of Two Potentially Extinct Species in WA

Snakes on the Brain: Essays on Snakes, Science and Society #2

I often wonder what exactly about snakes makes them such polarizing figures throughout human history. We tend to react in extremes when it comes to these often maligned creatures, and both human parties, whether the fascinated or the fearful, view the other as either misguided or perhaps certifiable. To this day it remains surprising to some that fans of snakes, such as me and many other perfectly rational folk, even exist, let alone work with and study these stunning, adaptive, mysterious beasts.

These essays are my menial attempt to bridge some of the gap between the fascinated and the fearful, while exploring some aspect of science or natural history. While I make no claim of authority, I will say that I aim to provide as much reasoning and references for my views wherever necessary throughout. Where I fall short, I apologize and request your unyielding criticism, dear reader, as both punishment for the current and polish for future essays.

 

Essay 2. Hide and Sea Snakes: The Rediscovery of Two Potentially Extinct Species in WA

“No one knows the diversity in the world, not even to the nearest order of magnitude…We don’t know for sure how many species there are, where they can be found or how fast they’re disappearing.” — Edward O. Wilson

Extinction is a bitch. Unless humanity has some serious new biological technologies which I’m yet to hear about, there is no return. The loss of a species is truly a terrible thing, an artwork of nature lost to the ages, leaving nothing but memories and, if we’re very lucky, some physical remains from which we may interpret the mode of their life and demise. In these marvelous times, the early 21st century, the rates of species extinction are unfathomable. I mean quite literally, it’s impossible to count exactly how many species at any given moment we are relegating to history’s dark corners through habitat destruction, overexploitation, and…well, let’s face it, I could list the ways humanity is contributing to this decline for the next the several pages (1).

Furthermore, we don’t even know how many species of plants and animals currently exist, not to mention the unfathomable numbers of fungi, bacteria, archaea and viruses, all constantly mutating and evolving. With around 1.5 million species currently described, it’s astonishing that biologists predict at least one-third of all species remain to be discovered (2) (incidentally, we don’t even have a great idea how to define a species! See (3) for a review of this issue in the Bacteria and Archaea). Human nature, it seems, is often to simply proceed at will using ignorance as a map, until the stacking negative consequences force us to reign in our “progress” and examine our actions more objectively, a skill we are apparently developing when it comes to balancing our population requirements with those of other organisms and the planet’s natural resources.

What a depressing way to start! Kill me now, or let’s have some good news! Luckily, while we will discuss population declines and extinction, I truly do intend to discuss a rather more cheerful topic; the recent rediscovery of potentially extinct species. While tempting to view these situations as a somewhat miraculous, phoenix-like revival, they often share more in common with finding a mystery five-note in the back pocket…Score! Still, for conservationists who frequently are in the painful position to observe and record the decline of their favourite study species as they attempt recovery efforts (or at least learn something about how to prevent future declines in conspecifics), these discoveries are occasions for tremendous joy, even shock, like a long deceased friend contacting you out of the blue for a meal and a catch up. Even so, the joy is short-lived, for a species so rare it was thought extinct must be either especially cryptic and/or nearly impossible to find, that or it must truly be in critically low population numbers right on the brink of collapse, and extinction is still a real threat.

It is with thus with much joy and some trepidation that I write about the findings of D’Anastasi et al. (2016) (4) describing the discovery of not one, but two sea snake species, the Leaf Scaled Sea Snake (Aipysusrus folliosquama) and the Short Nosed Sea Snake (A. apraefrontalis), which recently disappeared from their only known geographic range. Both species were known only from the Ashmore and Hibernia Reefs, an isolated area of the Timor Sea, home to an incredible diversity of sea snakes. A study in 1973, for example, collected more than 350 snakes from 9 species and observed many more, while estimates of almost 40,000 snakes were made for Ashmore Reef in 1994 (5). However, populations of all sea snakes in the region began a steep decline for completely unknown reasons in the early 1990s, and continued to do so until several species disappeared completely. Neither of these species, known only from this tiny area of the Timor Sea, had been recorded in surveys since 2002.

The severe declines in these and other sea snake species on the reefs came along quickly. Further frustration and despair would’ve been in ample supply for the conservationists working on these isolated reefs, with no explanation for the declines, and no option but to observe and record the losses while searching for answers. Extinction seemed likely for these rare, open-ocean reef dwelling snakes (both were in fact listed as “Critically Endangered” on the IUCN Red List and Australia’s EPBC Act, one step shy of “Extinct in the Wild”, or when no individuals are maintained in captivity, “Extinct”). That is until the authors of (4) discovered both species not far off the northwest coast of Australia, around Western Australia’s Ningaloo Reef and further south at Shark Bay.

The paper by D’Anastasi et al. (2016) (4) from James Cook University’s ARC Centre of Excellence for Coral Reef Studies entails the search for and successful field observations of these species. After their disappearance and listing as Critically Endangered in 2002, no more sightings occurred in their known home range, though older anecdotal evidence suggested they may occur in coastal Western Australia (5). The most interesting evidence for their presence was from just one or two specimens of each species, deposited in the WA museum. A single A. foliosquama was found washed up on Barrow Island in 2010, with two A. apraefrontalis caught in 2012, one as prawn trawling by-catch and one washing up on a beach near Broome. These were mostly dismissed as probable vagrants, washed out of their natural geographic range by powerful ocean currents. However to others, this all suggested the possibility of undiscovered populations. Why not survey the coastline in the hope of discovering the hidden outposts of these rare sea snakes?

How does one go about mounting such a survey? With sweat, for one. Let it not be said that field biologists are lazy, particularly those who are fit enough to make the marine environment their office. Aside from the technicalities of mapping out and planning a thorough but efficient search, to cover maximum territory for optimal time/cost, the physical effort was incredible. Over 200 hours of survey were conducted at Shark Bay, Ningaloo Reef and other northwest coastal regions, as well as at the Scott Reef in the Timor Sea.  The team performed more than 30 hours of both snorkel and scuba surveys, as well as over 25 hours of so called “Manta Tow” survey to cover a greater area. Developed in 1969 to assess crown-of-thorns starfish densities, this method involves towing a buoyant ‘manta board’, complete with waterproof recordkeeping sheets, behind a boat constant speed while a harnessed in observer clings to the board, using a snorkel and goggles to observe underwater as they pass. Around 40 hours by-catch prawn trawling surveys were also conducted around Shark Bay and Exmouth, and opportunistic sightings were also recorded wherever possible. As said by more than one field biologist in their time, the only way to find something is to look for it.

This mammoth effort was rewarded with gusto. Several individuals of the species Aipysurus apraefrontalis, the short nosed sea snake, were spotted around the Ningaloo Reef. Imagine the elation of finding this little known species of sea snake, 15 years after the last one was seen, 1700km south of its known distribution, and when all but a few were holding out hope for its continued existence. Not only that, two individuals observed appeared to be in the middle of courtship, hopefully a sign indicating a healthy breeding population. How very sweet for this stunning, golden yellow and cream banded sea serpent which had seemed destined to join the museum cupboards of the Dodo and the Dinosaurs. Further specimens were collected near Exmouth in WA Department of Fisheries prawn trawl by-catch surveys, another good indicator of a viable breeding population in the area.

But the story continues. The second discovery came only a few hours boating further south of Ningaloo. Another of Ashmore Reef’s lost sea snakes, the Leaf Scaled Sea Snake (Aipysusrus folliosquama), was found happily drifting among the sea grass flats of Shark Bay, a significant change from their typical setting of isolated coral atolls and reefs in the Timor Sea. To find this coral reef specialist in sea grass beds is very odd indeed, and the description as a shallow water tropical reef specialist requiring significant cover and structure will need some review. As with A. apraefrontalis, can we be sure this an established breeding population? While certainty is a rare commodity, a total of 16 A. folliosquama were caught in by-catch surveys between 2013 and 2015, all from Shark Bay and surrounding areas. It seems they hit the jackpot!

All’s well that ends well, no? In fact, not, and at this point some interesting questions start to arise. Ashmore and Hibernia Reefs supported diverse, abundant populations of sea snakes. For such seemingly successful animals in what appeared a very suitable habitat, how could such rapid population declines occur? What impacts are they under threat from in the waters off northwest Australia? Furthermore, now that we know they’re here just off the WA coastline, what can we do to minimize the stresses on these potentially new populations and increase their chances of survival? Can we prevent them from slipping away again?

In Australian waters, sea snakes themselves are not harvested for any commercial purposes, however through parts of southeast Asia there continues to be a small local market for sea snakes, usually for the colourful skins of sea kraits (sea snakes of the Laticaudidae subfamily, less common in Australia than in southeast Asia, all which lay eggs on land rather than on reef/rocky substrates like the Hydrophiinae subfamily, the true sea snakes), as an imported menu item, or for traditional medicine (6). Being in Australian waters, and since 1983 within the Ashmore Reef National Nature Reserve, direct harvesting is not likely to have much impact on these isolated populations, which are themselves classified as protected marine fauna under the Nature Conservation Act of 1992.

Trawl fisheries generally pose a much greater threat. Sea snakes need to surface to breath, using lungs which, aside from a few notable adaptations (extreme elongation, one dominant lung, a devascularised posterior “scuba tank” unique to sea snakes), are rather like ours. While they obviously possess a phenomenal breath holding ability, around 4 hours under optimal conditions, they can actually drown just like a person, dolphin, emu, or a crocodile. Add to this damage from being net-dragged across the benthos or crushed in a turbulent net by hundreds of kilos of rocks, crustaceans, and fish including sharks and rays, all struggling and making repeated attempts to escape, and the impacts of these fisheries are obviously a potentially serious threat (7).

Luckily the Ashmore and Hibernia Reefs have some reprieve from our constant plundering of the ocean. At least locally, the depth just off the edge of the coral platforms and the coral itself makes for difficult-to-impossible trawling conditions. Trawling is more difficult at depths and around structure, the potential for snagging and damage to the net being an important financial consideration. Furthermore the trawling rates and rates of decline do not correlate; while rates of trawling have remained relatively steady, sea snake numbers began to decline dramatically in 1994. Trawl fisheries, an initially likely culprit, seem to be in the clear for the moment.

So, direct human harvesting and the local trawl fisheries both seem to have little impact on these disappearing sea snake populations on the reefs. What then could have caused such rapid declines? Several possible causes, at very different spatial scales, are currently under suspicion; firstly, on the small scale of cells, tissues and organisms themselves, the potential for disease or demographic reasons for these declines has to be considered; secondly, on the middle scale, habitat loss might be to blame, with coral bleaching events occurring in 2003, though these could hardly cause the declines from 1994; on a large scale, environmental changes, such as shifts in temperature and/or prey abundance due to human induced climate change, are also on the suspect list (5). Investigations into these areas will hopefully provide much needed insight in the near future, maybe even an answer as to why these populations collapsed.

As for the newly discovered coastal populations, what can the observations tell us? One thing we can infer with some confidence, from the aforementioned courting/breeding pair of A. apreafrontalis spotted off Ningaloo Reef, and the substantial number of A. folliosquama found during the rather short survey, is that these are most likely true local breeding populations, rather than ephemeral waifs floating adrift on the currents, being fed into the survey areas from some outside source population. This is further supported by the apparent strong population structure of A. folliosquama, Shark Bay populations being genetically distinct from the washed up specimen from Barrow Island, itself distinct from historical Ashmore Reef samples. This all suggests that the Barrow Island specimen may be of a separate coastal breeding population, yet undiscovered. Along with the habitat extension, it seems that populations  of A. folliosquama may really be out there in hidden in the WA sea grass beds, and A. apraefrontalis may be casually courting one another of Ningaloo and other reefs without our knowing! Unfortunately, while this is all rather hopeful conjecture, we can just as easily assume that whatever afflicted the Ashmore Reef populations can also affect these “unknown” populations, and they may disappear before we ever know they existed. One can rarely ever know what diversity and complexity has been lost, or how it was lost, without the benefit of painful hindsight.

If these populations are true, established breeding populations as we suspect, one troubling thought comes to mind. Despite the relative safety of the Ashmore and Hibernia Reefs from trawling impacts, the now known extension of these two species’ geographic ranges and habitat to coastal areas including sea grass beds, and the fact that the vast majority of specimens were caught in prawn trawl by-catch surveys, suggests the impact of trawling on coastal populations may be much higher. In fact, these coastal populations might naturally be subjected to all manner of man-made coastal disturbances, such as industrial/agricultural run-off, seismic activity from mineral and gas exploration, increased recreational activities such as boating and fishing to compete with, and much more. Being so isolated, it is easy to assume that the reef populations were somewhat protected from many of these activities, and yet they’re gone. What does this mean for our chances to protect the newly discovered coastal populations? With all the increased human impacts are we doomed to fail? Or, does their mere continued presence indicate some resilience, perhaps due to the amount of structural variation in coastal environments, or their sheer size and continuity around the coastline, which the outposts in the Timor Sea did not have?

In summary, we know little, as is most often the case. What we know is that we don’t know the true population size, distribution, or spatial ecology of these rediscovered sea snakes. More field observations are necessary to understand both the ecology of these populations and the threats they face, as well as surveys of other coastal areas for more unknown populations if we are to have a thorough inventory to base conservation efforts on. Such are the difficulties involved in working with rare animals and small population sizes. For now though, let us take five to give the fine people behind these discoveries, and to all who work with endangered species, fighting for tiny populations who persevere at the edge of oblivion, a seriously deserved round of applause. It is very close to the least we could do. We can, and should, do much more.

PS On further rediscovered reptile news…

As I write this essay another small step was made in restoring our reptile biodiversity! This time in the spotlight is a lizard species which, throughout my childhood, had been presumed extinct. The Pygmy Blue Tongue Lizard (Tiliqua adelaidensis) is a true pygmy of the robust and moderate sized blue tongue lizards. Within the Tiliqua genus most species reach over 40cm in length, while the T. adelaidensis tops out at a tiny 18 cm. After an absence from their native habitats for 30 years, the future seemed uncertain for these little gems. As a kid I knew them only from pictures of deceased museum specimens in my reptile encyclopedia, the status next to them reading “Presumed Extinct”. While well preserved, they were somewhat less inspiring than the rest of the creatures in the book, perhaps due to signs of dessication and rigor, and the final shame of a finely engraved voucher label attached to the hid legs, as if just another artifact of history. Then, while driving along a country road one day in 1992, a herpetologist outside of Adelaide accidentally ran over an eastern brown snake sunning itself on the road. Upon examination, he found two “extinct” T. adelaidensis inside its stomach. Not only that, surveys found local populations living in spider holes in the surrounding native grasslands, and study taught us much about their ecology (8).

As of January 2016, Zoos South Australia confirmed the successful captive breeding of the Pygmy Blue Tongue Lizard (9). Twenty years after first being fascinated and saddened by pictures of these creatures which I thought I would never see, I am currently sipping a cup of tea and looking at images online of newly born babies. The tiny, tiny offspring of this diminutive species of blue tongue are coloured more like some of our speckled Ctenotusspecies, but the stocky little body, small tail, and big head are characteristic Tiliqua. They’re damned cute. My first pets were also in the genus (mine were Southern Blue Tongued Lizards,T. nigrolutea), and I have an inordinate fondness for the Tiliqua, from the common garden visitors and the desert dwellers to this spider-specialist dwarf. To find both of these articles, the lizards and the sea snakes, making the rounds and gaining interest on social media networks, all in one week, caught me by surprise. Perhaps there is some hope for humanity after all.

Read Essay 3.

Ciao,
Janne

Snake Catching Professonals

Your SnakeOut Brisbane.

References

  1. Proença, V. &  Pereira, H. M. (2013) Comparing Extinction Rates: Past, Present, and Future. Encyclopedia of Biodiversity (Second Edition). P167–176
  2. Costelo, M. J. (2015) Biodiversity: The Known, Unknown, and Rates of Extinction. Current Biology 25, R362–R383
  3. Rosselló-Móra, R. & Amann, R (2015) Past and future species definitions for Bacteria and Archaea. Systematic and Applied Microbiology. Volume 38, Issue 4, 209–216
  4. D’Anastasi, B.R., Van Herwerden, L., Hobbs, J.A, Simpfendorfe, C.A., Lukoschek, V. (2016) New range and habitat records for threatened Australian sea snakes raise challenges for conservation. Biological Conservation. 194. 66–70
  5. Lukoschek, V., Beger, M., Ceccarelli, D., Richards, Z., Pratchett, M. (2013) Enigmatic declines of Australia’s sea snakes from a biodiversity hotspot Biological Conservation 166. 191–202
  6. Van Cao NThien Tao NMoore AMontoya ARedsted Rasmussen ABroad KVoris HKTakacs Z.(2014) Sea snake harvest in the gulf of Thailand. Conserv Biol. 28(6):1677-87
  7. Wa ssenberg, T.J., Milton, D.A., Burridge, C.Y. (2001) Survival rates of sea snakes caught by demersal trawlers in northern and eastern Australia. Biol. Conserv. 100, 271–280.
  8. Armstrong, G. & J. Reid (1992). The rediscovery of the Adelaide Pygmy Bluetongue Tiliqua adelaidensis (Peters1863). Herpetofauna22 (2):3-6.
  9. http://www.abc.net.au/news/2016-02-24/monarto-zoos-pygmy-blue-tongue-lizard-breeding-success/7195136