Raine Island - Part 2: Management concerns and actions
Sea turtles, given their reproductive strategies (laying eggs on low-lying beaches), have been highlighted as particularly vulnerable to predicted sea level rise and different climate regimes (Fuentes et. al. 2010). The 'Great Barrier Reef Climate Change Action Plan 2007-2012' - see for example https://www.nccarf.edu.au/localgov/case-study/great-barrier-reef-climate-change-action-plan-2007-2012 developed principally by the Great Barrier Reef Marine Park Authority was the catalyst from which the identified environmental risks at the island and potential management actions were assessed for risk and developed into a plan of action. This project now titled the 'Raine Island Recovery Project' is a partnership between the Commonwealth GBRMPA, Queensland Parks and Wildlife Service and Department of Environment and Heritage Protection, the Traditional Owners and other stakeholder groups. The project is now actively seeking commercial business partners to help fund the project and, along with other stakeholders, continue research, monitoring and management actions with the objective of achieving significantly improved outcomes for this rookery. Further information on this project can be found at https://www.ehp.qld.gov.au/wildlife/animals-az/green-turtles-raine-island.html
Dr Colin Limpus and fellow researchers with the Queensland Parks and Wildlife Service (QPWS) (2003) first observed that green turtle hatchling numbers did not seem to be at expected levels after the 1996-97 nesting season. High densities of adult females had lead researchers to expect tens of thousands of hatchlings entering the water at night during a return trip in February 1997 which included a film crew set to record the event. When only sporadic small numbers of hatchlings were encountered it was clear that there had been significant reproductive failure, at least within that season. Follow up monitoring and research over the next decade, which has intensified since 2010 indicates that low incubation success is occurring every year and that there may be multiple environmental factors leading to this (see for example at https://www.ehp.qld.gov.au/wildlife/animals-az/green-turtles-raine-island.html).
Understanding what is happening has taken time, and a significant part of this has been because of the island's isolation at over 600km by vessel from the nearest State management base in Cairns. Field trips have typically been undertaken in December for the peak nesting season but follow up trips in February/March, during what should be peak hatchling emergence, have been infrequent due to a combination of logistical difficulties (peak period of the cyclone season, insufficient funding) and other marine park monitoring and management priorities.
One of the early difficulties for this project was gathering more data on actual levels of hatchling production. At that time (2010) evidence supporting concerns about production was mainly limited to analysis of clutches that had emerged because they could be identified by hatchling tracks leading from them. This, while supporting anecdotal evidence about low production was time consuming and selective in its analysis. Techniques were developed to count hatchlings as they emerged from multiple nests along the beach (50m sand trenches were dug and hatchlings temporarily trapped and counted) and nests were marked at the point of lay using a Differential Global Positioning Systems (DGPS) and could then be relocated on subsequent trips with only a 40mm error. Data collected between 2010/2014 on incubation success has verified the alarmingly low rates of production (QPWS Internal Report 2013). In February and March 2014 approximately 2500 hatchlings were estimated to have emerged from the island when up to 370 000 could have been expected, taking into account the numbers of nesting turtles and their relative success in laying 8 weeks earlier, (Pers. Comm. Dr Andy Dunstan, DEHP).
Significant efforts have been made to survey the island's topography. Data from water level sensors (measuring tidal inundation of the nesting beach) and visual observations during Spring Tides all support the theory that large areas of the beach become flooded during large tides and storm events. Developing embryos can only withstand these conditions for a limited period before mortality rates climb. Investigation of nests mapped by DGPS and then excavated after the due hatching date confirm the low hatching success of eggs with most embryos dying in the early stages of development. During the high density nesting season of 2013/2014 around 50% of nests/eggs were also destroyed by nesting turtles further reducing hatchling production. Hatchling success was around 10% as compared with upwards of 90% in comparable green turtle rookeries (Pers. Comm. Dr Andy Dunstan, DEHP).
While inundation appears to be a major factor it does not fully explain hatching failure. During a high density season huge amounts of sand are moved by turtles and this can result in sand ramps being formed against the interior cliff allowing nesting turtle access to the higher level interior. This area is well above inundation height and hatching success (2013/2014) of nests was significantly higher, at more than 50%. However similar embryo mortality patterns were still observed, just at a lower level. Within the beach area inundation did not fully explain survival or demise of nests. Recent laboratory incubation experiments also suggest that developing embryos may in fact be able to survive longer periods of inundation (in water-logged sand) than previously thought (pers. comm. Dr Andy Dunstan, DEHP).
It may be that a secondary effect such as a microbial pathogens, toxins or 'microbial oxygen debt' is having a compounding impact. This has been documented at large Costa Rican Olive Ridley sea turtle rookeries (Valverde et. al. 2010). This is now being investigated by researchers at the Queensland Department of Environment and Heritage Protection and James Cook University with on-site and laboratory studies proposed as a major element of the 2014-15 seasons work.
A further impact on overall hatchling production is also evident. The sand on the island is made up largely of coral fragments (55%) and foraminifera tests (45%) and when dry it binds very poorly. Combine this with a high density of turtles all trying to dig nests at the same time and the result is chaos. Under these circumstances very few females are able to successfully dig a nest and lay eggs on a particular night and after repeated failures over a number of days they may jettison eggs in the sea and begin to reabsorb egg follicles to fuel their own ongoing energy needs. Around 60,000 female turtles were recorded at Raine Island during the 2013-14 season. In perfect conditions this would mean individuals nesting successfully an average of 6 times, once every 12 nights, resulting in 5000 turtles nesting per night. In reality in late November 40,000 turtles were trying to nest with almost 0% success per night. This occurred most probably due to an initial 'bottleneck' arrival of nesting turtles combined with extremely dry sand conditions. A few days later rainfall that bound the sand together made digging a nest much easier for the females. Nesting success increased to a still very low 20% with around 20,000 turtles ashore per night. So turtles prepared to lay around 6 nests in a season, may just not be laying as many nests as they were capable of when they arrived at the island.
Hatchlings will emerge from those eggs that are successfully laid and incubated in the sands of the island after approximately 60 days. However their troubles are not over then with a number of bird species in particular Nankeen Night Herons (Nycticorax caledonicus) taking significant (but as yet unquantified numbers) of hatchlings and then reef fish and shark species targeting them as they cross the reef flats at night. While this can all be considered as natural predation, when it is coupled with the problems identified around adults successfully producing hatchlings in the first place it means that the number of hatchlings reaching the pelagic phase of their life-cycle may be far below what is required to sustain the population.
There are also significant risks to the adult turtles from the small (1 - 2m) phosphate cliffs that ring much of the guano caked centre of the island where most of the seabirds are found. Nesting turtles are able to find their way up onto these cliffs through a number of sand ramps around the island and then tumble off, landing upside down from which there is no escape. It has been estimated (Limpus et. al. 2006) that perhaps up to 1500 adult females turtles die in this way in one season, along with others that become disorientated on low lying back beach areas during the heat of the day.
Management Actions - to date
Fence construction
One of the first direct management actions focussed on fencing off some of the main areas where adult turtles were accessing the central parts of the island. Not only were they tumbling off the small cliffs to their eventual death but also significantly disturbing nesting attempts by seabirds in the central parts of the island. These fences over the past 3 years have proven very effective in reducing the number of deaths of adult turtles. It is estimated that 500 (plus) females were saved during last season by fencing efforts (Pers. Comm. Dr Andy Dunstan, DEHP).
Trials of sand movements
One of the key ideas that have been considered over the past several years has been re-nourishing the island with imported sand. The thinking is that if incubating embryos are drowning during large tides then raising the height of the sand will significantly improve their chances of survival. It may also solve problems where turtle have been identified trying to dig nests in areas of shallow sand overlaying beach-rock. It has been estimated that approximately 50 000m³ of sand may be enough to adequately cover nesting areas.
There are risks involved in a project like this at an iconic, World Heritage Listed, National Park (Special Management Area) Scientific, surrounded by a Commonwealth Marine Park Special Management Area and co-managed under an Indigenous Land Use Agreement with the Wuthathi People, Erubam Le, Meriam Le and Ugarem Le Native Title holders. And on top of all this it is one of the most photographed and filmed sites on the Great Barrier Reef with even legendary natural history documentary maker Sir David Attenborough having filmed there in 1956 and possibly again late in 2014.
There are concerns that there would be impacts on the seabirds, the sand may not be stable or have some other unpredicted impacts on the island. However there is also a sense that an adaptively managed project may have minimal risk of negative impacts and may result in significant improved hatchling production. Some trials have been undertaken using sand on the island to increase depths in some levels; one season of data has proved to be inconclusive in its effect. There is also the issue of dry sand causing nesting failure; perhaps a different type of sand that binds better might achieve better results but this may have real environmental impacts? Larger scale trials, not introducing new sand but rather re-profiling areas of the existing beach are planned for 2014-2015.
It is evident that management agencies are faced with a relatively complex set of conditions at an isolated location and while headway has been made over the past four years there is much more to be done. A 'Prospectus' was recently released by the Queensland Government seeking a major sponsor for the project and a short 'You Tube' video narrated by Sir David Attenborough highlights the issues and asks for help. These can all be found at https://www.ehp.qld.gov.au/wildlife/animals-az/green-turtles-raine-island.html
The future for Raine Island's turtles
One of the key questions raised by the ongoing work at Raine Island is how much should humans interfere with 'natural' systems? These types of questions along with others around themes like eco-engineering, re-wilding and assisted migration are becoming more common (e.g. Marris 2011). Older management approaches of focussing on protecting the 'status quo' (some specific state identified as the bench-mark) and trying to keep out feral plants and animals, minimise human impacts and maintain current bio-diversity may no longer be as valid in the 21st Century. We are going to have to re-think how we approach protecting our environments and species because by any reasonable measure the human footprint continues to get heavier.
Perhaps the work at Raine Island will be an early and successful model of management for the Great Barrier Reef that uses intervention actions funded by multiple sources, driven by many stakeholders and coordinated by a State/Commonwealth Government partnership. If so the outcome will be a positive boost to an iconic species that continues to play such an important role in the lives of people and ecosystems throughout northern Australia, the Torres Straits and right around the tropical world.