Dugong and sea turtle poo sheds new light on the Great Barrier Reef’s seagrass meadows


Samantha J Tol, James Cook University; Alana Grech, James Cook University; Paul York, James Cook University, and Rob Coles, James Cook University

Just like birds and mammals carrying seeds through a rainforest, green sea turtles and dugong spread the seeds of seagrass plants as they feed. Our team at James Cook University’s TropWATER Centre has uncovered a unique relationship in the seagrass meadows of the Great Barrier Reef.

We followed feeding sea turtle and dugong, collecting samples of their floating faecal matter. Samantha then had the unenviable job of sifting through hundreds of smelly samples to find any seagrass seeds. These seeds range in size from a few centimetres to a few millimetres, and therefore can require the assistance of a microscope to be found. Once any seeds were found, they were stained with a chemical dye (Tetrazolium) to see if they were still viable (capable of growing).

PhD candidate Samantha Tol holding dugong poo collected from Cleveland Bay in Townsville.
TropWATER, JCU

Why is this important for turtles and dugong?

Green sea turtles and dugong are iconic animals on the reef, and seagrass is their food. Dugong can eat as much as 35 kilograms of wet seagrass a day, while sea turtles can eat up to 2.5% of their body weight per day. Without productive seagrass meadows, they would not survive.

This relationship was highlighted in 2010-11 when heavy flooding and the impact of tropical cyclone Yasi led to drastic seagrass declines in north Queensland. In the year following this seagrass decline there was a spike in the number of starving and stranded sea turtles and dugong along the entire Queensland coast.

The seagrass team at James Cook University has been mapping, monitoring and researching the health of the Great Barrier Reef seagrasses for more than 30 years. While coral reefs are more attractive for tourists, the Great Barrier Reef World Heritage Area actually contains a greater area of seagrass than coral, encompassing around 20% of the world’s seagrass species. Seagrass ecosystems also maintain vibrant marine life, with many fish, crustaceans, sea stars, sea cucumbers, urchins and many more marine animals calling these meadows their home.

These underwater flowering plants are a vital component of the reef ecosystem. Seagrasses stabilise the sediment, sequester large amounts of carbon from the atmosphere and filter the water before it reaches the coral reefs. Further, the seagrass meadows in the Great Barrier Reef support one of the largest populations of sea turtles and dugong in the world.

Seagrass meadows are more connected than we thought

Samantha’s research was worth the effort. There were seeds of at least three seagrass species in the poo of both sea turtles and dugong. And lots of them – as many as two seeds per gram of poo. About one in ten were viable, meaning they could grow into new plants.

Based on estimates of the number of animals in the coastal waters, the time it takes for food to pass through their gut, and movement data collected from animals fitted with satellite tags, there are potentially as many as 500,000 viable seeds on the move each day in the Great Barrier Reef. These seeds can be transported distances of up to 650km in total.

Green Island seagrass meadow exposed at low tide.
TropWATER, JCU

This means turtles and dugong are connecting distant seagrass meadows by transporting seeds. Those seeds improve the genetic diversity of the meadows and may help meadows recover when they are damaged or lost after cyclones. These animals help to protect and nurture their own food supply, and in doing so make the reef ecosystem around them more resilient.

Understanding recovery after climate events

Seagrass meadows have been under stress in recent years. A series of floods and cyclones has left meadows in poor condition, and recovery has been patchy and site-dependent.

This research shows that these ecosystems have pathways for recovery. Provided we take care with the environment, seagrasses may yet recover without direct human intervention.

The ConversationThis work emphasises how much we still have to learn about how the reef systems interconnect and work together – and how much we need to protect every part of our marvellous and amazing reef environment.

Samantha J Tol, PhD Candidate, James Cook University; Alana Grech, Assistant Director, ARC Centre of Excellence for Coral Reef Studies, James Cook University; Paul York, Senior Research Scientist in Marine Biology, James Cook University, and Rob Coles, Team leader, Seagrass Habitats, TropWATER, James Cook University

This article was originally published on The Conversation. Read the original article.

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Traditional hunting gets headlines, but is not the big threat to turtles and dugongs


Helene Marsh, James Cook University and Mark Hamann, James Cook University

Recent calls for a ban on legal traditional hunting of dugongs and marine turtles imply that hunting is the main threat to these iconic species in Australia. The science indicates otherwise.

While more is being done to address traditional hunting than any of the other impacts, the main threats to their survival often pass unnoticed.

The real threat to sea turtles

The draft Recovery Plan for Marine Turtles in Australia evaluated 20 threats to the 22 populations of Australia’s six species of marine turtle. Climate change and marine debris, particularly “ghost nets” lost or abandoned by fishers, are the greatest risks for most stocks.

If you’re a marine turtle, a likely cause of death is getting tangled in a discarded fishing net.
AAP Image/Department of Heritage and Government

Indigenous use is considered to be a high risk for three populations: Gulf of Carpentaria green turtles, Arafura Sea flatback turtles and north-eastern Arnhemland hawksbill turtles.

However, in each of these cases it is the egg harvest, not hunting, that causes concern. International commercial fishing is also a high risk for the hawksbill turtle, whose future remains uncertain. Traditional hunting of marine turtles in Australia is limited to green turtles.

Is hunting a threat?

The Torres Strait supports the largest dugong population in the world and a globally significant population of green turtles. Archaeological research shows that Torres Strait Islanders have been harvesting these species for more than 4,000 years and the dugong harvest has been substantial for several centuries.

Our research shows that the Torres Strait dugong population has been stable since we started monitoring 30 years ago and that the harvest of both species is sustainable.

The situation for dugongs is very different in the waters of the Great Barrier Reef south of Cooktown. The Great Barrier Reef Outlook Report classifies the condition of the dugong population in this region as poor.

Modelling indicates that the southern Great Barrier Reef stock of the green turtle, which live and breed south of Cooktown, is increasing.

Nonetheless, both green turtles and dugongs died in record numbers in the year after the extreme floods and cyclones of the summer of 2010-11. Dugongs stopped breeding in the Great Barrier Reef region south of Cooktown.

Thankfully, our current aerial survey indicates that dugong calving has resumed as inshore seagrass habitats recover. There is no evidence that the 2011 losses significantly affected green turtle numbers.

Working together

Traditional owners are the first managers of our coastal waters, with cultural practices extending back thousands of years. They have the most to lose from any loss of turtles and dugongs. It is therefore in their best interests, and the government’s best interest, to work in partnership to protect and sustainably manage these species.

Longstanding tensions between traditional owners and tourist operators are behind much of the opposition to traditional hunting in the Cairns area. Some of these tensions have been relieved by the Gunggandji Traditional Use of Marine Resources Agreement signed in June 2016.

Under this agreement, the traditional owners decided to cease hunting turtles and dugongs in the waters surrounding Green Island, Michaelmas Cay and Fitzroy Island.

The Gunggandji agreement is the seventh to be signed between the Great Barrier Reef Marine Park Authority and traditional owners. In addition, there are two Indigenous land use agreements that address hunting issues in the Great Barrier Reef.

In the Torres Strait, dugong and turtle hunting is managed through 14 (soon to be 15) management plans. There are similar agreements with traditional owners and management agencies in other regions in northern Australia.

Indigenous rangers are crucial to implementing all these agreements in collaboration with management agencies and research institutions. Rangers deliver the practical, on-the-ground arrangements to conserve these species in their Sea Country.

The Great Barrier Reef Marine Park Authority has implemented an Indigenous Compliance Program that authorises trained Indigenous rangers to respond to suspicious and illegal activities that they encounter as part of their work.

Indigenous rangers and community members from Badu Island in Torres Strait help JCU scientists fit a dugong with a satellite tracking device.
Takahiro Shimada/James Cook University

Indigenous rangers also remove marine debris from remote beaches. The community-based organisation GhostNets Australia has worked with 31 coastal Indigenous communities to protect over 3,000km of northern Australia’s saltwater country from ghost nets. These community projects have been instrumental in rescuing turtles, clearing ghost nets off beaches and identifying key areas to aid management agencies to better understand the impact.

Traditional owners from the Torres Strait and the northern Great Barrier Reef also play a valuable role in intervention works at Raine Island, one of the world’s most significant green turtle rookeries. This includes rescuing stranded turtles, using fences to stop turtles from falling over cliffs, and altering beach profiles.

What about welfare?

Traditional hunting raises animal welfare issues. The turtle and dugong management plans developed by the Torres Strait communities explicitly address animal welfare. The Torres Strait Regional Authority has been working with a marine mammal veterinarian and traditional owners to develop additional methods of killing turtles humanely.

Indigenous hunters who breach state and territory animal welfare laws can be prosecuted. But more widespread animal welfare problems, not associated with hunting, are largely hidden and ignored. The Queensland Strand Net Program reported that 879 turtles died of their wounds from vessel strike between 2000 and 2011.

An immature female loggerhead turtle severely injured by a boat strike near Gladstone. This turtle was determined to be unrecoverable and was euthanased by a local veterinarian in May 2016.
Takahiro Shimada/James Cook University

Other serious animal welfare issues are associated with animals drowning in nets and being caught in and ingesting marine debris. In addition, the potential impact of emerging threats like underwater noise pollution and water quality remain as substantial knowledge gaps. These matters tend not to make the headlines.

Australian waters are home to some of the world’s largest populations of marine turtles and dugongs. A comprehensive and balanced approach to their conservation and management is required to enable our grandchildren and their children to enjoy these amazing animals.

The Conversation

Helene Marsh, Dean, Graduate Research, James Cook University and Mark Hamann, Senior Lecturer in Environmental Science (marine focus), James Cook University

This article was originally published on The Conversation. Read the original article.

Article: Australia – Queensland


Dugong Numbers Falling

The following link is to an article reporting on the falling numbers of Dugongs off the Queensland coast.

For more visit:
http://www.abc.net.au/news/2012-05-30/reef-dugong-numbers-hit-20-year-low/4041452