Sentinel Species Research

Webinar: Cetacean Science and Conservation

Cetacean Science and Conservation

Listen and engage with experts on a variety of topics related to cetacean science and conservation, from the environmental drivers of cetacean distribution to the applications of local ecological knowledge in conservation management.

Following the short talks, members of the audience were invited to ask questions on this topic.

Speakers:

Dr Helen Czerski – moderator
Dr Clare Embling – University of Plymouth
Dr Mingli Lin – Chinese Academy of Sciences & Institute of Zoology
Michael Mwang’ombe – Kenya Marine Mammal Research & Conservation
Dr Gill Braulik – University of St Andrews

You can watch a recording of the webinar below:

Sentinel Species Research

Webinar: Tropical Seabird Ecology

Tropical Seabird Ecology

In the second episode of the 2022 Bertarelli Foundation’s marine science webinar, Helen Czerski introduced a panel of speakers who are all working on and around themes of tropical seabird ecology.

Seabirds are beautifully adapted for life in the ocean, join us as we discuss, learn and wonder about these charismatic and highly visible predators of marine ecosystems.

Following the short talks, members of the public were invited to ask questions on this topic.

Speakers:

Dr. Helen Czerski – moderator
Alice Trevail – University of Exeter
Annette Fayet – Norwegian Institute for Nature Research
Peter Carr – Institute of Zoology
Robin Freeman – Zoological Society of London

You can watch a recording of the webinar below:

Any unanswered questions from the live webinar will be available on the website shortly.

Improving MPA ManagementSentinel Species Research

Drifting Fishing Gear Poses Significant Risks to Marine Protected Areas

Researchers hope their findings will help managers mitigate the impacts of drifting fishing gear in protected areas

Marine Protected Areas (MPAs) protect biodiversity within their boundaries by regulating fishing. However, the impacts of drifting fishing gear, especially drifting fish aggregation devices (dFADs), are not necessarily taken into account.

Now, a team of scientists led by David Curnick from the Zoological Society of London, UK, has shown the potential harm that dFADs could cause to MPAs. Their study, published in the journal Conservation Biology, found more than a third of dFADs posed a risk to biodiversity in the Chagos Archipelago MPA.

dFADs are floating platforms that attract tuna fish in particular, causing them to accumulate around the devices, making them easier to catch. More than 100,000 dFADs are deployed every year, but they have drawbacks including depleting tuna stocks and catching excessive juveniles and bycatch, such as sharks. They can also be lost and abandoned, becoming marine pollution and stranding in sensitive areas or tangling marine animals, such as turtles, in their trailing nets.

A drifting fish aggregation device (dFAD) beached on a reef in the Chagos Archipelago. Photo: Dan Bayley

A cause for considerable management concern

Using the MPA surrounding the islands and atolls of the Chagos Archipelago as a case study, Curnick and his colleagues modelled the transit of dFADs through the region from 16 different entry points. The devices’ movement was modelled across months and years to account for changing prevailing currents.

The researchers found that over a third (37.5%) of dFADs that drift into the MPA pose a considerable management concern by either beaching on sensitive habitats, such as coral reefs, or drifting through and accumulating fish that could then be exported outside the MPA and into fishable areas.

“The interactions between static MPAs and drifting fishing gears have long been overlooked. However, if left unchecked, we find that drifting fish aggregation devices could reduce the effectiveness of MPAs,” says Curnick. “As such, we need to ensure that MPA managers and stakeholders account for the possible impacts of drifting fishing gears and mitigate against them when required.”

The highest risk of dFADs beaching or remaining in the MPA for longer periods came from those entering the MPA from the east and west. The largest atoll in the region, the Great Chagos Bank, was the most likely to be affected by beaching.

Interdisciplinary approach helped to boost the study’s impact

Curnick says the interdisciplinarity of the project team helped the study succeed. “This project brought together academics, conservationists and fisheries scientists, generously supported by the Bertarelli Foundation,” he says. “By incorporating each other’s expertise and insights, we have produced a more holistic and impactful assessment of the risk posed by dFADs which we hope will lead to a review of their management around the Chagos Archipelago.”

And the approach is designed to be replicable in other MPAs and territories: “We hope the paper will provide a useful reference for others seeking to address the impacts of drifting fishing gears in their waters,” Curnick concludes.

Article details:

David J. Curnick, David A. Feary, and Geórgenes H. Cavalcante (2020)“Risks to large marine protected areas posed by drifting fish aggregation devices,” Conservation Biology

Sentinel Species Research

Restoring Seabird Islands

By Peter Carr, ZSL

Peter Carr

New research published this week in Restoration Ecology, led by scientists at ZSL’s Institute of Zoology, shows the potential benefits to breeding seabirds of converting coconut plantations to native habitats after invasive predators have been eradicated.

Red-footed Booby © Peter Carr, ZSL

On many Pacific and Indian Ocean islands, colonisation by humans brought invasive species, the destruction of native habitats, and widespread growth of coconut plantations, leading to the decimation of seabird populations. The coconut industry on oceanic islands has since crashed, leaving the legacy of abandoned coconut plantations that, by themselves, create species-poor biomes. When an island’s flora is dominated by abandoned coconut plantations and it has invasive rats, it becomes an avian desert.

Experts from the Institute of Zoology, Zoological Society of London, along with colleagues from the Royal Botanic Gardens, Kew, the University of Exeter, and Heriot-Watt University, have been researching the possible outcomes for breeding seabirds (e.g., Red-footed Booby and Lesser Noddy) of eradicating rats from oceanic islands, with and without conversion of surrounding abandoned coconut plantations.

Lesser Noddy © Peter Carr, ZSL

Working for over a decade, collecting data in the Chagos Archipelago, central Indian Ocean, scientists counted every breeding seabird on all 55 islands of the archipelago, and mapped and recorded the habitat they were breeding in. By comparing the number of seabirds breeding in a specific habitat on rat-free islands, they were able to predict the number of seabirds that could potentially colonise an island if invasive rats were eradicated, and abandoned coconut plantations were converted to native habitats. This is especially relevant in the Chagos Archipelago, as some 94% of the terrestrial landmass is rat-infested, where the vegetation is dominated by abandoned plantations.

One island, Ile du Coin in Peros Banhos atoll which, at 1.26km squared, is the fourth largest in the Chagos Archipelago, was hypothetically ecologically restored. This island has rats, and 92% of its vegetation is made up of former coconut plantation. At present, there are 51 pairs of breeding seabirds on this island, made up of three generalist species (Brown and Lesser Noddy and Common White Tern). Scientists predict that, following rat eradication, without any habitat management, the number of breeding pairs could rise to 4,306 pairs of 14 species. However if 1 km squared of abandoned plantation is converted to equal measures of native savannah and forest (example shown below), the number of breeding pairs could potentially increase to 319,762 of 16 species – more than the entire archipelago at present.

Native seabird breeding habitat, Chagos Archipelago © Peter Carr, ZSL

This research has practical applications throughout the Tropics. It shows that in order to restore tropical oceanic seabird islands that have been ecologically degraded, due to introduced predators and the destruction of native habitat, eradicating the predator as a single intervention method is unlikely to result in fully functional, seabird-driven ecosystems. On degraded islands where invasive rats and abandoned coconut plantations exist together, to restore seabird-driven ecosystems, rats must be eradicated, but also the plantations must be converted to native habitat.

In the Chagos Archipelago, as elsewhere in the Tropics, restoring seabird islands is no longer a ‘green dream’, it is a matter of funding and political goodwill. This research shows the requirement for an ecosystem-wide approach in order to fulfil these green dreams, and demonstrates the potential colossal gains to the family of birds that are suffering the greatest decline in number – seabirds.

You can access the paper here, and find out more about our work in the Chagos Archipelago here.

Sentinel Species Research

Podcast: Seabirds – Our Important Ocean Voyageurs

Ocean Matters - New episode available now

Episode 3: Seabirds – Our Important Ocean Voyageurs

Seabirds are an incredibly versatile group of animals – they roam freely on land, soar majestically through the air and are equally at home underwater. They’re critically important if we are to maintain a healthy ocean, but half of all seabird populations are declining, and one in three is threatened with global extinction.

In this episode of Ocean Matters, physicist and oceanographer Helen Czerski explores the vital link between seabirds and the sea, discovers how can seabirds help the ocean recover, and crucially, how can we help the seabirds.

Come with us on this scientific adventure. Subscribe now, wherever you get your podcasts, so that you never miss an episode of Ocean Matters.

Subscribe and listen here

Sentinel Species Research

Monitoring and identifying shark species in the Chagos Archipelago

Monitoring and identifying shark species in the Chagos Archipelago.

Recent work published by our researchers has shown that differences in movement strategies between two closely-related reef shark species can influence how vulnerable they are to poaching risk in the Chagos Archipelago and that by studying these movements, we can help to inform enforcement decisions in the MPA. Network analysis led by Dr David Jacoby, investigated the movement and space use of silvertip sharks (Carcharhinus albimarginatus) and grey reef sharks (Carcharhinus amblyrhynchos) around Peros Banhos and Salomon atolls in the Chagos Archipelago and showed that despite living side-by-side, the two species move through the MPA in very different ways. The study used acoustic tracking to study how individuals from these two shark species moved within the MPA. This method involves catching sharks, surgically implanting acoustic tags and setting up an array of underwater receivers which record the tag ID as a tagged shark swims past. From this, the researchers were able to highlight key movement corridors that MPA enforcement patrols can focus on to help protect the sharks from illegal, unregulated and unreported (IUU) fishing activity. This study also showed that silvertip sharks were more wide-ranging and therefore more vulnerable to IUU activity than grey reef sharks.

Another way to monitor species in the MPA is to use DNA. Genetic analysis can be used to identify the diversity of species in the territory and even explore whether there are distinct populations within species. One recent monitoring technique that is gaining attention in ecosystems all over the world is species detection using environmental DNA, also known as eDNA. As animals pass through their environment, they leave traces of DNA behind them. In the MPA surrounding the Chagos Archipelago, we can collect eDNA from the water and use it to determine what species are present and this is a great way to detect shark species that we otherwise might not see.

To achieve genetic monitoring and detection through eDNA, researchers must first know the genetic sequence of the species they want to study. To this end, researchers Nick Dunn (from ZSL and Imperial College London) and Shaili Johri (from Stanford University) have sequenced and published the mitochondrial genome sequences of the grey reef shark, silvertip shark, whitetip reef shark (Triaenodon obesus) and silky shark (Carcharhinus falciformis) from the Chagos Archipelago. Mitochondrial DNA is commonly used in genetic studies because it is easier to target than nuclear DNA and can be used to identify populations within species. To do this, small fin clips were taken from each of the species during tagging expeditions in the territory and their DNA was sequenced using two contrasting DNA sequencing techniques. Shaili used a handheld device called the Oxford Nanopore MinION to sequence whole mitochondrial genomes and Nick produced his sequences using a more conventional approach on an Illumina sequencer that involves breaking DNA into small fragments and reproducing the complete sequence by using overlapping fragments, a bit like a puzzle. The mitochondrial genome sequences produced were the first ever published for the grey reef shark and the silvertip shark, and a first from populations in the Chagos Archipelago for the whitetip reef shark and the silky shark.

The sequences produced from the two techniques were over 99% similar, showing that both methods can be used in future research as the few differences were most likely to be due to differences between the individuals sequenced rather than errors. These mitochondrial genome sequences will be used to produce eDNA detection protocols for the species, which will help researchers understand how eDNA can be used to monitor shark species in the MPA. The sequences and methods used can also be used to investigate the connectivity of sharks in the Indian Ocean and to determine how significantly Chagos Archipelago reef sharks contribute to the shark fin trade.

References

Dunn, N., Johri, S., Curnick, D., Carbone, C., Elizabeth, A., Chapple, T. K., et al. (2020) Complete mitochondrial genome of the gray reef shark , Carcharhinus amblyrhynchos ( Carcharhiniformes : Carcharhinidae ). Mitochondrial DNA Part B 5, 2080–2082. doi:10.1080/23802359.2020.1765208.

Jacoby, D. M. P., Ferretti, F., Freeman, R., Carlisle, A. B., Chapple, T. K., Curnick, D. J., et al. (2020) Shark movement strategies influence poaching risk and can guide enforcement decisions in a large, remote Marine Protected Area. J. Appl. Ecol. doi:10.1111/1365‐2664.13654.

Johri, S., Chapple, T. K., Dinsdale, E. A., Schallert, R., and Block, B. A. (2020a) Mitochondrial genome of the silky shark Carcharhinus falciformis from the British Indian Ocean Territory Marine Protected Area . Mitochondrial DNA Part B. doi:10.1080/23802359.2020.1775147.

Johri, S., Chapple, T. K., Schallert, R., Dinsdale, E. A., and Block, B. A. (2020b) Complete mitochondrial genome of the whitetip reef shark Triaenodon obesus from the British Indian Ocean Territory Marine Protected Area . Mitochondrial DNA Part B. doi:10.1080/23802359.2020.1775148.

Johri, S., Dunn, N., Chapple, T. K., Curnick, D., Savolainen, V., Dinsdale, E. A., et al. (2020c) Mitochondrial genome of the Silvertip shark, Carcharhinus albimarginatus, from the British Indian Ocean Territory. Mitochondrial DNA Part B Resour. doi:10.1080/23802359.2020.1765210.

News piece by Nick Dunn

Sentinel Species Research

Remarkable increase in turtle numbers on uninhabited islands

Dr Nicole Esteban and Dr Jeanne A. Mortimer authored a new study that reveals a massive increase in the number of turtles nesting on the Chagos Archipelago in the British Indian Ocean Territory, one of the world’s largest Marine Protected Areas (MPAs).

The British Indian Ocean Territory (BIOT), a British overseas territory that is located in the Indian Ocean about halfway between Tanzania and Indonesia, spans 640,000 km² and tops the list of global marine no-take areas. The Territory has some of the most biodiverse waters on the planet with over 220 species of coral, 855 species of fish and 355 species of molluscs swimming through its water. BIOT also contains the Chagos Archipelago, a group of seven atolls comprising more than 60 individual tropical islands.

Dr Esteban, your study revealed an increase of between 225% and 525% from 1996 to today for the critically endangered hawksbill turtle, and between 465% and 930% for the endangered green turtle. Were you expecting these results?

There haven’t been any detailed studies of the numbers of turtles besides the very baseline figures that we had from 1970, 1996 and 2006. We didn’t actually expect the number of turtles to have increased as much as they did. We were quite surprised.

What do you think the results mean for the conservation of these turtle species?

It’s fantastic news. In terms of conservation efforts, hawksbills are one of the most endangered species of marine turtles; they’re critically endangered on the IUCN Red List.

The British Indian Ocean Territory is a nesting refuge for a large proportion of the turtles nesting in the Western Indian Ocean – up to 51% of all hawksbills nest there. The fact that there’s such a large proportion nesting on uninhabited islands, well-protected by the MPA, is a really good for their conservation.

Do you think that this success is because of the MPA?

I think we have to be a little bit cautious because the MPA has only been formally in existence for just under ten years, and it takes 30-40 years to be able to document the recovery of sea turtle numbers. However, exploitation of turtles has been prohibited in the Territory since the 1970s so we can certainly attribute the recovery of sea turtle numbers in the British Indian Ocean Territory to long-term sea turtle conservation and protection. Laws were introduced in the early 1970s that protected turtles in the Chagos Archipelago and I would expect that this recovery will continue with the additional protection provided by the MPA.

One of the ways that you documented turtle activity was by counting turtle tracks. But how did you know that a single turtle didn’t make multiple tracks?

In fact, each turtle does make multiple tracks, and one of the assumptions that we made was to estimate how many tracks each turtle makes before laying eggs. Typically a turtle emerges from the ocean multiple times and may dig several trial nests before actually laying a clutch of eggs. This is because she may encounter obstacles on the beach or sand that is too soft or too hard before she is finally able to lay eggs. In our data analysis we’ve made the assumption of an average of 1.8 tracks for every egg clutch laid. This is based largely on data from turtles in Seychelles which are genetically related to those in the Chagos Archipelago and utilise very similar nesting habitats.

The other thing to bear in mind is that it’s really difficult to go to a remote island and count the number of tracks because much of the beach gets washed clean every spring tide. Therefore much of the data collected, especially in the remote outer islands, was based on counts of “body pits” high up on the beach platform. Body pits are the depressions turtles leave on the beach when they dig nests. These body pits can last for weeks or months, so they’re a much more reliable source of information.

How did you get involved with the Bertarelli Foundation, the funders of this study?

The Bertarelli Foundation started a marine science programme which involved a number of projects carried out in the British Indian Ocean Territory. Our team applied for a grant to fund key research relating to hawksbill and green turtles breeding and foraging across the five islanded atolls of the Chagos Archipelago.

Were there any other unexpected discoveries?

At the time we began our study, seagrass meadows (the favourite food of green turtles) were believed to be relatively rare in the Chagos Archipelago. We anticipated that most of the green turtles that nested in the archipelago would migrate to foraging sites elsewhere in the Western Indian Ocean. Thanks to funding from the Bertarelli Foundation, however, we’ve discovered that after nesting in the MPA some of the satellite-tracked green turtles remain within the archipelago and forage on the Great Chagos Bank, the largest living coral atoll in the world. With the help of these satellite-tracked turtles we were able to discover large areas of deep water and previously unknown seagrass meadows in the MPA.

What comes next?

We still have many things to learn about the ecology of sea turtles in the Chagos Archipelago. We would like to do more surveys of nesting activity in the remote uninhabited islands of the archipelago. We need to try to reduce the assumptions that we’re using to calculate total number of turtles nesting.

We also want to learn more about the survival rates of egg clutches and the hatching turtles they produce, so that’s another area of enquiry. We’ve started looking at the effects of temperature on incubation and how beach litter affects the success of turtle nesting. We’re also starting to test different technologies to enhance the ability to monitor remotely.

There’s lots to find out!

This research was published in Oryx and was supported by the Bertarelli Foundation.

Mortimer, J. A., Esteban, N., Guzman, A. N. and Hays, G. C. (2020) “Estimates of marine turtle nesting populations in the south-west Indian Ocean indicate the importance of the Chagos Archipelago,” Oryx. Cambridge University Press, pp. 1–12. DOI: 10.1017/S0030605319001108.

Sentinel Species Research

Use of Environmental DNA to Investigate Biodiversity

Use of Environmental DNA to investigate biodiversity

Environmental DNA, or eDNA, is genetic material that is left behind in the environment as organisms pass through it. The material can originate from skin cells, scales, mucus, faeces or wounds, and because organisms have unique genetic sequences, it can be used to provide us with information on the presence of target species.

Sampling for eDNA in the field is a relatively straightforward process and begins with the collection of water samples. During an expedition to Diego Garcia in British Indian Ocean Territory in September 2019, Nick Dunn (PhD student at ZSL and Imperial College London) took eDNA samples from different locations around the atoll. At each of the 18 locations, he sampled water from two depths using a five litre Niskin bottle, which is essentially a chamber with two spring-loaded stoppers at each end. Attached to a rope, the bottle was sent down to a depth of 40m and a messenger weight sent down to trigger the spring to close the chamber and allow the team to bring the water sample back up to the boat. The 40m water was decanted into a storage container and a surface water sample was then collected. The water samples were stored on ice in a cool box and taken back to land for processing.

A Niskin bottle containing a sample of water from a depth of 40m.

Processing eDNA involves passing the water through an extremely fine filter to separate all the cells and DNA in the sample. As DNA can degrade quickly in water, Nick ensured that this was done as soon as the team returned to land each morning and evening. Three 1-litre subsamples from each container were passed through separate filters, a process which took between ten and 20 minutes because the filters were so fine. The filters were then placed in a preservation solution so they could be transported back to the UK for analysis without the DNA degrading.

Equipment used to filter the water samples.

Working on eDNA is beneficial because you do not need to rely on chance encounters with animals to collect data and investigate the biodiversity of an area. The next steps, which are currently underway, involve finding out what species’ DNA has been collected in each sample using genetic sequencing methods. This will give us a clearer picture of what species are present around the island of Diego Garcia and if different areas are home to diverse sets of species.

Sentinel Species Research

Guano Versus El Niño

Original post:

How Bird Poop May Save Coral Reefs.

Warming sea surface temperatures have destructive effects on coral reefs, as shown during the 2015-2016 El Niño global bleaching event.

Corals rely on a highly important symbiotic relationship with an algae, called zooxanthellae. When sea temperature rises these algae can become toxic to the coral and are thus expelled, causing the coral to loose its color and appear “bleached”. Nonetheless, corals can eventually recover from bleaching events in the right circumstances and if given enough time.

Nitrogen and phosphorus occur naturally at very low levels on coral reefs, making them a notoriously nutrient-poor environment. These elements are key to the photosynthesis of the plants and algae on which coral reef ecosystems rely and act as limiting factors. To the surprise of researchers in BIOT, it seems that seabird’s guano (rich in nutrients) can provide an essential “boost” triggering coral recovery.

Indeed, seabirds are known to defecate frequently and most of this guano ends up in coral reefs ecosystems (directly or indirectly). A recent study states that this nutrient enhancement is critical for corals after a bleaching event.

The same study investigated on the coral saving guano by looking at ten islands. They found that reefs surrounding islands with a substantial seabird population had a greater growth of calcareous algae This particular seaweed serves as glue for reefs to form a barrier and is an indicator of a healthy ecosystem. Therefore, scientists suggest that guano provides optimal nitrogen to phosphorus ratios essential to reefs recovery and that we can’t replicate. Moreover, reefs surrounding healthy populations of seabirds experienced a healthier and more resilient fish population than reef with no birds.

“There is no example that is as clear cut and effective in enhancing the functioning of coral reefs in the face of climate change.”