Let me introduce you to… dugongs!

By Solène Derville, Postdoc, OSU Department of Fisheries, Wildlife, and Conservation Science, Geospatial Ecology of Marine Megafauna Lab

Today let me take you on a journey into the tropical waters of the Indo-Pacific Ocean, far from Oregon’s beautiful coasts. Although I have been working as a postdoc on the OPAL project for a year, the pandemic has prevented me from moving to the US as planned. Like so many around the globe, I have been working remotely from my study area (Oregon coastal waters), imagining my study species (blue, fin and humpback whales) gently swimming and feeding along the productive California Current system. One day, I’ll get to see these amazing animals for real, that’s for sure.

But in the meantime, I have taken this year as an opportunity to work with the GEMM lab, while continuing to enjoy the marvels of New Caledonia, a French overseas territory where I have lived for more than 6 years now. Among the animals that I get to approach and observe regularly in the coral reef lagoons that surround the island, the dugong (Dugon dugon) is perhaps the most emblematic and intriguing. This marine mammal is listed as vulnerable in the IUCN Red list of threatened species and has been the focus of important research and conservation efforts in New Caledonia over the last two decades1–3. During my previous post-doctoral position at the French Institute of Research for Sustainable Development, I contributed to some recent research involving satellite tracking of dugongs in the region. This work has led to a publication, now in review4, and will be the topic of my oral presentation at the 7th International Bio-Logging Science Symposium hosted in Hawaii in a couple weeks.

While I was analyzing dugong satellite tracks, writing this paper with my colleagues and preparing for the symposium, I learned a lot about these strange “sea cows”. Dugongs belong to the Sirenian marine mammal order, just like manatees (West Indian, Amazonian and West African species), which they are often mistaken for (watch out: Google Images will misleadingly suggest hundreds of manatee pictures if you make a “dugong” keyword search). The physiology and anatomy of dugongs is actually quite different from that of manatees (Figure 1). They also live in a different part of the world as they are broadly distributed in the Indo-Pacific coastal and island waters. Dugongs form separate populations, some of which are very isolated and at high risk of extirpation. They are found in 37 different countries, with Australia being home to the largest populations by far (exceeding 70,000 individuals5).

Figure 1: Manatee vs Dugong, can you tell them apart? Among other things, dugongs and manatees have a very different body shape. As the famous Sirenian specialist Helene Marsh said, a dugong essentially looks like “a manatee that goes to the gym”5! Illustration by S. Derville.

Sea cow or sea elephant?

Through the tree of evolution, the dugong and manatee’s closest relative is not the one you would think… other marine mammals like cetaceans or pinnipeds. Indeed, molecular genetic analyses have placed the Sirenians in the Afrotheria Superorder of mammals. Therefore, it appears that dugongs are more closely related to elephant and golden moles than to whales and dolphins!

As a memory aid to help remember this ancient origin, we may notice that both elephants and dugongs have tusks. Mature male and female dugongs have erupted tusks, although the females’ only erupt rarely and at a very old age. Interestingly, tusks are used by scientists to determine age. Analyses of growth layers in bisected dugong tusks have revealed that dugongs are long-lived, with a maximum longevity record of 73 years (estimated from a female individual found in Western Australia5).

An (almost) vegetarian marine mammal

Dugongs and manatees are the only predominantly herbivorous aquatic mammals. Given that manatees use both marine and fresh water ecosystems they tend to have a broader diet, eating many kinds of submerged, floating or emergent algae and seagrass (even bank growth!). On the other hand, dugongs are a strictly marine species and primarily feed on seagrass, which may look very similar to seaweeds, but are in fact marine flowering plants. Seagrass tend to form underwater shallow meadows that are among the most productive ecosystems in the world6. In fact, dugong grazing influences the biomass, species composition and nutritional quality of seagrass meadows7,8. Just like we take care of our gardens, dugongs regulate seagrass ecosystems. But there is more. Recent research conducted in the Great Barrier Reef indicates that seagrass seeds that have been digested by dugongs germinate at a faster rate9. As well as playing a role in dispersal10, it appears that dugongs are pooping seeds with enhanced germination potential, hence participating to seagrass meadow resilience.

Figure 2: Dugong mother and calf feeding on a dense seagrass bed (a) and solitary adult foraging in a very sparce seagrass bed (b). Seagrass grows in many different types of meadows, which may vary in density, species composition and substrate. For instance, seagrass species of the Halophila genus are among the preferred dugong’s meals although may be very thinly distributed (c). Photo credit: Serge Andréfouët, New Caledonia.

Unlike manatees, dugongs cannot feed over the whole water column and are strictly bottom feeders. They use their deflected snout (Figure 1) to search the seabed for their favorite food (Figure 2). The feeding trails left by dugongs in dense seagrass meadows are easily detectable from above, just like the sediment clouds that they generate when searching muddy bottoms. Although seagrass is undoubtedly the main component of the dugong’s diet, they may incidentally (or not) ingest algae and invertebrates5.

A legendary animal

The etymology for the word Sirenian comes from the mermaids, or “sirens” of the Greek mythology. These aquatic creatures with the upper body of a female human would sing to lure sailors towards the shore… and towards a certain death. The morphology of dugongs and manatees shares some resemblance with mermaids, at least enough for desperate and lonely sailors to think so!

In addition to having a scientific name rooted in legends, dugongs are also important to contemporary human cultures. In tropical islands and coastal communities, marine megafauna species such as dugongs are considered heritage, due to the strong bond that their people have forged with the ocean5. Dugongs may play an important cultural role because they can be part of the socio-symbolic organization of societies, associated with the imaginary world, or simply because they are seen as companions of the sea, which people frequently encounter. For New Caledonia’s indigenous people, the Kanaks, dugongs can be totem to tribes. Like other large marine species (whales, sharks), the dugong is also considered as an embodiment of ancestors11.

Dugongs have been hunted throughout their range since prehistoric times. Archaeological excavations such as those conducted on the island of Akab in the United Arab Emirates12, indicate that dugong hunting played a role in ancient rituals, in addition to providing a large quantity of meat. The cultural value of dugongs is recognized by multiple countries, which have therefore authorized indigenous dugong hunting, sometimes under quotas. For instance, in Australia, dugongs may be legally hunted by Aboriginal and Torres Strait Islander people (Figure 3) under section 211 of the Native Title Act 1993.

In New Caledonia, the dugong has been protected since 1962 and its hunting is only authorized in one province, with a dispensation for traditional Kanak celebrations13. However, in view of the critical situation in which the New Caledonian dugong population finds itself, estimated at around 700 individuals in 2008-201214, no hunting exemptions have been issued since 2004.

Figure 3: “Naath” (dugong hunting platform), hand colored linocut by Torres Strait Islander artist Dennis Nona. The art piece represents traditional dugong hunting where the hunter is guided by the phosphorescent glow the dugong would leave in the water at night.

What future for dugongs?

Despite legislations to forbid dugong meat consumption outside specific traditional permits, poaching persists, in New Caledonia and in many of the “low-income” countries that are home to dugongs. As climate change and demography intensifies risks to food security, scientists and stakeholders fear for dugongs. Moreover, dugongs entirely rely on seagrass ecosystems that are also disappearing at an alarming rate (7% per year6) as a result of coastal development, pollution and overfishing.

Can we preserve dugongs in regions of high climate vulnerability and where people still have low levels of access to basic needs? Can dugongs play the role of “umbrellas” for the conservation of the ecosystem they live in? I do not have the answer to these questions but I certainly believe that people’s well-being and environmental conservation are tightly intertwined. I hope that rising transdisciplinary approaches such as those supported by the “One Health” framework will help reconnect human populations to their environment, and achieve the goal of optimal health for everyone, humans and animals.

References

1.        Garrigue, C., Patenaude, N. & Marsh, H. Distribution and abundance of the dugong in New Caledonia, southwest Pacific. Mar. Mammal Sci. 24, 81–90 (2008).

2.        Cleguer, C., Grech, A., Garrigue, C. & Marsh, H. Spatial mismatch between marine protected areas and dugongs in New Caledonia. Biol. Conserv. 184, 154–162 (2015).

3.        Cleguer, C., Garrigue, C. & Marsh, H. Dugong (Dugong dugon) movements and habitat use in a coral reef lagoonal ecosystem. Endanger. Species Res. 43, 167–181 (2020).

4.        Derville, S., Cleguer, C. & Garrigue, C. Ecoregional and temporal dynamics of dugong habitat use in a complex coral reef lagoon ecosystem. Sci. Rep. (In review)

5.        Marsh, H., O’Shea, T. J. & Reynolds, J. E. I. Ecology and conservation of the Sirenia: dugongs and manatees, Vol 18. (Cambridge University Press, Cambridge, 2011).

6.        Unsworth, R. K. F. & Cullen-Unsworth, L. C. Seagrass meadows. Curr. Biol. 27, R443–R445 (2017).

7.        Aragones, L. V., Lawler, I. R., Foley, W. J. & Marsh, H. Dugong grazing and turtle cropping: Grazing optimization in tropical seagrass systems? Oecologia 149, 635–647 (2006).

8.        Preen, A. Impacts of dugong foraging on seagrass habitats: observational and experimental evidence for cultivation grazing. Mar. Ecol. Prog. Ser. 124, 201–213 (1995).

9.        Tol, S. J., Jarvis, J. C., York, P. H., Congdon, B. C. & Coles, R. G. Mutualistic relationships in marine angiosperms: Enhanced germination of seeds by mega-herbivores. Biotropica (2021) doi:10.1111/btp.13001.

10.      Tol, S. J. et al. Long distance biotic dispersal of tropical seagrass seeds by marine mega-herbivores. Sci. Rep. 7, 1–8 (2017).

11.      Dupont, A. Évaluation de la place du dugong dans la société néo-calédonienne. (Mémoire Master. Encadré par L. Gardes (Agence des Aires Marines Protégées) et C. Sabinot (IRD), 2015).

12.      Méry, S., Charpentier, V., Auxiette, G. & Pelle, E. A dugong bone mound: The Neolithic ritual site on Akab in Umm al-Quwain, United Arab Emirates. Antiquity 83, 696–708 (2009).

13.      Leblic, I. Vivre de la mer, vivre de la terre… en pays kanak. Savoirs et techniques des pêcheurs kanak du sud de la Nouvelle-Calédonie. (Société des Océanistes, 2008).

14.      Hagihara, R. et al. Compensating for geographic variation in detection probability with water depth improves abundance estimates of coastal marine megafauna. PLoS One 13, e0191476 (2018).

Observing humpback whales through the clear New Caledonian waters

Solène Derville, Entropie Lab, French National Institute for Sustainable Development (IRD – UMR Entropie), Nouméa, New Caledonia

Ph.D. student under the co-supervision of Dr. Leigh Torres

Drone technology has illustrated itself as particularly useful to the study of cetacean in the GEMM Lab (see previous post by Dawn and Leila) and in the marine mammal research community in general. The last Conference on the Biology of Marine Mammals in Halifax staged several talks and posters describing the great potential of drones for observing animal behaviors, collecting blow samples, estimating the size and health of animals, or estimating densities. The GEMM Lab has been conducting leading research in this field, from capturing exceptional footages of lunge feeding blue whales in New Zealand, to measuring gray whale health on the Oregon coast.

Using drones in New Caledonia

In September 2017 I participated in a scientific cruise undertaken by Opération Cétacés /IRD to study New Caledonian humpback whales, and we were lucky to be joined by Nicolas Job, a professional diver, photographer and drone pilot. It was one of those last minute decisions: one of our crewmates canceled the week before the survey and we thought “who could we bring on instead?”. We barely knew the man but figured it would be good to get a few humpback whale drone images… We invited him to join us on the research expedition only a few days before the trip but this is not the kind of opportunity that a photographer would pass on!

Far from trying to acquire scientific data in the way the GEMM Lab does with blue whales and gray whales, we were only hoping to take “pretty pictures”… we were not disappointed.

Once we got past a few unexpected issues (YES you need to wear gloves to protect your fingers when trying to catch a flying drone (Fig 1), and NO frigate birds will not attack drones as long as they don’t smell like fish), Nicolas managed to fly the drone above our small research boat and capture footage of several humpback whale groups, including mothers with calf and competitive groups.

Figure 1: Frigate birds are known to attack birds in flight to steal their meal straight from their beak…luckily they did not attack our drone! On the contrary, it seems like they could help scientists one day as it has been suggested that UAV builders could learn from their exceptional soaring behavior that allows months-long transoceanic flights (photo credit: Henri Zemerskirch CEBC CNRS) .

As I said, no groundbreaking science here, but this experience convinced me that drones can bring a new perspective to the way we observe and interpret animal behavior. As a known statistics/R-lover in the lab, I often get so excited by the intricacies of data analysis that I forget I am studying these giant, elegant, agile, and intelligent sea creatures (Fig 2). And the video clips that Nicolas put together just reminded me of that.

The clear waters of the Natural Park of the Coral Sea allowed us to see whales as far as 30 meters deep in some areas! This perspective turned our usual surface observations into 3D. We could see escorts guarding maternal females and preventing other males from approaching by producing bubble trails. Escorts also extended their pectoral fins on either side of their body, a behavior supposed to make them look more imposing in the presence of a challenger. Competitive groups were also very impressive from above. During the breeding season, competitive groups form when several males aggregate around a female and compete for it. These groups typically travel at high speed and are characterized by active surface behaviors such as tail slaps, head lunges, and bubble trails.

Figure 2: This female humpback whale was encountered in 2016 and 2017. Her white flanks make her particularly easy to recognize. On both occasions it put on a show and kept circling the Amborella oceanographic vessel for more than an hour. To provide a sense of scale, the vessel on this drone footage is 24 m long (photo credit: Nicolas Job).

Drones and seamounts

Since the discovery of humpback whale offshore breeding areas in Antigonia seamount in 2007 and Orne bank in 2016, a lot of research has been conducted to better understand habitat preferences, distributions and connectivity in oceanic waters of New Caledonia (see previous post). Surveys have always been strongly multidisciplinary, including boat-based observation, biopsy sampling, and photo-identification, satellite tracking, in situ oceanographic measurements and acoustics. Will drones soon become an essential component of this toolbox?

One potential application I could imagine for my personal research questions would be to use aerial photogrammetry to measure the size of newborn calves. Indeed, we have found that offshore seamounts are used by a relatively great number of mothers with calf (Derville, Torres & Garrigue, In Press JMAMM). This finding is counter intuitive to the paradigm that maternal females prefer sheltered, shallow and coastal waters as shown in many breeding grounds around the world. Yet, we believe unsheltered oceanic areas might become more attractive to maternal females as the calf grows bigger and more robust to harsh sea states and encounters with competitive adult males. Drone photogrammetry of calves could likely help us confirm this hypothesis.

But for now, I will leave the science behind for a bit and let you enjoy the sheer beauty of this footage!

Film directed by Nicolas Job (Heos Marine) with images collected during the MARACAS3 survey (Marine Mammals of the Coral Sea: IRD/ UMR Entropie/Opération Cétacés/ Gouv.nc/ WWF/ Ministère de la Transition écologique et solidaire).

Exploring the Coral Sea in Search of Humpbacks

By: Solène Derville, Entropie Lab, Institute of Research for Development, Nouméa, New Caledonia (Ph.D. student under the co-supervision of Dr. Leigh Torres)

Once again the austral winter is ending, and with it ends the field season for the scientific team studying humpback whales in New Caledonia. Through my PhD, I have become as migratory as my study species so this is also the time for me to fly back to Oregon for an intense 3 months of data analysis at the GEMM Lab. But before packing, it is time for a sum-up!

In 2014, the government of New Caledonia has declared all waters of the Economic Exclusive Zone to be part of a giant marine protected area: the Natural Park of the Coral Sea. These waters are seasonally visited by a small and endangered population of humpback whales whose habitat use patterns are poorly known. Indeed, the park spans more than 1.3 million km2 and its most remote and pristine areas therefore remained pretty much unexplored in terms of cetacean presence… until recently.

In 2016, the project WHERE “Humpback Whale Habitat Exploration to improve spatial management in the natural park of the CoRal Sea” was launch by my PhD supervisor, Dr. Garrigue, and I, to conduct surveys in remote reefs, seamounts and shallow banks surrounding New Caledonia mainland. The aim of the project is to increase our understanding of habitat use and movements of humpback whales in breeding grounds over a large spatial scale and predict priority conservation areas for the park.

Fig. 1. A humpback whale with our research vessel, the oceanographic vessel Alis, in the background.

This season, three specific areas were targeted for survey during the MARACAS expeditions (Marine Mammals of the Coral Sea):

– Chesterfield and Bellona reefs that surround two huge 30- to 60m-deep plateaus and are located halfway between New Caledonia and Australia (Fig. 4). Considered as part of the most pristine reefs in the Coral Sea, these areas were actually identified as one of the main hotspots targeted by the 19th century commercial whaling of humpback whales in the South Pacific (Oremus and Garrigue 2014). Last year’s surveys revealed that humpback whales still visit the area, but the abundance of the population and its connection to the neighboring breeding grounds of New Caledonia and Australia is yet to establish.

Fig. 2. The tiny islands along the Chesterfield and Bellona reefs also happen to host nesting sites for several species of boobies and terns. Here, a red-footed booby (Sula sula).

– Walpole Island and Orne bank are part of the shallow areas East of the mainland of New Caledonia (Fig. 4), where several previously tagged whales were found to spend a significant amount of time. This area was explored by our survey team for the first time last year, revealing an unexpected density of humpback whales displaying signs of breeding (male songs, competitive groups) and nursing activity (females with their newborn calf).

Fig. 3. The beautiful cliffs of Walpole Island rising from the Pacific Ocean.

Antigonia seamount, an offshore breeding site located South of the mainland (Fig. 4) and known for its amazingly dense congregations of humpback whales.  The seamount rises from the abyssal seabed to a depth of 60 m, with no surfacing island or reef to shelter either the whales or the scientists from rough seas.

Fig. 4. Map of the New Caledonia Economic Exclusive Zone (EEZ) and the project WHERE study areas (MARACAS expeditions).

During our three cruises, we spent 37 days at-sea while a second team continued monitoring the South Lagoon breeding ground. Working with two teams at the same time, one covering the offshore breeding areas and the other monitoring the coastal long-term study site of the South Lagoon, allowed us to assess large scale movements of humpback whales within the breeding season using photo-ID matches. This piece of information is particularly important to managers, in order to efficiently protect whales both within their breeding spots, and the potential corridors between them.

So how would you study whales over such a large scale?

Well first, find a ship. A LARGE ship. It takes more than 48 hours to reach the Chesterfield reefs. The vessel needs to carry enough gas necessary to survey such an extensive region, plus the space for a dinghy big enough to conduct satellite tagging of whales. All of this could not have been possible without the Amborella, the New Caledonian governement’s vessel, and the Alis, a French oceanographic research vessel.

Second, a team needs to be multidisciplinary. Surveying remote waters is logistically challenging and financially costly, so we had to make it worth our time. This season, we combined 1) photo-identification and biopsy samplings to estimate population connectivity, 2) acoustic monitoring using moored hydrophone (one of which recorded in Antigonia for more than two months, Fig. 5), 3) transect lines to record encounter rates of humpback whales, 4) in situ oceanographic measurements, and finally 5) satellite tracking of whales using the recent SPLASH10 tags (Wildlife Computers) capable of recording dive depths in addition to geographic positions (Fig. 6).

Fig. 5. Claire, Romain and Christophe standing next to our moored hydrophone, ready for immersion.

Satellite tracks and photo-identification have already revealed some interesting results in terms of connectivity within the park and with neighboring wintering grounds.

Preliminary matching of the caudal fluke pictures captured this season and in 2016 with existing catalogues showed that the same individuals may be resighted in different regions of the Park. For instance, some of the individuals photographed in Chesterfield – Bellona, had been observed around New Caledonia mainland in previous years! This match strengthens our hypothesis of a connection between Chesterfield reef complex and New Caledonia.

Yet, because the study of whale behavior is never straightforward, one tagged whale also indicated a potential connection between Chesterfield-Bellona and Australia East coast (Fig. 6). This is the first time a humpback whale is tracked moving between New Caledonia and East Australia within a breeding season. Previous matches of fluke catalogues had shown a few exchanges between these two areas but these comparisons did not include Chesterfield. Is it possible that the Chesterfield-Bellona coral reef complex form a connecting platform between Australia and New Caledonia? The matching of our photos with those captured by our Australian colleagues who collected data at the Great Barrier Reef  in 2016 and 2017 should help answer this question…

Fig. 6. “Splash” was tagged in Chesterfield in August and after spending some time in Bellona it initiated a migration south. Seamounts seem to play an important role for humpback whales in the region, as “Splash” stopped on Kelso and Capel seamount during its trip. It reached the Australian coast a couple of days ago and we are looking forward to discover the rest of its route!

While humpback whales often appear like one of the most well documented cetacean species, it seems that there is yet a lot to discover about them!

Acknowledgements:

These expeditions would not have been possible without the financial and technical support of the French Institute of Research for Development, the New Caledonian government, the French  Ministère de la Transition Ecologique et Solidaire, and the World Wide Fund for Nature. And of course, many thanks to the Alis and Amborella crews, and to our great fieldwork teammates: Jennifer Allen, Claire Bonneville, Hugo Bourgogne, Guillaume Chero, Rémi Dodémont, Claire Garrigue, Nicolas Job, Romain Le Gendre, Marc Oremus, Véronique Pérard, Leena Riekkola, and Mike Williamson.

Fig. 7A. The teams of the three 2017 MARACAS expeditions (Marine Mammals of the Coral Sea).

Fig. 7B. The teams of the three 2017 MARACAS expeditions (Marine Mammals of the Coral Sea).

Fig. 7C. The teams of the three 2017 MARACAS expeditions (Marine Mammals of the Coral Sea).

The seamounts are calling and I must go: a humpback’s landscape

Solène Derville, Entropie Lab, Institute of Research for Development, Nouméa, New Caledonia (Ph.D. student under the co-supervision of Dr. Leigh Torres)

The deep ocean is awe-inspiring: vast, mysterious, and complex… I can find many adjectives to describe it, yet the immensity of it prevents me from picturing it in my mind. Landscapes are easy to imagine because we see them all the time, but their hidden ocean counterparts of seascapes with several kilometer-high seamounts and abyssal trenches are hard to visualize.

When I started a PhD on the spatial ecology of humpback whales, a species typically known for its coastal distributions, I never imagined my research would lead me to seamounts. Lesson of the day: you never know where research will lead you… So here is how it happened.

About twenty years ago when my supervisor, Dr Claire Garrigue, started working on humpback whales in New Caledonia, she was told by fishermen that humpbacks were often observed in prime fishing locations, about 170 km south of the mainland. After a little more investigation into this claim, it was discovered that these fishing spots corresponded with two seafloor topographic features: the Antigonia seamount and Torch Bank (Fig. 1), These features rise from the seafloor to depths of 30 m and 60 m respectively and are surrounded by waters about 1500 m deep. This led Dr. Garrigue to implement an ARGOS-satellite tagging program to follow the movements of humpbacks leaving the South Lagoon (one of the main breeding area in New Caledonia, Fig. 1). Sure enough, most of the tagged whales (61%) visited the Antigonia seamount (Fig. 2; Garrigue et al. 2015)⁠.

Map of New Caledonia and our study areas: the South Lagoon and the Southern Seamounts. Light grey lines represent 200m isobaths. Land is shown in black and reefs in grey.
Figure 1: Map of New Caledonia and our study areas: the South Lagoon and the “Southern Seamounts”. Light grey lines represent 200m isobaths. Land is shown in black and reefs in grey.

Figure 2: ARGOS tracking of 34 humpback whales tagged between 2007 and 2012 in the South Lagoon. The Antigonia seamount and Torch Bank are completely covered by tracklines.
Figure 2: ARGOS tracking of 34 humpback whales tagged between 2007 and 2012 in the South Lagoon. The Antigonia seamount and Torch Bank are completely covered by tracklines.

 

Seamounts are defined as “undersea mountains rising at least 100m from the ocean seafloor” (Staudigel et al. 2010). Most of them have a volcanic origin and the majority of them are located in the Pacific Ocean (Wessel 2001). But what is the link between these structures and marine life? The physical and biological mechanisms by which seamounts attract marine wildlife are diverse (for a review see: Pitcher et al. 2008)⁠. In a nutshell, topography of the ocean floor influences water circulation and isolated seabed features such as seamounts affect vertical mixing and create turbulences, consequently resulting in higher productivity.

For instance, have you ever heard of internal waves? Contrary to the surface waves people play in at the beach, internal waves propagate in three dimensions within the water column and can reach heights superior to a 100m! When these waves encounter steep topography, they break, similar to what a “normal” wave would do when reaching shore. This creates complex turbulence, which in turn may attract megafauna such as cetaceans (see com. by Hans van Haren).

The importance of seamounts for cetaceans is often referenced in the literature, however, few studies have tried to quantify this preference (one of which was recently published by our labmate Courtney Hann, see Hann et al. 2016 for details). So what importance do these seamounts serve for humpback whales in New Caledonia? Are they breeding grounds, do they serve as a navigation cue, a resting area, or even a foraging spot (the latter being the less likely hypothesis given that humpback whales have never been observed feeding in tropical waters)?

To answer this question, an expedition to Antigonia was organized in 2008 and about 40 groups of whales were observed in only 7 days! The density of this aggregation, the high occurrence of groups with calves and the consistent singing of males suggested that this area may be associated with breeding or calving behavior. Several other missions followed, confirming the importance of this offshore habitat for humpbacks.

Looking through all this data I was struck by two things: 1) whales were densely aggregated on top of these seamounts but were rarely found in the surrounding area (Fig. 3), and 2) other seamounts with similar characteristics are only a few kilometers from Antigonia, but seem to be rarely visited by tagged whales.

What is so special about these seamounts? Why would energetically depleted females with calves choose to aggregate in these off-shore, densely occupied and unsheltered waters?

 

Figure 3: 3D surface plot of the seabed in the Southern seamount area. Humpback whale groups observed in-situ during the boat-based surveys conducted between 2001 and 2011 are projected at the surface of the seabed: blue points represent groups without calf and white points represent groups with calf. Antigonia and Torch Bank have a clear flat-top shaped which classifies them in the “guyot” seamount type. Most whale groups aggregated on top of these guyots.
Figure 3: 3D surface plot of the seabed in the Southern Seamounts area. Humpback whale groups observed during the boat-based surveys (2001-2011) are projected at the surface of the seabed: blue points represent groups without calf and white points represent groups with calf. Antigonia and Torch Bank have a clear flat-top shaped and are called “guyots” seamounts. Most whale groups aggregated on top of these guyots. For 3D interactive plot: click here.

I will spend the next two months at the GEMM lab in Newport, OR, trying to answer these questions using ocean models developed by New Caledonian local research teams (at IRD and Ifremer). I will be comparing maps of local currents and topography of several seabed features located south of the New Caledonia main island. The oceanographic model used for this study will allow me to analyze a great number of environmental variables (temperature, salinity, vertical mixing, vorticity etc.) through the water column (one layer every 10m, from 0 to 500m deep) and at a very fine spatio-temporal scale (1km and 1day, even 1 hour at specific discrete locations) to better understand humpback whale habitat preferences.

Figure 4: Modeled Sea Surface Temperature for July 15th 2013 (model in progress, based on MARS3D, development by Romain Legendre). A temperature front occurs in the middle of the study area, along the Norfolk ridge. On this image, a cold eddy is forming right on top of the Antigonia seamount.
Figure 4: Modeled Sea Surface Temperature for July 15th 2013 (model in progress, based on MARS3D, development by Romain Le Gendre). A temperature front occurs in the middle of the study area, along the Norfolk ridge. On this image, a cold eddy is forming right on top of the Antigonia seamount.

 

Looking forward to uncovering the mysteries of seamounts and sharing the results in December!

Literature Cited

Garrigue C, Clapham PJ, Geyer Y, Kennedy AS, Zerbini AN (2015) Satellite tracking reveals novel migratory patterns and the importance of seamounts for endangered South Pacific Humpback Whales. R Soc Open Sci

Hann CH, Smith TD, Torres LG (2016) A sperm whale’s perspective: The importance of seasonality and seamount depth. Mar Mammal Sci:1–12

Pitcher TJ, Morato T, Hart PJ, Clark MR, Haggan N, Santos RS (2008) Seamounts: ecology, fisheries & conservation. Oxford, UK: Blackwell Publishing Ltd.

Wessel P (2001) Global distribution of seamounts inferred from gridded Geosat/ERS-1 altimetry. J Geophys Res 106:19431–19441

Staudigel H, Koppers AP, Lavelle JW, Pitcer TJ, Shank TM (2010) Defining the word ‘seamount’. Oceanography 23,20–21.

From Oregon to New Caledonia: Crossing latitudes

**GUEST POST** written by Solène Derville from the Institute of Research for Development, Nouméa, New Caledonia. Entropie Lab

Last term I posted about the analysis of Maui dolphin habitat selection I have undergone under Dr Leigh Torres’ supervision at OSU. The results of this work are now compiled in a manuscript which I hope to submit for publication very soon.

Since I last posted on this blog, many things have changed for me: I went back to France at the end of May (with a heavy heart from leaving Newport and my dear lab mates) and I have graduated from the Ecole Normale Supérieure of Lyon and successfully completed my Biology Master’s degree. In September, I will start a PhD on the spatial ecology of Humpback Whales in New Caledonia. I will work at the French ‘Institut de Recherche pour le Développement’ in Nouméa, New Caledonia, under the co-supervision of Dr Claude Payri, Dr Claire Garrigue, Dr Corina Iovan (IRD) and Dr Leigh Torres (GEMM Lab, OSU).

Before telling you a bit more about my project and this summer field season, I would like to introduce the beautiful place where I will be spending the next 3 years. New Caledonia is an archipelago located in the southwest Pacific Ocean, east of Australia. This special overseas French collectivity includes a main island (Grande Terre) and several other islands such as the Loyalty Islands. New Caledonia’s lagoon is the largest in the world and was added to the list of the UNESCO world heritage sites in 2008, because of its exceptional biodiversity including many emblematic species such as humpback whales, dugongs, marine turtles, manta rays…and many others.

).new+caledonia+mapNew Caledonia location in South Pacific Ocean (map: http://springtimeofnations.blogspot.jp

map_of_new-caledonialonelyplanet

Map of the New Caledonian Archipelago (map: http://crosbiew.wordpress.com).

Moreover, the ‘Natural Park of the Coral Sea’ was established very recently by the New Caledonian to protect this biodiversity hotspot. This monumental marine park spans 1.3 million square kilometres and is, to date, the largest protected area on the planet. As the detailed management plan for this park will be progressively established in the coming years, there is a local need for more information about marine mega-fauna space use in order to define key areas for wildlife conservation. Thus, the description of the humpback whales ecological niche in New Caledonian waters is the next logical step to initiate conservation planning. The effect of human activities needs to be investigated as the New Caledonian humpback whales population forms an isolated breeding sub-stock and is exposed to mining industry intensification, shipping, harbour construction and boat recreation associated to tourism development.

The general aim of my project is to investigate how humpback whales are using their habitat within and between reproductive areas of Oceania in order to facilitate their conservation at the scale of giant marine reserves (new generation of marine protected areas over vast surfaces exceeding hundreds of thousands of square kilometres). I will therefore focus on the spatial ecology of humpback whales in the New Caledonian Exclusive Economic Zone, with several specific aims:

1/ to quantify the spatio-temporal patterns and dynamics of humpback whale distribution in New Caledonian waters in order to identify key areas for the species and determine if these areas change over time or depending on social context.

2/ to assess the connectivity and movement patterns between areas of interest at individual scale.

3/ to document humpback whale use of habitat in relation to environmental factors and include these results in the broader-context of the South Pacific Ocean breeding areas.

4/ to provide a spatial and temporal assessment of the anthropogenic activities risks to humpback whales in New Caledonia.

I will rely on a large amount of data collected between 1991 and present, and provided by Opération Cétacés (an NGO involved in scientific research on humpback whales and other marine mammals in Oceania since 1996), including boat-based, land-based and aerial observations, satellite tracking and individual-based information (via Photo-Identification and genotyping).

This year, I am taking part in the summer field mission undergone by Opération Cétacés in the South Lagoon. I am currently living in Prony, a little village located along the southern coast of Grande Terre. No electricity, no internet, whale watching from 7am to 4pm on a daily basis: the real life!

In my next post I will tell you a bit more about this field trip with Opération Cétacés but for now, I will let you enjoy these few pictures!

IMG_3813

Prony Bay (© S. Derville)

IMG_3739

Rémi, Claire and Daisy standing next to the “Cap N’Dua” lighthouse from which land observations are made. Whales can be spotted up to 20 nautical miles offshore (© S. Derville) 

IMG_3820

View to the East of Cap N’Dua (© S. Derville)

2015-08-09-50D- 083
Breach observed a few days ago in the South Lagoon (© C. Garrigue)

2015-08-13-40D- 126

Inverted peduncle slap (the whale is lying upside down in the water and energetically slapping the surface with its fluke) (© S. Derville).