Young lemon sharks of Statia

Young lemon sharks of Statia

After the exciting news of the silky sharks on the Saba Bank two weeks ago, this time we move a bit Southeast from Saba to the Caribbean island of Sint Eustatius (better known as Statia) for another shark-story. Throughout Spring 2015 and Summer 2016, multiple observations were made of a, for Statia’s waters, undocumented shark species: the lemon shark. And when life gives you lemons..

It all began when I joined a trip organized by Save Our Sharks NL, a project of the Dutch Caribbean Nature Alliance to conserve sharks in the waters of the Dutch Caribbean. The trip brought us to Statia, where I met up with two of the owners of the Scubaqua Dive Center, Mike Harterink and Menno Walther. Mike shot a couple of pictures of a young shark in the shallow waters near the dive center. In addition, Menno shot a short video of two young sharks cruising in the same area. The young sharks observed on both occasions happened to be young lemon sharks (Negaprion brevirostris), a species that has not been documented before in the waters of this Caribbean island.

Shot of a young lemon shark cruising by the Scubaqua Dive Center, by Mike Harterink.
Shot of a young lemon shark cruising by the Scubaqua Dive Center, by Mike Harterink.

Figuring these observations were interesting, as no adult lemon sharks were observed during any of the dives of Scubaqua, I came into contact with Erik Boman. Erik lives on the island and focuses on the hu(uuu)ge (and awesome) marine snail, the queen conch (Lobatus gigas) for his PhD. at Wageningen University. Fortunately, Erik and his wife also observed young lemon sharks in shallow waters over multiple occasions. This time, however, the sharks were observed on the other side of the island. We teamed up with Paddy Walker (University of Applied Sciences Van Hall Larenstein) to write a short research note on the observations, to stimulate local conservation efforts towards shark species and to document this species for the island.

About Lemons
All of the observed lemon sharks were estimated to be between 50 and 65 cm. This is close to the size at birth for lemon sharks, which is a length of 60 to 65 cm. Throughout their life, these sharks can grow to a whopping length of 3.40 meters (although individuals of 2.40 meters are more common) and reach an estimated age of at least 25 years. Like many other shark species, lemon sharks reach maturity relatively late in their life, at an age of 12 to 16 years. Female lemon sharks give birth every other year to a litter of 4 to 17 pups, after a gestation period of 10 to 12 months. The pups will remain in the area of where they were born for several years. This behavior is known as natal philopatry (i.e. tendency to return to a specific area).

Where do these little sharks come from?
Good question! These are only observations only indicate that the shark seem to use the waters of Statia. Where they come from remains speculation. There are two possibilities: (1) the sharks were born in these waters and remained in the vicinity of the island, (2) the sharks were born elsewhere and visit Statia now and then. Before going into detail on both possibilities, I would like to stress that these observations are merely an indication for future research and do not prove that Statia’s waters act as a nursery or vital area for this species. For this, more research is needed!

If the sharks were born in the vicinity of Statia, you would expect existing observations of adult lemon sharks within the area. However, no adult lemon sharks have been observed on any of the dives of the dive center. Part of the island is rough, and not a lot of diving occurs there, so one possibility remains that the adults hang out on that side of the island. Young lemon sharks do exert natal philopatry, which means they normally have a tendency to return to their birth ground, which could explain the repeated sightings of a small number of young individuals within the same general areas.
However, the lack of observations of adult lemon sharks opens up the possibility that parturition did not take place around Statia. This means the sharks swam over from nearby reefs or islands. The closest island, Saint Kitts, is located on the same bank as Statia at a distance of approximately 13 km. The closest islands of which we know lemon shark occur in local waters is Sint Maarten (and the French Saint-Martin) (56 km), located on a different bank than Statia, with deep water separating both islands. Studies focusing on young lemon sharks in the Bahamas showed that these little guys have a limited home range of approximately 0.68 km2, making it less likely that the young sharks swam all the way from nearby islands. In other words, more research is needed to study the role of Statia’s waters in the lifecycle of lemon sharks (Super interesting!).

Publishing observations like this.
So why would we publish observations like this? I believe understanding biodiversity is one of the cornerstones of conservation science, and even small observations like this can contribute to that knowledge. Now we know that a specific life stage of this species frequents these waters, we can continue studying this species within the region. Information like this can also benefit local nature conservation NGO’s like STENAPA, St. Eustatius National Parks in their efforts to conserve local natural areas. In addition, a digital age asks for open access of observations and knowledge sharing. While writing up these observations, we heard of the new platform Science Matters. This all-digital, open access journal lets authors publish short notes about small observations that are worth sharing within their field. And, unlike many conventional journals, the reviewing process does not take months. Which is great!

Want to feed your inner-sharknerd? Read our paper!
Leurs, G., Boman, E. M., & Walker, P. A. (2018). Range extension of the lemon shark (Negaprion brevirostris) within the Dutch Caribbean: First records of young individuals in the waters of Sint Eustatius. Science Matters, 1–6.

If you have any inquiries about this article, please drop me a message. Thanks for visiting, you’re awesome!

A new shark for the Saba Bank

A new shark for the Saba Bank

As we set out to the immense Saba Bank to do regular dives last Thursday, our captain spotted two small sharks at the surface. One glance at the surface and I realized these sharks were a bit more special than the regular residents, Caribbean reef sharks and nurse sharks. In fact, I soon started screaming “Silkies!”, as the sharks that were swimming around the boat were silky sharks (Carcharhinus falciformis; I did not scream that scientific name though..). Next we quickly readied our gear and hopped in the water in the middle of the Saba Bank.

The last couple of months I have spent my time on the small Caribbean island of Saba, the place where I focused on shark movement ecology over two years ago. This time, we are here as my girlfriend, Ayumi, is working as the Saba Bank Management Officer for the Saba Conservation Foundation. This immense area is the largest submerged atoll in the Atlantic Ocean, one of the most biodiverse areas in the Caribbean Sea and the largest protected area within the Dutch territories.
We set out that morning to dive at known sites of the Saba Bank to collect data loggers and inspect a spawning aggregation site of red hinds (Epinephelus guttatus). At approximately 1.5 to 2 hours from Saba our captain spotted the two sharks, which were most likely attracted by the sound of the boat. As we jumped in two sharks became four, four became seven and the last couple of minutes in the water I counted up to 10 juvenile silky sharks as I swam back to the boat (I did not want to leave..).


Silky or reef shark, huh?!
Silky sharks have, unknowingly, been documented before by scientists working on the Saba Bank, but were misidentified as juvenile Caribbean reef sharks (Carcharhinus perezi). So what makes it a silky shark I hear you ask? Well, there are three main distinctive features of this species that can help you distinguish them from any other shark: (1) the first dorsal fin is rounded, (2) the first dorsal fin originates behind the end (free tips) of the pectoral fins, and (3) the second dorsal fin is small, with a free tip that is almost twice as long as the height of the fin. Personally, I quickly recognize silky sharks by the strong edge along both sides of the head in combination with feature 1 and 2.
Contrastingly, the first dorsal fin of a Caribbean reef shark is more triangular and located more anterior on the body compared to the silky shark. The body of silky sharks is long and slender, compared to the more robust body of Caribbean reef sharks. Also, the free-rear tips of both fins of reef sharks are short.


So why is this important?
Besides that documenting a new shark species for your personal species-list (nerd-alert) is pretty cool, I genuinely believe observations like these are important for a couple of reasons. First of all, to effectively conserve natural areas, you have to get a grasp on their biodiversity. What species occur within the area, and how do they use the area? Up until now, studies (onetwo and three) focussed on shark (and fish) diversity of the Saba Bank have missed this species, making observations like these very welcome additions to our knowledge of these coral reef systems and local shark populations.
Although silky sharks are common in the pelagic zone of tropical seas, they’re also listed as ‘vulnerable‘ on the IUCN Red List of Threatened Species. Being a pelagic sharks feeding on schooling fish like tuna, causes these sharks to be a major proportion of the bycatch of pelagic longline and purse seine fisheries. Being caught mostly on the high seas, this species also makes up a large proportion of the international fin trade. On the international Red List, this species has gone from “near threatened” in 2016 to “vulnerable” in 2017, and populations continue to decrease according to the assessment of IUCN. This previously undiscovered population within a shark sanctuary (the Saba Bank is part of the Yarari whale and shark sanctuary) can act as a refuge for this species within the wider region. More importantly, the individuals we observed were all small (± 120 cm total length) and within a small length range, indicating the Saba Bank homes a specific life stage of the population.


Little background story on those guys (and gals)
This species of shark got its name from the silk-looking skin (no joke), and has a circumglobal distribution in tropical waters. Within its geographical range the silky shark mainly occurs in pelagic habitats, although younger individuals prefer shallower reefs (which agrees with our observation). The size at birth is around 75 to 80 cm and the maximum size of this species is 3.30 meters. Males reach sexual maturity at a total length of 215 to 230 cm (9-10 years of age), and females at a slightly bigger size of 230 to 245 cm (± 12 years). Silky sharks reproduce viviparous with a placenta, meaning these sharks feed their pups through a placenta in the uterus (contrasting to oviparous and ovoviviparous shark species), before giving birth to live young. A female gives birth to 6 to 14 pups (although this fluctuates among regions within the species’ geographical range) after a gestation period of approximately 12 months. The diet of the species mainly consists of bony fishes like tuna, mackerel, mullet and other schooling fish. In addition, the diet can also consist of cephalopods and to a lesser extent of crustaceans.

These observations were not only very important to me, but to everyone onboard that day. We spent over 45 minutes in the water with them, without ever using bait or attract them in any other way.
See also this cool video about our encounter with the silkies, shot and edited by Ayumi!



If you have any inquiries about this article, my work or want to use any of my photos, please drop me a message. Thank you!

EEA Conference Bristol

EEA Conference Bristol

Last weekend the annual meeting of the European Elasmobranch Association (EEA) took place in the Bristol Aquarium (UK). Organized this year by the UK-based Shark Trust, a total of around 170 delegates from over 22 different countries attended and there were a total of 69 presentations given over the course of 2.5 days. Organized in 1996 for the first time by its founding members, this was actually the 20th anniversary of the EEA.

This was my first EEA conference and I have to say, if you’re into shark science, this is your annual ‘must visit’. From the velvet belly lantern shark (Etmopterus spinax) – probably the new favorite shark of every delegate – to angelsharks, sawfishes, skates and many other species. From behavioral studies like personality research in lemon sharks, to acoustic telemetry and conservation measures for better shark protection. This EEA conference program had it all!

The keynote and high impact speakers at this EEA were (according to my interest of course..):

By far the most impressive, and probably controversial, presentation was given by Dean Grubbs, who presented a rebuttal on the study by Meyers et al. (2007), which described a trophic cascade with increase of cownose rays as a response to a decline in large-bodied shark populations. Grubbs and co-authors described flaws in the paper and identified the cownose ray to be the scapegoat, as this vulnerable species was now targeted on a large scale to counteract the so-called cascading effects described by Meyers et al. I think this presentation really stimulated the audience, consisting of students, scientists and conservationists, to be more critical towards scientific publications and methods, but also to be more critical and accurate as a scientific reviewer.

I was glad to see presentations focussing on sawfish and angelsharks, two groups of elasmobranchs that are extremely vulnerable to anthropogenic stressors and which are normally a bit underrepresented. Colin Simpfendorfer, to me known as one of the best scientists in the field of shark ecology and acoustic telemetry, presented how eDNA can be a promising tool to study the presence of largetooth sawfishes (Pristis pristisin river systems. An interesting talk by Michelle Heupel used acoustic telemetry to determine movements of grey reef sharks (Carcharhinus amblyrhynchos)silvertip reef sharks (Carcharhinus albimarginatus) and bull sharks (Carcharhinus leucas) between small reefs on the Great Barrier Reef. Especially the visualization of the acoustic telemetry data and population connectivity was very inspiring, to read more about one of these methods read this paper.

Just before I had to leave on Sunday, my presentation was scheduled and I got the great opportunity to present the first acoustic telemetry data for the Duch Caribbean. For this opportunity I would like to thank the Shark Trust and the EEA!

Overall, the EEA is the perfect platform for students with a passion for elasmobranch research to meet new people and high-level scientists. For scientists, from both in- and outside Europe, the EEA is a perfect platform to communicate their findings with fellow shark researchers. In the end, it doesn’t get better then nearly three days filled with shark and ray science!

Hope to see you all during the 21st meeting of the EEA next year!

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Documentary airing on NatGeo

Documentary airing on NatGeo

I am very glad and proud to announce that the documentary ‘Hunting the Hammerhead‘ is airing this Sunday on National Geographic in The Netherlands and Belgium.

The documentary, presented by Craig O’Connell of the O’Seas Conservation Foundation, will bring you the true magnificence of the Great Hammerhead Shark (Sphyrna mokarran). Every Winter this largest species of hammerhead visits the shallow waters of the Bahamian island of Bimini. For what reason? We’re not entirely sure, but the documentary will give you some valuable insights on the ecology and morphology of this beautiful, yet endangered species.

Hunting the Hammerhead is a production of Earth Touch and will be broadcasted globally by National Geographic. In addition, Smithsonian Channel broadcasts the documentary also in the US. The majority of the documentary was shot in the waters of Bimini in February and March 2015. I was lucky enough to be there as Craig asked me to join him to go to Bimini to try and test the laser photogrammetry technique (see our paper on LPT on white sharks) and to assist with the documentary underwater. I have only seen some raw snapshots of the documentary, but at least one shot is a ‘one-in-a-million’, for shark research. One that could prove why these animals actually have these odd hammer-shaped heads.

Now the documentary premieres on National Geographic here in The Netherlands and in Belgium. So if you don’t want to miss the documentary of the year, make sure to put one of the following dates in your agenda:

  • Premiere: Sunday 21 August 17.05
  • Monday 22 August 00.05 (repeat)
  • Saturday 27 August 00.00 (repeat)

If I haven’t convinced you enough right now, check out the trailer to hype you up for this Sunday!

Thank you to everyone involved, it was an amazing experience to work with you all!


Conservation in the Desert

Conservation in the Desert

Expedition to the beautiful Mauritania

In West-Africa lies a large country that probably not many Europeans ever heard about, the Islamic Republic of Mauritania. I had the privilege to travel to the biggest national park of Mauritania, as you might expect from me by now, for a shark related study (yes, sand sharks..).

The Country
Nowadays the name, The Islamic Republic of Mauritania, would possibly scare off many Western travelers considering the continued threat of Islamic extremists in Western countries from elsewhere in the world. This, together with the fact that the Dutch Foreign Ministry issues a somewhat alarming advice to travelers planning to visit this part of the Sahel region, doesn’t give a potential travelers a positive image of this country and a lot of them will leave Mauritania for what it is.

To my personal experience this is all nonsense. I am not saying that everybody should go take their bags and travel to Mauritania, because I know that’s not what you’re going to do. However, I want to and have to do justice by the beauty of the country and the experiences that the people of Mauritania have given me in just over 2 weeks.

First, a little on the country itself. For your reference, Mauritania is located to the North of Senegal, South of Western Sahara and on its Southeastern border lies Mali.  With just over 3 million people and over 25 times the size of The Netherlands, Mauritania is not really a densely populated country to say the least. The capital Nouakchott (pronounced as Newakshot) is located on the coast with the Atlantic Ocean and has an estimated population of 960,000 (est. 2013, although more recent records state its somewhere between 1 to 2 million people). A vast majority of the country is covered by desert, which will of course will not come as a surprise to you given the fact that Mauritania is part of the semiarid Sahel region. Mauritania was considered the center of the Berber region in the 11th and 12th centuries. Islam was established in the region and later nomads of Arabic tribes dominated the region. France established several trading posts along the Atlantic Coast of Mauritania and the country used to be a French colony since 1920. The native people of Mauritania used to have a nomadic lifestyle up until the 1950’s, but after severe droughts in the region, people started to settle in villages and cities. In 1961 Mauritania got full independence from France.

Most used languages are Arabic and French, which meant my most used language for these weeks would be a creative mix of English, sign language and the one or two words of French that I remembered from high school. Okay, let’s increase that a bit to three or four words (and one of them is requin).. Anyway, challenge accepted!


The Mission
I got the opportunity to join an expedition to the Banc d’Arguin National Park (Parc National du Banc d’Arguin; PNBA) for the World Wildlife Fund in cooperation with the University of Groningen (The Netherlands). The university, together with another Dutch research institute (NIOZ), have been doing research in this national park for a long time. The reason why scientists are so interested in the Banc d’Arguin is that it closely resembles the original state of our own Wadden Sea, where both institutes also have been conducting scientific studies for a long time. What makes it even a better study site is that the migratory birds that we find on our mudflats in the Wadden Sea in summer, leave during the Northern winter to spend their time on the much warmer Banc d’Arguin in West-Africa. This national park is the perfect opportunity to  study an ecosystem that resembles one of our own, but that still appears to have all the trophic levels (i.e. big predators) and healthy sea grass beds. Among scientists and conservationists who have interest in the park there was some major concern about the predatory trophic level, as they saw that sharks and rays were being fished by local Imraguen (regional tribe) fishermen at large numbers, and that is where I came in. My job was to talk to people within the park to find out how the fisheries for sharks and rays are structured, what and who drives the market and what the possible conservation measures could be to preserve the elasmobranch populations of the Banc d’Arguin.


The Expedition
So the expedition started off at 13th of May and we had some interdisciplinary missions. For me the main thing was clear and I got the help of Prof. dr. Han Olff (Professor of Community and Conservation Ecology, University of Groningen), and two of his Mauritanian PhD. students Hacen and Sidi Yahya. Within 2.5 weeks (until the end of May) we had to do experiments for the two Phd. studies, and do the interviews and visit nearby villages within the PNBA. Complicated, but the best way to learn as much about the park as possible within the given time frame. Especially because the people I was with know the PNBA better than anyone else.

So after flying over the Sahara for a couple of hours suddenly these small concrete blocks appear in what looks like the middle of the desert. The plane starts to descent and I know that its my destination, Nouakchott. Given the time that I had to prepare this trip (I know that I was going ± 3 weeks prior to the trip), I didn’t really know what to expect. The arrivals at Nouakchott is a bit chaotic to say the least, more like a market where you feel everyone wants to help you with taking your suitcases off the belt (the belt looked and sounded a bit like somebody was manually rotating it). Once we collected all our suitcases and bags, we had to go through customs (or military), which check mainly if you’re not bringing in alcohol into the Islamic country. Once we cleared customs, Hacen was waiting for us to drive us to our hotel. That day we visited the house of Sidi Yahya’s family and had a quick cup of tea (which normally lasts a couple of hours according to Arabic traditions) and we had an appointment with an UN official about our plans in the Banc d’Arguin. The next morning we packed our bags again, loaded them on two 4×4 trucks together with a lot of boxes and bags full of supplies and we left for the small village of Iwik. Driving through the capitol I quickly saw the beauty of the Arabic culture, nearly all men are dressed in a “boubou” with a white or black turban. The women were all dressed in what is called a “mulafa”, which covers the whole body as well as the head. Even in the capitol you can’t escape from the sand, literally everywhere you look you can find sand (a walk on the side of the road actually feels like a walk on the beach!). To make it even more Arabic, you see camels and donkey’s in the middle of the city!

50 km North of the capital we stopped at a place called Belawakh, a place where sharks and rays caught in the region are dried and packed for transport to other countries. I won’t go into details about the shark trade and fisheries of Mauritania in this blog, but will post the report I will write for the WWF and their international shark project after it is finished. The only thing I want to say about it now is that I’ve never seen someone cutting off the fins of a shark.. until this day. Just for a soup in Asia.


After our visit to Belawakh, we continued our trip through the desert. Surprisingly for 4 hours of the 5-hour drive this involved driving on good, asphalt roads to the village of Chami. In Chami we left the asphalt road and drove straight into the desert for the the last hour before we reached Poste d’Iwik, the station of the national park in Iwik. We were welcomed by the crew of the station, who were very happy to see us and within an hour we were drinking our first glass of tea with them. Compared to our Western living standards, the station is a bit primitive to say the least. No running water, limited electricity as the station is completely solar powered and 1 hour away from the closest telephone network (only a satphone for emergencies). Surprisingly, the station communicates with Nouakchott and nearby villages by radio communication and in the radio house (± 200 m away from the station) a satellite disc receives a WiFi signal from Nouakchott. However, the disc broke down three days into the expedition, which disconnected us from the rest of the world. Great way to experience the desert for the first time!

One of the coolest things about the stations is that we had three golden jackals (Canis aureus) living around the station. During daylight hours they were very, very skittish, but at night they would easily come within 3 meters from us, attracting by the leftovers of our diner that the crew would put outside for them. Walking through the desert to the radio house late at night to connect to the internet, I could see their eyes reflecting the light coming from my headlamp as they checked me out from a short distance. Such cool animals!

The first week of the expedition we investigated the drying pits of Iwik and Ten-Alloul and spoke with people involved in the trade of sharks and rays within the national park. Drying pits are big holes in the sand ranging from 2.5 m2 to 12 m2 of which the walls are wrapped with plastic sheets. The catch (sharks, rays or catfish) are, once gutted and finned (for sharks and guitarfish), thrown into the pits with sand or a minimum amount of salt and left to dry for up to a month. Once dried the meat and fins are each exported to different countries for different markets. It is a very sad sign to see the amounts that are caught by these local fishermen and it becomes imminently clear that these traditional fisheries are far from sustainable. The interviews we did with locals from the villages mainly involved drinking tea and discussing very interesting aspects of the fisheries, while communicating with the help of translators. The second week of the expedition involved talking to more people from the trade in Iwik and with representatives of the villages of Tessot and Arkeiss. During the whole expedition we conducted field work on the mudflats and sea grass beds to establish experiments for one of the PhD studies.

At the end of the expedition and back in Nouakchott, we did an interview on the Guedj Market, which appeared to be the end of the market chain in Mauritania. From there the products are exported to different countries and follow different routes.


The Experiences and the Result
I know this is a very brief description of what I experienced in this extraordinary country during this expedition. I became deeply interested in the Arabic and Mauritanian culture, tea, people and of course, nature. Although communicating with a large part of the crew of the station involved only basic English and French words, I think I’ve never felt so welcome while traveling abroad right from the start. However, this language barrier also prevented me to get to know even more about the Mauritanian people, their religion and their culture, but I guess if I ever return I will have to work on my French a bit more.

The result from our investigation is however a sad, I saw 13 new species of elasmobranchs (i.e. sharks and rays; of which at least 2 shark species are endemic to West-Africa), but this is the first trip during which I did not see any sharks or rays alive. I saw someone cutting off the fins of a shark right before my eyes just for a bowl of soup 12.000 kilometers away, which makes you realize what the problem exactly is. Strangely it motivates you, it motivates to do something about the unsustainable exploitation of these species in a very, very special ecosystem.

To end on a positive note, this expedition was extremely successful given the time I had to prepare it. I would like to thank all the amazing people that I’ve met along the way, especially the crew with whom I stayed and worked at Poste d’Iwik. The PNBA management for allowing us to undertake the expedition. And of course Han, Hacen, Sidi Yahya and Reinier (WWF Netherlands), thank you for showing me the beautiful Mauritania, the Banc d’Arguin and giving me the opportunity to join this awesome expedition. See you all soon!

As stated before, I will be writing a report on this expedition starting in the beginning of August. Once the report is finished I will share more details on my findings and on the expedition in a new blog post. If you have questions before that time, please contact me.
All photographs in this post are copyrighted, ask me for permission to use them.



TV-interview: SHARKS!

TV-interview: SHARKS!

On Wednesday 9th of March I was asked to tell my story on Dutch tv. In the TV-show L1 Avondgasten I was asked about my passion for sharks, my research studies and my moments underwater with these magnificent animals. The interview allowed me to reach a diverse audience here in The Netherlands to show them what its like to study sharks and to be in the water with them. Right after the live TV-interview ended I was asked to join the Radio-team to elaborate on the topic on live radio.

Watch the interview (in Dutch) here.

Recap & Highlights of 2015

Recap & Highlights of 2015

As we approach the end of 2015 and we prepare to make the best of 2016, I think it’s always a good time to look back on these 12 months. Like it has been for the last couple of years, there was one theme dominating my work this year: shark research.

2015 started off with the best shark research/diving trip in the world: great Hammerheads, bull sharks, nurse sharks and Caribbean reef sharks of Bimini. Right now I realize that I launched this website only a couple of months ago so there is no article on that trip (yet), but since I keep looking at my hammerhead photos from that trip, I’ll write something up in the (near) future. I was asked to join the trip organized by friend and colleague Dr. Craig O’Connell (O’Seas Conservation Foundation) who I met in 2013 when we conducting different projects on white sharks in Gansbaai, South Africa. We worked with the most awesome crew, made a documentary on hammerheads, went to see and dive with the most amazing sharks and stayed in a beautiful house on South-Bimini (a.k.a. paradise). But most importantly: we conducted two valuable scientific studies on bull sharks and Caribbean reef sharks (Marcella Uchoa MSc. project), and laser photogrammetry and dorsal fin ID on great hammerheads (Craig and myself). But more on the Bahamian shark paradise in a future article!



As soon as I got back from 7 weeks Bimini, I had to continue with some courses for my MSc. degree and had to come up with a research proposal for a Master thesis. Working through summer on a part-time job (no highlight…) and writing up a research proposal made sure my next project was ready to kick-off: studying the spatiotemporal distribution and diurnal patterns of Caribbean reef sharks and nurse sharks off Saba (Dutch Caribbean). I just returned from this trip, as you can read in my trip reports of Saba and the Saba Bank, St. Maarten and Statia.


In addition to these two research trips and studying for my MSc. Marine Biology, 2015 was a great year in numbers. In 2015 I:

  • Published three articles: 2 scientific articles (1 published, 1 accepted) and 1 in a magazine for the Institute of Dutch Biologists (NIBI).

    Leurs, G.
    , O’Connell, C. P., Andreotti, S., Rutzen, M., & Vonk Noordegraaf, H. (2015). Risks and advantages of using surface laser photogrammetry on free-ranging marine organisms: a case study on white sharks Carcharodon carcharias. Journal of Fish Biology, 86(6), 1713–1728. doi:10.1111/jfb.12678

    O’Connell C.P. & Leurs, G. (ACCEPTED). A novel and minimally invasive technique to assess several life-history characteristics of the endangered great hammerhead shark, Sphyrna mokarran. Journal of Fish Biology.

    Post Scriptum: Haaiengroei vastleggen met lasercamera (Dutch). Bionieuws (NIBI). Interviewer: Janneke Razenberg. Read online.

  • Published one of my Great Hammerhead photographs in the new book ‘Aarde op 1‘ of the Dutch World Wildlife Fund (WWF/WNF).
  • Assisted in the making of “Hunting the Hammerhead” by Earth Touch and Smithsonian, which will premiere in 2016.
  • Two new shark species: great hammerhead (Sphyrna mokarran) and the blacknose shark (Carcharhinus acronotus).
  • Caught and tagged: 5 Caribbean reef sharks and 1 nurse shark.
  • Visited 4 new Caribbean islands.
  • Spent countless hours behind a computer..
  • Met and worked with the most inspiring people!

Goals and resolutions for 2016.
(Not a big fan of new year resolutions, but when it comes to studying and work, I always make lists..)

  • Finish my MSc. Marine Biology
  • Plan next projects or trips (Aussie?!).
  • Publish at least one more paper before the end of my MSc.
  • Dive with at least one new species of elasmobranch.
  • Visit extremely beautiful places with the best people in the world!

Thank you to everyone who was part of 2015, you are awesome!

Happy holidays!


Saba and the Saba Bank

Saba and the Saba Bank

It has been two weeks since I came back from a field trip to the Dutch Caribbean and now its time to look back and reflect on how everything worked out. The goal of the trip was to expand the existing network of acoustic receivers in the Dutch Caribbean EEZ and to catch and tag additional sharks in the area to study their movements. Please read my trip reports of St. Maarten and Statia and my initial post about this project for more information, in this post I will focus on the island where I was stationed for the longest time during the trip: Saba.

Unlike the work on St. Maarten and Statia, the work on Saba was a bit more complex. This year we wanted to place receivers and tag sharks on the immense Saba Bank. To give you an idea about the size of this bank compared to the islands we worked at, the Saba Bank is the dark blue area Southwest of Saba. With a total surface area of 2200 square kilometers (for comparison, Saba is 13 square kilometer), we were pretty sure we needed a bit more time to get our work done here.

But before we went to the Saba Bank it was time to retrieve the receivers that are in the waters around the island itself. Since October 2014 8 acoustic receivers have been recording the acoustic signals emitted by tagged sharks, my job was to retrieve this year-round data and to replace the batteries of each receiver. This means a full day of tracking down the 8 receivers around the island, dive them up, race back to the office, download the data, replace the batteries, race back to each location to place the receivers back underwater before sunset. Since the receivers had been in the water for a year, I had to clean some of them because of growth on the housing. There were even some little crabs, brittle stars and bivalves on living on some of them! So, this is what a new receiver (left) and a receiver that has been in the water for a year (right) look like next to each other. (side-note: imagine bringing two of these new receivers through airport security, yes.. that was an adventure!)


So after some diving around Saba, it was time to prepare for the job on the Saba Bank: place 8 receivers and catch and tag nurse sharks (Ginglymostoma cirratum) and Caribbean reef sharks (Carcharhinus perezii) with acoustic tags. Right from the start we knew this was going to be the most difficult area to work with and to get everything done in time. The positions of the receivers on the Saba Bank ranged between a 30 minute to a 2.5 hour boat drive, making it impossible to place more than three receivers on one day. Since you don’t have any protection from nearby land, sea conditions on the Bank can be significantly worse compared to the waters off Saba. Maybe the most important challenge was dive safety: since the Saba Bank is a marine park we didn’t want to anchor the boat, since that is going the destroy precious corals. That means that the persons on the boat should always have an eye out for the divers in the water to rule out the possibility for a diver to get lost at sea. I kind of had that feeling once, after coming back to the surface and not seeing the boat or any of the nearby islands (Saba or Statia).

The thing that makes the Saba Bank very special is that there’s probably only a handful of people that ever dove on those dive spots and the fact that nobody knows exactly what is down there. There’s only 6 fishermen who fish on the immense Bank and there is no recreational diving allowed. So when jumping off the boat you get this sudden feeling of extreme excitement and curiosity, but nothing in the world couldn’t prepare me for such a beautiful reef system!

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Reefs as far as the visibility reached (>40 meters) and huge schools of fish, some of the dive spots probably even had one the highest fish abundance I’ve ever seen. Barrel sponges and brain corals of more than two meters across and all the reefs were looking incredibly healthy, further underlined by the diversity of fish living on and in the reefs.
There was only one harmful fella on the reef: the invasive lionfish. Ever since there were some individuals (accidentally) introduced in Florida in the 1990’s the lionfish is spreading extremely fast throughout the West Atlantic and Caribbean Sea, out competing other reef predators and decimating reef fish. To protect the reefs divers start hunting them with a spear, but the fast reproductive nature and their depth ranging much deeper than divers ever can dive to allows this fish to thrive in these waters. Coming across a couple of lionfish we tried to attract some sharks by hanging over the drop-off of the reef (a sudden drop of the bottom into great depths) with the speared lionfish still on the spear. Unfortunately without any luck.


After quickly placing the receivers, we always took our time to look around and to enjoy the beauty of the marine life surrounding us, after all I think that is the most important part of the job! One of the best dives was during an early morning, we set out at 06.00 to place three receivers and try to catch the first sharks on the Bank. On the third dive me and Dahlia placed the receiver on the most beautiful reef system ever, close to the drop-off. Just at the end of the dive we noticed that this was a perfect spot to start fishing, we just saw two juvenile Caribbean reef sharks cruising by along one of the smaller drop-offs! So after resurfacing we quickly prepared our rods and immediately started fishing. Not long after one of the rods went off, and we worked the shark up. Almost at the surface we could see it was a small Caribbean reef shark!


Once the shark was close to the boat it was time to bring him/her up on the boat for a quick and smooth tagging procedure. As soon as the shark was on the boat it is key that the shark is turned on its back as quickly as possible to initiate the trance-like state called ‘tonic immobility‘ and to limit stress. This state acts as a natural anesthetic and is used by shark scientists around to world. Once the shark was calm the procedure would start with taking out the barbless hook, applying the acoustic tag and quickly take notes as sex and total length. This whole procedure would only take about 5 minutes before the shark is placed back in the water.

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That day turned out to be a huge success, as we tagged 4 sharks: 3 juvenile Caribbean reef sharks (~100cm) and 1 nurse shark (206 cm). The next day we left port even earlier (03.30) as we wanted to fish further away from Saba. We started fishing under a beautiful sunrise and that day we caught two more juvenile Caribbean reef sharks which were also close to 100 cm in total length. Without a doubt the best birthday I ever had!

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What surprised me is that we only caught juvenile Caribbean reef sharks all around 100 cm, possibly indicating that these sharks were all of the same age and maybe even related (we happened to catch all of them in one certain spot). This surprised me because I didn’t expect juvenile sharks to spend their years growing up in an area which is known for its bigger predatory sharks (tiger sharks and hammerheads) that form a potential threat for smaller, juvenile sharks. However, we caught the juveniles on a shallow reef area, and normally the bigger sharks stay in deeper waters or near the drop-off. The fact that we manage to tag a certain age group of this species is very exciting for future studies.

Once the work on the Saba Bank was finished I spend some more days on Saba helping out other students during some dives and pre-analyzing my data. The reefs of Saba and the Saba Bank are extremely beautiful, as is the marine life that makes these reefs their home.

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Now back in The Netherlands I am back behind a desk, making sense of huge R codes, analyzing the shark data from Saba and writing a paper about it. Once my analysis are finished I will post some preliminary results here on my website, after all it is the first acoustic shark tagging data from Dutch waters!

My awesome time and the work wasn’t possible without the help of the Saba Conservation Foundation and all its awesome crew: Dahlia, Koki, Jelle, Leslie, Kai, Pouchie, Gia. People that helped us out on the boat (and with a boat!), Laszlo, Jarno, Serena, Kenji and Bradley. And my awesome Dutch friends: Céline, Jonas, Youp, Rick, Rimco and all the rest of the people that I’ve met during this awesome field trip! Special thanks to Youp, who made some stunning photos of the tagging days.

See you next time Saba.


Hammerhead in a book!

Hammerhead in a book!

Proud and honored that one of my photographs of a great hammerhead shark (Spyrna mokarran) was published in a book of the World Wildlife Fund (Dutch: Wereld Natuur Fonds). The book called ‘Aarde op 1’ takes its readers around the world in 177 photographs. The book pays a short visit to South-Bimini to get a glimpse of the normally illusive great hammerhead in the crystal blue waters of the Bahamas.

The book is currently only available in Dutch and can be ordered here.


First shark tagged at SXM!

First shark tagged at SXM!

After our field trip to Statia, we continued our trip to the island of St. Maarten (SXM). However, our time here was limited, we had only four days to deploy an array of eight acoustic receivers and try to tag the first shark for Sint Maarten.

Upon arrival at SXM we were met by people from the Sint Maarten Nature Foundation, together we made sure we had all the right materials needed to build the setups which hold the receivers underwater and in place for at least up to a year. After we were finished shopping, I was headed out to my friends and fellow WUR (Wageningen University) students Jurgen and Milco’s place in Phillipsburg, where I would stay during my time on the island. After meeting Jurgen’s brother, Werner (who came over for the week from Brussels), we headed out to have dinner and catch up over some good cocktails (the mudslide).
Side note: Jurgen and Milco’s project focusses on fish abundance and diversity around St. Maarten, an awesome project made even more awesome (and important!) when this baby tiger shark (Galeocerdo cuvier) showed up on their BRUV station footage! Highlighting once more the importance of the region for sharks and the studies currently conducted in the Dutch Caribbean.


Next day it was time for business, with the receivers activated is was time to head out to the Sint Maarten Marine Park (Man of War Shoal Marine Park) to deploy the first 4 receiver setups at popular dive sites known for their presence of sharks. On the boat (and onshore as well) we were happy to be in the good company of Etienne (Captain/Marine Park Ranger) and Melanie (local dive guide), who both helped us very much during our time on St. Maarten. The first dive was on a dive site called ‘Shark Hotel’ named after its shark presence and recent shark feeding events (which were cancelled due to some allegedly dangerous shark-human interactions), desperate to see some sharks I jumped in to deploy the receiver together with Melanie. Once we secured the receiver on the sea floor, I turned around (knowing from the first shark project I worked on that sharks will approach humans from behind to maximize their own safety) and yes, there were four Caribbean reef sharks checking us out! Since we had to deploy three more receivers that day, the duration of the dive was only 15 minutes, but I managed to get some good pictures of an adult female and a juvenile (sex unknown).



More than happy that the sharks came close, we continued for a short dive along the adjacent reef. I could easily tell from the sharks behavior and approach strategy that these sharks were used to be fed in the presence of divers. If that is a good thing? There is two sides to that story and both have their pro’s and con’s, a discussion that has been going on throughout the “world of shark fanatics” and of which you can expect a blog post on in the future.

All the other deployments went according to protocol and the next day we deployed four more receivers, two around the islands off the East coast of SXM and two on the West side of the island. The dives, although most of them under 15 minutes, were extraordinary. A Southern stingray (Dasyatis americana) feeding in front of a newly deployed receiver, a green sea turtle (Chelonia mydas) resting on a wreck, another green sea turtle joining us on our safety stop and thousands of beautiful reef fish (from a school of bar jacks (Caranx ruber) inspecting the alien object that we just placed to the rather cute looking spot-fin porcupinefish (Diodon hystrix)).




Since all the receivers around the Dutch part of Sint Maarten were now in place, there was only one job left: try to catch and tag a shark inside the Dutch Caribbean waters of SXM! That was our goal for our last full day on the island. We waited for Tadzio (Manager of St. Maarten Nature Foundation) to take us out to sea on this special (but choppy) day. We also welcomed Irene and Paddy from the Save Our Sharks project onboard and I am happy that we could take Milco, Jurgen and Werner (which was going to be there first nurse shark!) on the boat to help out in addition to Erwin (lead scientist on the project), Melanie and myself (yeah, not much space left on that boat!). With some vital equipment missing, a bilge pump of one of the outboard engines broken and choppy weather we pulled it off! I am honored that I could catch and help tag a beautiful 130 cm male nurse shark (Ginglymostoma cirratum). That’s a first for me (being it the first shark I caught, dehooked and helped tag) and a first for Sint Maarten (being it the first acoustically tagged shark in their waters).

© Tadzio Bervoets/St. Maarten Nature Foundation

Since all the receivers around St. Maarten were in place and we successfully tagged and released a beautiful nurse shark, we had something to celebrate. It was Halloween after all!

No, I didn’t kill anyone. Yes, that is fake blood.

After a great night it was time to go back to Saba to work on the Saba Bank, little did we know that the boat we needed for the Saba Bank work needed to go to St. Maarten for maintenance two days later. This caused us to lose some vital time in our schedule (which already was tight), but making the best of the situation this provided an opportunity to go back to St. Maarten with my friends and roommates from Saba. We stayed one night in St. Maarten and we could stay with friends in their luxurious apartment including jacuzzi, swimming pool and sea view (!). After an unforgettable night is was time to head back on the boat to Saba.


These amazing trips (they were actually two separate trips) to St. Maarten weren’t possible without the help and company of a bunch of amazing people. First of all, huge thank you to the St. Maarten Nature Foundation and its employees Tadzio, Etienne and Marissa for all the help and fun both on land and on sea! To Melanie, Irene and Paddy for the good talks and great help. Special thanks to my supervisor Erwin for giving me the opportunity to learn and assist in this fascinating study. Shout out to Jurgen, Milco and Werner for the awesome nights at SXM and for letting me stay in your apartment. Last but not least to Ayumi, Leonie, Youp, Céline and Jonas for the unforgettable night on our second trip. Good times!

The work on the Saba Bank promised to become a major challenge, more on that in a new blog post.

See you in three weeks SXM!