Statia: ready to track sharks!

Statia: ready to track sharks!

Three weeks into my field trip to the Dutch Caribbean, the second island is ready to track sharks: St. Eustatius (or Statia). After Saba, which has had an operating network of receivers to detect tagged sharks for more than a year now, Statia has its own acoustic receiver array in place to track Caribbean reef sharks (Carcharhinus perezi) and nurse sharks (Ginglymostoma cirratum) which have been tagged around the Dutch Windward Islands.

After two weeks of preparation work and data retrieval on Saba (see previous post, more about the data in future posts) I flew over to Statia to meet with the team of STENAPA (Statia’s National Park Foundation) and my supervisor and lead scientist of the shark tagging study Dr. Erwin Winter (IMARES) who flew in from The Netherlands. The main goal of this trip and the collaboration with STENAPA was to install the receiver array around the island that enables us to track sharks that are tagged either locally or elsewhere in the waters of the Dutch Caribbean.


So once I arrived in Statia it was time start with the job, as we only had 4 days on the island. With a quick lunch and visit to the hotel, we went to the office of STENAPA to construct the setups that hold the receivers in place. This means we had to make 8 setups with two heavy cinderblocks as weights, a rope to attach the receiver and a sub-surface buoy to make sure the receiver is placed vertically in the water column. Next was probably one of the most important tasks of the whole deployment proces: where do we want to place the receivers?
For this you have to take into account that the combination of transmitters that we use to tag the sharks and the VEMCO VR2W receivers that have to pickup the signal, has a minimal detection range of 450-500 meters from the receiver. Depending on sea conditions (i.e. water bubbels or particles in the water column can negatively influence the range of an acoustic signal) this detection range can be as high as 800 meters on very good days. The receivers act as data loggers, they can record the date, time and unique code of every shark passing through its detection range. Having a battery life of ±15 months and a memory large enough to store up to 1.000.000 detections, this means that after approximately a year the receivers have to be retrieved, data has to be downloaded by means of a bluetooth connection and than the receivers have to be re-deployed. This is another thing that has to be taken into account when placing the receivers, they’ve to be in dive range (depth: 0-40m).


Based on this detection range and the dive range we looked at the bathymetric maps (i.e. depth maps of the waters around the island) of the island, shark sightings by marine park managers and interns and a previously conducted BRUVS (Baited Remote Underwater Video Station) study. Most important is that we want to find out the parts of the island which are most frequently visited by sharks, highlighting the importance of coverage of the whole island.
With the deployment plan in place and all the receivers setups ready, the next day was deployment day! After activating the receivers in the morning it was time to deploy the first 4 receivers. Unfortunately the dives aren’t that exciting, dive down to 15 to 30 meters with the receiver array, check if the blocks are placed on a sandy patch (to protect the coral reefs) and if the receiver is not blocked by large reefs or wrecks in the direct vicinity. After the check, we give a signal to the boat through a sequence of pulls on a rope and than we take the carabiner off the receiver array to disconnect the line with the boat. So after like 5 minutes of bottom time, we slowly make our way up to the boat and after a 3 minute safety stop at 5 meters we resurface and go to the next location.


Unfortunately we don’t have the permit yet which permits us to catch and tag sharks on Statia (as this has to be done according to Dutch legislation), but once we get the permit this will happen at a later stage.
For now, Statia is ready to track the sharks that left the waters of Saba and it will allow tracking of sharks that will be tracked in the (near) future. However this allowed us to spend an afternoon with Tim (an intern at STENAPA, also from Wageningen University!) to try to search for the endangered Lesser Antillean Iguana (Iguana delicatissima). It was a huge success, as we found adults of both sexes and even tiny newborns!

We would like to thank all the people that helped to make this short trip to Statia successful, especially the people from STENAPA: Jessica, Matt, Tim, Sarah, Claire and all the other staff members and volunteers. It were an awesome few days, hope to see you all soon!

I’ve been on St. Maarten for the last couple of days to work on the receiver array for the Dutch part of the island (the Northern part is French) and hopefully catch and tag some sharks. Blog post about this will come once I get back to Saba.


Dutch Sharks across the Atlantic

Dutch Sharks across the Atlantic

As my passion for sharks expanded when I was younger, so did my knowledge that The Netherlands is not particularly known for its high elasmobranch abundance and diversity in its European continental waters. We do, however, have some smaller elasmobranchs like the small-spotted catshark (Scyliorhinus canicula), spiny dogfish (Squalus acanthias), starry smooth-hound (Mustelus asterias) and the thornback ray (Raja clavata), but sightings by divers are rare. A much rarer visitor to the Southern part of the North Sea is the enormous basking shark (Cetorhinus maximus) and there is some anecdotal evidence that the predatory porbeagle shark (Lamna nasus) enters the Dutch EEZ (Exclusive Economic Zone) on rare occasions.

However, the Kingdom of The Netherlands is not only ‘The Netherlands’ in Northwestern part of Europe, but the Kingdom also consists of the Dutch Antilles in the Caribbean. I am not going to burn my fingers on trying to explain you the complexity of our Kingdom, but most important is the fact that there are 6 Caribbean Islands part of the Kingdom of The Netherlands along with the EEZ of each island. A country has the rights to exploit all the resources within its EEZ, but is also responsible for conserving its natural resources. This makes an unique situation: large predatory sharks in Dutch waters across the Atlantic Ocean.

Since a lot of the sharks in the waters of the Dutch Caribbean EEZ are threatened with extinction due to overexploitation in combination with their k-selected life history traits (e.g. slow growth, late maturity, etc.), I was very happy to read that the Dutch government announced on September 2nd that the EEZ around Bonaire and Saba will become shark sanctuaries. Unfortunately, as sanctuaries are a major step in the right direction, they do not grant full protection for migratory species or species with large home ranges. Marine life migrates independently from boundaries set by governments, meaning that sharks might be protected in the waters of one country, but the sharks are targeted once the cross the border of another country during their migration (e.g. white sharks are protected in South Africa, but not in Mozambique as they migrate up the Eastern coast of Africa). This means that sharks (and all other marine life of migratory nature) are only fully protected by an interconnected network of protected waters that circumvents their home range or migratory routes. Theoretically this means that the sharks around Saba island are only fully protected if they stay within the island’s EEZ.

In October 2014 the Dutch research institute of IMARES in collaboration with the Saba Conservation Foundation tagged 12 sharks – 8 Caribbean reef sharks (Carcharhinus perezi) and 4 nurse sharks (Ginglymostoma cirratum) – with acoustic transmitters as part of the Save Our Sharks project generously supported by the Dutch World Wildlife Fund (WNF) and the Dutch Ministry of Economic Affairs. Now this tagging study is continued, supported by the Dutch Postcode Lottery. As part of my first Master Thesis for Wageningen University, I am going to analyze the first-ever acoustic telemetry data of sharks in the Dutch Caribbean to discover the spatiotemporal use of Saba by the two focal species. In addition, we are conducting a short field expedition (11 October – 1 December) to retrieve this data from the acoustic receivers, tag 12 more sharks on the Saba Bank and place more acoustic receivers around St. Maarten, St. Eustatius and on the Saba Bank. The outcome of this study can be used to evaluate if the sharks mainly occupy the waters of Saba, or that the venture possibly outside the boundaries of protection, highlighting the importance of an interconnected network of protected areas for these animals.

After reading this piece on shark conservation and the current project, you might wonder why conservation of shark populations is so important. To give you some food for thought:

Please keep an eye on this page for field updates and if you would like to have a more regular update, consider following me on Instagram and Facebook.

Publication on white sharks

Publication on white sharks

During a 2013 field project in Gansbaai, South Africa we collected valuable data for over 6 months on the unique dorsal fin notch pattern and length of white sharks (Carcharodon carcharias). Combining two non-invasive methods like dorsal fin photo ID (see Andreotti et al. 2014) and parallel laser photogrammetry, we succeeded to measure (and re-measure) individual white sharks in both the summer (inshore) and winter (around Deyer Island & Geyser Rock) area.

This projected resulted in the following scientific publication:

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

This study employed a non-lethal measurement tool, which combined an existing photo-identification technique with a surface, parallel laser photogrammetry technique, to accurately estimate the size of free-ranging white sharks Carcharodon carcharias. Findings confirmed the hypothesis that surface laser photogrammetry is more accurate than crew-based estimations that utilized a shark cage of known size as a reference tool. Furthermore, field implementation also revealed that the photographer’s angle of reference and the shark’s body curvature could greatly influence technique accuracy, exposing two limitations. The findings showed minor inconsistencies with previous studies that examined pre-caudal to total length ratios of dead specimens. This study suggests that surface laser photogrammetry can successfully increase length estimation accuracy and illustrates the potential utility of this technique for growth and stock assessments on free-ranging marine organisms, which will lead to an improvement of the adaptive management of the species.

Paper is available at Wiley Online Library.

The Ocean Awareness Project

The Ocean Awareness Project

As a result of my passion for marine life, but being unable to directly get involved in actual field projects at a younger age, I volunteered for a direct-action marine conservation organization. But as I succeeded further in my educational career, I realized that the most effective conservation method of marine life is science. The gathering of scientific data and the outreach of scientists to communicate their findings with the media and general public is fundamental for conservation. Above all, scientific data allows governments and NGO’s to aim their actions in certain directions to protect the oceans from over-exploitation or further damage (e.g. through the implementation of no-take zones or Marine Protected Areas).

As a matter of spreading (scientific) information to a wide public I started Oceaware (The Ocean Awareness Project). The original idea was to start off with a Facebook-page and then develop a website and work on its charitable status to turn it into a non-profit organization. This charitable status would allow us to accept donations to fund unique and fundamental research projects (e.g. development of an underwater camera trap), but due to relatively high notary costs to get this status here in The Netherlands this idea is currently on hold. We are however working on a new website, but please be patient as the time available for working on the website is limited. I will post an update on this page if the new website is live.

In the meantime you can give us your support by following us on Facebook and sharing our information! As we are currently with a small team (3 volunteers), we are always looking for new people to strengthen our international team. Please do not hesitate to contact me if your interested in a position at Oceaware (please, provide me with some information about your interests and experiences).



Welcome to my new website!

Through this page I want to give you all some more information about my work, including field updates during different research projects, interesting blogs, (scientific) publications and photography/videography.
I will keep you all posted about future projects that are currently still in preparation phase, keep an eye on this page as I will post more information soon!

If you have any further requests for information or questions, please send me an email.
Thank you for your visit and I look forward to hear from you!