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

Abstract
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!

Welcome!

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!