Whale Scientists Story: Jeroen Hoekendijk

Jeroen Hoekendijk is a 33 years-old Dutch marine mammalogist currently working on his PhD on marine wildlife detection using aerial and satellite imagery. Here is his story.

Jeroen Hoekendijk and a seal

It all started with an orca encounter in Canada

I’ve always been fascinated by the sea, the oceans, and everything inside it, but I never considered making a career out of it. That changed when I was 21 when my dad convinced me to join my parents to Canada and Alaska. During a multi-day kayak trip, we had some (very) close encounters with orcas. At that very moment, I decided to study marine biology and marine mammals in particular. Deadlines to subscribe for the (at that time) only marine biology BSc in the Netherlands were approaching fast, and I was still in Alaska. Luckily, I was able to contact my brother in the Netherlands, and he helped me with the paperwork and housing arrangements.


I obtained both my BSc. and MSc. in marine biology from the University of Groningen (RuG) in the Netherlands. In total, this took me 6 years.

Internships and volunteering experience

During my MSc, we had to do 2 internships (six months each). I also volunteered at the local rescue center for 12 years.

Spatial wildlife detection

My first internship was at the Royal Netherlands Institute for Sea Research (NIOZ) with Geert Aarts and Kees Camphuysen. During this internship, I developed a new photogrammetric method to determine marine mammals’ exact spatial position (more particularly harbor porpoises) at the sea surface. This internship included fieldwork, but also a lot of coding, from which I still benefit today. It was advertised a year before I applied when I was still a bachelor student. During that year, I could volunteer within the same project. A year later, I could continue the research as part of my master’s. This internship included a lot of coding, from which I still benefit today.

Common dolphin - Jeroen Hoekendijk
Common dolphin – Jeroen Hoekendijk

Marine mammals genetics

My second research project was at the University of Groningen, in the newly established molecular genetics group of prof Per Palsbøll. This group works mainly on genetic research of cetaceans. For this internship, I switched to the field of molecular genetics, examining the taxonomic status of fin whales. I spent most of my time in the lab and learned a wide array of molecular techniques. These I could use during my first job after my MSc, working in a genetics lab at the RUG on various cetacean related projects.

A pod of humpback whales - Jeroen Hoekendijk
A pod of humpback whales – Jeroen Hoekendijk

During my second internship, I got the opportunity to volunteer twice at the Center for Coastal Studies in Provincetown, Massachusetts. There, I met some incredible people that work with marine mammals in many ways. I worked in the humpback photo-ID program, participated in surveys to collect photos and biopsies of humpback, fin, and right whales, joined a necropsy, and helped during the disentanglement of a humpback whale with the Marine Animal Entanglement Response Team. I’ve learned so much during my time there, and I really hope to return someday. The density of whales is extremely high there. One time in Spring, I saw a fin, humpback and right whales, white-sided dolphins and grey seals, all during a single beach walk!

Volunteering at the local rescue center

For the last 12 years or so, I also volunteered for a Dutch cetacean rescue and rehabilitation team named SOS Dolfijn. In the beginning, they had dedicated rehabilitation facilities. Various small cetaceans (mainly harbor porpoises, but I also worked with white-beaked dolphins and a common dolphin) were taken into this center until they were healthy enough to be released back into the wild. In the last few years, SOS Dolfijn didn’t have a rescue center, but new facilities are being constructed. In the meantime, stranded animals are being released back into the sea directly or are euthanized if they are sick or injured.

Stranded sperm whales - Jeroen Hoekendijk
Stranded sperm whales – Jeroen Hoekendijk

PhD life

Currently, I’m a PhD student at the NIOZ. In this project, I develop detection algorithms to detect and count seals from aerial and satellite imagery, using ‘machine learning’ and ‘computer vision’ techniques. I found this PhD position as it was advertised on various media online.

Due to global warming, the Arctic sea ice is disappearing fast, potentially with significant consequences for animals living in this region, such as seals. Arctic seals use the sea ice for pupping and molting and as resting areas between foraging trips. The sheer size of the area, the ice, the harsh conditions, and the darkness of the polar nights make it extremely challenging to monitor the effects of these changes on the ice-depended seals distributed throughout the region. Therefore, we aim to develop alternative approaches to detect and count seals, using satellite imagery and Machine Learning techniques. These technical aspects and the opportunity to learn, develop, and apply new methodologies make this project particularly attractive to me.

Grey seal - Jeroen Hoekendijk
Grey seal – Jeroen Hoekendijk

During my PhD, I’m learning a lot of new things about automated wildlife detection. The field of automated wildlife detection has boomed over the last five years or so, making it super exciting, with lots of opportunities. However, sometimes this also makes it challenging, and trying to stay up to date with the most recent developments and applications can be a bit overwhelming.

What does the future hold for Jeroen?

For now, I’m putting all my efforts into my PhD. During my holidays, I try to go out in the field and photograph marine mammals.

Jeroen’s advice to aspiring marine mammalogists

For me (and many of my friends and colleagues), it turned out that the internships/research projects during my master’s have played a key role in my career. Both my internships have led to job opportunities. There are many great and exotic opportunities and some with fantastic fieldwork as well. However, not all may lead to job opportunities. Therefore, here is my advice: think carefully about what you want from an internship. Perhaps sometimes the most fun ones are not the most useful ones.

A story from the sea

All my holidays focus on whale watching. I feel both humbled and privileged when I think about all the unique encounters and experiences I’ve had over the years, and I’m incredibly thankful for the people I’ve met along the way. But there’s one moment (that I shared with my mother) that undoubtedly stands out.

Mexican Lagoon

Earlier this year, devoid of a mobile signal and oblivious to the pandemic that was slowly tightening its grip on our planet, we were sailing the Pacific along the Baja peninsula (Mexico). Guided by Mark Carwardine, we were making our way towards the San Ignacio Lagoon, one of the winter sanctuaries of grey whales. During the second half of the 19th century, the lagoon became a large whaling scene. The greed and bloodlust reduced the number of eastern Pacific grey whales from tens of thousands to just a few hundred within years. Many men were killed, too, by mothers defending their calves, gaining the grey whales their nickname: Devil Fish. Since the ban on whaling, these grey whales have made a remarkable recovery, and scientists now believe there are around 30.000 individuals.

Grey whale in San Ignacio Lagoon – Jeroen Hoekendijk

Grey whale paradize

Interestingly, these “devil fish” are now popular for their kindness, and tourists (like myself) travel the world to observe their surreal spectacle. During the breeding season, grey whales approach the small whale watching boats (or ‘pangas’) operated exclusively by local guides and let enchanted tourists pet them. Only part of the lagoon is open for whale watching; the rest is exclusively reserved for the whales. Our boat anchored inside the Lagoon, and soon grey whales surrounded us. We spent the following two days watching the whales from the pangas. Wherever you looked, you’d see blows, flukes, spy hops, and breaches. Several times a whale decided to approach the panga, turn on its side, and look you straight in the eye. It’s hard to describe the experience. I saw many (curious) cetaceans up close. Still, I felt like I was in a different world: Planet Grey Whale.

Itchy whales

Perhaps the whales behave like this to satisfy an itch. The grey whale’s body, especially its head, is covered by parasites barnacles, and so-called whale lice. Occasionally, one of these lice would even jump host and attach itself to my fingers. But when mothers are pushing up their newborn calves towards the boats, you can’t help but wonder if there are other reasons why these barnacled behemoths seek out our company. Either way, the caress of our hands “spans an abyss of abuse and apology,” as my good friend Philip Hoare would later phrase it.

An itchy grey whale – Jeroen Hoekendijk

We live in an era of global destruction, habitat degradation, biodiversity loss, and struggling to stop the Anthropocene mass extinction. The only way forward is to find ways to coexist with nature. Of course, the grey whales in the San Ignacio lagoon would be better left alone. Still, if it wasn’t for the tourist industry, the revenue it generates, and local operators’ efforts, the lagoon would have been transformed into a salt winning plant years ago.

Bottlenose dolphin - Jeroen Hoekendijk
Bottlenose dolphin – Jeroen Hoekendijk

Make sure you check out our other stories here.

You can reach Jeroen on his instagram down below:

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