Fulmar Stomach Contents Expose North Sea Plastic Soup

Marine ecologist Susanne Kühn lifts a large box from a shelf in her office. The shelving racks are easily overlooked in the cosy chaos of this former classroom of the old nautical college in Den Helder. Kühn shares the room with three colleagues, each occupying a corner of the room with their desks. A big filing cabinet serves as a room divider, and tiny fish bones are drying in petri dishes on a tray. 'A real scientist's room', says Kühn, as she places the large box on a table. The label reads NETHERLANDS in black marker.

The cardboard lid reveals a pile of storage bags, each containing specimen jars, filled with pieces of plastic. You can make out the occasional baggie or netting, but most jars contain slivers and splinters in various shades of brown. With the plastic is a yellow label with a country code (NET), year and number, because each of the jars corresponds to one of the stranded fulmars that Kühn has dissected and studied here in Den Helder.

Since 2002, the stomach contents of these Northern fulmars have served as a marker for the plastic content of the North Sea. Kühn assumed responsibility for this project in 2020, which is conducted by Wageningen Marine Research at the behest of the EU and OSPAR. She talks about the birds with compassion and fascination in equal measure. Their death is tragic, but they also carry 'important messages', like stranded bottles.

The Fulmar Threshold-Value

Jan Andries van Franeker, Kühn's predecessor, conducted biological research on seabirds in the eighties. 'Jan began to notice a pattern: fulmars' viscera often contained plastics', Kühn says. 'This was not just the case among fulmars from the North Sea, but also those he encountered in Antarctica, where he conducted ecological research.' The monitoring project was launched upon Franeker's recommendation. 'Helped by the fact that the plastic soup in the ocean had made it to the international agenda.'

An average of forty Northern fulmars per year are required for a representative sample. 'The number of birds that get stranded varies per year. We don't know why, exactly.' Kühn studied 14 fulmars in 2021 and 66 in 2022. The 2023 report is based on 26 birds. Kühn determines the plastic content of the North Sea by determining the percentage of the examined birds that have plastic in their stomachs and how much. This percentage is then compared to the so-called Fulmar Threshold Value, determined by the EU.

'No more than 10 per cent of the fulmars may have over 0.1 grammes of plastic in their stomachs per year', Kühn explains. 'In 2023, 58 per cent of the birds exceeded this threshold value.' Because the number of birds investigated in that year was too low, Kühn prefers to consider the five-year average. 'I studied 231 birds between 2019 and 2023. 53 per cent exceeded the threshold value.'

So, the North Sea isn't doing well? 'Yes and no. The plastic percentage has dropped on average in the last two decades, but at this rate, we will not meet the threshold value before 2087.'

Volunteers with bierds in their freezer

Opening one of the freezers in the cooling cell, Kühn explains the origins of the birds she studies. 'I pick up birds that are stranded on the beaches of Texel, where I live. However, the majority of the birds are collected by volunteers who encounter them while combing the beaches. I also keep an eye on waarneming.nl, where hobbyists record the live birds they see, as well as dead ones. I always send them a message to see if they can retrieve the bird.'

Kühn lifts a large container from the cooler. Upon removing the lid, some ten packages the size of a rugby ball appear. Each package contains a frozen fulmar wrapped in plastic. Kühn lifts one wrapped in a transparent bag branded with the AC/DC logo. She immediately knows which person in her network supplied the bird-despite the network being quite extensive. Volunteers along the entire Dutch coast, including the islands, store fulmars in their freezer until Kühn has found a way to get them to Den Helder. 'If a colleague makes a trip to Zeeland, down south, I ask them to bring back a bird for me.'

A brief instructional video on how to pick up a dead fulmar has been available since 2021. 'That is for new volunteers. Most of the birds are collected by volunteers that have been helping out for quite a while longer. They are indispensable to this research.'

Fulmars as an indicator species

In the dissecting lab, Kühn displays a fulmar. She places the bird on the steel slab under the big ventilation unit and the animal's chest is wide open. The stomachs have been removed and are displayed on a napkin, like deflated balloons. Using her index and middle finger, Kühn shows how far the bird can open its beak. 'They grab fish from the sea and swallow them whole.' The meal reaches the glandular stomach first, which is the largest of the two balloons by far. There, the food is digested. 'The remaining bones are then transferred to the much smaller gizzard, where they are crushed to powder.'

This digestive system makes the fulmar suited as an indicator species. 'Gulls that eat plastic regurgitate it. Fulmars don't. The plastic they ingest takes the same route as the fish bones.' On top of that, the birds spend their whole life at sea. 'They are small albatrosses, really', Kühn says, spreading the large wings out in the slab. 'They hover over the water where they get everything they eat. Plastic included.'

Their large beaks enable the fulmars to ingest large chunks of plastic. But most of the plastic Kühn finds is finely ground. To ensure even the smallest plastic fragments are retrieved, the stomachs are rinsed over a filter. 'I remove the plastic with tweezers and place it in a petri dish to dry.'

Sorting and weighing plastic

A microscope is required to sort the plastic. 'We separate the plastic from organic materials and then separate the plastic according to type,' Kühn explains. The EU requires plastic to be divided into two categories. The first is the pellets, small grains that are used in manufacturing plastic products. The second is consumer plastics, which is basically the 'other'-category. The scientists categorise even further on their own initiative. 'We believe that this data will prove valuable in time.'

Once categorised, the plastic is weighed. At the start of this century, the amount of pellets roughly equalled that of consumer plastics. Now, there is a notable improvement with regard to pellets: their share in the total amount of plastics has dropped. 'Pellets used to reach the sea through the sewer system. Over the last two decades, industries appear to have become increasingly aware of the losses they incur as a result of resources being wasted this way.' The share of consumer plastics is decreasing at a much slower rate and has remained stable since the nineties.

However, Kühn has seen changes in the composition of the plastics. 'Balloons, for example, are an item I see less of. The explanation is simple: public pressure has led to a ban on releasing balloons in almost all coastal municipalities.'

All about the North Sea

The Netherlands is not the only EU member state that monitors the fulmar. All North Sea countries monitor their coasts. Every five years, Kühn merges the collective results in a report. 'I am currently working on the 2019-2023 assessment.' Even so, she agrees to give a little preview. 'The decline in the plastic content of Dutch fulmars has stagnated in the past three years, while the decline continues in England and Germany. It is difficult to determine why at this time, but it is a striking difference.' Thus, the fulmar continues to prove itself, thanks to scientists who persist in reading the messages they bring to the coast.

At the end of the interview, Kühn extracts a stuffed fulmar from a paper bag. Unlike its dissected sister, this bird has every feather in place. But that's not why Kühn decided to bring the bird. It's the scent. 'You can smell the sea in their feathers', she says. The bird in the lab emitted the scent of decay, but Kühn is correct: this bird smells of the salty North Sea. Of the water and the wind that blows across it.