Skitt fiske! Stickleback fieldwork in the age of covid-19

Fieldwork blog special by: Joost Raeymaekers, Benedikt Berger, Arun Gowda and Thijs Bal

Fieldwork is an essential part, and often the start of many studies in ecology and evolution. In the week of 9th March 2020, all was ready for our team to leave for Belgium and the Netherlands for a new study on stickleback fishes. However, Norway announced the first lock-down, and the university wisely decided to cancel all travel. In the beginning, this was not much of a problem, as we could continue to work on ongoing projects. However, after a few months, we had to find a solution, especially for Benedikt and Arun, who didn’t have had a chance yet to collect data for their master and PhD thesis, respectively. Now, stickleback fishes are very abundant in Norway, but only in Belgium and the Netherlands we find many co-occurring populations of three-spined and nine-spined stickleback, allowing us to directly compare how they adapt to different environments. We were therefore extremely grateful that the faculty gave us green light to finally travel in October to our wonderful stickleback field sites.

Fieldwork during covid-19 times in Belgium, October 2020. Clockwise: a) Tintin’s space shuttle at Brussels airport; b) flat earth experience in Flanders; c) field team bubble; d) the beautiful Dommel River; e) checking the 1st stickleback catch.

The fieldwork was not going to be as usual. All our activities had of course to be covid-proof. We did so by staying in our “bubble” of four and spending a lot of time outdoors. In order to minimize indoor lab activities, we also decided to process all the samples in the field. Below you can see how Arun sets up his own little lab in the back of the car.

The mobile stickleback field lab.

Furthermore, we usually study sticklebacks in spring, so we were excited to see what is different in the fall. Belgium and the Netherlands are densely populated, so the creeks, ponds, ditches and streams we are investigating aren’t always very natural. Still, they can be quite of a jungle, and a basic degree in acrobatics can be useful when wading through them with a fishing net and a bucket. Lush vegetation made the access to some of the sites more challenging than in spring. Below you can see some of our most natural and most urban field sites.

A selection of our most natural field sites.

It is strange to catch fish in the middle of the city, or with the dooming view of a nuclear power plant in the background. The differences between the urban and natural sites are dramatic, but both three-spined stickleback and nine-spined stickleback seem to cope well with either environment. How they manage to do so is one of our research questions.

A selection of our most “urban” and “industrial” field sites. In the top right figure, Arun is looking for “the stickleback particle” at the nuclear power plant of Doel near Antwerp. On the left, Thijs is exploring the urban stickleback habitat in the city of Lokeren.

Sticklebacks reproduce over summer, so fish densities are generally higher in fall than in spring. This made it quite easy to reach sufficient sample size for both species of stickleback, including individuals from two different age classes (adults and young of the year). However, we also had to find new sampling locations, as four important field sites completely dried out. This is not uncommon for some headwaters in the middle of summer. However, it is exceptional to find so many dry sites in fall. Three consecutive warm summers with strong heatwaves are to blame. This is bad news for all aquatic life, but unfortunately climate change is kicking in, and we will see more of these extreme weather events over the years to come. Luckily, other sites were fine, and we still encountered a few places with plenty of fish. Below you see some of our favorite fish encounters.

Freshwater fish diversity of Belgium and the Netherlands. Top right: three-spined stickleback (Gasterosteus aculeatus). Middle right: European perch (Perca fluviatilis). Bottom right: common roach (Rutilus rutilus). Top left: stone loach (Barbatula barbatula). Middle left: Northern pike (Esox lucius). Bottom left: stone loach (Barbatula barbatula), common gudgeon (Gobio gobio) and the invasive topmouth gudgeon (Pseudorasbora parva). Central: spine loach (Cobitis taenia).

There is also a great diversity of aquatic invertebrates at our sampling sites. Have a look to some of these fantastic treasures below!

Some of the most spectacular aquatic invertebrates observed during our trip. Top right: water scorpion (Nepa cinerea). Middle right: water stick insect (Ranatra linearis). Bottom right: dragon fly larva. Top left: duck weed (considering that we don’t know the name of the spider). Bottom left: Great diving beetle (Dytiscus marginalis).

Some really spectacular guests ended up in our nets too. Can you tell which of the top models below is not an invasive species?

Top left: Benedikt Berger (rare sighting!). Bottom left (in Benni’s hands): red swamp crayfish (Procambarus clarkii). Top right: Chinese mitten crab (Eriocheir sinensis). Bottom right: marsh frog (Pelophylax sp.).

Most of our study sites are surrounded by farmland. Many years of field work have taught us that whenever there is cattle, there are usually plenty of stickleback in a nearby ditch. It is therefore no secret that stickleback scientists love cattle. And, the love is often mutual.

Three-way interaction between cattle, stickleback and Arun.

There is always a time that we don’t catch anything, especially in endless ditches with, unsurprisingly, not a single cow at the horizon. The Norwegian expression “Skitt fiske” is often used to wish someone good luck with the catches before a fishing trip. However, literally it means quite the opposite, and this was certainly one of those days.

Skitt fiske!

After more than two weeks searching for good study sites across Belgium and the Netherlands, we managed to complete the fieldwork successfully. Luckily, we could count on the logistic support of the team of Filip Volckaert at KULeuven, helping out with waders, hand nets and other field equipment. Moreover, for the sites in the Netherlands, we got help from RAVON, a Dutch NGO engaged in nature conservation, and from Manon De Visser and Jakob Gismann. Mathilde Le Moullec and Nicolas Haumont joined us for some of the Belgian sites. Thanks everyone for the great team work and to make this field trip possible during these special times!

Top: selfie with Mathilde Le Moullec, the proud catcher of a bug. Later on she did well with fish too. Right: Nicolas Haumont, keeping us at 2 meter social distance, as to effectively protect his fishing grounds. Bottom: Thijs, Benedikt, Filip and Arun in action – or the moment when you get both your former PhD supervisor and your PhD and Msc students in the same ditch!

On the last day, our mission was to prepare for our return to Norway, where a ten-day quarantine was awaiting us to comply with covid-19 travel regulations. Consequently, a combination of Belgian beers and chocolates seemed justified to fill up the empty space in our luggage. A new purpose for an old tradition!

Views from Belgium. Top left: engaging with a local bike club interested in aquatic ecology. Top middle: Arun eliminating the empty gaps between his Belgian chocolates. Top right: optimizing caloric intake for field work. Left: Arun and a perfectly served Duvel. Right: the historical city of Bruges. Bottom left: Arun practising his PhD defense in the fancy promotion hall at KULeuven. Bottom middle: desperately looking for an open chocolate shop. Bottom right: schol!