Sea trouts are making a come-back in Helsinki

Brown trout (Salmo trutta)

​My main project this year saw me follow conservationists and researchers along the streams of Helsinki, as they looked for endangered Brown trouts (Salmo trutta) and restored their habitat.

Trouts are born in rivers in spring. The babies (the “fries”) are tiny and have many predators, including older trouts, but if they survive, they will grow in the river for a few years. At some point, there won’t be enough space and food for everyone, and the largest and most aggressive ones will hold the most bountiful spots. The others will migrate to the sea (or to a lake, but in Helsinki the streams end directly in the Baltic Sea), and come back in autumn to lay their eggs in gravel beds. Unlike some species of salmons, Brown trouts don’t die after spawning. They go back downstream, and return the next year.

That’s of course how it happens in an ideal world. Nowadays, Finnish rivers are too warm, they carry too much sediment, they have been dug (so they look more like straight ditches than meandering brooks)… and there are way too many dams that prevent fish movement. In the face of all this, dedicated people are fighting to free rivers and bring back the fish.

Sign along Longinoja illustrating the differences between a ditch (left then top) and a healthy stream (right then bottom)

​The sea trouts of Helsinki have been on my mind for a while. I first learnt about them when I saw some pictures by other local photographers, several years ago. I then visited Longinoja, a stream in eastern Helsinki where a lot has been done for the fish. There are info signs along the brook, with an English translation available online. It was absolutely brilliant to read about the trouts’ lifecycle, their struggle and all the conservation work that was (and still is) done for them. The Longinoja project won the Finnish Biodiversity Award in 2017-2018.
Last autumn, I photographed the trouts for the first time. Later, I got in touch with Henrik Kettunen, a researcher and conservationist, and he gave me tons of information about the trouts and their conservation. Once again, it was fascinating to listen to him, and it made me realize how much work it takes to restore stream ecosystems, monitor them and learn from the whole process, year after year.

In June, after I came back from Central Asia, I joined Henrik and Mika for a session of “brook yoga”. Why this name? Well, as they look for newborn trouts in the water, they continuously bend and twist, and on a warm summer evening, they quickly get sweaty… as if they were doing yoga!
We went there at night, because it’s when the baby trouts are resting near the shore, thus they are more visible. Timing is an issue though: you want to go early enough in the season so that the fries haven’t moved too far from where they were born yet. That informs future conservation measures, because it tells which gravel bed renovations have worked well, and which haven’t. Obviously, successful renovation methods will be re-used. At the same time, you don’t want to go too early, because some trout eggs may not have hatched yet. And to complicate matters even further, weather conditions make hatching time different every year. Oh, and with stream restoration come more places for the fish to hide and evade detection, so a lower figure doesn’t necessarily mean there are fewer fish. All this together makes it difficult to compare fry numbers year on year.
In terms of photography, it was challenging because it was dark, but the bright light of lamps helped with focusing, and I removed a lot of noise in post-production. I found that “brook yoga” really photogenic, and for the first time I really felt like I was doing conservation photography. Needless to say, I was spent when I came home at 2am, and slept very well!

Trout fry

​Later, I joined Henrik and Teemu for some restoration work in Haaganpuro, a stream that’s closer to home. Trouts lay their eggs in gravel beds, and they have some very specific preferences. Ideally, the bottom of the river in such areas forms a gradient around 10%. If it’s too steep, gravel and eggs will be washed away by the strong flow. On the other hand, if it’s too flat, silt and sand will accumulate, smothering the eggs. When they lay their eggs, female trouts move the gravel, forming a nest in the shape of an underwater mound. Those females come in all sizes, and a big one might just scatter the gravel if it’s too small, or a small one will not manage to dig into the gravel if it's too big. Thus, different gravel beds should be made of different stone sizes, to accommodate all fish. So yeah, it’s a tricky balance to find!
In addition, yearly maintenance is needed so that gravels are in the optimal shape when the migrating trouts are back. Pouring water cleans the gravel, freeing space among the pebbles for the eggs. That’s what you see in these images.

90% of insect biomass in a stream comes from fallen leaves

​It’s not only associations that are involved in trout conservation. Each autumn, researchers from the Natural Resources Institute Finland (LUKE), a government agency that operates under the Ministry of Agriculture and Forestry, catch trouts to count them, measure them and tag them. They do so with electrofishing: they stun the fish so that they can be caught and handled. Again, I found the process very photogenic and I tried to show general scenes but also details. The fishermen, Ari and Mikko, worked together. Ari carried the electric devices, while Mikko picked the stunned fish up and stored them in a bucket filled with water that he carried at the hip. After covering a given stretch of river and collecting all the fish they could find, they settled down on the side and started measuring and weighing all the trouts. Mikko did the manipulations while Ari wrote the data down. After that, they released the animals and continued up the stream. This procedure provides a picture of the evolution of fish abundance in the stream. This year, even though lots of fries were found in June, the numbers were lower than expected in September. Something happened in Longinoja during summer.

Passer-bys are often intrigued by the researchers' work

Scanning a trout for chip

Measuring the length of the river stretch that was fished

In early October, trouts were caught again with a very precise objective: equip them with PIT (Passive Integrated Transponder) chips that can be detected with a special device. With such a chip, a fish can be re-identified if it is caught a second time, and weight and length can be compared from one year to the other. Additionally, the chips are used to study fish movements in the stream, with the help of a pair of gates equipped with a scanner. If a fish is detected by both gates, we can deduce that it’s moving either up or downstream.
The trouts are again caught with the electrofishing method. After being measured and weighed, Annie made an incision in their belly and inserted the chip inside. It doesn’t impair them in any way, but stays there all their life.

​This sounds like a lot already, but it’s only a part of trout conservation in Helsinki. Join me next month as I tell you about trout spawning and reflect on the power of storytelling for nature conservation!