As darkness falls, creeks are buzzing with activity. In the torchlight, you can see fry, about 2 centimetres long, exploring the area around their spawning nest in near-shore waters. Over the next few months, the fry will spread out along the creeks in Helsinki, and if they survive their first few years, they may eventually grow into sea trout weighing up to nine kilograms.
The monitoring of trout fry in creeks in Helsinki starts in May. The number of newly hatched fry is one of the most important indicators of the reproduction of the endangered trout and the state of creeks.
In Helsinki, fry counting has been carried out for almost a decade, mainly by volunteers and in cooperation with clubs and associations. As there are over 30 kilometres of trout creeks in Helsinki, monitoring would be difficult without citizen observation.
“Helsinki has seen promising results in the restoration of trout waters, and fish population monitoring has played a key role in this. You could say that the success is due to the contribution of skilled volunteers,” says Henrik Kettunen, a trout expert from the City of Helsinki.
The number of fry indicates the level of success of creek maintenance
As trout are at their most vulnerable at the beginning of their lives, fry loss can indicate problems with water quality, such as chemical discharges, for example. Observation of fry has also helped better identify the environments in which trout spend the beginning of their lives. As a result, creek restoration efforts are now better able to cherish the calmly flowing near-shore waters that are important for fry.
In addition to fry counting, trout populations are monitored through electrofishing surveys carried out by professionals every autumn. They show how well trout have made it through the summer.
“However, without fry counting we wouldn’t know in which parts of the creeks fry hatch, how successful the restoration measures have been and where water quality problems occur,” Kettunen says.
Fry observation requires a trained eye
The counting of fry will continue until Midsummer. Anyone can contribute to the data collection by reporting their observations via a web application named Taimenkartta(Link leads to external service).
The best time to observe fry is at dusk, when daylight does not create reflections on the water surface. A torch is all you need. It is important not to step in the water to avoid accidentally trampling the delicate fry.
The City organises guidance on counting fry for those interested. In May, two public nature excursions were also organised to teach people how to observe fry.
“Monitoring takes some experience and knowledge. Initially, fry are very small, stationary and difficult to spot. But once you learn to recognise their typical hiding places and behaviour, you start to understand the life of trout in a whole new way,” Henrik Kettunen says.
The restoration of trout creeks will continue
There are seven natural trout creeks in Helsinki. At the turn of the millennium, wild trout had completely disappeared from Helsinki, but the population has since been revived thanks to restoration efforts by municipalities and volunteers.
Important restoration measures include opening dams, removing other barriers to migration, building spawning grounds, making straightened channels more winding and providing shade for creeks by using riparian vegetation, for instance.
Improving water quality is equally important. For example, chemical discharges can cause deterioration in water quality in small creeks, which at worst can destroy the entire population of trout fry. There is now also more information available on the harmful impact of household chemicals, such as roof moss removers.
Volunteers can also contribute to the restoration of creeks. Volunteer-based restoration projects are organised every year in August and September. The City of Helsinki organises such events together with Helsingin Perhokalastajat ry (Helsinki Fly Fishing Club), Virtavesien hoitoyhdistys (Finnish River Restoration Association) and Skes ry (Finnish Association for Promoting Fishing Tourism), among others.
