A total of 123 trout fry were counted in a 30-metre stretch of the redd in the Mätäjoki River in Strömberg Park in Pitäjänmäki in mid-May.
This is an excellent number: during the eight-year fry monitoring efforts, the largest number of fry observed in a similar stretch of redd in Helsinki was 160. This record number was counted in the best fry area of Haaganpuro creek in 2023.
”The observed quantities in Mätäjoki are as good as can be expected at this stage. The number may go up as we move further into May and the last batch of fry emerges from spawning nests,” says counting participant and trout expert Henrik Kettunen from the City of Helsinki.
It was feared that the number of trout fry in the Mätäjoki River would have suffered due to an error made in the renovation of Strömberg Park in April. Three water filtering dams were built along the Mätäjoki River flowing through the park for the duration of the work, and one of them was built on top of trout spawning nests. The renovation of the park aims at improving the habitats of migratory fish.
According to Kettunen, one of the reasons for the smaller than expected impact could be that when the eggs were covered by the dam, some of the egg pockets were deep within the gravel cover.
Excellent year at other counting sites, as well
The habitats of migratory fish have been improved in creeks in Helsinki for the past twenty years through cooperation between the voluntary network and municipalities. The work is also evident in Haaganpuro creek and in Longinoja located in Malmi, where the numbers are closing in on record numbers of fry based on counting efforts in May.
Although the spawning was successful, the fry are faced with a challenge of their own during the summer. They must face adversities such as heat, predators and other environmental factors. Natural Resources Institute Finland monitors the density of fry in the autumn with the help of electrofishing, which will shed some light on how the fish have fared over the summer.
It is very important that the fragile fry be left alone now. Wading in breeding sites can destroy trout fry with lengths of a mere twenty millimetres.
“The fry are still only the length of half a matchstick. Even a slight misstep on a moist beach can easily crush some of them, so you really should not walk around trout creeks right now,” Kettunen says.
There are seven trout creeks in Helsinki, with a combined length of roughly 33 kilometres. In total, more than a hundred spawning nests are discovered in the creeks of Helsinki every autumn. The extremely endangered trout is protected and fishing in creeks is prohibited.