Exposed rocky shorelines – a grayling favourite

During a couple of sunny days in spring we had the opportunity to go out and learn more about one of the most iconic fish species of the Bothnian Bay – the grayling – and it’s favourite habitat on the exposed, rocky shores. Together with our fish expert collegues we searched for grayling eggs along the rocky shores in order to gather data on what type of habitat they prefer for spawning. How exciting for us, who mostly concern about underwater vegetation during our SEAmBOTH inventories, to see the value of these exposed, low-vegetation shorelines for spawning fish.

Hardly any underwater plants in sight, but plenty of potential places for the grayling to lay their eggs on in the rubble. The shoreline is exposed, with some semi-sheltered areas within. The bottom substrate consists of gravel mixed with small rocks. Especially in the outer archipelago of the SEAmBOTH area these type of unique habitats can be found (Photo by Petra Pohjola, County Administrative Board of Norrbotten)

The grayling (Thymallus thymallus) is a fish species belonging to the group of salmon fishes. It normally lives in freshwater lakes and streams, but in the northern Gulf of Bothnia you may find it in the sea. Some of the sea-living graylings spend time in the sea and when it’s time to spawn they swim upstreams into rivers. Others spend their whole lives in the sea, and as recently found out, spawning there as well.

By the use of water binoculars and a large strainer, grayling eggs were located and identified. (Photo by Linnea Bergdahl, County Administrative Board of Norrbotten)
The grayling drop their eggs on the bottom where they sink into the crevices between the rubble. There they remain (if all goes well) until it’s time to hatch a couple of weeks later. A greyling egg floats around in the middle of the picture (Photo by Petra Pohjola, County Administrative Board of Norrbotten)
Close up of grayling eggs settled between small rocks on the shallow bottom (Photo by Petra Pohjola, County Administrative Board of Norrbotten)

The number of graylings have been declining overall. More so on the finnish side of the Baltic Sea where it is today classified as critically endangered. In the northern Sweden, the project “Skydd av harren i Bottenviken och Norra Kvarken” financed by the Swedish Agency for Marine and Water Management has since last year been investigating the occurence of sea-spawning grayling and mapping the habitats they use. By understanding better where these populations are, and what type of places they require for reproduction, we have a better chance to protect such places and ensure a bright future for the graylings within the northern Bothnian Bay and whole Baltic Sea.

Written by Linnea Bergdahl, County Administrative Board of Norrbotten

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