Order: Salmoniformes Family: Salmonidae Subfamily: Thymallinae
Foto: Ari Saura
Description: The grayling is easily distinguished from Finland’s other native salmonids by its broad, high and colourful dorsal fin. The flesh is white with a hint of the scent of thyme. The scaly cover and pigmentation of the skin give an impression of parallel horizontal stripes.
Origin and distribution: As the only representative of its genus in Europe, grayling spread to Finland from the east during the Quaternary period. Native grayling populations are common in northern Finland, but also occur locally in bigger lakes and streams in the east of the country. The unique sea-spawning populations are weak nowadays and occur only in sparse numbers in the Gulf of Bothnia, in places where the salinity does not exceed 5.5‰. Current freshwater populations in southern Finland, excluding parts of the River Vuoksi watershed, originate from translocations. The majority of populations in northern Finland are indigenous.
Reproduction: Unlike many other salmonids, grayling spawn in the spring. In Finland, the main spawning period extends through May to early June. The spawning grounds of different populations are located either at rapids or in shallow, rocky near-shore areas with gravel bottoms, at depths ranging from 0.2 to 4 m. Grayling mature at an age of 3−6 years and a length of approximately 30 cm. The female can produce 2,000−20,000 eggs, with a diameter of 2.5−3.5 mm. Larvae hatch after 3−4 weeks of incubation when they are about 10 mm long.
Diet, growth and migrations: After hatching, grayling larvae feed on zooplankton. The young grow rapidly, attaining a length of 10 cm by the autumn. Juveniles and adults feed on benthos, insects on the surface, and fish. Grayling are quite local, and live in sparse shoals. However, after the first summer dispersal is efficient. The growth rate varies, a 40-cm fish being anything from 4 to 10 years old; the oldest grayling can be up to 15 years old. The record for the heaviest ever caught in Finland is 2.28 kg.
Fishing and catches: The grayling is an important species for both subsistence and recreational fishing, with annual catches of 250−470 tonnes. Fly-fishing for grayling is a challenging and exciting sport. River catches of grayling are significant, especially in northern Finland, although numbers have declined in dammed rivers. Sea stocks have collapsed since the early 1900s, when they were still reasonably strong. In eastern Finland, e.g. in parts of the Lake Saimaa complex, some tonnes of grayling are caught every year. The closed season is from 1 April to 31 May, with exceptions for rod and lure, and fly-fishing and for fishing in northernmost Lapland. The legal minimum catch length is 30 cm, though locally it may be somewhat greater.
Vulnerability, threats and management: In Finland, the grayling is evaluated as a least concern (LC) species except in sea areas, where it is classified as near threatened (NT). The globally unique sea-spawning grayling stocks in the Gulf of Bothnia might even be considered endangered.
Native grayling populations in coastal rivers and brackish waters have been declining steadily, and the anadromous stocks that once inhabited rivers on the west coast have completely disappeared. Some populations in the eastern lake-district have also declined or even become extinct. Various reasons are given for the situation: damming of rivers, flow-regulation, dredging, land-use practices with a deleterious effect on water quality, and even intensive fishing. In river habitats, silting, eutrophication and springtime acidic pulses may jeopardize reproduction of the species. Grayling embryos are also sensitive to fluctuating temperatures.
Hatching of grayling eggs and releases of larvae began in central Finland in the 1920s with eggs introduced from Lake Ladoga, Russia. Rearing of hatchery brood stocks started in the 1960s, initially as a private business. Since then, releases of young-of-the-year grayling have been successfully used to enhance depleted populations and to create new ones. Established translocated populations inhabit the rivers Kymijoki and Vantaanjoki in southern Finland. To conserve the genetic diversity of the species, governmental hatcheries currently hold 11 grayling brood stocks from several watersheds. The annual release totals some 1.5 million one-summer-old individuals.
Comments: As the Latin name thymallus implies the grayling has a mild aroma of fresh thyme. It has long been considered a great delicacy. The Saame have also used it for medicinal purposes. The muscle tissue contains 4−8 g fat and 1.6 mg Omega-3 fatty acids per 100 g.