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Arctic grayling (Thymallus arcticus)

The Arctic grayling is one of the most widespread freshwater fish of the Northern Hemisphere. This species inhabits all Siberian rivers and a large part of North America. There are four universally recognized subspecies of the Arctic grayling: West-Siberian, East-Siberian, Kamchatka, and American (Alaskan) subspecies.

Graylings can be vary a lot by their colors. So, small fish are most often quite light, with pinkish or pearly hue; they grow darker as they grow. The largest specimens (especially males) are very dark, and their dorsal and ventral fins are covered with bright stripes and spots. In addition, the color of grayling depends on the color of the water and the bottom in the given river or lake.

The scale cover is blue-silver with turquoise or olive tint. There are small black spots from the head to the middle part of the body. The gill covers are gray with a turquoise hue. There is a black spot on the lower jaw. From the pectoral to the ventral fins, two parallel yellow-brown stripes are visible. There is a large scarlet red spot above the ventral fins. The caudal stem, anal and caudal fins are red-maroon. The ventral fins with 4-6 longitudinal oblique stripes are cherry red, and the pectoral fins are gray-yellow. On the dorsal fin there are 6-20 almost horizontal rows of red-maroon spots. In its front part, the spots are small with a dull fringing, and in the rear part, their size is increasing; they take shape of rounded or elongated, narrow vertical stripes merging with a narrow edge line of the same color.

There is a large difference between all subspecies of Arctic grayling in the head and body shapes, and also in the patterns of the dots and stripes on the dorsal fin. There are also biological differences separating these subspecies. In fact, there are now data that these subspecies may be separate species.

The range of the West-Siberian grayling covers the lower parts of the Ob and Yenisei Rivers. The East-Siberian subspecies (Thymallus arcticus pallasi) inhabits the Arctic Ocean basin from the Lena River to Eastern Chukotka. In the Lena River, it lives only in the middle and lower reaches of the river, and the upper Lena basin inhabits another species – the Upper-Lena (Baikal-Lena) grayling (Thymallus baikalolenensis). The East-Siberian grayling also inhabits many river basins along the northern and northwestern shores of the Sea of Okhotsk. The Kamchatka subspecies of Arctic grayling (Thymallus arcticus mertensi) inhabits the Kamchatka Peninsula; Paren, Penzhina and Anadyr basins; and also the Taui and Yana Rivers near Magadan (northern coast of the Sea of Okhotsk).

The main range of the American subspecies of the Arctic grayling (Thymallus arcticus signifer) is Alaska and Canada. In Asia there are only a few lakes and small rivers situated right near the Bering Strait where this fish is found.

These main subspecies of the Acrtic grayling differ well by the pattern at the dorsal fin, by the shape of the head and by the body colors, as well as by their biology. The West-Siberian grayling has relatively short and wide dorsal fin with a pattern of large spots and a bright metallic luster. By the large males of the East-Siberian grayling, huge dorsal fin can reach the base of the caudal fin; on its rear part, between the fin rays, there are 5–7 continuous dark red stripes. Kamchatka grayling has slightly smaller dorsal fin; it does not have continuous stripes, but only elongated merging spots. On the relatively small dorsal fin of the Alaskan grayling of the Asian populations there are rows of speckles or dots. The Kamchatka grayling differs from the East-Siberian also by its relatively large head and mouth sizes. There is also difference in the body shape: the East Siberian is more wide and hunchbacked, and the Kamchatka grayling is longer and not as wide. In contrast to the Kamchatka grayling, the tail of the East-Siberian grayling is rather bright red. Small fish less than 25 centimeters in length are more difficult to distinguish.

In northeastern Asia, the biology of grayling is different on the different slopes of the Arctic-Pacific Divide. In the drainages belonging to the Arctic basin, this fish inhabits small streams and brooks, often near the river sources. Here grayling have no competitors and feed until autumn, when they go downstream into bigger waters to winter. In contrast, in salmon streams of the Pacific slope of the divide, you can catch Arctic grayling only in the middle and lower reaches of a river. They are never found on the upper 40–50 km stretches of mountainous streams with big gradients. This total absence of grayling in fast brooks and the upper parts of rivers is caused by competition with dwarf Dolly Varden. These numerous small fish eat the same food (invertebrates), occupy the same type of holding water (small pools), and have better adaptations to living in shallow streams with swift current. This strong competition forces Arctic grayling to go downstream, to stretches with lower gradients and bigger pools.

Arctic grayling is spawning in spring or early summer – usually during the period of the spring flood peak in this drainage. The spawning grounds are usually located in the side channels and sloughs, remote from the main channel, with a small current and a sandy-pebble bottom; the water in such places remains transparent even during floods. The spawning of the lake graylings can be observed not only in the inlets, but also directly in the lake near the shores.

The growth speed of Arctic grayling depends on the life conditions. These include the size of a lake or river, the duration of the open-water period, and the amount of available food. In big lakes and salmon rivers on the coast of the Sea of Okhotsk and Kamchatka, this fish can reach 0.8–1.2 kg in only seven to ten years. The record fish in the Russian Far East were caught not far from Magadan, in the Lake Chistoe (55 cm, 2 kg) and in the Yama River (53 cm, 1.8 kg). In the north (tundra zone) the grayling growth is much slower. Ten-year-old fish normally are 400–600 g, and the biggest specimens (sometimes up to 20 years old) here are only 1.2 kg. In small, mountainous lakes and creeks of the Upper Kolyma region around 900–1200 m in elevation, the dwarf, slowly growing grayling stocks are found. These grayling weigh 100–200 g at the age of 7 to 8 years.

Grayling populations are very vulnerable, in case of intensive fishery, their abundance decreases sharply, and the size of the fish decreases. The effects of fishing are exacerbated many times by deforestation and water pollution. Suspended sediments, discharged into the rivers by the placer gold mines, are very harmful for fish. The development of gold placers destroys the spawning grounds of grayling and other salmon fish, and their juveniles cannot grow and develop normally in constantly muddy water. Feeding conditions of adult fish also deteriorate sharply. Of course, its growth rate in such places decreases sharply. In the upper reaches of the “golden” Kolyma, where grayling used to be the most common fish, the longnose sucker, burbot, and common minnow predominates nowadays – these fish are better adapted to the polluted water.

Ilya Sherbovich