Their main food source is the golomyanka, a cottoid oilfish found only in Lake Baikal. Baikal seals eat more than half of the annual produced biomass of golomyanka, some 64,000 tons.[1] In the winter and spring, it is estimated that more than 90% of its food consists of golomyankas.[2][9] The remaining food sources for this seal are various other fish species, especially Cottocomephorus (about 7% of the diet during the winter and spring) and Kessler's sculpin (about 0.3% of the diet in the winter and spring), but it may also take some invertebrates such as Epischura baikalensis, gammarids and molluscs.[4] During the autumn the Baikal seal eats 50-67% fewer golomyankas than in the winter and spring, but significantly more Cottocomephorus, Kessler's sculpins and stone sculpins.[4] A total of 29 fish species have been recorded in the diet.[4] They feed mainly during twilight and at night, when golomyankas occur in depths as shallow as 10–25 m (33–82 ft).[1][4] During the day, golomyankas are typically found deeper than 100 m (330 ft).[1] Baikal seals can dive up to depths of 400 m (1,300 ft)[4] and more than 40 minutes.[1] Most dives last less than 10 minutes and generally only 2–4 minutes.[1] Baikal seals have two litres more blood than any other seal of their size and can stay underwater for up to 70 minutes if they are frightened or need to escape danger.