Why are Baikal Seal's eyes so big?

The Baikal seal, endemic to Lake Baikal, evolved from an ancestor of the Arctic ringed seal about 400,000 years ago, which is in contrast to the Paratethys species. Males and females of this small true seal species are very similar, but adult males are slightly larger than adult females

The Baikal seal (Pusa sibirica) belongs to the genus Pusa, along with two other species that make up this largely allopatric group: the ringed seal (P. hispida) and the Caspian seal (P. caspica). Baikal seals are a uniform dark silvery color with a grayish tinge on their backs and a lighter yellowish-gray on their bellies (Fig. 1). They are between 1.1 and 1.4 m long and weigh between 50 and 100 kg, with adult males being slightly larger than adult females.

Baikal seals (Pusa sibirica) and Caspian seals (P. caspica) share characteristics such as their small size, delicate skulls, and affinity for ice. According to mtDNA haplotypes, Caspian seals evolved from a common ancestral type of Pusa 60 million years ago and later became isolated in the Caspian Sea. Baikal seals evolved from an ancestor similar to the Arctic ringed seal and became isolated in Lake Baikal 40 million years ago (Sasaki et al., 2003).

This chapter analyzes the characteristics, taxonomy, distribution, abundance, and ecology of the Baikal (Pusa sibirica) and Caspian (P. caspica) seals. Both share characteristics such as their small size, delicate skull, and affinity for ice. According to mtDNA haplotypes, Caspian seals evolved from a common ancestral type of Pusa 60 million years ago and later became isolated in the Caspian Sea. Baikal seals evolved from an ancestor similar to the Arctic ringed seal and became isolated in Lake Baikal 40 million years ago. Baikal seals feed primarily on four species of fish: the greater golomyanka (Comephorus baicalensis), the lesser golomyanka (C. dybowskii), the yellowfin scorpionfish (Cottomefourus growndingki), and the longfin scorpionfish (C), all of which are of little commercial value. In captivity, an adult Baikal seal eats up to 5.6 kg of fish per day. 

Baikal seals are closely associated with the ice. In winter, when Lake Baikal is covered with ice, they can be seen in the lake, near vents. They give birth to their pups in ice caves (homes), similar to ringed seals, and also prefer to molt on the ice. In October, they move to bays and lakes where the ice first forms, occupying areas where they will later breed.