Unlike human nostrils which remain open at all times, the relaxed nostril position for pinnipeds is in a closed position. Like this harbor seal (Phoca vitulina) they voluntarily open them when at the surface of the water to sniff or breathe.
[Photo and caption by Karli Chudeau]
Berta, A., Sumich, J.L., & Kovacs, K.M. (Eds.). (2006). Marine Mammals: Evolutionary Biology (2nd ed.). pp. 244-250. San Diego, CA: Academic Press.