Because the seal's physiology restricts the flow of blood during the dive, peripheral tissues use muscles' oxygen stored with myoglobin and metabolized glycogen and starch to meet the body's energy demands. The harbour seal's chief predator is the killer whale. The seal must also be on the lookout for some shark species, and humans. The harbour seal is protected against commercial exploitation, but is still hunted by some native populations and may be shot by fishermen. New threats to harbour seal populations are pollution and the reduction of their food stocks.
Some seals die when they become entangled in fishermen's nets.
Parasites and disease are an increasing threat to a growing population. The Vancouver Aquarium Marine Science Centre has rescued and rehabilitated marine mammals for nearly 40 years. The goal of the program is to rescue abandoned marine animals and rehabilitate them for release into the wild. The majority of animals accepted and rehabilitated each year are harbour seal pups. She is 3 years old and weighs 33.80 kgs, and eats daily 1.5 kgs of herring.