Spring at Sea

By Amie Arnet, Public Education Lead at Deep Bay Marine Field Station

When people think about spring, they often associate it with colourful flowers, baby animals and a time for renewal and warm weather following a cold, grey winter. These qualities of spring are not unique to the land as the oceans also have the same qualities during spring from migrating animals, blooming plants, and even their share of spawns and baby animals. Spring is an excellent season to enjoy the wonders of our oceans.

Spring is a very busy time for Pacific herring as an estimated 93 thousand tonnes of herring move inland to spawn usually near the end of March or early April. Female herring will lay up to 20,000 eggs in one spawning event. However, the survival rate is about one per 10,000 eggs. This is in large part due to high predation from other species. Herring are often called a “cornerstone species” as they represent only a fraction of biomass in the food web, but still play an important role in the larger ecosystem. The herring spawn has helped shaped some migratory systems to follow this sudden increase in biomass. The once endangered Brant goose relies on this abundant food source to obtain protein to complete its migration to northern breeding grounds. Larger animals such as Sea Lions also depend on this food source as they happily feed near the shore. The roaring of these “lions” is another great way the oceans welcome spring back to the coast!

As the temperature and daylight increases in the spring, it creates a welcoming environment for phytoplankton to bloom. Phytoplankton is a microscopic marine plant which is another important food source for many animals in the ocean ecosystem. Some blooms can be harmful, producing toxins, blocking sunlight or depleting oxygen in the water, but these are rare. When phytoplankton blooms in the spring, it causes the rest of the ocean to bloom as well.

Larger mammals also migrate back to the area during spring. Humpback whale sightings in the Salish Sea have been increasing in the spring in recent years. Humpbacks migrate from warmer breeding grounds such as Hawaii and Mexico to the cooler waters of the Pacific Northwest to take advantage of the increase in krill and small fish, such as herring. The population dropped to only 1,200 whales due extensive hunting until the 1960s, but now the whales are believed to have almost made a full recovery in the area.

When the snow begins to melt and the sunlight makes a longer appearance, it’s a great time to think of the sights and sounds of spring – Humpback whales breaching, sea lions roaring and Brant geese happily feeding on herring eggs.