Listen to the Capelin

If you want to know the future of the fishery around Newfoundland and Labrador guess who you should talk to?

It’s a tiny fish that’s about 20 centimetres long and weighs in at 25 grams. When it’s trawled and dumped on the deck of the boat it smells like cucumber and its silvery underbelly sparkle like diamonds in the sunshine.

One more hint? Historically, it was a popular fertilizer and most people want at least one meal of it a year. You got it. It’s the Mallotus villosus, or to its friends, the capelin.

“A lot of people enjoy a good feed of capelin, as do many marine species as well,” says Department of Fisheries Research Biologist Fran Mowbray, Pelagic Fish Section Head in Newfoundland.

Pelagic fish live in the middle and upper portions of the ocean or lakes. Small pelagic fish such as capelin, herring and sandlance have a unique position in the food web and are important forage species, meaning they are food for marine fish, mammals, and birds. Mowbray has been working on small pelagic fish at DFO since 1993 and with capelin since 1999.

While capelin are small, they are a mighty important forage fish for two reasons. They are one of the most energy rich species which means that predators don’t need to catch as many to gain the same amount of nutrients. It’s like drinking a protein shake.

Their second important function is that capelin are sometimes referred to as the “canary of the ocean,” as capelin abundance, growth and maturation change quickly in response to changes in the ecosystem. In this way they give us a heads up when changes have occurred that may impact their predators or other marine life.

That’s a big job for a little fish. Plain and simple, capelin are the key.

Capelin are high quality, easy to access, and on the menu for species of every size. Other forage species and invertebrates feast on capelin eggs and larvae.

“Once the spawn is deposited it’s like the buffet is open. Flatfish and cod will come in and everybody will gorge. This is a smorgasbord for them. It’s not there for a long time but while it’s there it’s a great opportunity for a lot of different species.”

If the capelin larvae survive the feeding frenzy, “They’ve got a couple years to go to make it to spawning age, with lots of mouths out there who want to eat them as well as a variable food supply for themselves,” Mowbray said.

As the capelin grow larger, so do the species that feed on them. All ages of fish, seals, whales and seabirds snack away at the tiny fish.

Capelin swim in schools during feeding and spawning migrations, and seabirds take advantage and dive in for a quick bite. Like seabirds, whales come near shore, not just to draw in tourists, but in search of schools of capelin to feed on.

So, we know what eats capelin, but what do capelin eat? To answer this, we need to start at the basis of life in the ocean.

“It all starts with phytoplankton, a microscopic organism that gets its energy from photosynthesis, like many above ground plants and organisms. Then you have the zooplankton, aka bugs, that eat the phytoplankton, and the forage fish eat these zooplankton. The forage fish transform these zooplankton into valuable fat and protein that is then readily available to fish, seabirds and mammals.”

This means forage fish are the middle species in the marine food chain.

DFO has tracked capelin populations since the 1940s, but began counting them in earnest in the 1980s.

DFO uses several different methods to gather information about capelin. Every spring it uses a combination of hydroacoustics (otherwise known as fish finders) and trawls to determine the quantity and quality of capelin.

The Pelagic Fish Section also enlists citizen observations through science websites, such as e-capelin run by WWF, as well as a smaller group of dedicated enthusiasts who fill out daily spawning journals. They use this data to track changes in habitat use and timing of spawning.

“Knowing the number of capelin that spawned in a given year is important, but not as important as knowing how many will spawn next year and the year after,” Mowbray explained.

Capelin live short lives, with most initially spawning at age two or three and dying after. “The males have near a hundred per cent mortality and in a good year maybe 40 per cent of the females will live”. However, their predators live much longer.

“In order to use capelin abundance for management of species such as cod we need to be able project capelin abundance a couple years forward.” To that end, DFO has been surveying capelin larvae since the 1980s.

“Three decades of monitoring has shown us that capelin abundance is not driven by the number of eggs that are deposited, but by the environmental conditions those eggs experience when released. Environment is key to the survival of these little fish.”

In the fall of 2018, scientists will survey capelin over a larger area to gather information needed to provide an absolute estimate of capelin abundance throughout their area of distribution.

“Traditionally people have seen capelin in certain areas, but we never really know for sure where or when they are going to show up. These small fish are somewhat unpredictable.”

The amount of capelin is at a constant ebb and flow. “You can have tremendous year to year change in capelin abundance, from millions of tons to tens of thousands.” The spring capelin abundance index, which ranged in the two to four million-tonne range collapsed following a record cold year in 1991, and has never quite made it back to the same level,” Mowbray said.

“You know it’s a harsh environment out there and capelin take a huge hit when the feeding conditions and hatching conditions are poor.”

However, don’t count them out.

“Each female capelin produces thousands of eggs so when the environment is right the population can go from nothing to something remarkable. Years of study and monitoring are helping us understand some of the interactions involved in these changes. And, we are now focused on how best to use this understanding to forecast capelin abundance in years to come.”

Keep listening. Capelin may have small mouths, but they have a lot to say.