Getting the strait goods

An oceanographic research team uses creative ways to measure what’s going on in the Strait of Georgia

by Valerie Shore

Cross the Strait of Georgia by ferry over the next three or four years and there’s a good chance you’ll also be conducting oceanographic research.

Well, not you personally. But below you, deep in the bowels of the ferry, sophisticated instruments will be measuring water conditions as the vessel plies back and forth across the strait. What those instruments reveal may one day help fisheries managers predict changes in fish abundance.

“Our goal is to find out what it is that makes the Strait of Georgia a particularly good environment for fish in some years, but bad in other years,” says Dr. John Dower, a fisheries oceanographer in UVic’s department of biology and school of earth and ocean sciences. He’s part of a new research initiative known as STRATOGEM—the Strait of Georgia Ecosystem Modelling project—which seeks to understand the complex physical and biological dynamics at work in the strait.

“The Strait of Georgia is one of the most productive areas on the B.C. coast, particularly for juvenile fish, yet we know surprisingly little about how it works,” says Dower. To get some answers, he and STRATOGEM partners at the University of British Columbia (UBC), the Department of Fisheries and Oceans (DFO), and Parks Canada are focusing on three key physical processes: the Fraser River outflow, which carries vital nutrients; windstorms, which mix the water; and inflow from the open ocean, also a rich source of nutrients.

These processes—which vary annually, seasonally, daily and sometimes minute by minute—can combine to make conditions ideal or poor for the growth of plankton, the microscopic plants and animals that form the base of the marine food chain. “What we have to do is untangle how these processes condition the water column to be good or bad for plankton growth,” says Dower. “Then we can use ecosystem modelling to come up with rules about what makes a good or bad year for fish.”

But first they need the data. A constant problem with marine field work is getting out on the water often enough. The team has come up with two novel solutions. One is B.C. Ferries. By next spring, a ferry on each of the three main routes that cross the strait will be equipped with instruments to measure water temperature, clarity, salinity, and nutrient and plant-life content. “We’ll get snapshots of what’s happening in the surface waters several times each day,” says Dower.

To get the deeper 3-D picture, the team goes out monthly to nine test sites around the strait, where water samples are taken from surface to seafloor. Speed is critical. “The strait is such an active place, with tides, currents and the Fraser River plume, that we need to work as quickly as possible,” explains Dower. A traditional ship would do the circuit in two days. But a Coast Guard hovercraft, whisking along at about 80 kph, can do the job in eight hours.

By the end of the four-year project, the team hopes to have enough data for predicting trends in productivity in the Strait of Georgia. The hope is that fisheries managers will incorporate these environmental factors into their models for predicting salmon returns, for example.

“This could be the earliest heads-up they could have that we’re looking at a really strong or poor salmon run several years down the road,” says Dower. “It won’t be precise, because so many things can happen to these fish in the intervening years. But it’s a start.”

The STRATOGEM project is funded by the Natural Sciences and Engineering Research Council.

Not all plankton are created equal …

And this is what makes John Dower’s part in the STRATOGEM research so challenging.

As a fisheries oceanographer, Dower wants to know how physical processes in the Strait of Georgia—such as currents, tides, winds, the Fraser River outflow, and ocean inflow—affect the amount and distribution of plankton in the water. More plankton can mean more food for fish.

“My group is looking at how plankton distribution changes through the seasons across the sites we’re measuring in the strait, and how we can link those changes back to the sorts of physical measurements that my colleagues at UBC are interested in,” says Dower.

For years, it was believed that the classic marine food chain goes in a linear fashion from large phytoplankton (plant plankton) known as diatoms, to zooplankton, small shrimplike animals such as krill and sea lice. They in turn get gobbled by small fish, which become dinner for larger fish, and so on.

But it’s not quite that simple. In years with fewer windstorms to mix the water, smaller phytoplankton known as flagellates seem to predominate. They aren’t big enough to interest the zooplankton that fish feed on. So another step has to be added to the food chain to get things big enough for the fish to eat. And that’s not a good thing. “The more steps in the food chain, the less energy there is at the top for the fish,” says Dower.

That’s why precise measurements of phytoplankton species and abundance are so critical.

“In some years, conditions combine to create the right phytoplankton at the right time, which can lead to good fish food. That’s the argument we’re trying to make.”