Spring graduate Matthew Robertson aims to create fish population models that contribute to more sustainable fisheries.

For his PhD thesis, he set out to explain why two species of flatfish — yellowtail flounder and American plaice — followed diverging paths of recovery after the collapse of both stocks in the 1990s.

Mr. Robertson says stock assessment models try to track the size of the population over time and, right now, is basically an exercise in counting fish: how many born, how many die, how many of those deaths come from the fishery.

“We know the ecosystem also influences those things,” he said. “So, we’re trying to figure out new ways to include this information because we’re working towards ecosystem-based fisheries management.”

On June 1 Mr. Robertson receives his doctorate in fisheries science during spring convocation at the St. John’s Arts and Culture Centre. His family travelled from his hometown of Hampton, N.H., to attend the ceremony.

He also has a new job as a research scientist with the Marine Institute’s Centre for Fisheries Ecosystems Research, where he’ll continue the work he began as a student.

‘Awesome scholarship’

In 2020 Mr. Robertson received the Vanier Canada Graduate Scholarship, valued at $50,000 per year for three years of doctoral studies.

“It’s an awesome scholarship to get. I was lucky and I was able to continue my research unhindered by financial challenges.”

He completed a bachelor of science (honours) in marine biology in 2016. Two years later, he received a master of science in oceanography from Louisiana State University, where he studied local monitoring of small-scale fisheries in the East African country of Tanzania.

Switching climates

Working on his master’s degree persuaded him to return to a cooler climate for his PhD.

“I realized I liked Atlantic Canada’s climate a lot more than the southern U.S., and I really like Newfoundland and Labrador,” he said.

When he’s not modelling fish populations, he spends his time walking in the woods with his dog, an Australian shepherd that needs plenty of exercise.

He also squeezes in time for touch football and Ultimate Frisbee and his new fly fishing hobby.

Flatfish collapse

Mr. Robertson says the collapse of flatfish stocks was a combination of fishing and environmental pressures, such as cold water temperatures, on the Grand Banks in the late 1980s and early ’90s.

Yellowtail flounder quickly recovered, while American plaice have not.

“American plaice were actually more cold tolerant historically, and they were more distributed in the northern part of the Grand Banks, and that seems to be the part that was the hardest hit. In the spatial modelling I did, we saw that almost all the fish in the north were gone after the early ’90s, while many in the south remained.”

Team building

Mr. Robertson is building a research team called the Fish Ecology and Stock Assessment Lab to continue the work he started with his doctoral degree.

He is recruiting a master’s student to study predator-prey dynamics on the Grand Banks using stomach-contents data from Fisheries and Oceans Canada.

“We’re trying to see if there are new ways to understand prey populations.”

They’ll examine forage-fish species, such as sand lance, capelin or northern shrimp. Sand lance are tiny, eel-like fish that burrow in sandy seafloors, leaving only its head sticking out to safely eat plankton.

“They live on the southern Grand Banks and haven’t received as much attention as other forage fish, but they’re really important. They have a big influence on flatfish and cod.”