I started this as my honours thesis at Memorial University, testing an idea from the textbooks: that a summer full of predators leaves fewer but bigger young cod. It won the VP Research Award and became my first paper as lead author.
Co-authored with Dr. Robert Gregory, Dr. Paul Snelgrove and Dr. Emilie Geissinger. Published in the Canadian Journal of Fisheries and Aquatic Sciences, 2024.
Young Atlantic cod spend their first summer in shallow eelgrass along the Newfoundland coast, and how they fare there shapes the fishery for years. The usual assumption is that predators pick off the smallest, so a summer with lots of predators should leave bigger survivors. Fisheries and Oceans Canada had been seining the same Newman Sound beaches every two weeks for more than two decades, which meant I could test that idea in the wild instead of in a lab tank.
Worked with my supervisors to turn a textbook assumption into a test I could run on existing field data.
Cleaned and structured years of beach-seine catches and fish lengths from 12 sites in Newman Sound.
Picked 15 years that split cleanly into many or few predators and many or few young cod, using cut-offs set from the long-term data, not chosen to fit a result.
Used each predator species’ mouth-size ratio to count only the fish big enough to swallow a young cod on each trip.
Measured how each season’s size spread shifted, then modelled length and size spread in R.
Published in CJFAS in 2024, with me as first and corresponding author.
Young cod grew biggest when both predators and other young cod were scarce.
That was the opposite of what I expected. In years with many predators, young cod came in every size and stayed smaller on average, rather than losing their smallest members.
With few predators around, young cod ended the season clearly bigger…
…but when young cod were crowded, predator numbers made almost no difference.
In the paper I set out why fewer predators meant bigger young cod. Here are a few of the reasons.
In the paper: .