Cutting new trails’ in assessing Northwest Atlantic fish stocks
Dr. Noel Cadigan and a team of Marine Institute (MI) researchers are trying to build better models to assess Grand Banks fish stocks.
These new models will account for how fish productivity – such as reproduction, growth and mortality rates – varies over time and space in the mathematical and statistical calculations used to evaluate those stocks.
The ultimate goal is to improve stock assessments and contribute to more sustainable fisheries management plans for Northwest Atlantic species, such as American plaice, yellowtail flounder, redfish and witch flounder (grey sole).
The work began two years ago with the appointment of Dr. Cadigan as the Ocean Choice International (OCI) Industrial Research Chair in Fish Stock Assessment and Sustainable Harvest Advice for Northwest Atlantic Fisheries.
“New assessment and ecosystem models that are able to provide stock-specific results will improve the evaluation of those stocks and lead to the development of precautionary harvest strategies and fishing operations that help preserve the structure, productivity and diversity of ecosystems,” said Dr. Cadigan.
“The real measure of success will be the adoption of our new assessment models by fisheries managers. We’re really cutting new trails here and that takes time.”
Time and space
As a quantitative fisheries scientist with MI’s Centre for Fisheries Ecosystem Research (CFER), Dr. Cadigan focuses on practical and theoretical marine population and ecosystem dynamics, statistical and mathematical modelling, and computational science.
He is also a cross-appointed member of Memorial’s Department of Mathematics and Statistics and spent more than two decades with Fisheries and Oceans Canada before joining MI. He says stock assessments focus on three basic questions.
“The basic objective of stock assessment models is to estimate the size of the stock and how that has changed over time. Once we assess these first two questions, then we provide advice on what the size of the stock should be. That’s the difficult one.”
To help with this, the research team is trying to understanding how different fish populations respond to their locations, changes in their ecosystems and to a changing climate.
They’re also trying to understand how mobility factors into their computations.
Dr. Cadigan says the spatial models for a highly mobile species, such as Atlantic cod, are very different than those for the less mobile American plaice and that one model does not fit all.
“A species’ mobility also depends on its life stage. American plaice may be highly mobile as larvae, but they seem to be less mobile as adults,” he said. “The adults are quite capable of long-distance movement, but they just don’t seem to do this often. The larvae are not actively mobile, it’s passive mobility.
“We want stock assessment models that use all available information on productivity,” he continued. “That’s the tough nut to crack. Most stock assessments just treat the stock over the whole area, so the big challenge is to bring the spatial variations into it.
Dr. Cadigan says they have spatial information, so they’re looking at how growth rates and maturation rates change over space, how mortality rates may change over space and how the level of fishing may vary.
The research team now numbers 11 people, including Dr. Cadigan: two junior research chairs, Dr. Gin Gao and Dr. Fan Zhang; two post-doctoral fellows; and six graduate students enrolled in MI fisheries science programs.
They’ve produced 10 peer-reviewed papers that have been published or submitted for publication and held three presentations and workshops, including last year’s Northwest Atlantic Redfish Symposium to review current scientific information on redfish and identify future research activities.
“The research chair enables us to educate the next generation of fisheries scientists in quantitative and computational methods for fish stock assessment,” said Tom Brown, director of CFER. “This will expand fish stock assessment expertise, advance our understanding of stocks and develop improved assessment tools to provide better harvesting advice and contribute to sustainable fisheries management plans.”
Through the Ocean Frontier Institute, Dr. Cadigan’s team is collaborating with other Memorial researchers, national and international experts, Fisheries and Oceans Canada, and industry. The Ocean Frontier Institute is a partnership between Memorial, Dalhousie University and the University of Prince Edward Island.
A sustainably managed ocean today and well into the future is a priority for Ocean Choice, says Blaine Sullivan, president of Ocean Choice International.
“This project demonstrates the tangible impact of academia, industry and government working together to improve science, and in turn, the sustainability of our marine resources to help ensure the fishery remains healthy and viable for future generations of harvesters and processors,” he said.
“As a locally owned fish harvesting and processing company, we have a deep commitment to sustainability. Over 90 per cent of the species that we harvest are certified under the Marine Stewardship Council or are under a robust fishery improvement program.”
The $2.5-million industrial research chair was funded by Ocean Choice International, the provincial government’s InnovateNL, the Robert and Edith Skinner Wildlife Management Fund at the Fisheries and Marine Institute, Ocean Frontier Institute and MI.