Using Northern gannet to study young-of-the-year mackerel



This research project funded by WWF-Canada and Fisheries and Oceans Canada aims to shed new light on the early life dynamics of Atlantic mackerel in the Gulf of St. Lawrence, Canada. Growth rate achieved during the first 3 months of life (proxy for survival potential) is determined using the otoliths of young-of-the-year (YOY) juveniles collected from the regurgitations of the Northern gannet, one of the main predators for the stock.



The last strong recruitment event for the mackerel stock occurred in 1999, and recruitment has been low since then with notable effects on the ecosystem the fishery. Declining mackerel biomass has impacted commercial landings, which have decreased from $30M in 2005 to less than $9M in 2015. During the same period, the Bonaventure Island Northern gannet colony, the largest in North America, has experienced a continuous decline. This colony comprises more than 100,000 individuals preying over a 200 km radius area centered at the heart of mackerel fishing grounds. Gannet readily regurgitate their stomach content when captured at their nests for monitoring purposes, offering an excellent opportunity to sample early juvenile mackerel stages that otherwise avoid both plankton samplers and commercial fishing gear.

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MSc student Safouane Khamassi joined the Northern gannet monitoring team during the summer of 2017 at Bonaventure Island from early June to late September. YOY mackerel appeared in the regurgitations as early as the second week of August, and were regularly sampled until gannet left the colony to return to their overwintering area in late September. Individual growth trajectories of juvenile mackerel are currently being derived from otoliths with the goal of describing potential periods of high growth-selective mortality prior to first winter, which could be interpreted as survival bottlenecks for this stock.