Consumption of Northern contingent Atlantic Mackerel (Scomber scombrus) by various predators

Abstract

Atlantic mackerel is a forage fish species preyed upon by various predators, including seabirds, pinnipeds, cetaceans, tuna and groundfish. We assessed the potential order of magnitude of total mackerel consumed by each of these groups, and any change therein. This is a first step to incorporate ecosystem considerations within the mackerel stock assessment and inform assumptions on the natural mortality rate. We concluded that an ensemble of predators is likely driving overall natural mortality patterns, with apparent changes in the relative contribution of each predator group over time. The reliability of consumption estimates varied between predators, but there was indication that overall absolute removals might have increased over time, despite possibly large interannual variations. Depending on the functional response between each predator and mackerel density, this increase could translate into a rise in the natural mortality rate, as estimated spawning stock biomass has been below or near the limit reference point since 2011. The likely increase in mackerel consumption is also inverse to changes in fishery landings; during the 10 last years (2012-2021) mackerel consumption by predators became likely at least twice as high as reported Canadian landings (<11 kt).