Investigating the suitability of the Slope Sea for Atlantic bluefin tuna spawning using a high-resolution ocean circulation model

Abstract

Motivated by recent evidence of Atlantic bluefin tuna spawning in the Slope Sea, we investigated the spatio-temporal distribution of oceanographic conditions that are conducive to successful spawning by bluefin in this region. Specifically, we considered advection patterns and water temperatures based on a new high-resolution ocean circulation model. After validating model velocities and temperatures using observations, three criteria were used to evaluate the success of simulated bluefin spawning during 2013: water temperature at spawning locations, mean water temperature along larval trajectories, and larval residence time within the Slope Sea. Analyses of satellite-based, decade-long (2008-2017) datasets suggest that conditions, specifically water temperatures and advection patterns, in the Slope Sea in 2013 were representative of typical years. The temperature criteria are more frequently satisfied in the southern and southwestern parts of the domain, whereas the residence time criterion favors more northern areas further from the Gulf Stream. The probability map of successful spawning locations shows a maximum near the northwestern bight of the Slope Sea. Spawning success is near-zero through most of June, increases in July, and peaks in early-to-mid August. Overall, water temperatures and retentive capabilities suggest that the Slope Sea provided suitable conditions for successful spawning of bluefin during 2013.