September 19, 2025 — The Slope Sea may hold a key to better understanding Atlantic bluefin tuna.
This summer, scientists journeyed to the Slope Sea on two exploratory surveys to examine how Atlantic bluefin tuna use this area for reproduction (also known as spawning). The first survey was a cooperative longline survey to look for spawning fish. The second survey followed closely on their heels to look for the results of that spawning—larval, or baby, bluefin tuna.
The objective was to document the potential contributions of spawning between the Slope Sea and other spawning areas like the Gulf of America. Next they will analyze DNA from both larval and adult bluefin tuna to estimate the population (stock) size. Atlantic bluefin tuna has been managed as having two primary stocks—one that spawns in the Mediterranean Sea (the eastern) and the other in the Gulf of America (the western). Recent research suggested the Slope Sea could be a major spawning ground comparable to the Gulf of America. Genetic research has shown the two stocks are interconnected. This year’s survey aims to clarify remaining uncertainties about bluefin tuna stock structure and spawning dynamics.