Billions of tuna fish sandwiches and casseroles later, a new study is shedding light on the collapse of bluefin tuna populations that were once abundant off the coast of Northern Europe. The species virtually disappeared from the region in the early 1960s and is still rare today.

Photo Credit: Bluefin tuna fill a Danish auction hall, 1946 (Census of Marine Life – Blegvad, H. 1946. Fiskeriet i Danmark)

A team of ocean historians with the Census of Marine Life points to a 50-year burst of fishing from 1900 to 1950 that decimated the bluefin in the North Atlantic. Those findings come on the heels of the release by other affiliated researchers, of the latest results of modern electronic fish tagging efforts off Ireland and in the Gulf of Mexico. These modern methods reveal remarkable migrations and life-cycle secrets of the declining species.

The study of bluefin numbers in the North Atlantic used sales records, fishery yearbooks and other sources. What they found was that bluefins thrived in northern European waters such as the North Sea and the Norwegian Sea for a few months each summer until an industrialized fishery geared up in the 1920′s. After that, the floors of European fish market halls were filled with bluefin.

Back in the 1800′s, Danish fishermen welcomed the bluefin tuna as a partner in the catch of the garfish species. The bluefins pursued garfish into nets that fishers set close to shore. By the 1920′s, new fishing equipment enabled boats to haul in tons more at a time, and canneries soon opened, bringing tuna to the masses. The bluefin was also targeted by sport fishermen, further reducing its numbers.

The authors say the fish was a top predator in the North Atlantic ecosystem, feeding largely on herring and mackerel, squid and other species. By one estimate from the 1950′s, some 30% of all herring consumed by its predators in the area were eaten by bluefin tuna.

Experts believe there are two stocks of Atlantic bluefin tuna, one that spawns in the Mediterranean Sea, the other in the Gulf of Mexico and the Florida Straits. It’s theorized that the two stocks forage together in the North Atlantic and travel to opposite sides of the ocean to reproduce.