World Ocean Census - Extract 6 - Unlocking the mystery of the disappearing tuna

23 January 2010

Sixth amazing extract from The World Ocean Census: A global survey of marine life: Painting a Picture of the past - Unlocking the mystery of the disappearing tuna .

Brian MacKenzie, a Census researcher at the Technical University of Denmark, focused his research on historic tuna populations in various parts of the North Atlantic, which ultimately turned him into a private detective. Rather than working in a traditional laboratory or field setting, MacKenzie spent an enormous amount of time in libraries, government buildings and other document repositories. Wading through catch records, newspaper clippings and old sportfishing magazines, he discovered that abundant bluefin tuna populations once existed in places where they are no longer found today.

MacKenzie’s investigation into the history of bluefin tuna was initially prompted by happenstance and then fostered by an insatiable curiosity. “I was sitting in a library one day and came upon a book about tuna in Danish waters written in 1949, when commercial and sportfishing of tuna took place. I started to read it out of curiosity more than anything else and discovered that there was a story there that really needed to be told. The book reported on bluefin tuna that were up to 200 kilograms in weight and 2 meters long – none of which are seen off the Danish coast today.”

MacKenzie and his colleagues were prompted to widen their investigation. They found that the rise and fall of bluefin tuna fisheries in northern European waters were replicated elsewhere: fisheries developed and crashed off the coast of Brazil and northern Argentina in the late 1950s and early 1960s, and the fishery in the Black Sea ended in 1986. These findings prompted MacKenzie to carry out further research. Today he deciphers how fishing and environmental variables, such as sea temperature, food abundance and water circulation, may affect the presence or absence of tuna in specific areas that may influence migratory and feeding behaviors. The goal of his team is to figure out exactly what happened to the bluefin tuna population so that changes, if needed, can be made to prevent such population declines from occurring again.

Text and images reprinted with permission from World Ocean Census: A Global Survey of Marine Life by Darlene Trew Crist, Gail Scowcroft and James M. Harding Jr., Firefly Books, 2009.

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