Blue Ocean Institute

Mar 18th

Giving Swordfish the Green Light (and a red flag)

Many years ago I had a job where I had to sort through old files containing papers that related to several authors’ past proposed book projects. Most had been successful, resulting in a book being published – sometimes to great acclaim, other times not – but a few that had started out promisingly had never come to fruition. The documents were in chronological order, and as I quickly moved through time – sometimes advancing an entire year in just a few pages – I could see when and how a project had jumped the tracks. It was very sobering to see that so many good ideas – projects that take years of the authors’ lives to put together – never see the light of day.

This week, I had an experience that was, in some ways, the exact opposite of that. I dug into the history of the resurgence of swordfish populations from being at a point where they were so severely overfished that they were on the brink of commercial extinction. (Commercial extinction is defined as a state when so few individuals of a species are left – and thus the effort and expense to find and catch them so great – that that it is no longer profitable to fish for them.)

My interest in the history of fish population rebuilding was recently piqued when I heard that 21 commercially important fish species have been rebuilt since 2001 through effective fishery management.  I rooted around and found some archived articles that chronicled the events as they happened.

Swordfish are prolific breeders and for years it was thought that their populations were resistant to fishing pressure because they reproduced so readily. That turned out to be a false assumption. As swordfish populations dropped, environmentalists tried to steer policy toward protecting them. A campaign was launched to bring attention to the plight of the swordfish and reduce their popularity in the marketplace. It became clear that legislative action was going to take a while. Meanwhile, back in the ocean, one of the major problems faced by the swordfish population was that fish were being caught when they were so young that they hadn’t yet had a chance to reproduce. This resulted in fish being taken out of the water without any chance to create a replacement population, creating an inevitable – and dramatic – decline in numbers.

In 1999, the International Commission for the Conservation of Atlantic Tunas (ICCAT) established a ten year rebuilding plan for North Atlantic Swordfish to protect their nurseries. This plan has proven to be successful and the most recent Swordfish population assessment conducted in 2009 indicated that the population in the North Atlantic Ocean is now above levels that scientists have identified as a healthy population.

Since swordfish populations are currently abundant enough to withstand commercial fishing pressure, Blue Ocean Institute’s seafood guide now lists Atlantic and Pacific Swordfish as rating a light green ranking and Mediterranean Swordfish as yellow.  But… perhaps you will notice the small red flag that indicates that these fish may contain levels of mercury that pose a health risk.

The mercury that enters the ocean – and ultimately is ingested by the fish that dwell there – originates at coal burning plants. Efforts are underway to help the public understand the threat posed by eating fish high in mercury and the threat to human health overall as a result of the pervasive spread of mercury throughout the environment.

My happiness at swordfish’s resurgence was dampened, of course, by the knowledge that even though their populations are rebuilt, we now need to monitor our consumption carefully to make sure that we don’t expose ourselves to too much mercury for our personal situations. It differs for everyone: pregnant women, women of childbearing age, and children need to be most careful. And, of course, I can’t help but wonder what mercury exposure does to the health of the swordfish themselves as well as other top predators. (Being a top predator makes a difference, because as a swordfish eats smaller fish – each of which has bioconcentrated the mercury to which they themselves have been exposed – it means that the large predator is eating concentrated amounts of mercury.)

I am hoping that one day I will be able to flip through old copies of Audubon magazine – perhaps from the year 2015 or 2020 – and reminisce about the successful campaign to reduce mercury in fish by limiting the emissions from coal burning plants.

We’ll see.


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