Sunday, April 19, 2020


The thresher shark weighed about 400 pounds, and I had been pulling on it long enough that I had begun to worry that the fish might not survive the fight.

I usually release all of my sharks, but every now and then, one exhausts itself to the point that it effectively dies on the line.  That doesn’t happen very often, but when it does I never consider it much of a tragedy, because it typically happens with threshers, which are one of the best-eating sharks in the ocean.  A dead thresher just meant that I’d have a full freezer, and that a few of my friends would be eating fish, too.

But I didn’t want this particular thresher to die.  In part, that was because of its size; a 400-pound fish would yield more meat than I could reasonably eat, and it would be tough to find enough people who would take the excess.  I didn’t want any of the fish to go to waste.  Yet I also had a more basic concern. Many of our popular offshore food fish, including thresher sharks, have elevated levels of mercury in their flesh, enough to possibly cause health problems if too much of that flesh is eaten. 

“cautions parents of young children and certain women to avoid certain types of fish that typically have higher mercury levels: tilefish from the Gulf of Mexico; shark; swordfish; orange roughy; bigeye tuna; marlin; and king mackerel.  [emphasis added]”
There is probably a natural tendency to downplay the risk of such mercury contamination.  I’ve been fishing offshore for just about all of my adult life, and regularly ate shark and tuna without ever giving it much thought.  But then I worked with someone whose wife had an addiction to sushi, and ate it nearly every day, until a routine blood test revealed elevated mercury levels, and her doctor put her on chelation therapy as a result.  Not too much later, I was at my fishing club’s annual Christmas party, and one of the folks at the table, who spends a lot of time fishing offshore and eats an inordinate amount of tuna, mentioned that he had found himself in a similar situation, and had to undergo chelation therapy, too.

Fortunately, the last time I saw the big thresher, it still seemed strong and healthy as it swam away, because the idea of killing the fish was a lot less attractive than it once might have been.

Some of the mercury tainting fish flesh occurs naturally, but most is of human origin.  An article in Oceanus, the magazine of the Woods Hole Oceanographic Institution, explained that

“The biggest single source is the burning of fossil fuels, especially coal, which releases 160 tons of mercury into the air in the United States alone.  From there, rainfall washes the mercury into the ocean.
…High-sulfur (‘dirty’) coal tends to be high in mercury as well, and mercury tends to stick to sulfur.  When dirty coal burns, the mercury is released into the atmosphere along with the sulfur.  From there, they can be washed back to Earth by rain or they can diffuse directly into bodies of water.
“That’s bad news…because bacteria use sulfur in biochemical reactions that eventually convert the mercury into methylmercury, the highly toxic form that accumulates to deadly levels as it passes up the food chain.”
The good news is—or at least was—that the level of methylmercury in at least some offshore fish was beginning to decline.  Researchers at New York’s Stony Brook University conducted an extensive study of methylmercury levels in bluefin tuna, and reported that

“The date demonstrate that, while tissue concentrations were higher than in most other fish species, there has been a consistent decline in mercury concentrations in these fish over time, regardless of the age of the fish.
“The rate of decline parallels the decline—over the same time period—of mercury emissions, mercury levels in North Atlantic air, and mercury concentrations in North Atlantic seawater…
“…the finding appears to indicate that changes in mercury levels in fish tissues respond in real time to changes in mercury loadings into the ocean.  The study suggests that mercury levels may be improving as a result of declining coal use, reducing emissions that drift over the Atlantic.”

“The Trump administration on Thursday gutted an Obama-era rule that compelled the country’s coal plants to cut back on emissions of mercury and other human health hazards, a move designed to limit future regulation of air pollutants from coal- and oil-fired power plants.
“Environmental Protection Agency chief Andrew Wheeler said the rollback was reversing what he depicted as agency overreach by the Obama administration.  ‘We have put together an honest accounting measure that balances’ the cost to utilities with public safety, he said.”

“completed a reconsideration of the appropriate and necessary finding for the Mercury and Air Toxics Standards, correcting flaws in the 2016 supplemental cost finding while ensuring that power plants will emit no more mercury into the air than before.  After primarily considering compliance costs relative to the [Hazardous Air Pollutants] benefits of [Mercury and Air Toxics Standards], EPA is concluding that it is not ‘appropriate and necessary’ to regulate electric utility steam generating units under section 112 of the Clean Air Act.”
However, the Associated Press took a deeper look at the new EPA action, and observed that

“The EPA move leaves in place standards for emissions of mercury, which damages the developing brains of children and has been linked to a series of other ailments.  But the changes greatly reduce the health benefits that regulators can consider in crafting future rules for power plant emissions.  That undermines the 2011 mercury rule and limits regulators’ ability to tackle the range of soot, heavy metals, toxic gasses and other hazards from fossil fuel power plants.”
The AP also noted that

“EPA staffers’ own analysis said the [former] rule curbed mercury’s devastating neurological damage to children and prevented thousands of premature deaths annually, among other public health benefits.”

“one reason focus was placed on the freshwater angler scenario was increased confidence in modeling the exposure pathway given our ability to link patterns of U.S. [Energy Generating Utility] mercury deposition (relative to total deposition) over specific watersheds to sampled fish tissue concentrations in those same watersheds.”
Research linking mercury concentrations in saltwater fish with the mercury emissions from U.S. industry was supposedly not considered because in such research

“the authors utilize U.S. [Electric Generating Utility] deposition (as a fraction of total) in specific broad fishing regions (e.g., Atlantic) to estimate the fraction of methylmercury in commercially sourced fish caught in those broad regions attributable to U.S. [Electric Generating Utilities].  Both of these simplifying assumptions mask the potential complexity associated with linking U.S. [Electric Generating Utility]-sourced mercury to methylmercury concentrations in these commercial fish species.  In particular, a larger region such as the Atlantic likely displays smaller-scale variation in critical factors such as fish species habitat/location, patterns of mercury deposition, and factors related to the methylation of mercury and associated bioaccumulation/biomagnification.  In developing these kinds of more sophisticated models aimed at factoring commercial fish consumption into a benefits analysis involving U.S. [Electric Generating Utility] mercury, additional analysis could be needed to understand this critical element of spatial scale and the generalizing assumptions used by these authors in linking mercury emissions and deposition to commercial fish.”
The language used is telling.  The EPA never found any fault with the saltwater fish study.  Instead, it used speculative phrases such as “mask the potential complexity,” “a larger region such as the Atlantic likely displays smaller-scale variation,” and “additional analysis could be needed” to cast doubt on peer-reviewed science and avoid having to consider research that would militate against the agency’s desired conclusion.

For saltwater fishermen, and for anyone who enjoys consuming tuna, shark and other offshore fish, the bottom line is that the EPA has discounted mercury’s threat to their health, in order to relieve coal-burning utilities of the cost of complying with regulations designed to minimize mercury emissions.

So if you enjoy sushi, or a grilled thresher steak, the EPA is forcing you to decide whether having a good meal is worth putting your good health at risk.

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