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.
A
2016 paper, which appeared in the Marine Pollution Bulletin, called common
threshers an “elevated risk, low reward” food species, due to the relatively
high levels of mercury found in its flesh, while the United
States Food and Drug Administration has issued an advisory which
“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.”
The
Environmental Protection Agency downplayed the impact of the relaxed regulations,
saying that it
“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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