High on Mercury

The waters of Palm Beach County, Florida is one the last places on earth where you can see large numbers of Goliath Groupers like aggregated during the spawning season months of August and September.

Florida’s Goliath grouper are one of my favorite fish. In addition to being quite large, the unflappable nature and unique appearance of these animals make them great photo subjects, especially here off South Florida’s Palm Beach Coast where the underwater visibility is often very good and the local population is robust. The revival presence of these giant groupers have created a big-ticket attraction for local dive operations and the envy of dive destinations around the world.

The waters of Palm Beach County, Florida is one the last places on earth where you can see large numbers of Goliath Groupers like aggregated during the spawning season months of August and September.

This is especially true during August and September, the months these fish aggregate in large numbers to spawn. Jumping in the water to come face to face with 20, 30 or sometimes as many as 90 mature goliaths is a pretty special treat. But though populations have rebounded dramatically around Florida, life is not entirely rosy for these big fish.

Back from the Brink

By the late 1980s overfishing had decimated populations of goliath groupers in Florida waters. In 1990, the fish were placed under complete protection through a Federal Moratorium under the Magnuson-Stevens Fisheries Act initiated by NOAA’s National Marine Fisheries Service (NMFS). In the years since, goliath numbers have rebounded on both Florida’s east and west coasts, but their numbers were so low that another ten years would pass before spawning in aggregations would be documented.

Today, protection efforts are seen as a success, as mature fish can once again be found on reefs and wrecks, and spawning aggregations occur on an annual basis. But this recovery has also sparked strong opinions and divided emotions. Some special interest groups want the goliaths reopened to commercial harvest, and others push for limited recreational access. On the other side of the argument, those in favor of continued protection feel that the goliaths cannot handle the pressure of a harvest, which would quickly remove large breeders from the population and send stocks crashing. This fear is not unfounded. The Atlantic Goliath Grouper (Epinephelus itajara) as well as other members of its kind are in serious decline throughout the rest of the fish’s natural range. Outside of Florida, their numbers are now near zero; with organizations like the IUCN (International Union for Conservation of Nature) currently having them Red Listed as ‘Critically Endangered’.

While this argument goes on, an even darker specter is now emerging that threatens these fish: mercury. The same year goliaths were placed under protected status, the job of monitoring the species was put into the hands of scientists at both the National Marine Fisheries Service (NMFS) and Florida State University (FSU). FSU’s Research Ecologist, Dr. Chris Koenig, and his colleagues, began a detailed study of the fish’s natural history. My own introduction to Dr. Koenig’s research began during a Goliath grouper spawning aggregation survey trip in Florida’s southern Gulf Mexico in 2001.

Dr. Chris Koenig and his research team from Florida Atlantic University (FSU) conducting sampling from a live Goliath Grouper before releasing it back into the wild.
Dr. Chris Koenig and his research team from Florida Atlantic University (FSU) conducting sampling from a live Goliath Grouper before releasing it back into the wild.

Since then Chris has kept me up to speed on the latest findings as they continue to collect volumes of data using nonlethal capture and sampling methods from hundreds of Goliath groupers ranging between juveniles to full adults measuring 220 cm (7.2 ft) in length. The most recent information came from a MARFIN Project Final Report for NOAA on Regional Age Structure, Reproductive Biology and Tropical Patterns of Adult Goliath Grouper in Florida. Submitted by Florida State University (FSU) fish biologists, Chris Koenig and Felicia Coleman. In the report’s section on Diet and the Dynamics of Heavy Metal Contamination, FSU doctoral student, Chris Malinowski, found levels of methylmercury in adult Goliath groupers that were, to say the least, frightening.

Heavy Metal

Methylmercury, abbreviated as MMHg, is particularly nasty stuff with a propensity to accumulate appreciably in the tissues of fish, and to cause direct harm to the fish and to human consumers. This highly toxic compound was the cause of the worst epidemic of mercury poisoning in modern history. In the spring of 1956, residents of the Japanese city of Minamata came down with a range of symptoms that were the stuff of nightmares. These included acute ataxia (lack of voluntary coordination of muscle movements), numbness in the hands and feet, pronounced distortion of vision, hearing and even speech impairments sometimes resulting in complete loss of those functions. Even more dire symptoms of Minamata disease, as it was soon called, included insanity, paralysis and coma followed by death within weeks of the first onset of symptoms. It was eventually determined that these maladies were caused by eating fish contaminated with large amounts of mercury dumped into Minamata Bay from a nearby chemical plant. Birds, domestic animals and more than 900 people died from this contamination. Many more suffered sublethal effects.

For insights on methylmercury, I went to Christopher Malinowski, a Ph.D candidate who has been working with Dr. Koenig since 2012. Malinowski’s work started as a preliminary study after reading a paper on mercury concentrations in goliath groupers in one area of Florida’s west coast, published by FWC fishery biologist Douglas H. Adams and Christian Sonne in 2013.

Adams and Sonne’s work was based on tissue samplings from 56 goliath groupers (42 post-mortem), collected primarily from the Tampa area. These samples showed methylmercury concentrations levels in the muscle tissue of fish in a 4.5-year age range to average 0.63 ug/g (microgram per gram = parts per million [ppm]). Brain, gonad, kidney and liver tissue samples produced similar results. The highest levels were in livers, with concentration from around 2.87 ppm among juveniles as small 11.2 cm (4.4 inches), to elevations as high as 22.68 ppm among older fish that measured up to 218 cm (7.16 feet) in length.

“The Adams (2013) paper prompted my interest in how and where these fish were getting it, and how it impacts their health and survival,” Malinowski said during a phone conversation. He explained that expansions on that first study revealed not just patterns of accumulation, but also that these elevated methylmercury levels are not a localized event, but one impacting the fish through its entire range in Florida waters.

Goliaths spend the first five to six years of their life (a notably long time for a fish to spend in a nursery environment) among the mangroves found in estuarine habitats. By the time they are ready to move offshore and populate coastal reefs and wrecks, they are approximately 110 cm (3.6 ft) in length. Although they are technically old enough to breed at this point, another two to four years will pass before they start joining reproductively active adults during the spawning season. Data thus far shows that goliaths don’t reach peak fecundity till around 12 to 15 years of age, with the most viable fish measuring between 170 cm (5.6 ft) and 200 cm (6.5 ft) in length, tipping the scales between 250 and 500 pounds.

Malinowski began finding MMHg concentrations in the muscle tissues (filet portion) among the younger fish in the 140 to 160 cm range (approximately 7 to 10 years old) averaging 1.5 ppm, with maximum figures as high as 2.6 ppm. More disturbing, older fish in the 170 cm to 220 cm size class, concentrations were through the roof with figures as high as 4.5 ppm.

The graph above the linear regression between the total Hg (THg) amount of methylmercury (MMHg) levels found in muscle (measured in ppm) in relation the length (measured in cm) of Goliath Grouper Epinephelus itajara sampled in Florida. Here we can see that both sexes (males and females) show a significant relationship between Hg concentration and length (p
The graph above the linear regression between the total Hg (THg) amount of methylmercury (MMHg) levels found in muscle (measured in ppm) in relation the length (measured in cm) of Goliath Grouper Epinephelus itajara sampled in Florida. Here we can see that both sexes (males and females) show a significant relationship between Hg concentration and length (p<0.01), with males containing significantly more Hg than females(p< 0.05). All levels exceed U.S. EPA’s highest risk for human consumption (dangerous to eat): Hg = 0.3 ppm ww (Karimi et al. 2012), and NRDC health advisory limit; Hg = 0.5 ppm ww. Note: ww=wet weight, ppm=parts per million.

The US Food and Drug Administration’s “action level” (which the FDA may prohibit sale of fish) is 1.0 ppm. In comparison, the US Environmental Protection Agency (EPA) draws their red line for being dangerous to consume at 0.3 ppm, and Natural Resources Defense Council (NRDC), draws their line at 0.5 ppm. This is considered a “very high” threshold for human consumption.

While two-thirds of commercially caught fish and shellfish we eat are generally well below those numbers, there are some that are significantly above that range. Tilefish from the tropical Atlantic and Gulf of Mexico fall in at the top of the EPA’s list, averaging 1.45 ppm of mercury. Swordfish and large species of sharks (mako, thresher, lemon, sandbar, etc.) come in second and third averaging anywhere between 0.97 and 1.00 ppm of mercury, where as King mackerel makes fourth place averaging 0.73 ppm of mercury.

Doing simple calculation, using that 0.1 microgram per kilogram of body weight and apply it to a 200-lb. (90 kg) person could consume a total of 9 micrograms of mercury in one day. Using the figures for King mackerel and multiply it with the weight of a standard serving size of six ounces (about 170 grams), the total dosage of mercury you would be ingesting will be (0.976 x 170 grams) 124.1 micrograms. Not good. Whereas the exact same size portion of Goliath grouper, with concentration level of 4.5 ppm of methylated mercury will be six times higher at a whopping 765 micrograms.

To put it into perspective, the EPA’s current reference dose – the amount of methylmercury to which an individual can be exposed on a daily basis without adverse health consequences – is 0.1 micrograms per kilogram of body weight per day. Subsequently, the amount of Goliath grouper that the same 200-lb. individual could safely consume (using the EPA’s 0.1 micrograms per kilogram of body weight per day) would amount to a maximum of 2 grams, which would hardly amount to one mouthful.

I don’t know about you, but I think the very notion of eating a fish with that much mercury in it would be very unwise.

Canary in the Coal Mine

Think Minamata disease is confined to humans? Think again. In addition to finding methylmercury levels in the muscle tissue of goliaths to be as high as 4.5 ppm, Malinowski determined that concentration levels in the fishes’ internal organs like the liver were as high as 32 ppm. Equally worrisome, several of the larger fish from which tissue samples were extracted also displayed active lesions on their gills, liver, and kidneys.

These finding showed that, not only is there a correlation of high mercury levels in relation to age among Goliath groupers, but also that these fish are not immune to the ravages of long term mercury poisoning. The saturation levels FSU is finding in the goliath population are showing blood chemistry health results consistent with malnutrition, disease and lower disease resistance, cell damage, and nerve and muscle functioning. The result of these health impairments, and mercury offloaded by females into their eggs, could be reduced growth and development, viable offspring, mobility, and survival rates.

It is findings such as this that show that Florida’s Goliath groupers may very well serve as the proverbial canary in the coal mine. What is affecting them is most likely a result of what humans are doing to their environment, which will come back to haunt us one day. Maybe it already is.

 

Editor’s Annotations: This article was first published in DAN’s Alert Diver Magazine Spring 2017 issue, as well as posted on their website AlertDiverOnline.com