Mercury Levels in Saltwater Fish Caught by New Jersey's Recreational Anglers: Low Risk from Most Species

(from Jersey Coast Anglers Association November 2010 Newsletter)

In the early morning fog on Barnegat Bay Inlet, we watch fishermen gather in small boats, each one with two or three fishermen. Even the faint chill cannot dampen the thrill of fishing, the faint swell of the surf, and the freedom of the open water. Common Terns drift low over the gentle swells searching for schools of Bluefish, whose own feeding will drive schools of small bait fish to the surface where the terns can catch them. When the terns begin to coalesce into a dense swirling flock, dipping toward the water, the fishermen take note and begin to move toward the action. The bait fish, Anchovies, Silversides, or Herrings, are trying to avoid the voracious bluefish feeding from below, and the terns diving from above. Terns dive downward from the thick mass of swirling birds, each successfully plucking a fish from the frantic school swirling at the surface, forced up by a hungry school of Bluefish just below them. The terns flash white as they gather and dive, flashes that can be seen from miles away by other terns and by fisherman. We’ve enjoyed the frenzy ourselves, pulling up a Bluefish on every rod before the fish and birds disperse. Of course electronic fish finders and GPS have supplemented tern-watching, as clues to locating fish schools.

We have spent the last twenty-five years studying mercury, lead, cadmium and other metals in fish and wildlife, often near heavily contaminated sites, like Superfund waste sites, former nuclear weapons factories of the Department of Energy sites, and contaminated harbors and bays. For the last seven years, however, we have been working with the Jersey Coast Anglers Association (JCAA), and the Jersey Coast Shark Anglers (JCSA) to examine levels of mercury in fish caught by recreational fishermen along the Jersey shore. It is an exciting project because recreational fishing is an important cultural and economic part of New Jersey life.

We’ve spent a lot of time in recent years at the docks for various New Jersey tournaments, sharing the excitement of the weigh-ins. After admiring the large Mako, Tuna, Striped Bass, Fluke or Bluefish, we ask permission, and take a small, thumb-sized core of flesh from each fish for heavy metal analysis. We have done similar sampling at tournaments around the State and have received samples of other fish from fishermen.

Fishing is Important for New Jersey Residents

Fishing is important to New Jersey, both as a commercial and recreational enterprise worth about $2 billion annually, as well as contributing to the $16 billion dollar coastal tourism income. Fish are an important source of protein, and fishing is a popular pastime all over the World, including our urban areas, such as the New York-New Jersey metropolitan area and along the coast. But fish are also our main source of mercury exposure, and we have been studying mercury in fish for many years. Over the years our studies, often involving interviews with anglers fishing along the Jersey shore and in the NY-NJ harbor, have shown that unlike many freshwater fishermen, people fishing along our coasts eat most of the fish they catch. Many fishermen eat more fish than EPA or FDA recognize as “typical”. Also there is a wide range of information and interest about mercury in the fish they catch, and many people do not know which fish have low mercury levels, and which have high levels. We started this study to provide information to the fishermen themselves about which fish had high or low levels of mercury, and might pose a risk, particularly to pregnant women and their offspring.

Fish are tasty and nutritious, however, they are also the major source of mercury exposure for the general public, and people who eat fish frequently, “high-end consumers” we call them, and who eat fish that are high in mercury, may develop symptoms of mercury poisoning. These people are likely to find their way to specialty clinics, like the Clinical Center at New Jersey’s Environmental and Occupational Health Sciences Institute (EOHSI), where we work. These cases (mostly stemming from eating commercial fish and tuna sushi) prompted us to investigate the levels of mercury in a variety of fish. It is well known that certain predatory fish such as Shark, Swordfish, and large Tuna, are high in mercury, but which fish are low in mercury, we wondered. Now after several years of study and analysis, we have some answers.

Benefits and Risks of Eating Fish

Fish is a good source of protein and nutrients, particularly as an alternative to red meat. Fish offer high quality protein, low in cholesterol, and omega-3 polyunsaturated fatty acids (PUFAs) which promote cardiac health and baby development. Over the past 15 years, people have responded to the health benefit messages by eating more fish. Adults who eat fish frequently (once a week or more) generally have lower cholesterol and a reduced risk of heart disease compared to those eating fish less than once a month. Likewise, pregnant women who eat fish are less likely to have low birth weight babies than are those who don't eat fish.

However, contaminants in fish, such as mercury and polychlorinated biphenyls (PCBs), can cause health problems, especially in unborn babies and children. And the mercury in fish counteracts some of the benefits of the PUFAs.

Government Agencies and Fish Consumption Advisories

Different state and federal agencies issue fish advisories telling people a few of the fish species to avoid because of high contaminant levels. The Food and Drug Administration issued advisories based on methylmercury that pregnant women and women of childbearing age who may become pregnant should avoid eating four types of marine fish (shark, Swordfish, King Mackerel, and Tilefish), and should limit their consumption of all other fish to just 12 ounces per week (see FDA.gov website). While this is helpful, it does not tell people what fish they can eat safely.

People who fish or like to eat fish are interested in what fish are low in mercury. It is easy to guess which fish are at the top of the food chain and will be high in mercury (shark, swordfish), but not whether medium-sized predatory fish (Bluefish) or bottom dwellers (flounders) have dangerous levels of mercury. Also, age and size are important because older fish have longer to accumulate mercury than do younger fish. Guessing isn't good enough!

Our research with mercury levels in fish purchased in supermarkets indicated that the levels in some fish are sufficiently low as to provide little risk, even to high end consumers, while this is not the case for other species. Swordfish and fresh tuna steaks had the highest levels, and were in the range that could potentially provide health problems for unborn babies (see JCAA article on Toxins in Fish, January 2005). People who want to eat fish more often need to know the relative levels of mercury in fish so that they can make their own decisions about which to consume and which to avoid. Our study is aimed at providing this information for recreational saltwater fish.

Our study of "Mercury in New Jersey Coastal Fish"

Our objective was to determine mercury levels in fish species commonly caught by recreational anglers in New Jersey's bays, estuaries and the ocean, and to understand whether these levels varied in different parts of the state, or different seasons and how these vary with size of fish. We enlisted both individual anglers and clubs from the Jersey Coast Angler’s Association, and from the Jersey Coast Shark Anglers to help us collect a range of different species of fish, with a range of sizes of each type of fish. In many cases, we went to fishing tournaments, and took a small sample for fish at the time of weigh-in, and we also went out with DEP sampling boats to obtain some smaller fish for comparison with those that fit the legal size limits. This study was unique because it involved collaboration between anglers and scientists, between fishing clubs and scientists, and it involved fish that people are actually catching and eating (rather than only those caught by electroshocking, seines, or other trap methods.

Total mercury was then analyzed in our laboratory at Rutgers University and the Environmental and Occupational Health Sciences Institute. About 90% of the total mercury in fish is methylmercury, the most highly toxic form of mercury.

Findings to Date on Mercury Levels in New Jersey’s Coastal Fish

The results for mercury in parts per million (micrograms of mercury per gram of fish muscle) are shown in Figure 1 below. In this figure, the vertical line is the average or mean value, the box represents 25th and 75th percentiles, the horizontal line indicates the range of values for that species, and the number of fish analyzed (n) is given on the right. Thus for any species on the graph, 25% of the fish had mercury levels that fell below and 25% of the fish were above the small box. It is apparent that for some species, particularly tournament species, we had very large samples that yield quite reliable mercury results, while other species are under-represented. Overall, mercury levels vary by fish species, with some species being consistently high. Large predatory species have higher mercury levels than smaller species that feed on plant or invertebrate marine organisms. Mako Shark had the highest levels, followed by Bluefin Tuna, Striped Bass, and Bluefish. The lowest levels were in Ling, Bonito, Dolphin, Winter Flounder, Triggerfish, Porgy, and Fluke.

In general, mercury levels increased with the length (and weight) of the fish for Bluefish, Mako Shark, Striped Bass, Windowpane, Dolphin (Mahi Mahi), Fluke, Southern Kingfish, Ling, Porgy, and Atlantic Croaker . That is within each of these species, larger fish had higher mercury levels than smaller fish, suggesting that given a choice, it is better to eat the smaller fish. The figure below shows the increase in mercury with size for Bluefish and Striped Bass. Fish that are below the legal size range were obtained from NJDEP fisheries trawls.

We also found that mercury levels were generally higher in fish from southern New Jersey, and can vary seasonally, as shown in the following graph for Striped Bass. But we’ll write more about that another time when we have more samples.

Basis for Health Risk Calculation

The U.S. Food and Drug Administration have set a level of 1 ppm of methylmercury in fish. This is not a risk-based level. In our samples only a few Striped Bass and Bluefish, and most Mako, exceeded 1 ppm. Our results are for total mercury of which about 90% is methylmercury. Other agencies provide health-risk based values of how much mercury one can ingest per day with impunity. The Environmental Protection Agency has calculated a Reference Dose for methylmercury of 0.1 microgram per kilogram of body weight per day. In other words, a 70 kilogram (154 pound) adult should be able to consume up to 7 micrograms of mercury per day without adverse effects. At a higher level of consumption, the mercury will accumulate in the body, and is likely to cause symptoms. However, the Centers for Disease Control and Prevention uses a more lenient Minimal Risk Level of 0.3 micrograms per kilogram per day, which could be consumed over a 70 year lifetime without adverse effect. This would be equivalent to 21 micrograms per day. There are reasons behind both numbers.

Assuming that a dinner portion of fish weights 8 ounces (227 grams), and that the mercury concentration is only 0.1 parts per million (0.1 micrograms per gram of fish), 8 ounces or 227 grams would provide 22.7 micrograms of mercury, which slightly exceeds the more lenient CDC level. Thus such a “high end consumer” (8 ounces per day) should be eating fish that have even lower mercury levels. There are people who eat 8 ounces of fish per day, although eating fish 3-4 times a week is more common.

Overall, the research shows that many fish taken by NJ fishermen are relatively low in mercury and do not pose a threat. Those that average below 0.1 ppm generally will not pose any threat to people who eat them 3-4 times a week. In the graph, this includes the species from Ling to Fluke. Among commercial fish, Tilapia and Catfish are examples of species with less than 0.1 ppm on average.

On the other hand, consuming on a regular basis fish with levels over 0.3 ppm (0.3 micrograms per gram) should clearly be avoided by pregnant women and small children. This includes canned white or Albacore. People who eat fish several times a week should choose from the lower mercury species, while an occasional high mercury meal should be OK for adults. The data acquired in this study will allow fishermen and their families to make informed decisions about which species to eat, and how much to eat. We look forward to our continued studies with the fisher people of New Jersey.

This work would not be possible without our dedicated field and laboratory personnel: Chris Jeitner, Mark Donio, Taryn Pittfield, and Sheila Shukla. We thank Tom Fote and Clubs of Jersey Coast Anglers Association, Fred Beigert and Brad Porrion of the Jersey Coast Shark Anglers, the many members of the tournament voluntary committees and of course the many fishermen who allowed us to or requested that we take samples for analysis.

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