Researchers investigating causes of death in the
common loon (Gavia immer) have often noted some mortality from ingestion of lead
fishing tackle, but the extent of the problem varies widely from region to
region. In 1992, Dr. Mark Pokras of Tufts University published a paper
showing that 52% of the dead loons he examined from New England (16 of 31
adult birds) died from lead poisoning due to ingestion of lead sinkers.1
His report was recently updated to include more loons collected through the
year 2000. In this sample, 44% of the dead adults (111 of 254) died from
lead-tackle ingestion.2 But several other studies, including two
conducted in Minnesota and one in Wisconsin and several other states, have
noted much lower lead-related mortality rates—from 1.9 to 6.5% (below).
Status of Minnesota Loon Population
Minnesota has more loons than all other states combined, excluding Alaska. In the 1980s, the Minnesota DNR’s rough estimate of the state’s loon population was 10,000 birds. Today, the agency places the number at about 12,000. Since 1994, the DNR has conducted an annual loon monitoring survey that serves as “an early warning system” to detect changes in the loon population. The survey shows that the loon population is holding steady. In the latest report (May 2000), program coordinator Rich Baker concludes that “Minnesota’s common loon population remains healthy in both number of adults and number of juveniles observed within the index areas.” 3
Pokras study drew much attention to the loon/lead issue, prompting the
Environmental Protection Agency (EPA) to propose a nationwide ban on the
manufacture, sale and use of small lead and zinc sinkers in 1994. But after a
groundswell of public opposition, the agency withdrew its proposal because there
was not enough data to support it. Three eastern states (New York, New Hampshire
and Maine) have imposed some type of lead ban to address their own
A bill that would ban the sale and use of lead sinkers and various other types of fishing tackle containing lead has recently been introduced in the Minnesota Legislature. Proponents maintain that lead fishing gear is ingested by water birds, particularly loons, causing lead poisoning and endangering the Minnesota loon population.
Causes of Loon Mortality in Minnesota
There is no disputing the fact that some lead sinkers and jigs are ingested by loons and cause lead poisoning. But lead poisoning appears to be far down the list of mortality causes in Minnesota. There have been two Minnesota studies that address the loon/lead issue, one published by the Minnesota Pollution Control Agency (PCA) in 1992 4 and the other by the Minnesota Zoo in 1998.5 Here are the causes of death found in these studies:
(56 adult loons)
|Summary-The PCA study was intended to assess the effects of mercury
on loons; the findings on lead poisoning were incidental. There was no
attempt to determine if the lead poisoning was a result of ingestion of
lead fishing tackle or some other form of lead. However, one of the
study’s authors recalled that out of 6 adult loons that died from lead
poisoning, “about 2 or 3” had lead sinkers in their bodies, so the
mortality rate was 5.4%.
The PCA report states, “Seventeen percent of the necropsied birds died of lead poisoning.” But that figure is misleading because it represents the percentage of diseased loons (41 birds) that died of lead poisoning (7 birds; 7/41=17%), not the percentage of total adult loon deaths (56 birds) that died from ingestion of lead sinkers (3 birds; 3/56=5.4%). The latter statistic must be used to make a fair comparison with the Pokras study and other similar studies.
There is no reason to believe the authors were
concealing the facts; the study was simply not intended to evaluate lead-tackle
ingestion in adult loons, so the results were not stated in those terms.
Unfortunately, the anti-lead forces have chosen to put their own spin on the
(p. 6), frequently reporting the 17% rate rather than the 5.4% rate.
The PCA report also identifies other possible causes of lead poisoning including ingestion of spent lead shot and ingestion of sediments or organisms containing lead.
Together, the two Minnesota studies analyzed 102 dead adult loons for lead poisoning and found that only 5.8% (6 birds) had died from ingesting lead sinkers. Although the studies were not designed to evaluate loon mortality from ingestion of lead fishing tackle, the low mortality rates are validated by a much more comprehensive study published in 1999 by the National Wildlife Health Center (NWHC) in Madison, Wisconsin.6 The study, “Prevalence and Effects of Lead Poisoning Resulting from Ingestion of Lead Fishing Sinkers and Other Fishing Tackle on Selected Avian Species,” examined 2,749 birds of various species. Of these, 313 were healthy, sick or dead common loons collected from nine states: Minnesota, Wisconsin, Maine, New York, New Hampshire, North Carolina, Florida, California and Alaska. The following table breaks down the results:
Lead-Tackle Ingestion/Death Rates – NWHC Study
Sick (brought in from rehabilitation centers)
with lead tackle
Lead-Tackle Ingestion Rate
Lead-Tackle Death Rate
loons that had ingested lead tackle eventually died in the rehabilitation
One interesting aspect of this study is that none of the 48 dead loons examined died from ingesting lead fishing tackle. Of the 156 sick loons, only 6 had ingested lead tackle and they subsequently died. X-rays indicated lead tackle in 5 of 109 healthy loons, but none of the birds showed signs of lead poisoning. In all, 1.9% of the loons tested (6 of 313) died of lead-tackle ingestion. This finding is especially surprising in that some of the loons sampled came from New England. Even if all the loons that had ingested lead tackle were to die, the combined death rate would only be 3.5%, slightly lower than that found in the Minnesota studies.
Other notable sidelights:
•34 of 109 healthy loons examined were from Minnesota; none had ingested lead fishing tackle.
•Historic records at NWHC reveal that only 4.1% of dead loons (14 of 340) collected from various states (mainly in the Midwest) over a 25-year period had ingested lead tackle. These are not the same birds examined in the current study.
There is no doubt that the 44-percent mortality rate in the Pokras study is too high. But what about the 5.8% rate seen in the Minnesota studies? We all would prefer to see no lead-related loon deaths, but biologists are more concerned about the welfare of the population than the fate of individual birds. Nobody knows what the tolerable mortality rate should be, but as long as the loon population is holding up at an acceptable level, there is no immediate need for a lead ban.
In the PCA study, 22% of the loons tested for mercury contamination had levels high enough to impair reproduction. Even though mercury levels were not identified as a direct cause of death, the study warned that “Mercury contamination may threaten loon populations in Minnesota.” Similar mercury levels were seen in the Minnesota Zoo study. Even though mercury may not have killed these loons, it would have affected their ability to reproduce had they survived. Mercury may have also contributed to their death by weakening them to the point where they were more susceptible to predators, infection, boat collisions and other threats.
Gill nets have long been identified as a serious problem for loons. The birds may accidentally swim into a net while diving for fish, or they may spot a fish gilled in the mesh and try to catch it, ensnaring themselves. But the extent of the problem is unknown, because the dead loons are rarely turned in to authorities.
The skyrocketing popularity of personal watercraft also spells trouble for loons. The birds prefer solitude, particularly at nesting time, and the incessant commotion or intentional harassment of nesting birds by irresponsible jetskiers and boaters may cause loons to abandon their nests. There have also been documented cases of jetskiers intentionally running over loons and chicks, or chasing them until they are exhausted. Judy McIntyre, Director of the North American Loon Fund, identifies jetskis as the greatest current threat to breeding loon populations.
But all causes of loon deaths pale in comparison to oil spills and disease outbreaks that occur when the birds concentrate in coastal areas or on the Great Lakes. In late fall of 1983, for example, 592 dead loons washed ashore on Lake Michigan in the Upper Peninsula. The birds died from botulism acquired by eating sick or dead fish. And in the spring of 1996, an estimated 400 loons were killed by a large oil spill off the coast of Rhode Island. The latter birds were not included in Pokras’ study because “full necropsy data was not available.”
While Minnesota studies found that only 5.8% of loon
deaths were a result of lead-tackle ingestion, the figure was an alarming 44% in
Pokras’ New England research. But not all studies have found New England
lead-mortality rates to be so high. Of all the New England loons examined in the
NWHC study, only 7.5% (4 of 53) had ingested lead sinkers. The NWHC study
included any loons that could be collected (dead or alive), not just dead
Although the rates were much lower in the NWHC study, there is no doubt that lead-sinker mortality is higher in New England than in other parts of the country. The variance appears to be a result of the different character of lakes (and loons) in the two regions. Pokras points out that the heaviest incidence of lead poisoning occurs in a heavily fished 5-lake region in New Hampshire. The lakes, most of which are only a short drive from Boston, are deep, clear, infertile and very heavily developed. As he described the situation, “on weekends, you can walk across the lake from boat to boat.” There are practically no natural nesting areas, so the birds nest on floating platforms installed by loon-preservation groups. The loons commonly hang around docks and fishing boats, hoping to pick up lost or discarded bait, a behavior that greatly increases their odds of ingesting fishing gear. Adding to the problem is the fact that the lake basins have a high density of lost sinkers that are easy to see because the bottoms are so clean.
Fortunately, the unusual circumstances that result in so much lead ingestion in these New Hampshire lakes do not exist in Minnesota. Our loons are not nearly as tame, our lakes are not as crowded, the bottoms have a lighter density of sinkers, and most bottoms are silty, so a lost sinker or jig would simply disappear in the loose material.
Sinker density in different regions was investigated in a 1999 study conducted by the Arizona Cooperative Fish and Wildlife Research Unit.7 Researchers used metal detectors to search for lost or discarded lead-tackle items along the shorelines and in the shallows of various lakes, then made estimates of the abundance of various tackle items. No Minnesota lakes were surveyed, but in one Wisconsin lake (Turtle-Flambeau Flowage), researchers found an average of 1.2 sinkers/acre. This compares to a rate of 202.4 sinkers/acre in Umbagog Lake on the New Hampshire-Maine border and 404.7 sinkers/acre on the Missisquoi Refuge, Vermont. While this small sample is far from definitive, it sheds some light on why the lead-mortality rate in New England studies is so much higher than in Minnesota-Wisconsin studies.
In an attempt to assess sinker density in deeper water, researchers swam transects in two New England lakes (Umbagog and Rangely Lake, ME) using metal detectors to collect a variety of tackle items. Their findings were surprising in that they recovered more lead bullets (not shot) than lead sinkers. In Umbagog, the divers recovered an average of 16.2 sinkers/acre and 20.2 bullets/acre. In Rangely, they found 28.3 bullets/acre and no sinkers. Together, the recovery rate was 8.1 sinkers/acre and 24.3 bullets/acre, meaning the density of bullets was exactly three times a great as the density of sinkers. One can’t help but wonder: Have other researchers been missing something? And are lead sinkers getting too much of the blame for loon deaths?
A recent paper, “Lead poisoning in North American Wildlife from Lead Shot and Lead Fishing Tackle,” 8 shows how an environmental organization (HawkWatch International) can skew the results of a study to suit their own purposes. Their paper misrepresented the findings of the PCA study by stating that “17% of adult loon deaths in Minnesota could be traced to lead poisoning from fishing tackle.” The statement is deceptive for two reasons. First, the 17% death rate resulted from lead poisoning in general, not poisoning from lead tackle specifically. Second, the calculation does not represent the percentage of lead poisoning in “adult” loons; it is the percentage in all diseased loons, including juveniles and chicks. The rate of lead poisoning in adult loons was 10.7%, and half of that (5.4%) could be attributed to ingestion of lead tackle.
Although Pokras’ studies present an unbiased
evaluation of the data he collected, there are some indications (besides the
NWHC data) that the real lead-tackle mortality rates in New England are much
lower than his studies indicate. If the dead loons from the 5 New Hampshire
“hotspot” lakes are removed from Pokras’ sample, the mortality rate is
reduced from 44% to about 25%. And if the 400 loon deaths from the Rhode Island
oil spill are added to that sample, the rate drops to 9.7%, a much less ominous
What would be Banned?
The bills introduced into both the Minnesota Senate and House are considerably more restrictive than those passed in other states. Although the intent of the Senate bill’s author was to ban only small lead sinkers, the language of the bill would also ban a wide variety of fishing lures. For purposes of this legislation, a "lead sinker" means a device that: (1) contains lead, (2) weighs one ounce or less, (3) is designed to be attached to a fishing line, (4) is intended to sink the fishing line.
Since the bill bans any “device that contains lead,” any sinker or lure made of brass or other materials that have even a small amount of lead would be banned as well. Besides sinkers weighing 1 ounce or less, the ban would include split shot, jigs, weighted hooks, bottom walkers, jigging spoons, brass casting spoons, bladebaits, tailspins, Jigging Rapalas, weighted spinners, ice flies, nymphs and other weighted flies, even spinnerbaits with lead heads and crankbaits with lead rattles. For many anglers, this lead ban would mean junking most of the tackle they own.
Proponents of a lead ban say there are many good substitutes for lead and that the cost of converting to lead-free tackle would be “only pennies a year” for the average angler. But these contentions are not factual. Some Minnesota tackle companies have done extensive studies on lead substitutes and have been marketing some lead-free products. The problem is, most lead-free materials cost considerably more, and don’t work as well as lead because they’re lighter for their size. And some of these materials have another downside: They can’t be molded onto a hook to make jigs or other lures because their melting point is so high that the hook would be damaged. Here are the best alternatives known at this time:
•Iron. By far the cheapest alternative, iron has some major drawbacks. Because it has a high melting point, it can’t be cast like lead and instead must be formed as a pressed powder then heated to a temperature that will fuse the powder. Iron is much more difficult to shape than lead and weighs 30% less. Sinkers made of iron cost about 20% more than their lead counterparts and will rust in your tackle box. It is not feasible to make iron jig heads.
•Tin. Easy to cast because of its low melting point, tin makes a decent substitute for split shot because it is flexible enough to pinch onto the line. But it weighs 36% less than lead and is slightly toxic. Tin sinkers and jigs sell for twice the price of their lead counterparts.
•Tungsten. Like iron, tungsten must be formed from powder, but it must be heated to a much higher temperature to fuse it into a hard form. Consequently, it cannot be used for jig heads. The big advantage to tungsten is that it’s 70% heavier than lead. But tungsten sinkers cost 10 times as much as their lead counterparts and have another big drawback: The manufacturing process leaves a sharp burr on the hole of the sinker, so a nylon tube must be inserted to prevent cutting your line. A 4-pack of tungsten sinkers (1/4 oz.) sells for about $6.00 at Wal-Mart.
•Bismuth. This material weighs only 14% less than lead and is non-toxic. But bismuth is very brittle and may break if it strikes a hard object, so it must be combined with another material like tin. Bismuth is very difficult to mold because it expands when it changes from a liquid to a solid. Jigs and sinkers made of bismuth cost about 4 times as much as their lead counterparts. The price of a single 1/4-ounce bismuth-tin alloy jig head from Havoc Fishing Products (recommended on Minnesota DNR web site) is $2.89. A 1-ounce bismuth bucktail jig would sell for about $7.00.
Estimates of the cost of restocking a tackle box with lead-free sinkers and lures range from $50-$100 for a casual angler to $200-$500 for a serious one. And for a die-hard walleye, bass or muskie fisherman, the cost could well reach into the thousands.
Other economic downsides: A lead ban may deter some non-residents from fishing in Minnesota because the cost of restocking their tackle box would be prohibitive. Many will opt for a destination where there is no lead ban. Tackle manufacturers would suffer because of the expense of retooling, inability to sell their current inventory and lower sales for alternative products. Tackle-shop owners would also be stuck with their existing stock of lead sinkers and lures. The bill will put an end to a legitimate “cottage industry” in which hundreds of bait shops and other small businesses throughout Minnesota make and sell their own sinkers and jigs. But it will promote a “black-market” in lead tackle that will discourage manufacturers that are in compliance. Most importantly, increased tackle costs would discourage new anglers, especially kids, from getting into the sport.
From a practical standpoint, a lead ban would be nearly impossible to enforce. From a distance, an enforcement officer would not be able to tell whether or not an angler was using lead, and the illegal tackle would be removed or the line cut if an officer approached.
While there may be good reason for a lead ban in parts of the Northeast, there is no evidence to justify a ban in Minnesota. Nevertheless, the fact that the common loon is Minnesota’s state bird will generate a lot of passionate testimony by the anti-lead forces. They will produce gory photos, reams of studies from other states and even sinkers removed during necropsies that will appear to show that our loons are in trouble. But the fate of lead fishing tackle should depend on fact, not emotion. And the fact is—Minnesota loons are faring well.
Even Minnesota DNR loon experts are opposed to the lead-ban bill that has been introduced. Carroll Henderson, head of the DNR’s Nongame Wildlife Program, says there is a lack of current data on lead poisoning of loons in the state and believes more studies need to be done. “I don’t see that we would be supportive of any legislation like that at this point,” he said. “It’s before its time.”
Despite the lack of evidence to justify a lead ban, Minnesota tackle manufacturers will continue to research lead-free alternatives that can be used to produce fishing gear at an affordable cost. Without an economical alternative, many anglers will be priced out of the sport should there be a lead ban.
Pokras, Mark A. and R. Chafel. 1992. Lead toxicosis from
ingested fishing sinkers in adult common loons (Gavia immer) in New England. Journal of Zoo and Wildlife Medicine
Sidor, Inga F., Mark A. Pokras, Andrew R. Major, Kate M.
Taylor and Rose M. Miconi. 2003. Mortality of the Common Loon in New England.
Tufts University School of Veterinary Medicine, North Grafton, MA 01536.
Baker, Richard J. 2000. Minnesota loon monitoring
program, 6-year report: 1994-1999. Minnesota Department of Natural Resources,
Nongame Wildlife Program, St. Paul, MN 55155.
Ensor, Keren L., Daniel D. Helwig and Lauren C. Wemmer.
1992. Mercury and lead in Minnesota common loons (Gavia immer). 1992. Minnesota Pollution Control Agency, Water
Quality Division, St. Paul, MN 55155.
Pichner, Jimmy and Peregrine L. Wolff. 1998. Causes of
morbidity and mortality in the common loon (Gavia
immer). Minnesota Zoological Gardens, Apple Valley, MN 55124.
National Wildlife Health Research Center, Madison, WI
53711. 1999. Prevalence and effects of lead poisoning resulting from ingestion
of lead fishing sinkers and other fishing tackle on selected avian species.
Duerr, Adam E. and Stephen DeStefano. 1999. Abundance of
lost and discarded fishing tackle and implications for waterbird populations in
the U.S. Arizona Cooperative Fish and Wildlife Research Unit, Tucson, AZ 85721.
Sanborn, Wendy. 2002. Lead poisoning of North
American wildlife from lead shot and lead fishing tackle (draft). HawkWatch
International, Inc., Salt Lake City, UT 84155.
The Early Bird, Jeff Sundin
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