Giant liver fluke playing big role in deaths
By Mike Lynch
Continuing research on Adirondack moose is showing that the population is holding steady despite challenges associated with climate change, parasites and traffic on roads, according to a state wildlife biologist.
Jim Stickles, a wildlife biologist with the state Department of Environmental Conservation, told the Adirondack Park Agency board at its Oct. 17 meeting in Ray Brook that surveys have shown there are about 716 moose within its jurisdiction.
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“We haven’t seen any evidence that it’s going down, so it’s at least stable,” Stickles said. “And if it is growing, it’s growing slowly.”
In recent years, the state has been conducting studies on moose with research partners, including Cornell University. The studies are helping the DEC draft a management plan for the large animal but are also allowing scientists to better understand why the population hasn’t grown like those in neighboring states.
One of the reasons appears to be parasites.
In a recent study in the northern Adirondacks led by Cornell University doctoral candidate Jen Grauer, scientists found that parasites, particularly giant liver flukes, were common in moose that had undergone necropsies by state biologists.
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Of the 191 necropsies performed between 2000 and 2022, 60 died in motor vehicle accidents, 25 were killed by gunshots and 23 died by parasites. Grauer attributed the majority of gunshot wounds to DEC officers euthanizing diseased or injured animals.
But perhaps a more telling stat is that of 162 moose studied, 82 had giant liver flukes.
Giant liver flukes are parasitic flatworms carried by deer and moose that can grow up to eight centimeters long. In moose, they can cause liver failure and ultimately death. The large animals are especially vulnerable when they are suffering from other infections.
The necropsies are often done on animals that die in the frontcountry. Researchers have also tracked collared animals in the backcountry to learn more about them.
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Those studies found giant liver fluke to be the leading cause of death. In a study that tracked 29 juveniles, there were 12 deaths including eight from giant liver fluke. Research on adults that were tracked showed a similar percentage dying from the parasite.
“Parasites are currently seeming to be the biggest threat to moose, particularly the giant liver fluke,” Grauer said. “These threats do seem really driven by the presence and sometimes the abundance of white- tailed deer on the landscape and their overlap with moose.”
The giant liver fluke numbers were considerably higher than other parasites. For instance, scientists found 22 of 173 animals necropsied contained brainworms.
Findings were similar for tapeworm — 20 were found in 165 animals. Eight of 18 animals tested positive for neospora, a parasite found in coyotes and foxes that was only discovered to be an issue in recent years.
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Giant liver fluke and brainworm are believed to be passed on to moose by deer, which host the parasites but appear to be unaffected. Deer pass giant liver fluke on through their feces to snails and slugs, which shed them in wetlands. Moose then pick them up when feeding on aquatic vegetation.
Deer populations have increased in portions of the Adirondacks in recent years in places such as Clinton County, the Champlain Valley and the Lake George region.
The increase in numbers has been partially attributed to warmer winters, which cause less stress on the animal because there is more food and less snow. The increase in temperatures is also believed to be a negative for moose, which evolved in colder climates.
Infections from winter tick, which die off after a first snow, is another ailment of concern because the parasites have been found to be killing moose in other northeastern states. The tick is being found on Adirondack moose but not in large numbers that kill animals, Stickles said.
Top photo: A moose hangs out near the Saranac River in July 2019. Photo by Mike Lynch
Our poorly thought out game management in NYS that favors deer herd population over moose is obviously problematic. Simply put, you can’t have high populations of both. They have evolved differently and ranges tend not to overlap much. Add to the equation that there are no effective predators to either species in NYS and the problem is exacerbated.
Current white-tail deer populations in many areas dramatically overbrowse the forests to the point where they effect the health of the flora and fauna of woodlands of different types. DEC does not seem to be addressing this elephant in the room – too many deer in too many areas. Event current hunting pressure does not seem to be reducing numbers – especially in areas where effective hunting is essentially illegal near massed human habitation, villages, towns, and cities.
Frankly, I am surprised we still have ADK moose with the current state of the forests. I think the only reason they hang on is their abiity to use sub-surface aquatic plants as a major source of food, and the fact that the Park has a great deal of wetlands that allow this. But deer infitration into these areas obviously increase the risk of brain and liver parasites for moose. An effective predator in these areas would be beneficial. But this is a hard sell given our centuries-old penchant to persecute predators of all sorts. Messed up priorities of the self-appointed Masters of Nature.
“Humankind is challenged, as it has never been challenged before, to prove its maturity and its mastery – not of nature, but of itself.” Rachel Carson, 1962
Aye
Deer populations in the Adirondacks, where we also have moose, are relatively low. Just a few deer per square mile. It is estimated that we currently have less than 2 deer per square kilometer currently in the Adirondacks. Where I hunt the forage that moose and deer choose are quite different. Moose mainly sticking to things like willows and the like that deer don’t browse on.
What is “relatively low”? Apparently not low enough to allow for a large moose population. The populations will always find a cyclic balance because of food, disease, reproductive rate, and predation, but we may not like the result. Managing wildlife species naturally does not really allow for human preference for one species over another. The deer/moose population balance will always be in flux – that is how Nature works. But putting our thumbs on the scale is rarely helpful for both species. Using hunting instead of natural predation to manage populations has its limitations.
This is just another reason why the region needs more wolves. Ecosystems need large predators to cull weak, sick, and old animals. When deer populations are too high, they overbrowse, and when moose populations are dense, they are more likely to spread parasites and diseases. These species evolved alongside one another, and humanity has thrown that balance out of wack.
Exactly… Humans with weapons don’t have the God given senses to know which animals to take out. That’s why we have predators like wolves (and cougars to a lesser extent). But sadly there are those who don’t want them around.