Friday, March 28, 2014
WHAT CHEATS ALASKA HUNTERS OF MORE MOOSE: WOLVES AND BEARS, OR INSECTS AND HARES?
Dr. Stephen Stringham
January 25, 2012
For years now, the Palin/Parnell Board of Game has been trumpeting the claim that moose and caribou populations across Alaska are being kept below carrying capacity by predation. They’ve ignored rebuttals by numerous biologists that some of our moose populations are actually at or above optimum density, and are suffering as a consequence from malnutrition, pathogens, and increased vulnerability to harsh weather and predation. Recent newspaper articles by retired agency biologists Rick Sinnott and Vic Van Ballenberghe are particularly informative.
Their critics reply that even where moose are eating themselves out of house and home, some of these hoofstock are still being eaten by wolves and bears. The fewer moose that end up in predator bellies, the more can end up in human bellies. Even if we succeed in harvesting only one in ten moose that wolves would have killed, that’s still one more moose for our dining tables. End of story.
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Or is it. There is a vast scientific literature on predator-prey relationships. This covers not just wolves and bears preying on moose and caribou, but a huge range of species. In case after case, we find that predators can benefit prey populations by reducing the spread of pathogens (diseases and parasites) and by reducing competition from other herbivores. The issue is one of balance. Under what conditions do benefits outweigh costs? Under what conditions, if any, do wolves or bears indirectly help more moose or caribou survive than these predators kill?
Contrary to what some people might think, asking this question isn’t some kind of Liberal plot to trick Alaskans into sacrificing our traditional lifestyle as hunters. Just the opposite. It’s a “plot” to save our lifestyle.
If, Heaven forbid, you ever come down with cancer metastasizing throughout your body, you wouldn’t thank a doctor who refuses to consider any treatment but surgery because he doesn’t believe in medication or radiation. Nor should you thank a Board of Game that refuses to diligently consider any alternative to exterminating predators because killing is their single solution to all problems.
Elsewhere in North America, some moose populations are being devastated not because of too many predators, but because of too few to minimize spread of ticks, lung worms, brain worms and other pathogens. Anyone interested in this should pay particular attention to the wolves and moose of Isle Royale in Lake Superior. Although this is an island population of moose that can’t go anywhere else to escape from wolves, the moose have survived and often become so numerous that they are debilitated by malnutrition and parasites. They don’t get enough energy and minerals from their food, leading to bone disease. Parasites suck their blood, cause horrendous hair loss, and infect their brains. Debilitated moose are called “walking carrion.” If wolves get them before harsh weather does, these moose become predation statistics. If winter wins the race, they get eaten anyway, but now as scavenging statistics. Bad though pathogens are at Isle Royale, without culling of debilitated animals by wolves, infestation rates might be much higher. So we’ve got to wonder how important wolves are for limiting the spread of pathogens among our own moose?
A second role played by predators is limiting competition with other prey species for food. That’s particularly important where there isn’t enough food to go around -- which is currently true on the Kenai Peninsula. Food production has been shrinking rapidly for the past few decades (see Rick Sinnott’s Nov. 17 Alaska Dispatch analysis for details). Worse, a lot of the remaining food is being eaten by other herbivores. Among the most voracious are snowshoe hares, whose abundance can vary more than 100-fold between periods of scarcity and peaks like the current one. Browse is also lost to a plague of insects and plant pathogens such as Geometrid moths, Bruce spanworm, sawflies, fungi and root rot. (Read the article by Dr. John Morton, supervisory biologist for the Kenai National Wildlife Refuge).
Loss of moose foods to hares, rodents, insects, and pathogens, are all pieces of the carrying-capacity puzzle. Putting them together suggests a picture something like that shown below: Total food supply declining, insects and pathogens taking an increasingly large fraction of that total; snowshoe hares cycling with a peak roughly every decade, and moose having to survive on the fraction of food that’s left over.
Dr. Stephen Stringham illustration
That diagram is designed just to illustrate basic concepts, but not to represent the exact amounts of food grown or lost to each of those competitors or the exact height and timing of peaks in the hare cycle. Also, the jumps in carrying capacity after the 1947 and 1969 fires aren’t shown. But the basic pattern should be realistic enough to illustrate how the current bottleneck in carrying capacity happened.
Can carrying capacity be restored? Perhaps. For various reasons, wildfires and pesticides won’t solve the problem. So our best option may be reducing numbers of snowshoe hares far below the current peak and keeping them from rising so high in the future. The only method I see is enhancing predation on hares by owls and other raptors, as well as by mammalian carnivores such as lynx, fox, coyote, and wolf.
Wolf too? Yes. Arctic hares are a primary prey of wolves in the far north. Our local snowshoe hares are somewhat smaller, but they are also far more abundant, especially during periods like this. As hare numbers rise, there are more of them to catch; and they become easier to catch because of increasing malnutrition, disease, and parasitism. This is when wolves could take the biggest bite out of the hare population.
Better yet, the more that wolves feed on hares, the less they are likely to feed on moose. The relationship is probably shaped something like the following sketch.
How much does the diet of wolves shift from moose to hares as hare abundance increases? Dr. Stephen Stringham illustration
That much is common sense. To manage wolf-moose relations, we need ballpark figures for the percents of wolf diets that are made up of moose meat vs. hare meat at any density of moose and of hares. Hopefully, Alaska Department of Fish and Game (ADF&G) biologists are finally free to provide the answers.
Now back to our earlier question: Under what conditions, if any, do wolves or bears indirectly help more moose or caribou survive than these predators kill? Common sense suggests that when moose are well-fed, the only benefit they’d gain from predation on hares might be preventing hare numbers from peaking in the future. By contrast, when hare numbers are so high that moose become malnourished, hare predation by wolves could free up food for moose. I suspect that the relationship is similar to the following sketch:
One possible way that positive and negative influences by wolves on moose might relate to moose food supply. When moose food is scarce, due for instance to competition from hares, does wolf predation on hares benefit a moose population more than wolf predation on moose harms the population? Dr. Stephen Stringham illustration
A radical idea isn’t it? Whereas reducing numbers of predators might be a good idea when moose populations are predator-limited and alternative prey are scarce, just the opposite strategy might be advisable when moose populations are food-limited and hares are abundant -- as now appears to be true on the Kenai Peninsula.
To maximize food supply for moose, how many wolves would we need; how many coyotes, foxes, lynx, owls and other predators that eat hares?
In summary, wolves could benefit moose populations by curbing the spread of pathogens and by reducing food competition from hares. If there are any circumstances where those benefits to moose can compensate for wolf predation on moose, shouldn't wolf management aim at optimizing wolf abundance rather than on minimizing it?
These questions need to be answered now, before wolves and bears in 15A and 15C are decimated. Not the kind of comic-book biology answers we’ve been force-fed by the Board of Game for the past several years, but the kind of answers that only professional wildlife biologists can provide. Alaska has some of the world’s finest. Now that Corey Rossi is gone, maybe ADF&G will unmuzzle them so that they can provide us with the full benefit of their intelligence.
Recall the old adage: “Look before you leap.” That’s just as important in predator-prey management as in warfare. Inaccurate “intelligence,” coupled with panic and ulterior motives, launched us into a war with Iraq which has torpedoed our national economy and ruined the lives of thousands of Americans. The same kind of panic talk -- exterminate the wolves before they exterminate the moose -- is the ultimate justification for rushing into “intensive management” on the Kenai Peninsula. Rather than succumbing to panic, we need to make sure that drastically reducing wolf and bear numbers won’t do more harm than good.
Dr. Stephen Stringham, president of WildWatch LLC is a consulting wildlife biologist. He began his career researching moose on the Kenai Peninsula and went on to help pioneer a new strategy for managing hoofstock populations that markedly increases their productivity -- a strategy that inspired Alaska’s own management of moose and sheep. He earned his doctoral degree studying bears, then investigated predator-prey relationships. For the past two decades, his research has focused on wildlife behavior, the subject of his many newspaper articles and several books, including the Alaska Magnum Bear Safety Manual and When Bears Whisper, Do You Listen?
The views expressed here are the writer's own and are not necessarily endorsed by Alaska Dispatch. Alaska Dispatch welcomes a broad range of viewpoints. To submit a piece for consideration, e-mail commentary(at)alaskadispatch.com.
Posted by @Adelheid16 at 2:52 PM