National Geographic : 2016 May
96 national geographic • may 2016 range increased too, with bears now turning up in peripheral parts of the ecosystem where they hadn’t been seen in decades. Grizzly bears are hard to count, but the latest estimate from the Interagency Grizzly Bear Study Team, in just the core area of the ecosystem (they call it the Demographic Monitoring Area), and using an arcane mathematical model to extrapolate, puts that population at 717 bears. In the entire ecosystem, Gunther said, “I think we could easily be up around a thou- sand.” Based on such numbers, on the trend over recent decades, and on their belief that the Greater Yellowstone Ecosystem is now about as full of grizzly bears as it can be, many of the state and federal bear biologists suggest that it’s time to remove the Yellowstone grizzly from the list of threatened species. This is controversial. Everything about the grizzly is controversial. Some conservationists outside the agency circle have challenged the population estimates, the positive prognosis, and the advisability of delisting. They’re concerned about the likely effects of renewed sport hunting and the long-term food security of the Yellowstone population. Although that list of grizzly food items is extensive and diverse, just a few of the 266 deliver far more caloric intake than any others: cutthroat trout from Yellowstone Lake at spawning time, ungulate meat, whitebark pine nuts, and an unusual insect that aggregates in Yellowstone’s high country, the army cutworm moth (Euxoa auxiliaris). Each of those is an intricate story within the big saga. THE OMNIVORE’S DILEMMA T he cutthroat trout is the only trout native to Yellowstone waters. Rainbow trout, browns, brookies, and lake trout are all exotics, brought in since the park was established. Yellowstone Lake was a stronghold for the Yellowstone subspecies of cutthroat, the lake’s feeder streams offering shallow, well-oxygenated waters where it could spawn. Kerry Gunther’s first job at Yellowstone, as a fishery technician, involved monitoring cut- throat spawners in Clear Creek, one of the major lake tributaries, where he remembers a count of around 32,000 cutthroat spawners in one spring and early summer, all clambering into the shallows to mix their sperm and eggs in gravelly spawning beds. Grizzlies, black bears, coyotes, and other predators made good use of this easy food source. The first grizzly that Gunther ever saw was a big, dark-colored bear he encountered while snowshoeing in at the start of May 1983 to count spawning cutthroat. Being on snowshoes was no doubt a good reminder that you should never try to run from a grizzly. By 2006 the season’s count at Clear Creek had declined to 489 fish, less than a hundredth of the former number—therefore less than a hundredth the fat and protein available to bears fishing there. The decline con- tinued, and spawning-fish counts in other tributaries around the lake have fallen almost to zero. Three factors, in deadly combination, account for this collapse: prolonged drought, especially affecting the Bears on the Rebound After grizzlies gained federal protection as a threatened species in 1975, their numbers in and around the park grew, as did their distribution. Annual counts of females with cubs (offspring under a year old) are used to estimate the total population—now large enough that the bears may lose their protected status. The Greater Yellowstone Ecosystem is the southern limit of the bears’ range, which once extended as far as Mexico.