Species Introductions/Population Dynamics
Caribou Reintroduction in the Great Lakes

Wolf-Moose-Beaver population variance

Woodland caribou were hunted off Isle Royale in the 1920s; the last known animal was shot by a hunter in 1925.
Caribou are now absent from the entire U.S. side of the Great Lakes region and were listed as a Federally
Endangered species in 1983. Caribou reintroductions have met with variable success in the Great Lakes region.
The main causes for failures have been poachers, disease, and predation. The presence of white-tailed deer, as
carriers of the parasitic disease “brainworm” precludes caribou reintroduction because like moose, caribou are
highly susceptible to this pathogen. The presence of wolves and bear also precludes successful reintroduction since
the populations of caribou are not high enough to withstand the predation. In areas where these stressors are
absent, caribou reintroductions have been very successful. National Park policy dictates that animals which were
clearly removed from Parks by the actions of man should be reintroduced to the landscape whenever feasible.

The reintroduced caribou populations which occured in the mid 1980s in Ontario were acquired from the Slate Islands. Caribou
introductions in areas without wolf and white-tailed deer have been very successful (Long 2003, Bergerud & Mercer 1989)

Lynx Reintroduction potential
Canada Lynx were killed off of Isle Royale just prior to it becoming a National Park through the direct actions of
human trappers overharvesting lynx from the island. Since that time lynx numbers have plummeted across the
United States. They were named a U.S. Federally threatened species in 2000 and an Endangered species in the State
of Michigan in 1989. Reintroductions have been undertaken in several locations in the United States with varying
levels of success. Poaching and vehicle traffic were the most serious difficulties encountered in most
reintroductions of Canada lynx. Since Isle Royale has neither of these stressors, lynx reintroduction would be
expected to be very successful. Historically, Isle Royale supported resident populations of lynx estimated at 40-65
animals.

Wolf Introduction Project

Graph depicting the populations of wolf (red line), moose (blue line) and beaver (green line) at Isle Royale since monitoring began. Beaver seem to be in a steady state of decline, while wolf and moose are variable, but relatively stable. Dashed lines show logarithmic trends
over time.

Michigan wolf timeline
Photographs of “Big Jim”, a wolf born and hand-raised at the Detroit Zoo by Lee Smits that was subsequently released with three other zoo wolves on Isle
Royale in 1952. Jim was one of the wolves known to survive and assimilate onto the island. Photos by Lee Smits

In the 1940s and 50s wolves across North America were being
persecuted as vermin. Their numbers dwindled and few areas,
if any, in the United States had healthy wolf populations. Then
in 1949 one or two wolves made it to Isle Royale. Just after this a
proposal to make Isle Royale a refuge for wolves surfaced at the
same time that the Detroit Zoo wanted to “trade” several
surplus zoo-born wolves for more moose from Isle Royale. The
logistics of getting moose from the island did not work out,
but four fully vaccinated wolves from the zoo were sent to Isle
Royale in 1952. The zoo wolves had been sired by a male from
Michigan and a female from northwest Canada (likely the
Yukon). Negative interactions between the wolves and Isle
Royale residents happened quickly. The zoo wolves had been
hand-raised by humans and were more “dog-like” than wild.
The “tame” wolves created enough conflicts that it was decided
to remove the animals. One of the female wolves was captured
and returned to the Detroit Zoo. One male was shot and killed.
The remaining two wolves were shot at (but not hit). These
wolves were occasionally seen and presumably reverted to a
“wild-state” and augmented the population.

1840- extirpated from southern lower peninsula
1935- extirpated from lower peninsula
1949- wolves appear on Isle Royale
1952- wolves stocked on Isle Royale from Detroit Zoo
1955- last known wild breeding in mainland MI (at what
is now Pictured Rocks National Lakeshore)
1960- National wolf bounty repealed
1965- became a state protected species
1973- Federal Endangered Species listing,
thought to be 6 animals in the upper peninsula
1974- 4 wolves translocated from MN, all poached
1980s- emigration from MN, WI, ON
1990- documented wild breeding (2 pups born in UP)
1992- 21 wolves in upper peninsula
2012- wolves removed from Federal and State protection

Current Great Lakes wolf population

“Big Jim” with Mrs. Smits just prior to being shipped to and
released on Isle Royale. Photo by Lee Smits

MN = 2,921
MI = 687 (700-950 capacity)
Isle Royale = 10
WI = 782
ON = 8,800+

Wolf-Moose-Beaver population variance
The wolf population at Isle Royale, like many mammal
populations has fluctuated over time from the low of 1-2
wolves (when they first arrived) to a peak at 50 animals
in 1980.When the island wolves hit this peak they had
the highest density of any population in North America
(102 wolves/ 1000km2). The following year saw rapid
declines in the population due to interspecific fighting
and starvation. Disease was also possibly introduced at
this time. The wolf population average on the island is
22 individuals (which is still a high density, 41/1000km2).
The most common cause of death for Isle Royale wolves
is other wolves. The moose population is the primary
prey for wolves on Isle Royale. Even though wolves kill
moose for their food, they do not make a large impact
on regulation of the size of the total moose herd. Wolves
positively affect moose health by culling sick, wounded,
and old animals from the population. The population of
Wolf density in Wisconsin and Michigan’s upper peninsula. In 1980 wolf density on Isle Royale was at 102/ 1000km2, double what is
moose has grown from just a few animals to a peak of
considered very high density.
several thousand. The long-term average is around
1000 moose. Beaver populations on Isle Royale have
been in general decline for several decades. A secondary prey source for wolves, beaver are thought to be declining due more to habitat changes than
predation. Beaver were heavily trapped from the island in historic times and generally number several hundred individuals.
background photo by USFWS