Monday, September 17, 2012

Why You Can Hunt Bison, But Not Moose, on Kodiak Island, Alaska

Why can you go to Kodiak Island, Alaska and apply for a permit to hunt bison (Bison bison bison) but not moose (Alces alces)? Well the long and short of it is that moose do not exist on Kodiak Island, Alaska but bison do. Hugh?

Alaska as a state boasts over 200,000 moose according to wiki and moose are strong swimmers so there is no reason to presume that they could not swim the 30 miles from the mainland. Even without swimming they should have made it to the island during the last glacial maximum when there were  land bridges. Surely with over 3000 square miles (second largest island in the U.S.) of very rich moose habitat, with plenty of their preferred riparian habitat, over one hundred streams and rich, volcanic soil spurring on abundant plant growth during the long summer days the moose should be thriving on the island. The introduced Sitka-Black tailed deer thrives on the island, along with about 400 introduced mountain goats, and, strangest of all, the introduced plains bison.

Several hundred introduced plains bison (Bison bison bison)  survive on Kodiak Island

Even when moose were introduced to the island, and I have found several anecdotal reports that they have been, the moose did not thrive in what should be an ideal habitat for them. Again, why no moose?

The answer quite simply in my opinion- too many damn big bears.

Kodiak Bear- Ursus arctos middendorffi

The Kodiak Bear is the largest subspecies of brown bear in the world at about 1500 lbs for a peak condition male- about the same size  as a small allosaurus. Not only is it large, it is quite common at about 0.7 bears per square mile with a total island population of about 3, 500 for the entire island- but at times the population is concentrated in various drainages for fishing. The combination of rich feeding on berries, sedges, and marine resources and relatively moderate climate enables about a quarter of the population to forgo winter hibernation entirely.

But by far the food resource that allows the Kodiak to survive at such size and in such density is the five species of salmon that breed from May through September in the islands waters.

We can now start to see why this exceptional abundance of bears would make it a challenge for any colonizing moose on the island- moose prefer the same type of riparian habitat in which bears are going to be most concentrated. On the mainland this conflict is nullified because the two species are more diffuse than on an island. Also moose calves would just be hammered- unlike other ungulates moose will stand and fight for their calves instead of flee- but given the exceptional size of Kodiak bears that brazen tactic would probably backfire for the calf and adult.

But what about the other introduced herbivores on the island- how do they cope with bears. Well the Sitka deer does the best- it is inconspicuous, breeds quickly and generally not worth the effort of the bears. The mountain goats stick to mountain ranges of the island where bears do not pursue them. And what about those bison I mentioned?  Well here is an interesting article dealing with how bison got introduced to the island. Long story short, without any native large herbivores ranchers experimented with cattle on the island to provide food for local people. But the large bear population just took such a heavy toll on the cattle that it wasn't working out. So they switched tactics and brought bison, better able to defend themselves against the large bruins, to the island to provide regular meat. Tough resilient and even a match for the bears the bison are holding their own. It also helps that. unlike moose, they have the safety of the herd and prefer open spaces where bears can't ambush them. A recent series of dramatic photos in Yellowstone document a bear chasing down a bison badly burned from thermal springs. But even this badly wounded bison was actually able to fend off the bear and was eventually put down by rangers. So bison are pretty damn tough.

Its not that moose are not tough either- on the mainland they hold their own- but facing such large, numerous and hungry bears on Kodiak in dense riparian habitats- they could never establish a viable population.

We can see here that it is arguably the abundant marine resources, especially salmon, that allows Kodiak bears to proliferate to these sizes and at such densities which ultimately keeps out moose. And, for regular readers, this should ring a bell...where else have I talked about a predator dominated habitat supported by fish, but seemingly bereft of large herbivores- yes the Kem Kem.

Imagine if ursids were extinct and humans did not have any knowledge of the fishing propensities of many bears. Imagine a paleontologist discovering the remains of the giant Kodiak bear- but the next largest animal on the island is the red fox. What would this scientist think of this seeming ecological anomaly? Why did this type of bear, on an island no less, become so much larger and more common than the mainland variety?


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