Speaking of science - I'm not seeing any data to support your hypothesis, HM - that the habitat is saturated and the extras are forced on the Island. And the "spirit" bears are white black bears - not grizzlies - which is what this article is about.
As far as Grizzlies go: "
Within British Columbia, the Grizzly Bear is listed as “Vulnerable” (Blue-listed) by the BC Conservation Data Center (CDC) and as “Special Concern” (SC) by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) (CDC explorer, 2010; Hamilton et al. 2004). The species is not currently listed under the Federal Species at Risk Act (Schedule 1), however, it is listed on the BC Conservation Framework as Priority 2-Goal 2; as such, habitat protection and monitoring are recommended by the provincial government" (Hobbs et al. 2013).
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The other narrative I hear is that the fish resources are so poor - the grizzlies are swimming elsewhere to find grub. The caveat I would add is that they are either much better swimmers and/or have better eyesight than black bears. I know 1st hand that black bears have crappy distant eyesight - not as sure about the grizzlies.
Most of the outer Islands on the North & Central Coasts have no bears (exception Princess Royal) - but wolves. The in-between islands (between the outer and the mainland) generally have reduced population sizes of black bears. So - colonization is a slow work in progress wrt bear colonization.
Most of the outer islands also have limited - if any - mountains with snow pack (exception Princess Royal) - which is thought essential for grizzly mom & pup denning. So that might be a factor in grizzly colonization success, as well.
And as far as the "spirit"/kermode bears go - there is a line of them that runs from Terrace in the North to Princess Royal in the South. And black bears close to that line often have rings on their cuffs & necks. Must've been one real fecund & horny white black bear that made that trip North from Princess Royal after glaciation towards Terrace