SELKIRK GRIZZLY BEAR DNA MARK/RECAPTURE ANALYSIS

MARK/RECAPTURE EXPLAINED 1 ST you catch some animals in a popn and “mark” them Later on you catch animals in the same popn Some of those will be new animals, some will be recaptures You use the ratio of “marked” to “recapture” to get a popn estimate

MARK/RECAPTURE N = Popn size M = # initially marked n = # caught in 2 nd effort m = # recaptured

CRITICAL ASSUMPTIONS Marks must be permanent All animals have an equal probability of getting caught No changes in population between initial mark and later recapture

MARK/RECAPTURE example 1 st mark: Trap 20 mice, paint their toenails red Recapture: 1 week later, trap again; catch 16 mice, 4 have red toenails So, N = (20 x 16) / 4, which equals 80

What does this have to do with grizzly bears?

USE DNA as a MARK

50 barbed-wire enclosures 470 sq miles Visited each site 4 times Collected over 1,200 hair samples

RESULTS ID 15 different grizzly bears 9 females, 6 males 15 bears captured a total of 50 times Multiple capture sessions allows for more complicated analysis Test for diff male/female capture probability, diff capture prob among sessions, trap happy, trap shy

RESULTS Best model estimated 18 grizzly bears – 11 females, 7 males Density 14.1 bears / 1,000 sq km (naïve estimate) 9.7 bears / 1,000 sq km (SECR estimate) 3.6 bears / 100 sq miles 2.5 bears / 100 sq miles

COMPARISON: PROCTOR 2005 USBC # CELLS5077 POPN EST1833 DENSITY (#/1000 sq km)

CAUTIONS about mark/recap Point Estimate – says nothing about trend Density cannot be extrapolated to the entire ecosystem No info on reproduction

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