• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Ursus arctos; Alaska
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.619.5730; http://geochemistry.usask.ca/bill/Courses/Intro to isotopes/tutorials/brown bears salmon.pdf

Abstract We quantified the amount, spatial distribution, and importance of salmon (Oncorhynchus spp.)-derived nitrogen (N) by brown bears (Ursus arctos) on the Kenai Peninsula, Alaska. We tested and confirmed the hypothe-sis that the stable isotope signature (δ15N) of N in foliage of white spruce (Picea glauca) was inversely proportion-al to the distance from salmon-spawning streams (r=–0.99 and P<0.05 in two separate watersheds). Loca-tions of radio-collared brown bears, relative to their dis-tance from a stream, were highly correlated with δ15N de-pletion of foliage across the same gradient (r=–0.98 and –0.96 and P<0.05 in the same two separate watersheds). Mean rates of redistribution of salmon-derived N by adult female brown bears were 37.2±2.9 kg/year per bear (range 23.1–56.3), of which 96 % (35.7±2.7 kg/year per bear) was excreted in urine, 3 % (1.1±0.1 kg/year per bear) was excreted in feces, and <1 % (0.3± 0.1 kg/year per bear) was retained in the body. On an area basis, salmon-N redistribution rates were as high as 5.1±0.7 mg/m2 per year per bear within 500 m of the stream but dropped off greatly with increasing distance. We estimated that 15.5–17.8 % of the total N in spruce fo-liage within 500 m of the stream was derived from salm-on. Of that, bears had distributed 83–84%. Thus, brown bears can be an important vector of salmon-derived N in-to riparian ecosystems, but their effects are highly vari-able spatially and a function of bear density.