SEASONAL-CHANGES IN DIETS OF COASTAL AND RIVERINE MINK - THE ROLE OF SPAWNING PACIFIC SALMON

Feeding niches of riverine and coastal mink (Mustela vison) in southea st Alaska differ in prey composition and abundance and diving medium d uring spring and summer. In autumn, however, the upstream migration of spawning Pacific salmon (Oncorhynchus sp.) creates a pulse of food fo r mink. We hypothesized that diets of coastal and riverine mink, and t herefore their stable isotope ratios (delta(13)C, delta(15)N), would d iffer significantly during periods when salmon were absent, but that s almon carcasses would constitute a large portion of the diet of both g roups during the salmon spawning season. Stable isotope analyses of cl otted blood cells from 24 live-captured mink and muscle tissue from 25 mink carcasses were used to indicate the composition of diets of indi vidual mink in 1992 and 1993. These isotope values were then compared with stable isotope ratios of prey, using a multiple-source mixing mod el. Our results indicate that riverine mink depended on salmon (carcas ses and fry), with little seasonal or individual variation, whereas co astal mink relied on intertidal organisms in spring and summer, with m easurable (<25%) consumption of salmon carcasses when they became avai lable in autumn. Coastal and riverine mink in southeast Alaska differ strongly in their diets in spring and summer, with both groups relying on the abundant salmon carcasses during autumn.