The semi-aquatic mammals study which was initiated in September 1976 saw its first field season during 1977-78. Research efforts were concentrated in the Muskeg River drainage area and the Dover-Snipe River headwaters area. Live trapping and tagging of the four study species, beaver (Castor canadensis), muskrat (Ondatra zibethicus), mink (Mustela vison), and otter (Lutra canadensis), were conducted while the study areas were intensively reconnoitered. Analysis of 488 otter scats showed a predominance of fish remains (85.5% contained fish) while 198 mink scats had mammals as the predominant food item (67.7% contained mammalian remains). Beaver selected Populus species