The smell and hearing abilities of the North American river otter are acute. Smaller mammals include coyote, beaver and river otter. Threats to North American river otter populations in North America vary regionally. Beaver and river otter have been successfully reintroduced. Less common creatures include beaver, bobcat, coyote, fisher, mink, muskrat, red fox, and river otter. Aquatic mammals include beaver, muskrat, raccoon, river otter and mink. The continual decrease in prey numbers also causes problems for the southern river otter. This dilemma prevents, and consequently inhibits, recolonization or growth of North American river otter populations. At one time there were as many as fifty watermills powered by the River Otter. Smaller mammals include coyotes, marten, red fox, wolverine, river otter, beaver and lynx. The next town is Budleigh Salterton, beyond which lies the River Otter. Throughout the 1990s, there were several attempts to locate a surviving Japanese river otter. Furbearers include beaver, red and gray fox, bobcat, fisher, river otter, raccoon and mink. The North American river otter is sexually dimorphic. Weasel species, including the North American river otter are prevalent in the park.