Introduction

In this chapter we present data on the diet of the guild of semi–aquatic carnivores, the European mink (Mustela lutreola), the American mink (M. vison), the polecat (M. putorius) and the otter (Lutra lutra). These species share habitats in rivers, streams and lakes in northern Belarus. The data are used to test predictions from the hypothesis that the decline of European mink is caused by changes in prey availability, or by competition for food with other carnivores within the guild.

There are a number of carnivore species in Europe that may be termed ‘semi–aquatic’, species that live close to water, and which capture at least part of their food by swimming and diving. These include the otter, which feeds mostly on fish and some amphibians (for summaries, see Mason & Macdonald, 1986; Kruuk, 1995), the European mink with a diet of amphibians, small mammals, fish and crayfish (Sidorovich, 1992a), the American mink, which has been introduced in many areas since the 1930s and which feeds on small mammals, fish, amphibians and crayfish (for review, see Dunstone, 1993), and the polecat with a diet of mostly small mammals and amphibians (Sidorovich, 1992a). There have been no studies of this whole complement of semi–aquatic predators in any one area, however. Such an approach is necessary in order to assess possible competition for food, to draw comparisons between the effects of prey species on different predators, and to study the effects of these species on each other.

Introduction

European mink, Mustela lutreola (Linnaeus 1761) look so similar to American mink, Mustela vison (Schreber, 1777) that the two were formerly distinguished only as subspecies (Ognev, 1931; Heptner et al., 1967; for a review, see Novikov, 1939). This similarity offers not only a striking instance of convergence, but also a plausible explanation of the European mink's precipitous decline to the verge of extinction. In fact, phylogenetically the European mink is probably closest to the Siberian polecat, Mustela sibirica (Pallas, 1773), whilst the American mink is the most aberrant in the genus Mustela (Lushnikova et al., 1989; Graphodatsky et al., 1976; Youngman, 1982).

The European mink was formerly widespread in eastern Europe, but has declined over a long period and by 1990 was clearly endangered (Maran, 1994 b). Here, after reviewing briefly the species’ biology, we will present the results of an up–dated survey of the European mink's status. Against that background we will present a critical review of hypotheses that might explain its decline, dwelling in particular on two that we will subject to a preliminary test by presenting new data. These two implicate the American mink, first through the transmission of disease and second as a direct aggressor.