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The home range concept was applied first to terrestrial mammals (Burt 1943), and has since been influential in the development of theoretical models to explain the movements and distributions of a wide variety of animals. In the 1940s and 1950s, Gerking (1950, 1953, 1959) conducted a series of mark–recapture studies that led to the application of the home range concept in riverine fish ecology. In these studies, Gerking found that the majority of recaptured fish were collected from the original capture site and that experimentally translocated fish exhibited a strong tendency to return home. A series of similar mark–recapture studies followed Gerking's work and, although certain types of specialized movement were acknowledged (e.g. spawning migrations), most studies concluded that adult stream fish are normally sedentary (see reviews by Northcote 1978; Gowan et al. 1994; Rodríguez 2002). Many of these studies also found that a small proportion of fish were ‘strays’ that moved away from the site of capture or did not return home after translocation. This finding led some workers to propose that riverine fish populations consist of a behavioural dichotomy, comprising a dominant sedentary component and a smaller mobile component (e.g. Stott 1967; Northcote 1992).
The body of research relating to the restricted movements of adult stream fish forms the central tenets of what has become known as the ‘Restricted Movement Paradigm’ (RMP) (sensuGowan et al. 1994). However, aspects of the evidence underlying the RMP have recently been called into question. Gowan et al. (1994), for example, reviewed literature relating to the movements of riverine salmonids. They argued that mark–recapture studies used to support the RMP may be biased against detecting movement, because conclusions are based mainly on recaptures from the original capture site, and the fate of non-recaptured fish is largely unknown. Several recent studies have suggested that mobile behaviour by some species of stream fish is more common and biologically important than recognized previously (e.g. Gowan & Fausch 1996; Young 1996), although Rodriguez (2002) suggested that there remains strong evidence for the main tenets of the RMP.
It is evident that the movements of fish vary considerably between taxa and life-history stages (see Lucas & Baras 2001). However, environmental variables, including temperature, flow conditions, habitat heterogeneity, channel size and location within a watershed, have also been shown to strongly influence movements (Linfield 1985; Bruylants, Vandelannoote & Verheyen 1986; Gorman 1986). The RMP, with its emphasis on the occupation of restricted home ranges, has been based largely upon studies of fish in relatively small streams (Gowan et al. 1994). The tenets of the RMP therefore do not necessarily apply to fish in larger lowland rivers, where physical restrictions to movement (e.g. shallow riffles, see Schaefer 2001) are not as common. In a study of cyprinids in several large, lowland rivers in England, Linfield (1985) proposed an alternative model to the home range concept in which patterns of movement are viewed as ‘an infinitely variable combination of active movements’ that are influenced by environmental factors such as season, water temperature and flow. More recent radiotelemetry studies of fish in larger rivers have both provided support for the home range concept (Allouche, Thévenet & Gaudin 1999; Snedden, Kelso & Rutherford 1999) and expressed doubt as to its applicability (Baade & Fredrich 1998; Clough & Beaumont 1998).
A major impediment in assessing the applicability of the home range concept for describing riverine fish movements lies in the use of the term ‘home range’. Commonly cited definitions of home range (e.g. the area over which an animal travels in its day-to-day activities; Hayne 1949) are problematic because they fail to distinguish between free-ranging animals and animals that maintain fidelity to particular areas (Munger 1984). This important distinction has rarely been addressed in studies of riverine fish movements. For an animal to possess a measurable home range, it must exhibit ‘site fidelity’ − i.e. the extent of its displacement must be smaller than if its movements were random (Spencer, Cameron & Swihart 1990). In some instances, the existence of site fidelity is evident based on qualitative criteria − a fish recaptured after a year from the same pool where it was originally collected is likely to have exhibited fidelity to a home range that included the pool. In other instances, however, the existence of site fidelity is less clear − for example, would a fish be considered to exhibit fidelity to a home range if it was recaptured 500 m from the original capture site after a year?
In view of these scaling and definitional issues, as well as recent studies demonstrating high levels of mobility by some riverine fish, there is a requirement for tests of the home range concept as a theoretical basis for describing the movements of riverine fish (Matthews 1998). In this paper, I describe a radiotelemetry study that examines the movements of two species of fish [golden perch (Macquaria ambigua Richardson) and common carp (Cyprinus carpio L.)] in a lowland river in Australia. The study aims to determine whether the movements of golden perch and carp are compatible with the home range concept, or if alternative models of movement might be more appropriate.
The movements of golden perch and common carp have been the subjects of previous studies, although there has been little detailed examination of home range occupation or homing in rivers. Studies of golden perch in the Murray and Ovens rivers in south-eastern Australia revealed high levels of mobility at times (up to 10 km per day; Reynolds 1983), and provided little direct evidence of home range occupation or site fidelity (Reynolds 1983; Koehn & Nicol 1998). In a study of carp in the Murray River, Reynolds (1983) found that most fish were relatively sedentary and possessed a homing ability. Schwartz (1987) also reported homing by carp in a lake in Pennsylvania/Ohio, USA. In contrast, Koehn & Nicol (1998) found that carp made frequent upstream and downstream movements of > 100 km per month and they concluded that carp are a highly mobile species. The specific objectives of the current study are to compare the movements of these species and to determine whether individuals exhibit site fidelity and occupy measurable home ranges. In discussing the results of the study, I propose a conceptual model to explain the observed movement patterns, and discuss the potential implications of this model in defining the movement patterns of riverine fish.