Ecology of North American Freshwater Fishes. Stephen T. Ross Ph. D.
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result in an organism moving outside of its home range such that new habitats could be colonized or former habitats recolonized. Other aspects of movement are treated in subsequent chapters (especially Chapters 9 and 14). Evidence for the movement abilities of fishes comes from a variety of sources including observational studies on the colonization of new habitats and from studies using some sort of tagging procedure.
Movement Inferred from Colonization Studies
Colonization of newly available habitats by fishes has been studied on a variety of temporal and spatial scales, including those studies examining movement of fishes into newly available habitats following the retreat of the Wisconsinan ice sheets, the recolonization of habitats after amelioration of harsh conditions, such as complete dewatering of a stream reach, or the response of fishes, usually over a short time period, to newly created stream habitats.
During the Wisconsinan glacial advance, the Laurentide ice sheet covered eastern Canada including Ontario (Chapter 3; Figure 3.4) so that there were no ice-free habitats available for freshwater fishes (Mandrak and Crossman 1992). As the ice began retreating, large meltwater lakes and connecting rivers formed along the southern boundary of the ice sheet. Lake Algonquin was one such meltwater lake that covered parts of modern-day Lake Huron, Lake Superior, and Lake Michigan approximately 12,000 years ago (Hinch et al. 1991; Mandrak and Crossman 1992) (Figure 5.3). The area inundated by Lake Algonquin in Ontario also included the future basins of a number of smaller lakes and, as Lake Algonquin subsided, its fish fauna would have had access to these smaller emerging lakes (Hinch et al. 1991). In addition, fishes from Lake Algonquin also colonized lakes at higher elevations that were not directly inundated by the glacial meltwater—in this case by moving up the lakes’ outlet streams that flowed into the discharge of Lake Algonquin (Figure 5.3).
Prairie streams of the central United States, on the edge of the Great Plains and Osage Plains, are often subjected to periods of intense drought, such that streams may be reduced to a few isolated pools or totally dewatered (Matthews 1988). In spite of such extreme conditions as total drying of long sections of streambed, the fish faunas of these streams tend to be surprisingly resilient and fairly quickly recolonize reaches after stream flow resumes (Matthews 1987, 1988). The fish fauna of Brier Creek, an Oklahoma tributary to the Red River arm of Lake Texoma, has been particularly well studied since the late 1960s and provides an example of the ability of fishes to recolonize newly watered habitats (C. L. Smith and Powell 1971; Ross et al. 1985; Matthews 1987; Matthews et al. 1988).
In 1980, the region of southern Oklahoma was hit by a severe drought and high temperatures, resulting in the dewatering of large stream sections and even heat death of one of the common species (Orangethroat Darter) (Matthews et al. 1982; Ross et al. 1985). In spite of such extreme conditions, by the following year the fish assemblage of Brier Creek was essentially unchanged from previous years (Ross et al. 1985), indicating that fishes had recolonized habitats once stream flow resumed. Drought returned in the summer of 1982, and a 1.5 km section of the stream in the headwaters (station 2, Figure 5.4) was totally dry by autumn and remained so until heavy rains in March of 1983 (Matthews 1987). Once flow resumed, monthly collections showed that the fish fauna was rapidly rebuilt by species colonizing from refugia outside of the dewatered reach, followed by spawning of some of the colonizers; the fish fauna of this area of Brier Creek typically includes only 9–10 species, so colonization essentially reestablished the entire fauna in approximately four months (Ross et al. 1985; Matthews et al. 1988). The favorable stream conditions were, however, short lived. Flow ceased in July, and by September the section was reduced to one pool with no surviving fish (Figure 5.4) (Matthews 1987).
FIGURE 5.3. Dispersal from glacial meltwater lakes: Glacial Lake Algonquin in Ontario, Canada, and modern lakes in Canada and the United States. The black circles indicate lakes within the borders of Glacial Lake Algonquin or along the glacial outlet and colonized as Lake Algonquin subsided; the gray circles indicate higher elevation lakes colonized by fishes moving from the outlet of Lake Algonquin up through streams draining the lakes, as indicated by the arrows. Based on Hinch et al. (1991).
A long-term study to evaluate the impact on trout populations of new habitats created by the placement of log weirs in high-elevation streams in the Rocky Mountains included 500-m reaches of six streams and involved four species and three genera of salmonids (Brook Trout, Salvelinus fontinalis; Cutthroat Trout, Oncorhynchus clarkii; Brown Trout; and Rainbow Trout) (Gowan and Fausch 1996). Newly available habitats created by the weirs were primarily colonized by trout that were coming from outside of the 500-m study reaches; however, once the trout were in the new habitats they tended to remain there. Marked fish within the study reaches tended to be sedentary, but the presence of unmarked fish in the new habitats is a strong indication of the ability for long distance movement.
Movement Inferred from Tagging Studies
Clearly, the previous examples indicate that fishes are capable of moving through connecting waterways, but for a long time there have been questions of how far fishes routinely or periodically move and what proportion of a population is involved in movement. In 1959, Shelby Gerking summarized what was then known about movement in both marine and freshwater fishes. He identified 34 fish species (24 freshwater taxa; 10 marine taxa) characterized by restricted movement that was not associated with spawning. Following the classic work by Gerking, a view referred to as the “restricted movement paradigm” developed among fish ecologists: namely, that freshwater fishes for the most part had local populations and that extensive movement was uncommon. However, Gerking was careful to qualify his conclusions. First, he emphasized the importance of experimental design on the outcome of movement studies. Even if fishes tend to remain primarily in a home range, if the resampling area is small relative to the home range of the fish (keeping in mind that the home range is not known), then there is a bias toward finding few fish and concluding that long-range movement is common. Conversely, if the resampling area is large relative to the size of the unknown home range, then there is a bias toward finding many fish and concluding that fishes have restricted movement. Gerking (1959) was also careful to point out that restricted movement behavior was not universal among any given population and said, “That stray fish occur has never been doubted, and their importance in repopulation of decimated areas and the distribution of the species is not questioned.” In fact, Funk (1955), as cited by Gerking, proposed that lotic freshwater fishes had populations composed of a mobile group and a sedentary group (often referred to as “movers” and “stayers”). Funk (1955) also pointed out the problem of bias toward finding limited movement for fishes when sampling was concentrated in “limited areas near release sites.”
FIGURE 5.4. A. Brier Creek, a tributary to the Red River arm of Lake Texoma in Oklahoma. Numbers show sampling stations. Map based on C. L. Smith and Powell (1971) and Ross et al. (1985).
B. Recolonization of a dewatered section of Brier Creek, Oklahoma, following resumption of stream flow. Drying occurred in a 1.5 km reach at station two. Severe drought dewatered the stream again by September. Data from Matthews (1987).
Movement of freshwater fishes is generally studied by marking individuals in some way and then attempting to recapture them later (termed mark-recapture). As pointed out by Funk, sampling is almost always greater near the point of release compared to sampling at great distances from the release, especially if there are many potential routes of fish movement (as in lakes or in streams with numerous tributaries). As a consequence, sampling effort is unequal over distance from the point of release, so that short movements tend to be recorded more often than long movements. The change in sampling intensity with increasing distance from the point of release is referred to as “distance weighting” (Porter and Dooley 1993; Albanese et al. 2003). Thus unless the study compares recoveries against the probability of recapture (i.e., capture probability decreases as fishes disperse outward from the point of release) or, preferably, is designed to alleviate the issue of distance weighting, there would be strong bias for interpreting recovery data as supporting limited fish movement (Box 5.2).
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