dominant cyprinids are widely represented in drift throughout North American streams, including the western and central United States (Robinson et al. 1998), northern rivers in Canada and the United States (Muth and Schmulbach 1984), and southeastern streams (Gallagher and Conner 1980; Slack et al. 1998). As shown in the previous section for species with drifting eggs and larvae, distances traveled by larvae can exceed several hundred kilometers. In the Colorado River drainage, estimates of movement of native cyprinid larvae range from approximately 9 km for Humpback Chub (Gila cypha) and Speckled Dace in the Little Colorado River (Robinson et al. 1998), to over 200 km for Colorado Pikeminnow (Ptychocheilus lucius) in the Green River (Tyus and Haines 1991).
For percids, larvae of the commercially and recreationally important Walleye (Sander vitreus) and Yellow Perch (Perca flavescens) exhibit substantial drift with greatest abundances occurring at night (Gale and Mohr 1978; Corbett and Powles 1986; Johnston et al. 1995). The occurrence in drift samples of darter species in the genus Etheostoma has been documented in several studies, with peak abundances typically at night from 2100 to 0300 h (Gale and Mohr 1978; Lathrop 1982; Brown and Armstrong 1985; Paller 1987). Even Bayou Darters (Nothonotus rubrum), members of a genus that inhabits swift water and coarse substrata, show downstream drift of at least several hundred meters. This is at least far enough for them to travel between patches of riffle habitats that juveniles and adults of this species selectively occupy (Slack et al. 2004). Larval drift also occurs within the darter genus Percina. For instance, larval Snail Darters (Percina tanasi) show downstream transport of up to several kilometers, followed by return upstream movement of juveniles and adults (Kuehne and Barbour 1983). As shown earlier, this type of life cycle that includes downstream drift followed by upstream movement of juveniles and adults is greatly at risk from man-made barriers to movement. Indeed, the population of Snail Darters in the Little Tennessee River was extirpated by the infamous Tellico Dam (Ono et al. 1983). More recently, additional populations of Snail Darters have been discovered in several Tennessee River tributaries, although of the nine known populations, six are considered marginal (Williams et al. 1989).
TABLE 5.1 Prevalence of Larval and Early Juvenile Drift in Numerically Dominant Freshwater Fish Families of North America
TABLE 5.1 (continued)
Catostomids, the third most speciose North American fish family, are also well represented in larval drift. Historically, many western catostomids drifted long distances downstream from spawning areas, subsequently followed by upstream spawning movements of adults. In the Little Colorado River, Bluehead (Catostomus discobolus) and Flannelmouth (C. latipinnis) sucker larvae drifted at least 9 km downstream from the spawning area (Robinson et al. 1998). Another Colorado River endemic, the Razorback Sucker (Xyrauchen texanus) has even more extensive movements as larvae. Because of the close linkage of adult and larval distances, Razorback Suckers, along with other examples of larval drift, are included in the following section on adult movement.
MOVEMENT AT THE ADULT STAGE In the Great Lakes of North America, Lake Sturgeon (Acipenser fulvescens) adults make spawning migrations out of the lake habitats and into tributary rivers. For example, in Lake Superior, adult sturgeon travel upstream for spawning at a single riffle in the Sturgeon River, Michigan, a distance of 69 km (Auer and Baker 2002). After hatching, larvae drift downstream at least 45 km and in some cases 61 km. In reference to Figure 5.5, the distance from adult feeding area to the spawning area (A) is 69 km; the nursery area is essentially the lower 10 km of river habitat downstream of the spawning site, and so this distance (B) is approximately 59–69 km; the other distance (C) would include the movement within Lake Superior to juvenile and adult feeding grounds.
Most suckers (family Catostomidae) also exhibit seasonal spawning migrations in which they move upstream into small tributaries from larger streams or lakes. Depending on the species, distances moved vary greatly, and movement may occur in groups or in larger schools (Curry and Spacie 1984) (see also Chapter 14). Adults make the return downstream migration after spawning, whereas newly hatched larvae are passively transported downstream by water flow, with larval numbers often increasing in surface waters at night (Gale and Mohr 1978).
A striking example of extensive travel to spawning habitats by a catostomid is provided by the Razorback Sucker, a species endemic to the Colorado River system. In the Green River and its tributaries, movements of Razorback Suckers are bounded upstream by the Flaming Gorge Dam and downstream by Lake Powell and the Glen Canyon Dam. Within this reach there are two spawning sites known for Razorback Sucker—one in the Yampa River upstream from its confluence with the Green River, and one in the Green River downstream of the Yampa River (Tyus and Karp 1990; Modde et al. 1996; Figure 5.6). Fish in breeding condition may travel at least 30–106 km to reach the spawning sites, followed by equivalent downstream movement (Tyus and Karp 1990). After hatching from demersal, adhesive eggs, larvae drift downstream into nursery habitat (historically provided by large backwaters) (Modde et al. 2001). Another Colorado River endemic, the Colorado Pikeminnow, makes equally impressive long distance spawning movements (Tyus and McAda 1984).
FIGURE 5.6. Spawning movements in fishes as illustrated by the Razorback Sucker, (Xyrauchen texanus), an endemic catostomid in the Colorado River drainage. Spawning locations of Razorback Sucker are indicated by black dots. Based on Tyus and Karp (1990), Modde et al. (1996), and Modde and Irving (1998).
The most impressive long-distance movements occur in fishes that travel between salt and fresh water for purposes of spawning (diadromy) (see also Chapter 9). In fishes that spawn in fresh water and then spend part of their life in the sea where they feed (anadromy), one-way distances traveled can be hundreds or even thousands of kilometers. For instance, Chinook Salmon (Oncorhynchus tshawytscha) travel almost 2,000 km as the spawning adults move from the Pacific Ocean upstream to spawning sites in the Yukon River (corresponding to distance A in Figure 5.5) (Scott and Crossman 1973). Post-yolk-sac fish (fry) as well as parr (young salmonids during the first year or two of life) and smolts (older juveniles ready to return to the sea) make the return journey downstream and then out to sea (distances B and C in Figure 5.5). Once in the open ocean where they are actively feeding, Pacific salmon may travel over thousands of kilometers during that time (usually 1–6 years) they spend at sea (Healey and Groot 1987; Thorpe 1988; Walter et al. 1997).
SUMMARY
The process of forming fish assemblages, although complex, involves characteristics of the environment, characteristics of the fish species in the regional species pool, and characteristics of the fishes and other biota in the local environment. Fish assemblages tend to be structured rather than random groupings of species, although random processes may at times be important. Also, very few studies representing even fewer geographical regions have rigorously addressed the issue of structure in freshwater fish assemblages. A major factor seems to be the fit of the potential colonizer with the environmental features of the new habitat. Following this, trophic position (low or high rather than intermediate), and if there is parental care of young, are important attributes of successful colonizers.
Fishes show the ability to move long distances, and depending on the species, movement may occur at any life-history stage. Even within fish populations that are relatively sedentary, individuals may make periodic or aperiodic movements, most likely in response to assessing resource availability or the risk of predation. Although the terms movers and stayers have been used to describe the differences in movement among individuals in a population, data seem to indicate that the same individual can shift between the two states. Hence the terms apply more to the state of an individual rather than differences among individuals. As long as there are periodic water connections and sufficient time, the well-developed capability for movement in most fish taxa allows fishes to colonize new areas or to enter preexisting assemblages.
SUPPLEMENTAL
