Ecology of North American Freshwater Fishes. Stephen T. Ross Ph. D.
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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 READING
Albanese, B. W., P. L. Angermeier, and C. Gowan. 2003. Designing mark-recapture studies to reduce effects of distance weighting on movement distance distributions of stream fishes. Transactions of the American Fisheries Society 132:925–39. Explores the role of changing capture probabilities with distance from the release point in estimates of fish movement.
Belyea, L. R., and J. Lancaster. 1999. Assembly rules within a contingent ecology. Oikos 86:402–16. An overview of the literature on community assembly.
Fausch, K. D., C. E. Torgersen, C. V. Baxter, and H. W. Li. 2002. Landscapes to riverscapes: Bridging the gap between research and conservation of stream fishes. BioScience 52:483–98. Emphasizes the need to view streams and rivers as complex landscapes and the importance of access to these varied habitats by fishes.
Gowan, C., M. K. Young, K. D. Fausch, and S. C. Riley. 1994. Restricted movement in resident stream salmonids: A paradigm lost? Canadian Journal of Fisheries and Aquatic Sciences 51:2626–37. A reanalysis and counter argument to the restricted movement paradigm.
Mandrak, N. E., and E. J. Crossman. 1992. Postglacial dispersal of freshwater fishes into Ontario. Canadian Journal of Zoology 70:2247–59. An important paper on the glacial refugial origins of Ontario freshwater fishes.
Taylor, C. M. 1996. Abundance and distribution within a guild of benthic stream fishes: Local processes and regional patterns. Freshwater Biology 36:385–96. Uses field collections and manipulative studies to test predictions of hypotheses regarding the abundance and distribution of fishes.
SIX
Persistence of Fish Assemblages in Space and Time
CONTENTS