Ecology of North American Freshwater Fishes. Stephen T. Ross Ph. D.
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levels of fishes, especially the top predator, Lake Trout, had not reached preacidification levels by the end of the 13-year study of recovery—likely a reflection of the still recovering prey base.
Fishes also may show resilience to unfavorable spawning conditions by having extended reproductive seasons. The Longnose Shiner (Notropis longirostris), a cyprinid found in small, upland streams in the southeastern United States, has a short life span of only 1–2 years. However, resilience to poor spawning conditions is achieved by having a protracted spawning season that begins in February and can extend into October (Heins and Clemmer 1976; Ross 2001). Similar patterns of extended spawning seasons in association with short life spans are shown for numerous other southeastern minnows such as Red Shiner (Cyprinella lutrensis), Blacktail Shiner (C. venusta), and Weed Shiner (Notropis texanus) (Ross 2001).
In summary, resilience in fishes can be achieved by movement of adults or juveniles back into a previously disturbed area. Resilience to poor spawning conditions or unfavorable conditions for larval/juvenile survival occurs through elevated longevity of adults so that they can wait out poor years. On an annual basis, short-lived fishes show resilience to poor spawning conditions by having extended reproductive seasons. Overall, there is considerable variation in the resilience of fish species and fish assemblages to perturbations. Variation occurs across multiple levels including the nature, timing, and severity of the disturbance; the type and location of the aquatic system; species characteristics; and life-history stage (Schlosser 1985; Detenbeck et al. 1992; Albanese et al. 2009).
Levels of Persistence and Stability in Lotic Systems
Considering a wide range of studies, lotic systems tend to show moderate to high levels of persistence and low to moderate levels of stability, with the degree of stability influenced by the metric used to test it. In a survey of 49 primarily North American stream sites that had been subjected to various types of disturbance, Detenbeck et al. (1992) found full or nearcomplete recovery within two years. Analysis of 25 long-term studies (≥ 2 years; median = 11 years; range 2–45 years) designed or amenable to testing assemblage persistence and stability, and including from 3 to 95 species, showed 76% high persistence and 52% high stability in at least one type of measure (Table 6.1). Environmental harshness, especially if the harshness was related to anthropogenic impacts, had a strong effect on assemblage persistence and stability (Figure 6.5A). In systems judged to have low stress, 100% of the assemblages were persistent and 80% stable. In contrast, for systems judged to have moderate or high stress, only 22% were persistent and 11% stable. In systems with obvious human disturbance, only 14% of the assemblages were considered persistent or stable (Figure 6.5B). However, the sample size is too limited to separate the impacts of human versus natural disturbances; of the 10 studies having moderate to high disturbance, only three were disturbed by nonhuman impacts. The data in Table 6.1 are also biased by geographical region; most of the studies were at lower latitudes (mean latitude = 35.7°; range = 31°–42°) and 84% were done east of the continental divide. However, recall the challenges of assessing assemblage persistence and stability in western fish faunas with long-lived species. There is also a bias in stream size as only two studies dealt with large rivers.
FIGURE 6.5. Impacts of environmental stress (A) and the level of human disturbance (B) on the degree of persistence and stability of lotic fish assemblages, and (C) a comparison of assemblage persistence and stability in lotic and lentic systems. Numbers above bars show sample sizes. Based on data from Tables 6.1 and 6.2.
Examples of Persistence and Stability in Lotic Systems
Brier Creek, an Oklahoma tributary of the Red River (now inundated by Lake Texoma), is routinely subjected to extreme conditions and has been particularly well studied. In spite of extreme conditions, including total dewatering of some stream reaches, the fish fauna over an 18-year period showed strong persistence on a stream-wide basis, in that abundant species continued to remain abundant and rare species remained rare, with only a few exceptions. Stability of the Brier Creek fish fauna showed greater variation, as measured by indices of similarity of the sampled fish fauna among years. The fish fauna at individual collection sites (i.e., at the local assemblage level) showed less persistence and stability.
The timing of perturbations can have a major influence on the resultant impacts to aquatic organisms. If flooding in Brier Creek occurs when fish are spawning, there are severe impacts on larval survival. For instance, Harvey (1987) showed that larval cyprinids and centrarchids that were less than 10 mm TL were displaced downstream and killed by a major flood event.
Long-term data also exist for Piney Creek, a permanent upland stream in the Ozarks (Ross et al. 1985; Matthews 1986b; Matthews et al. 1988) that offers a more benign habitat (i.e., no dewatering and less temperature variation). Not surprisingly, Piney Creek fishes also showed high persistence; however, in contrast to Brier Creek, the fish fauna in Piney Creek also showed greater faunal stability, both overall and at the assemblage level. Piney Creek had a severe flood in 1982; however, immediately after the flood there were no major changes in rank abundance of the 10 most abundant species (Matthews 1986b). Less common species did show changes in abundance, so local assemblages were altered immediately postflood. Eight months after the flood, the overall fish fauna and the fauna at individual collecting stations had essentially recovered to preflood conditions, leading Matthews (1986b) to conclude that the Piney Creek fish fauna showed stability and persistence across years and across a range of flow conditions.
Although some studies have shown that fish assemblages rebound rather quickly from flooding, as discussed previously, and as documented also by Taylor et al. (1996) for mainstem and tributary sites in the upper Red River system of Oklahoma, other studies indicate that floods or droughts acted to change or reset assemblage structure. Matthews and Marsh-Matthews (unpublished data) have recently found that two severe droughts resulted in a substantial change in the Brier Creek fauna, which did not recover to its former state until 3–4 years postdrought. Another example of how fish assemblages are affected by perturbations emphasizes the significance of timing of the event. In Coweeta Creek, North Carolina, a severe drought resulted in three distinct assemblages over a 10-year period corresponding to predrought, drought, and postdrought conditions (Table 6.1) (Grossman and Ratajczak 1998; Grossman et al. 1998).
TABLE 6.1 Long-Term (≥ 2 years) Studies of North American Stream Fish Assemblages Organized from Low to High Levels of Stress and from Low to High Latitudes
For a downloadable PDF of all tables, go to ucpress.edu/go/northamericanfishes
TABLE 6.1 (continued)
TABLE 6.1 (continued)
In the Sierra Nevada mountains of California, a severe spring flood in Martis Creek shifted the assemblage from being dominated by native, spring spawning species, to domination by the nonindigenous, fall spawning Brown Trout (Salmo trutta) (Table 6.1) (Strange et al. 1992). The importance of timing of floods relative to life history is also shown by responses of a northwestern fish assemblage in the John Day drainage, Oregon. Fishes that spawned in late spring and summer, such as Speckled Dace and Bridgelip Sucker (Catostomus columbianus), showed high losses of young-of-year individuals to summer flooding, whereas early spring spawners, such as Rainbow Trout, were more susceptible to spring flooding when the developing embryos were still in the redds (gravel nests) (Pearsons et al. 1992). In addition, losses of fishes due to flooding were greater in stream sections with low habitat complexity, leading Pearsons et al. (1992) to suggest that complex habitats may act as sources of individuals for the colonization of structurally simple habitats.
Levels of Persistence and Stability in Lentic Systems
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