Influence of Habitat Complexity on Resistance to Flooding and Resilience of Stream Fish Assemblages

Abstract

The structure of fish assemblages in five reaches of a high desert stream in northcentral Oregon was determined by snorkeling before and after a summer flash flood and two spring floods. One reach in each of two other streams that were unaffected by the first flood was used as a reference system. Stream reaches varied in habitat complexity as measured by hydraulic retention. Following the floods, hydraulically complex stream reaches lost proportionately fewer fish, had generally higher fish diversities, and had higher fish assemblage similarity than hydraulically simple stream reaches. Fish assemblages were resilient, and certain species such as speckled dace Rhinichthys osculus were exceptionally good at recoloni/ing disturbed habitats. Successful recruitment of different fish species depended, in part, on flood timing. Young of the year of species that spawn in early spring (e.g., rainbow trout Oncorhynchus mykiss) were more negatively affected by early spring floods than summer floods. Species that spawn later in the season (e.g., cyprinids and catostomids) were more negatively affected by summer flooding. Higher fish diversities in hydraulically complex reaches (lower disturbance intensity) after floods support predictions of the intermediate-disturbance hypothesis and suggest that fish assemblage resistance may be related to overall habitat complexity in these small streams.

Effects of Hurricane Katrina on Freshwater Fish Assemblages in a Small Coastal Tributary of Lake Pontchartrain, Louisiana

“…These species may have avoided direct mortality by moving further upstream and occupying interstitial places within typical instream habitats (e.g., among cypress knees, aquatic vegetation, sunken logs). These habitats can provide refuge and slow the effects of the incoming surge much like debris dams do in spring floods in other stream systems (Pearsons et al 1992). In Bayou Lacombe, the greatest hurricane impacts on fish assemblages were associated with the physical destruction and alteration of habitats in the upstream reaches where certain species could not access refuge habitats.…”

Major flood disturbance alters river ecosystem evolution

“…Timing of the flood relative to the spawning season influences recovery times 17 as does its effect on habitat complexity 22 . Although juvenile coho salmon were markedly reduced, ocean adults from previous year classes spawned to rebuild populations despite lower habitat complexity.…”

Movement and Mortality of Adult Brown Trout in the Motupiko River, New Zealand: Effects of Water Temperature, Flow, and Flooding

“…We actually observed a similar reduction (65%) in juvenile brown trout abundance, resulting from the same March 2005 flood in the Rainy River, a tributary of the Motupiko River (J. Hay and J. W. Hayes, unpublished data). Channel morphology appears to influence the effects of floods on salmonids, greatest changes in abundance occurring at sites where bed load movement and geomorphic changes occur (Lamberti et al 1991;Pearsons et al 1992;Nislow et al 2002). Substantial bed load movement and removal of riverbed and bank vegetation were evident in the Motupiko and Rainy rivers as a result of the flood.…”