An Assessment of Fish Assemblage Structure in a Large River

Abstract

The Penobscot River drains the largest watershed in Maine and once provided spawning and rearing habitats to 11 species of diadromous fishes. The construction of dams blocked migrations of these fishes and likely changed the structure and function of fish assemblages throughout the river. The proposed removal of two main‐stem dams, improved upstream fish passage at a third dam, and construction of a fish bypass on a dam obstructing a major tributary is anticipated to increase passage of and improve habitat connectivity for both diadromous and resident fishes. We captured 61 837 fish of 35 species in the Penobscot River and major tributaries, through 114 km of boat electrofishing. Patterns of fish assemblage structure did not change considerably during our sampling; relatively few species contributed to seasonal and annual variability within the main‐stem river, including smallmouth bass Micropterus dolomieu, white sucker Catostomus commersonii, pumpkinseed Lepomis gibbosus, and golden shiner Notemigonus crysoleucas. However, distinct fish assemblages were present among river sections bounded by dams. Many diadromous species were restricted to tidal waters downriver of the Veazie Dam; Fundulus species were also abundant within the tidal river section. Smallmouth bass and pumpkinseed were most prevalent within the Veazie Dam impoundment and the free‐flowing river section immediately upriver, suggesting the importance of both types of habitat that supports multiple life stages of these species. Further upriver, brown bullhead Ameiurus nebulosus, yellow perch Perca flavescens, chain pickerel Esox niger, and cyprinid species were more prevalent than within any other river section. Our findings describe baseline spatial patterns of fish assemblages in the Penobscot River in relation to dams with which to compare assessments after dam removal occurs. Copyright © 2014 John Wiley & Sons, Ltd.

Dam Removal and Fish Passage Improvement Influence Fish Assemblages in the Penobscot River, Maine

“…We also observed a decline in relative biomass of adult Smallmouth Bass in the Orono stratum (Figure ), which may indicate that the former Veazie Dam impoundment served as local winter refugia habitat for adult fish, as was suggested by Kiraly et al. (2014a). The factors associated with these observed changes to resident fish assemblages are complex and likely associated with impoundments reverting to lotic habitats; however, we made no empirical measure of habitat change, and without such a measure, it is impossible to determine the specific mechanisms that drove the observed differences.…”

“…Kiraly et al. (2014a) found that Alewife was a significant indicator species in the Tidal stratum, and Smallmouth Bass and Pumpkinseed were both significant indicator species in the Orono stratum. We also examined the spatial distribution of American Eel Anguilla rostrata due to its status as a species of concern and its ubiquity in the watershed.…”

“…The results from those surveys include finding distinct assemblages associated with lentic habitat in former impoundments and evidence of habitat fragmentation between dammed sections of the river (Kiraly et al. 2014a).…”

“…Prior to the PRRP, multiple years of electrofishing surveys were completed to characterize baseline metrics of species richness, relative abundance, and assemblage structure. The results from those surveys include finding distinct assemblages associated with lentic habitat in former impoundments and evidence of habitat fragmentation between dammed sections of the river (Kiraly et al 2014a).…”

Biological zonation of the last unbound big river in the West Carpathians: reference scheme based on caddisfly communities

“…Along with the results provided elsewhere (Bitušík et al, 2006;Krno, 2007;Illéšová et al, 2008) we obtained important information on predisturbance longitudinal patterns in benthic assemblages of the Hron River. Dams affect the sediment dynamics and distribution, dispersal, and abundance of benthic macroinvertebrates and other aquatic organisms (Stanford et al, 1996;Kiraly et al, 2014). Multiple damming of a river may result in longitudinal modifications towards upstream or (more likely) downstream abiotic and biotic conditions (Ward and Stanford, 1983b) and subsequently in alternation of spatial organisation of the whole river ecosystem.…”