scholarly journals Do beaver dams reduce habitat connectivity and salmon productivity in expansive river floodplains?

PeerJ ◽  
2016 ◽  
Vol 4 ◽  
pp. e2403 ◽  
Author(s):  
Rachel L. Malison ◽  
Kirill V. Kuzishchin ◽  
Jack A. Stanford

Beaver have expanded in their native habitats throughout the northern hemisphere in recent decades following reductions in trapping and reintroduction efforts. Beaver have the potential to strongly influence salmon populations in the side channels of large alluvial rivers by building dams that create pond complexes. Pond habitat may improve salmon productivity or the presence of dams may reduce productivity if dams limit habitat connectivity and inhibit fish passage. Our intent in this paper is to contrast the habitat use and production of juvenile salmon on expansive floodplains of two geomorphically similar salmon rivers: the Kol River in Kamchatka, Russia (no beavers) and the Kwethluk River in Alaska (abundant beavers), and thereby provide a case study on how beavers may influence salmonids in large floodplain rivers. We examined important rearing habitats in each floodplain, including springbrooks, beaver ponds, beaver-influenced springbrooks, and shallow shorelines of the river channel. Juvenile coho salmon dominated fish assemblages in all habitats in both rivers but other species were present. Salmon density was similar in all habitat types in the Kol, but in the Kwethluk coho and Chinook densities were 3–12× lower in mid- and late-successional beaver ponds than in springbrook and main channel habitats. In the Kol, coho condition (length: weight ratios) was similar among habitats, but Chinook condition was highest in orthofluvial springbrooks. In the Kwethluk, Chinook condition was similar among habitats, but coho condition was lowest in main channel versus other habitats (0.89 vs. 0.99–1.10). Densities of juvenile salmon were extremely low in beaver ponds located behind numerous dams in the orthofluvial zone of the Kwethluk River floodplain, whereas juvenile salmon were abundant in habitats throughout the entire floodplain in the Kol River. If beavers were not present on the Kwethluk, floodplain habitats would be fully interconnected and theoretically could produce 2× the biomass (between June–August, 1,174 vs. 667 kg) and rear 3× the number of salmon (370,000 vs. 140,000) compared to the existing condition with dams present. The highly productive Kol river produces an order of magnitude more salmon biomass and rears 40× the individuals compared to the Kwethluk. If beavers were introduced to the Kol River, we estimate that off-channel habitats would produce half as much biomass (2,705 vs. 5,404 kg) and 3× fewer individuals (1,482,346 vs. 4,856,956) owing to conversion of inter-connected, productive springbrooks into inaccessible pond complexes. We concluded that beaver dams may limit the total amount of floodplain habitat available for salmon rearing in the Kwethluk river and that the introduction of beavers to the Kol river could be detrimental to salmon populations. The introduction of beavers to other large alluvial rivers like those found in Kamchatka could have negative consequences for salmon production.

2015 ◽  
Vol 72 (11) ◽  
pp. 1639-1651 ◽  
Author(s):  
Rachel L. Malison ◽  
Lisa A. Eby ◽  
Jack A. Stanford

Beavers (Castor canadensis) may strongly influence juvenile salmon production by damming spring brooks that are primary rearing habitats on expansive floodplains of large Pacific Rim salmon rivers. We studied three floodplain rearing habitats in the Kwethluk River, Alaska: free-flowing (beaver-free, n = 3) and beaver-influenced (below beaver dams, n = 4) spring brooks and early-successional beaver ponds (n = 4). We analyzed juvenile coho (Oncorhynchus kisutch) and Chinook (Oncorhynchus tshawytschwa) salmon movement, survival, densities, and growth using a multistate robust capture–mark–recapture design. Survival (46% to 80%) and densities (0.9 fish·m−2) were highest in beaver-free spring brooks. Ponds had lower salmon densities, producing less biomass per unit area than beaver-influenced or beaver-free spring brooks (1.87 ± 0.57 g·m−2 vs. 2.98 ± 1.22 and 3.23 ± 0.73 g·m−2). However, ponds covered 2× greater area than either type of spring brook and therefore produced more salmon biomass at the floodplain scale than either type of spring brook (175 kg vs. 149 kg in beaver-influenced spring brooks and 140 kg in beaver-free spring brooks). We conclude that beaver damming of floodplain spring brooks produces bigger juveniles and more total biomass, but spring brooks produce significantly more, albeit smaller, coho and Chinook juveniles. Thus, the presence of beavers on the floodplain increases habitat variation, which provides a larger range of growth opportunities for juvenile salmon.


2017 ◽  
Vol 15 (3) ◽  
Author(s):  
Francisco S. Álvarez ◽  
Wilfredo A. Matamoros ◽  
Francisco A. Chicas

ABSTRACT The ichthyofauna of the Río Acahuapa was analyzed sampling 17 sites that included the basin main channel and its tributaries. Fish were collected using dip-nets, seine-nets and electrofishing. Fish standard length and species abundance were recorded. Species origin and salinity tolerance criteria were used to classify fish species. Water physicochemical variables, habitat structure and sampling sites elevation were recorded. A total of 33 fish species were registered, 12.1% are primary, 45.5% are secondary and 42.4% are of marine derivation. Fish species richness declined with increase of elevation (R2=0.55, p=0.0006). Two assemblages of fishes were identified: the first one associated to sites of low elevations (19-184 masl), composed mainly of secondary and marine-estuarine fish species related with high temperature, water velocity, river width, dissolved oxygen and low sand and silt substrate cover; the second one associated to sites of middle and higher elevations (185-519 masl), composed by primary and secondary freshwater fishes related with high pH, logs and rocks substrate cover. In summary, elevation and environmental variables contributed to the composition and distribution of fish in the Río Acahuapa.


Abstract.—We compared epipelagic fish assemblages associated with juvenile (ocean-age 0) Pacific salmon <em>Oncorhynchus </em>spp. from neritic waters of the California Current and Alaska Current regions in the spring–summer and summer–fall periods of 2000–2004. Catches originated from rope trawl surveys conducted between latitudes 37°N and 60°N and spanned more than 1,100 km in the coastal and inshore habitats of each region. Catch data were used from the epipelagic sampling of waters from near surface to depths of about 18 m, primarily over the continental shelf. Catch composition, frequency of occurrence, and density were evaluated between regions and habitats for day sampling. Diel (night and day) catch comparisons were also made at a few localities in each region. In day catches from both regions, a total of 1.69 million fish and squid representing 52 fish families and 118 fish species were sampled from 2,390 trawl hauls. Ninety-seven percent of the daytime catch was composed of 11 fish families and squid in coastal and inshore habitats of each region: clupeids dominated catches in the California Current (72% and 76% of catch, respectively), and salmonids dominated catches in the Alaska Current (46% and 62% of catch, respectively). Juveniles comprised 81–99% of salmon sampled in both coastal and inshore habitats of each region. Frequencies of occurrence were highest for juvenile salmon in both regions, but average densities were highest for Pacific herring <em>Clupea pallasii </em>and Pacific sardine <em>Sardinops sagax </em>in the California Current region. Cluster analyses revealed distinct geographic breakpoints in coastal species assemblages off central Vancouver Island and in inshore species assemblages in southeastern Alaska. Species were found to cluster into six groups from coastal localities and four groups from inshore localities. Indicator species analysis and nonmetric multidimensional scaling revealed that most species of juvenile salmonids were located in northern localities. Although juvenile salmon had the most uniform distribution of any species group, their densities relative to associated species were dramatically lower in the California Current, suggesting a higher degree of interactions between juvenile salmon and other species in this region. Diel comparisons in both regions indicated substantially higher catches at night, particularly of clupeids, osmerids, and gadids. Salmonids were a relatively minor component of the night catch in both regions due to dramatic diel shifts in community structure. Additional study of diel interactions of juvenile salmon and associated species is needed to quantify habitat utilization dynamics in marine ecosystems.


2004 ◽  
Vol 133 (2) ◽  
pp. 371-384 ◽  
Author(s):  
Valerie A. Barko ◽  
David P. Herzog ◽  
Robert A. Hrabik ◽  
John S. Scheibe

Biologia ◽  
2017 ◽  
Vol 72 (4) ◽  
Author(s):  
Robert Czerniawski ◽  
Łukasz Sługocki ◽  
Monika Kowalska-Góralska

AbstractBeaver ponds favour lentic species over the original lotic animals. The typical lentic animals are zooplankton, which can be good predictors of hydrological changes in streams caused by beaver activity. We analysed the effects of beaver dams on the zooplankton communities in small lowland streams in stream-beaver pond-stream systems. All spatial changes in the composition of zooplankton reflected the effects of physical changes introduced by the beaver dams. The rapid increase in the density of the aforementioned taxa was possible because the features typical of stagnant water reservoirs are present in beaver ponds. The number of taxa and the abundance and biodiversity of zooplankton, especially planktonic rotifers, were higher in the dam and downstream sites than in the upstream sites. Therefore, the impact of beaver ponds on the composition of zooplankton in streams below the dams is considerable, and there is an increase in the organic matter downstream, which leads to trophic changes in the stream.


2008 ◽  
Vol 68 (4 suppl) ◽  
pp. 1119-1132 ◽  
Author(s):  
AA. Agostinho ◽  
FM. Pelicice ◽  
LC. Gomes

Reservoirs have been built in almost all of the hydrographic basins of Brazil. Their purposes include water supply for cities, irrigation and mainly, generation of electricity. There are more than 700 large dams and associated reservoirs in the large rivers of the country. These reservoirs favor local and regional economic development, but they also bring serious and irreversible alterations in the natural hydrologic regime of rivers, affecting habitat quality and the dynamics of the biota. In the impounded area, the main impact is the change from lotic to lentic water, which influences aquatic fauna, including fishes. Impacts of reservoirs present relevant spatiotemporal variations. Immediately after reservoir formation, fish species richness usually increases due to incorporation of surrounding habitats, but richness decreases as reservoirs age. However, impacts downstream of dams appear to be similar or stronger than those that occur within the reservoir. Dams promote discharge control, altering the seasonal cycles of floods. These effects are augmented when dams are constructed in cascades. Therefore, dams profoundly influence composition and structure of fish assemblages. Most affected species are the rheophilics and long distance migratory that require distinct habitats to fulfill their life cycles. Populations of migratory species may collapse or even disappear in intensely regulated stretches. Management actions taken to minimize impacts of dams in Brazil historically considered construction of fish passages, fishery control and stocking. The results of these actions are questionable and/or with clear failures. In this paper, we give emphasis to the Paraná River basin, the most affected by dams in Brazil. We describe some patterns in the alteration and decline in fish diversity in areas influenced by dams. We also discuss negative consequences in the fishery and ecosystems functioning. Finally, we argue the relevance and the success of the management actions taken and present some suggestions to improve conservation of the ichthyofauna in South American basins influenced by dams.


1993 ◽  
Vol 71 (7) ◽  
pp. 1439-1447 ◽  
Author(s):  
Hugh F. Clifford ◽  
Gillian M. Wiley ◽  
Richard J. Casey

There were different macroinvertebrate assemblages on the face of and in beaver dams compared with beaver ponds and main stream sites. The beaver dam featured a large proportion of simuliid larvae compared with the main stream sites of this stream and with areas of other studies of beaver-altered streams. The fauna of the dams was typical of fast-flowing habitats, whereas animals of the main stream sites (including the beaver ponds) were more characteristic of slow-flowing or lentic habitats. Cluster analysis separated the dam and main stream sites for each sampling date and year of our study based on the composition of the macroinvertebrates. Although the invertebrate assemblages of the dams differed from those of the main stream sites, both habitats included similar functional feeding groups, except for a shredder found only at the dams. There are similarities between the beaver dam fauna and the faunas of debris dams, woody snags, and lake outlets. Beaver dams are important in supporting large populations of simuliids and generally in maintaining a lotic fauna in slow-moving, low-gradient boreal streams.


Water ◽  
2021 ◽  
Vol 13 (24) ◽  
pp. 3641
Author(s):  
Mirosław Rurek

Currently, there are only two species of beavers described—the North American beaver (Castor canadensis) and Eurasian beaver (Castor fiber). Their natural habitats are confined to the northern hemisphere but instances of beaver introduction to regions of the world they do not normally inhabit have also been recorded. The activity of beavers leads to changes in the natural environment linked to hydrological and geomorphological and plant cover transformations. Beavers live in natural and artificial water reservoirs and rivers. If the water level in the river is too low, they build dams to create a comfortable living environment. This paper aims to present changes in the relief of the valley inhabited by beavers in which sediments accumulate. During the field study, detailed measurements of dams and of the spatial range of beaver ponds were made, and the thickness and spatial distribution of accumulated sediments were determined. In addition, measurements of geomorphological forms in beaver ponds were also made. The samples of sediments were subject to grain-size distribution analysis, the results of which allowed calculating sediment parameters. Beavers appeared in the Gajdówka valley in the southern part of the Tuchola Forest (Poland) in 2008. In 2008–2011 they built 17 beaver dams that impounded ponds. The beaver ponds and beaver dams were of different sizes. They either flooded the whole flat bottom of the valley or only raised the level of water in the riverbed. A characteristic feature of beaver ponds is that they capture sediments. Different landforms were created in the course of the formation and disappearance of beaver ponds. It was established that these include alluvial fans, levees, sand shadow dunes and microterraces formed by deposition and erosion. They do not occur in all ponds. Points at which mineral sediments are supplied to the watercourse, including beaver burrows and erosion hollows, are presented together with the points at which sediments are transferred from ponds upstream to ponds downstream the watercourse. Beaver activity during valley colonization shows changes in the landscape caused by their presence and in particular their impact on the relief and deposition of sediments. Analysis of contemporary changes in the morphology of the Gajdówka Valley leads to the conclusion that beaver activity has had an intense impact on the terrain relief of the valley inhabited by beavers.


2020 ◽  
Vol 71 (4) ◽  
pp. 419
Author(s):  
C. Duarte ◽  
H. M. V. Espírito-Santo ◽  
J. Zuanon ◽  
L. H. Rapp Py-Daniel ◽  
C. P. Deus

Studies of fish assemblages have demonstrated that the main channels of rivers contain ichthyofauna adapted to this environment. However, information regarding the effects of temporal and spatial variations on this ichthyofauna is scarce. Using data from benthic fish assemblages in a major tributary of the Amazon basin collected during two consecutive receding and two rising water seasons, we tested the hypothesis that there are marked variations in community composition between the receding and rising water seasons. An asymmetry in predictability was detected among samples from the receding and rising seasons. Predictability in terms of species composition was higher for receding than rising seasons. The continual disassembly and reassembly cycles (due to dispersal) of local communities across a spatially heterogeneous landscape could explain this difference. Depth and dissolved oxygen affected the distribution of some benthic fish species during the rising seasons. This study highlights the important contribution of marginal wetlands to the benthic ichthyofauna inhabiting the main channel of the Purus River, as well as other major Amazonian rivers.


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