Upstream Salmon and Society in the Pacific Northwest (1996) / Chapter Skim
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7 Habitat Loss
7 Habitat Loss
Pages 164-203
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From page 164... ...
Habitat alteration and loss that lead to reduced salmon production can occur when either of two conditions exists: anthropogenic perturbations transform freshwater spawning or rearing habitat to an un 164
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From page 165... ...
The important point is that habitat can be altered by the direct effects of human perturbations and by human prevention of natural disturbances (Sousa 1984, Wissmar and Swanson 1990~. Either can impair salmon production, especially when its spatial or temporal scale differs fundamentally from that of the natural disturbance regime of an area.
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From page 166... ...
NATURAL VERSUS ANTHROPOGENIC DISTURBANCES AND WATERSHED PRODUCTIVITY Natural disturbances play a crucial role in the various life-history phases of salmon. Pacific salmon evolved in freshwater environments that included a variety of natural disturbances, including seasonal high flows and floods, glaciers, droughts, wildfires, volcanism, landslides and debris flows, and seasonally extreme temperatures.
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From page 167... ...
It is therefore important to view human activity not only as a cause of habitat change, but also as potentially hindering natural disturbance patterns and recovery processes from creating and maintaining productive and diverse habitat. Productivity declines when habitat alteration and loss impair the successful completion of life-history stages in the context of a watershed's landscape, its natural disturbance regime, and its anthropogenic changes.
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From page 168... ...
. Natural disturbances large enough to have an important impact require recovery intervals that might include periods of high production followed by re-establishment of density-dependent regulating mechanisms and biological controls that cause a return to predisturbance levels.
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From page 169... ...
The spatial and temporal scales of anthropogenic habitat alterations that are imposed on salmon populations often differ in both frequency and magnitude from natural disturbance regimes. It is the natural disturbance regimes to which local populations are adapted and that have historically powered the creation of new, productive habitat: These characteristics must be retained or replicated if freshwater salmon habitat is to be sustained (Hill et al.
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From page 170... ...
0.1 - 1.0 0.01 - 1.0 Major floods; storms; rain-on-snow events 10 - 100 1 - 50 Debris avalanches and debris torrents 1 Go - 1 coo 20 - 200
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From page 171... ...
cover; relocation of holding areas. In areas affected by ice: decreased water temperatures; lower primary and secondary productivity; egg dewatering or scour during anchor ice formation and breakup Changes in the frequencies of riffles and pools; formation of large log jams; burial of some spawning sites but creation of new areas suitable for spawning; increased amounts of fine particular organic matter for processing by the benthic community, resulting in increased secondary production; destruction or creation of side-channels along the floodplain; increased secondary production and cover habitat in estuaries Extensive loss of pool habitat in the torrent track; loss of spawning gravels; loss of habitat complexity along edge of stream; destruction of side-channels and other overwintering areas; creation of new cover in the terminal debris dam; creation of new spawning areas in the sediment terrace upstream from the debris dam; short-term loss of aquatic invertebrates; possible damage to gills from heavy suspended sediment load; increased primary production
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From page 172... ...
172 TABLE 7-2 Continued UPSTREAM: SALMON AND SOCIETY IN THE PACIFIC NORTHWEST Approximate Recurrence Interval (years) Natural Anthropogenic Type of Disturbance Beaver activity Major disturbances to vegetation Windthrow Wildfire Insects and disease Slumps and earthflows 5- 100 0 (removal of beavers)
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From page 173... ...
. Spartan canopy and vegetative cover; decreased litterfall; short-term increase in summer flows from reduced evapotranspiration Low-level, long-term contributions of sediment and large woody debris to streams; partial blockage of channel; local baselevel constriction below point of entry; shifts in channel configuration; long-term source of nutrients Enhanced rearing and overwintering habitat; increased water volumes during low :llows; refugia during floods; possible blockage to upstream migration by adults and juveniles; elevated summer temperatures and lower winter temperatures; local reductions in dissolved oxygen, including areas under ice in winter; increased production of lentic invertebrates in pond; increased primary and secondary production downstream from pond Increased pool habitat; localized sedimentation; increased in-channel cover; increased summer temperatures and decreased winter temperatures; creation of eddies and alcoves along channel mat gins; increased secondary production Increased sedimentation of spawning and rearing habitat; increased pool habitat and in-channel cover' increased water volume in summer; increased summer temperatures and decreased winter temperatures; increased secondary production; reduced dissolved oxygen in spawning gravels; scour of egos and alevins in spawning gravels Increased pool habitat and in-channel cover: increased summer temperatures and decreased winter temperatures; increased water volume in summer; increased primary and secondary production Sedimentation of spawning gravels; scour of channels below point of entry; accumulation of gravels behind obstructions; possible blockage of fish migrations; increased pool habitat in coarse sediment and large woody debris depositional areas; destruction of side channels in some areas, creation of new side channels in others; long-term maintenance of aquatic productivity
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From page 174... ...
An estimated 250,000 stream crossings are associated with the road system, and most of the crossing structures might be unable to withstand storms with a recurrence interval of less than 25 years (FEMAT 19933. Road failures often result in debris torrents in small streams and can be particularly damaging to coho, steelhead, and sea-run cutthroat habitat.
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From page 175... ...
19911. Fine sediment can fill interstitial spaces and prevent their use by juvenile salmon for cover (Platte and Megahan 1975~.
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From page 176... ...
; various flood-control practices Short-lived toxicant (e.g., spill) ; major debris torrent Introduction of pathogen to drainage system; channelization Point-source sediment inputs; local thermal change; migration blockage in tributary Increased erosion at the watershed level; widespread loss of riparian vegetation; habitat simplification; multiple water withdrawals; dams Frequent discharges of long- or shortlived tox~cants; chronic anoxia; temperature or flows beyond tolerance .
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From page 177... ...
HABITAT LOSS 177 Relative Recovery Time Biological Recovery Mechanisms Short Moderate to long Fast Long Moderate to long Long Moderate to long Long Very long Very long Behavioral avoidance and refuge-seeking; increased growth among survivors; rapid recolonization of disturbed area Adjustment of populations and community structure to new habitat conditions; species migrations and new population establishment Behavioral and physiological avoidance; refuge-seeking; rapid recolonization Physiological acclimation; selection for tolerant species; behavioral avoidance and ref~uge-seekin:,; shifts in community organization Behavioral avoidance; recolonization; new species establishment Population and community adjustments; selection for tolerant species Local population and community adjustments; colonization by tolerant species; behavioral and physiological .
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From page 178... ...
, and single very large anthropogenic impact superimposed on natural disturbance regime (d)
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From page 179... ...
summarized studies of spawning requirements of Pacific salmon and noted that the area used by each spawning pair ranged from less than 1 m2 for pink salmon to 20 m2 for chinook salmon. They concluded that substrate-particle size composition does not constitute a comprehensive measure of the suitability of stream gravel for spawning; water depth, velocity, and proximity to cover were also important in determining suitability.
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From page 180... ...
Platts (1991) compared the results of 21 studies of the effects of livestock grazing on riparian zones and fish populations in western North America and found that 20 documented substantial damage to rip arian vegetation and 18 found substantial decreases in fish populations.
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From page 181... ...
In heavily used recreational areas, damage to streambanks and riparian zones can be severe. STREAMBANK ARMORING AND CHANNELIZATION Just as streambank erosion can alter fish habitat, prevention of all lateral channel movement can change the pattern of responses to natural disturbances in streams.
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From page 182... ...
Some types of armoring materials can provide habitat for juvenile salmon. For example, rock riprap consisting of large boulders with many interstices is used for cover in both summer and winter by salmon and steelhead in middle Columbia River tributaries (Mullen et al.
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From page 183... ...
The extraction of aggregate material from streams and rivers has local effects, such as altering bed elevations and channel morphology, that in turn affect other characteristics (e.g., spawning habitats, streambank morphology, channel patterns, riparian vegetation) and processes fe.g., bedload transport rates, connectivity of hyporheic and subsurface water zones)
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From page 184... ...
Although cutthroat trout continued to survive in Thornton Creek, the last adult coho salmon was reported in 1979, and none has appeared since then despite repeated fry plantings by school and volunteer groups. Conditions in this stream might be typical of small streams in heavily urbanized areas, where habitat loss has been extensive and permanent (Booth 19911.
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From page 185... ...
FLOOD CONTROL Prevention of damage by flooding is usually achieved through the use of flood-control dams, dredging to increase channel capacity, and dikes and levees to prevent rivers from overtopping their banks and spilling out onto the floodplain. Specific effects of dams are discussed in Chapter 9, but flood-control measures can have a serious effect on salmon habitat.
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From page 186... ...
Isolation of rivers from floodplains can in some instances be extensive (Sedell and Froggatt 1984~. The Pacific Northwest River Basins Council (1972; as quoted in Kaczynski and Palmisano 1993)
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From page 187... ...
19871. Some flushing is beneficial in that it removes fine sediment from the streambed, but excessive flushing can remove much of a stream's organic matter and adversely affect secondary productivity (Sedell et al.
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From page 188... ...
In most instances, the potential effects of flow reductions on rearing salmon will be mediated by the amount of pool habitat and by biological factors, such as food availability, population levels, competitors, and predators. Altering the flow regime of a stream can interfere with the upstream migration of adult salmon.
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From page 189... ...
It is likely, however, that some of the greatest impacts of alterations in groundwater on salmon habitat result from
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From page 190... ...
Like several other types of habitat alteration, loss of streamside vegetation can affect salmon in a variety of ways. Riparian vegetation mediates key interactions between aquatic and terrestrial ecosystems and in many respects controls the productivity of streams by influencing water, sediment, and nutrient dynamics; shading; inputs of fine particulate organic matter and woody debris; and the stability of streambanks and floodplain terraces (Beschta 1991, Gregory et al.
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From page 191... ...
Much of the historically most productive salmon habitat exists in lower river valleys and coastal lowlands where riparian zones are given the least protection (Sedell et al.
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From page 192... ...
Clear patterns have yet to be established, but increased temperatures at northern latitudes along the West Coast have tended to benefit salmon production in small, naturally cold streams by increasing available food resources (e.g., Holtby 1988) , whereas salmon productivity at southern latitudes usually declines when temperatures extend into thermally stressful
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From page 193... ...
found that adult chinook salmon behaviorally regulated their body temperature by pausing in areas of cool
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From page 194... ...
Their effects on native salmon populations are often poorly understood, but many species are known to prey on young salmon or compete with them for food or rearing sites at some stage in their life history. Temperature increases whether caused by riparian canopy removal, water impoundment, agricultural and urban runoff, or heated industrial discharges-create conditions favorable to many warm-water game species and might enable them to gain a competitive advantage or facilitate their predation on juvenile salmon.
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From page 195... ...
, scoured stream channels, and created conditions similar to those resulting from splash dams and log drives. When it became apparent that accelerated hillslope erosion had caused numerous debris torrents culminating in large, impassable logjams, fishery management agencies in the middle 1900s undertook aggressive programs of debris removal to facilitate adult salmon spawning migrations.
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From page 196... ...
In other areas of North America where habitat simplification has taken place, streams support fewer species and are less resistant to community disruption from natural disturbances (Kerr et al. 1985, Schlosser 19911.
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From page 197... ...
(1993) , citing several studies by the National Marine Fisheries Service, stated that about 70% of Washington's water diversions lacked proper screening in the late 1970s and that 30% continued to be improperly screened or designed even after efforts to improve screening.
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From page 198... ...
Pollution-abatement efforts have reduced sewage and industrial discharges over the last two decades and the upper estuary is no longer anaerobic in summer, but experimental releases of smells from hatcheries upstream have shown that a pollution block still exists in Grays Harbor and that exposure of smolts to water of poor quality has reduced seawater adaptation, increased infestation by a trematode parasite, lowered disease immunity, and possibly increased vulnerability to predation by birds and squawfish. Smolts in the Chehalis River system survive at roughly half the rate of smelts from a nearby, relatively unpolluted river (Seller 19891.
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From page 199... ...
, and there seems to be little hope of future establishment of such areas without considerable public resolve and financial commitment. SUMMARY Habitat for salmon in Pacific Northwest river basins has been lost or extensively altered over the past 150 years.
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From page 200... ...
200 Key Watersheds Tier ~ Tier 2 UPSTREAM: SALMON AND SOCIETY IN THE PACIFIC NORTHWEST ? \ FIGURE 7-4 Key watersheds in the Pacific Northwest identified in the president's forest plan.
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From page 201... ...
Catastrophic habitat loss can also occur as a result of natural disturbances, but the frequency and spatial scale of natural disturbancesunlike those of many human-caused disturbances are such that salmon's behavioral and physiological characteristics allow their populations to be resilient. Human activities have prevented natural disturbance regimes from creating
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From page 202... ...
Examples include flood control and wildfire suppression, both of which have interfered with processes that provide woody debris and nutrients to river systems. In addition, stream processes have been altered to the extent that they cannot respond to natural disturbances in a normal manner.
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From page 203... ...
The initial phase of the program has already helped to protect good habitats in six important salmon watersheds in this urban area, which includes Seattle (King County Surface Water Management Division 19959.
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