George R. Pess1, NOAA Fisheries, Northwest Fisheries Science Center, 2725 Montlake Boulevard East, Seattle, Washington 98112 Michael L. McHenry, Lower Elwha Klallam Tribe, 2851 Lower Elwha Road, Port Angeles, Washington 98363 Timothy J. Beechie, and Jeremy Davies, NOAA Fisheries, Northwest Fisheries Science Center, 2725 Montlake Boulevard East, Seattle, Washington 98112

Biological Impacts of the Elwha and Potential Salmonid Responses to Removal

Abstract The Elwha River dams have disconnected the upper and lower Elwha watershed for over 94 years. This has disrupted salmon migration and reduced salmon habitat by 90%. Several historical salmonid populations have been extirpated, and remaining popu- lations are dramatically smaller than estimated historical population size. Dam removal will reconnect upstream habitats which will increase salmonid carrying capacity, and allow the downstream movement of and wood leading to long-term aquatic habitat improvements. We hypothesize that salmonids will respond to the dam removal by establishing persistent, self-sustaining populations above the dams within one to two generations. We collected data on the impacts of the Elwha River dams on salmonid populations and developed predictions of species-specific response dam removal. Coho (Oncorhynchus kisutch), Chinook (O. tshawytscha), and steelhead (O. mykiss) will exhibit the greatest spatial extent due to their initial population size, timing, ability to maneuver past natural barriers, and propensity to utilize the reopened alluvial valleys. Populations of pink (O. gorbuscha), chum (O. keta), and sockeye (O. nerka) salmon will follow in extent and timing because of smaller extant populations below the dams. The initially high sediment loads will increase stray rates from the Elwha and cause deleterious effects in the egg to outmigrant fry stage for all species. Dam removal impacts will likely cause a lag in recolonization and population rebuilding. These negative sediment effects will be locally buffered by the extent of functioning , and management attempts to minimize sediment impacts. Resident life forms of char (Salvelinus confluentus), rainbow trout (O. mykiss), and cutthroat (O. clarki) will positively interact with their anadromous counterparts resulting in a positive population level response.

Introduction Dams, fishing, habitat degradation, hatcheries, climate change, and introduction of non-native The effects of dams on riverine ecosystems have species are considered the main causes of salmon been well-documented throughout the world population declines in the United States (NRC (Petts 1984, Ward and Stanford 1987). Dams 1996, Montgomery 2003). Many salmonids that alter hydrologic regimes and disrupt sediment occupy dammed have precariously low and organic matter transport (Petts 1984, Ward population levels and have recently been listed and Stanford 1987, Dynesius and Nilsson 1994), as either threatened or endangered under the leading to downstream changes in water quality, United States Endangered Species Act (NRC energy flow, and dynamics and 1996, Montgomery 2003). Coincident with these morphology (Ligon et al. 1995). Dams also affect listings, the removal of aging and uneconomical ecological functions and aquatic organisms by dams is now considered a viable river management blocking migration into upstream habitats (Petts and salmon restoration alternative in the United 1984, Ward and Stanford 1987, Kanehl et al. 1997). States (Stanley and Doyle 2003). Over 500 dams Perhaps the most obvious effect on fish popula- have been removed in the past two decades, with tions, especially anadromous populations such as over 20% of these removed since 1999 (Stanley salmonids, is blocking fish migration (Ligon et al. and Doyle 2003). Over 75,000 dams greater than 1995). Such blockages reduce population sizes, 2 m in height have been constructed in the United alter life history diversity, and shift the spatial States (Graf 1999), and approximately 85% of structure of meta-populations (Ligon et al. 1995, those dams will reach the end of their operational Heinz Center 2002, Beechie et al. 2006). design life by the year 2020 (Stanley and Doyle 2003). The number of case studies examining ef- 1Author to whom correspondence should be addressed. fects of removing of small dams (<15 m high) is E-mail address: [email protected] increasing (Stanley and Doyle 2003), but removals

72 PessNorthwest et al. Science, Vol. 82, Special Issue, 2008 of large dams (>30 m in height) with historically are based on recolonization hypotheses which large populations of salmonids are rare. The Elwha focus on salmonid response to increased habitat River in northwestern Washington is one such availability above the dams due to dam removal, case where large dams have impacted aquatic reduced habitat quality below the dams due to habitat condition and salmonid populations, but increased sediment supply from dam removal, are scheduled for removal for the purposes of and the role of resident populations in reducing salmonid restoration. or accelerating anadromous salmonid population The Elwha River dams have blocked upstream response. migration of salmonids to over 90% of the wa- tershed for over 90 years and have disrupted the Study Area downstream movement of habitat forming inputs The Elwha River flows for 72 km from its source such as sediment and wood. Together this has in the Olympic Mountains to the Strait of Juan de resulted in a loss of spawning and rearing habitat Fuca on Washington State’s Olympic Peninsula upstream of the dams, as well as reduced spawning (Figure 1) (Duda et al. 2008). It drains 833 km2, and rearing habitat below the dams due to habitat with 83% of the watershed protected within the degradation. The result of this and other impacts boundaries of Olympic National Park. Historically has led to a 90% reduction of salmonid popula- the Elwha River had 10 anadromous fish stocks tion size, a loss of specific upstream stocks, and (Table 1). Construction of two dams without fish a shift in species composition. passage facilities on the Elwha River at rkm 7.9 in Simultaneous removal of the two large dams on 1912 and 21.6 in 1925 directly reduced accessible the Elwha River will begin pending the comple- habitat for anadromous salmonids by 90% (DOI tion of infrastructure (Duda et al. 2008). How 1996). This resulted in the immediate decline of will ecosystem processes such as primary and several “upriver” life history types including secondary production (Morley et al. 2008), stream Chinook salmon, pink salmon, summer steelhead, channel and floodplain dynamics (Kloehn et al. sea-run cutthroat, and anadromous char. It is also a 2008), and aquatic habitat conditions change with major contributor to the population status the removal of the Elwha River dams? How will of all 10 anadromous salmonids, several of which changes to these processes and conditions affect are either critically low or extirpated (DOI 1996). resident and anadromous fish communities? The The combination of blocking upstream migration Elwha poses a unique situation because the action and overall loss of anadromous salmonids has also will allow existing salmon populations to access led to a potentially significant decline in marine and recolonize nearly pristine habitats above the derived nutrients (MDN) levels throughout the dams. Dam removal will also cause large-scale Elwha River Basin, which can effect aquatic and sediment disturbance that will impact salmon terrestrial ecosystem productivity (Gende et al. populations and their ability to recolonize. The 2002). salmonid populations will thus have expanded habitat and broad-scale impacts occurring simul- Methods taneously. Additionally, extant resident salmonid populations above the dams will be exposed to To assess existing impacts due to the Elwha River anadromous colonizers. These resident salmonids dams we used: 1) existing information (e.g., peer- will also be able to freely migrate downstream. reviewed publications, gray literature reports, We provide data on the impacts of the El- historical survey information); 2) remote sensing wha River dams to aquatic habitat and salmonid techniques; and 3) field surveys to quantify the populations, develop a list of factors that affect change in aquatic habitats and anadromous salmo- salmonid recolonization, and develop species- nid populations. We compared current salmonid specific predictions of salmonid response to the habitat utilization of aquatic habitats below the planned dam removals. Providing an ecological dams to examine correlations among habitat type, context of the impacts of the dams is necessary quality, and salmonid use at several life stages. because our recolonization hypotheses are based Aquatic Habitat both upon the long-term impacts of the dams as well as the effects their removal. Our predictions Several types of aquatic habitat data (e.g., habi- of salmonid response to the removal of the dams tat types, stream temperature) were available

Salmonid Responses to Dam Removal 73 Figure1. Map of the Elwha River basin.

74 Pess et al. TABLE 1. Anadromous salmonid populations of the Elwha River. Estimated population sizes following dam removal (DOI 1994, see Winter and Crain 2008) and current population sizes (McHenry et al. 2000) based upon escapement estimates.

Estimated Estimated Population Current Hatchery Species Size Escapement Contribution (%) Spring Chinook 91201 unknown 50 (WDFW 1993) Summer/Fall Chinook 212801 3000 unknown Coho 30400 2900 76 Chum 3420 1000 0 Pink 266000 150 0 Sockeye 7600 50 0 Winter Steelhead 7980 1800 83 Summer Steelhead 3420 100 0 Sea-run Cutthroat unknown unknown 0 Char2 unknown unknown 0

1Estimate of spring and summer/fall distribution based upon estimated proportional difference in life histories (McHenry et al. 2000). 2Bull trout and brook trout for reaches of the Elwha River upstream of the floodplain) forming processes and then to monitor dams (Hosey and Associates 1990, Munn et al. expected changes in wood loading following dam 1999), but equivalent data were generally lack- removal. During low flow periods, individual logs ing between and below the dams. To supplement (e.g., snags) (>30 cm diameter, >10 m length) and existing data sets, we used aerial photographs and logjams (accumulations of >50 pieces of wood) field surveys to further quantify habitat conditions. were located and measured within the mainstem We classified habitat units at the reach scale (i.e., and floodplain channels of the Elwha River. 100’s of meters) using attributes such as mainstem Individual snags were tagged with a numbered channels, floodplain channels, and as aluminum disc at both ends of the log. A global well as at the habitat-scale (i.e., 10s of meters) positioning system (GPS) was used to map each using attributes such as pools, , and glides snag and the following parameters were recorded: (Beechie et al. 2005). For each habitat unit, we taxon, decay factor (1 to 5), orientation, diameter measured surface area, estimated in-channel at breast height, diameter at top, overall length, cover, and identified the dominant and sub-domi- and root wad area. Logjams were also located nant channel substrate type. In pool habitats we using GPS and the following features measured: measured residual pool depth (maximum depth average height, width, and length; the number of minus minimum outlet depth) and the dominant key pieces within and their orientation; and an pool forming factor. Floodplain channels were estimate of the number of logs stacked on each classified by the type of water connectivity to the other within the jam (Abbe et al. 2002). mainstem. floodplain channels had We used sequential aerial photographs and con- a direct mainstem connection during summer low ducted interviews with both short-time observers flow. Over-flow channels had a direct mainstem and one long-time observer of fish populations in connection only during bankfull or higher flow the Elwha River to document changes in spawn- events. Groundwater channels did not have a ing area used by large concentrations (20 or more mainstem channel connection at their upstream pairs) of adult salmonid spawners over time. Aerial end, but had an identified source of sub-surface photographs (National Park Service and Washing- flow. Combination channels had each of the pre- ton State Department of Natural Resources) for ceding characteristics. the years 1939, 1955, 1974, 1990, and 2002 were We inventoried in-channel wood below Elwha used to document spatial changes in spawning Dam in 2001 and 2002. Our goal was to assess the area. For each photo year, we asked observers to relationship between wood and habitat (riverine and locate areas that supported consistent spawning

Salmonid Responses to Dam Removal 75 activity of pink and Chinook salmon. The recent nids do not seek refuge in the substrate during observers were typically fisheries biologists or daylight hours (Hillman et al. 1992). This allowed technicians who have worked on the Elwha River for an entire census of all habitats and since the late 1980’s. Long-term observers were the largest floodplain channels below the Elwha typically fisherman who had spent > 50 years on the dam. Night snorkels within selected habitat units Elwha River. We selected these taxa as indicators were necessary during the winter and spring as of overall spawning activity because water clarity juvenile salmonids generally seek refuge in the and flow conditions during their late summer/early substrate during daylight when water tempera- fall spawning period maximize detectability. Once tures are < 10 °C (Hillman et al. 1992, Roni and identified as a significant spawning site on the aerial Fayram 2000). photograph, a polygon was drawn to approximate the spawning area for each year analyzed. We Intrinsic Potential Maps used a geographic information system (GIS) to We combined topographic data, potential migra- conduct spatial analysis and graphically display tion barriers, existing salmonid habitat utilization changes in spawning area over time. data from below the dams, and salmonid habitat Salmonid Habitat Utilization preferences to develop intrinsic potential spawning maps for six salmonid species. Reach-level channel We assessed the spatial distribution of adult spawn- characteristics (slope and width) and form ing Chinook salmon in the lower Elwha River were derived from topographic data using hydro- from 2000-2003. Spawning ground surveys were logic and terrain modeling, respectively (Davies conducted by boat or on foot at 7-10 day intervals et al. 2007, Jenness 2006). Salmonid barrier data between August 1-October 15 in the mainstem from previous studies in the Elwha were used to and large floodplain channels of the lower Elwha identify limits to salmonid extent for each species River to enumerate spawning populations. During (Hosey and Associates 1990, Brenkman et al. each survey, we located active salmon redds and 2008). Current juvenile and adult habitat utiliza- recorded their location using GPS, and measured tion data below the dams were used to identify the stream depth, stream velocity, substrate size, relative importance of general habitat types such habitat type, distance to streambank, distance as differences in mainstem and floodplain channel to pool, and distance to nearest accumulation of use. Lastly we used species-specific information woody debris. on spawning habitat preferences based on stream Snorkel surveys were used to quantify the channel slope and bankfull width (Groot and seasonal distribution and abundance of all juve- Margolis 1991, Montgomery et al. 1999). nile and adult salmonids below the Elwha dam. All juvenile and adult fish species were identified Results and their lengths visually estimated during the snorkel surveys. Fish censuses were conducted Impacts of the Dams by dividing each habitat unit into three or four The primary impact of the Elwha dams on the sections of similar size (snorkel lanes). An ob- Elwha is the longitudinal dis- server in each lane moved upstream to count and connection of the upper and lower portions of identify each fish. On several occasions multiple the watershed (Figure 1). This has resulted in snorkel counts occurred within the same unit in two main effects. The first is that salmon are order to estimate observer variation (Hankin and blocked from migrating upstream above rkm 7.9 Reeves 1988). We calculated fish abundance as and subsequently utilizing most of the watershed. the number of species observed by size class of Second, disruption in the downstream movement fish per habitat unit (m2). We completed habitat of sediment and wood has caused habitat degra- surveys prior to any juvenile and adult enumera- dation and reduced habitat complexity between tion efforts in order to: 1) identify the distribution and below the dams (Kloehn et al. 2008). Habitat of habitat types within each reach; and 2) select loss and degradation have affected the distribution which habitat units to sample for juvenile salmonid and abundance of juvenile and adult salmonids, distribution and abundance. and have played a major role in the decline in Daytime snorkel surveys were conducted when salmonid populations in the Elwha since dam water temperatures were >10 °C because salmo- construction (Table 1).

76 Pess et al. Blockage to upstream migration Approximately 90% of the potential salmonid spawning and rearing habitat in the Elwha River basin has been inaccessible for over 90 years. As much as 146 km of mainstem and habitat are blocked to anadromous salmonids above the dams (Hosey and Associates 1990, Munn et al. 1999). However, those estimates did not consider floodplain channel habitats in seven low-gradient, alluvial valley bottoms, which constitutes an ad- ditional 41 km (28%) of the total area of available Figure 3. Total salmon spawning area in the lower Elwha habitat in the Elwha River. River between 1939 and 2002. Loss of access to these reaches has reduced habitat capacity for salmonid populations, and also habitat for salmonids. The decline in spawning led to decreased life-history diversity (Beechie et area was initially slow following dam construc- al. 2006). For example, historically the majority tion. The number and average size of spawning of spring Chinook, pink salmon, and summer sites was similar between the 1939 (22) and 1956 steelhead migrated upstream above Elwha dam in (23) photo years, and the total area of habitat de- the late spring and early summer to access river clined by less than 25% (Figure 3). The number habitats that have more suitable temperatures for of sites decreased from 23 in 1956 to 13 in 1971 holding and spawning (Figure 2). Over the last and available spawning area decreased by 60% 90 years such habitat has not been accessible from 1956 estimates. By 1990 only 12 significant and spring Chinook could only utilize the lower spawning sites remained in the lower Elwha and Elwha, where peak summer temperatures typically the total spawning area had decreased another reach 18-21 °C. 60% from 1971 estimates. Between 1991 and 2002 the decline in spawning area was reversed, as the river shifted course into the Hunt’s Road channel (HRC), exposing a relatively large area of newly created spawning habitat. The fifteen additional spawning sites include a total area of 19,000 m2, an increase of 56% from 1991.

A loss of in-channel wood Wood loading, in the form of snags and log- jams, below Elwha dam was four times higher in floodplain channels than in the mainstem (Figure 4). In the lower river, the majority of wood was Figure 2. Days per year (SE) of preferred (open) and det- mostly found in two locations – the HRC (rkm rimental (grey) temperatures for incubation of 2.5 to 1.5) and in the mainstem immediately Chinook salmon embryos in the Elwha River during above tidewater (rkm 0.5 to 0.3). Over half of 1992 to 1996. the snags below the Elwha dam were associated with the HRC (Figure 4). Three large logjams Loss of salmonid spawning habitat that fully spanned the HRC accounted for most of the wood volume in the entire lower Elwha. The construction of the Elwha dams truncated the Tracking individual piece locations in the lower alluvial transport of sediment which has resulted Elwha between years showed that the majority of in the coarsening of river bed in the middle and key, immobile pieces in the floodplain channels lower Elwha (Pohl 2004), leading to the loss were derived from local sources of wood such as of salmonid spawning habitat below the dams patches of mature floodplain forest immediately (Figure 3). From 1939 to 2002, the lower Elwha upstream, rather then the fluvial transport of wood River lost over 75% of the available spawning from locations further upstream.

Salmonid Responses to Dam Removal 77 Figure 4. Overhead view of large wood snags (open circles) and logjams (grey squares) in the Hunt’s Road channel and mainstem lower Elwha River (rkm 1.5 to rkm 2.5).

78 Pess et al. Figure 5. Number of overflow (black), surface water (grey), ground water (open), and combination (dotted),channel types in in Valley (above the dams; rkm 32.0 to 28.1), middle Elwha, and lower Elwha.

The continued importance of floodplain density of boulders and bedrock outcrops in the channels lower Elwha. Juvenile coho salmon densities were highest in the mainstem between rkm 3.0 and 4.0. An inventory of floodplain channels in the Geyser These relatively high densities were associated Valley (the first main valley in the upper Elwha), with logjams, as the mean density of 0.05 fish/m2 middle Elwha, and lower Elwha River revealed in logjams was an order of magnitude higher than that approximately 80% of the floodplain channels the mean density in non-logjam locations (0.005 had flowing water connected to the mainstem, 2 however the type of low-flow connectivity to the fish/m ) (Pess et al. 2003a). The highest densities mainstem varied by valley location (Figure 5). of juvenile Chinook salmon were found near the Geyser Valley had a relatively even distribution of mouth to rkm 1.0 (Figure 6a). water connection types with the majority being a Juvenile salmonid density was typically higher combination of surface and groundwater connected in floodplain habitats than in mainstem habitats channels (33%). The middle and lower Elwha and varied with water source (Figure 7). Water were dominated by surface water connections connection type was associated with salmonid (47% and 50%, respectively), whereas the number species distribution in the lower Elwha. We found of combination channels were less than all other that over 85% of the salmonids in groundwater channel types (10% and 7%, respectively). dominated channels were coho salmon, while 70% of the salmonids in surface-water channels Salmonid distribution and abundance were trout of varying size classes. We found between 25% and 40% of coho, Chinook, Species overlap was much greater for adults and rainbow/steelhead juveniles in the HRC (Figure than for juveniles (Figure 6b), with the highest 6a). The density of juvenile rainbow/steelhead in densities of adults between rkm 1.5–2.5 and rkm the mainstem was greatest immediately below 5.0–6.0. As with juvenile salmonids, high densities the Elwha dam. This reach also had the of adult salmonids between rkm 1.5 and 2.5 were highest stream channel gradient (>1%), the least associated with the HRC (mean density of 0.02 amount of accessible floodplain area, and highest fish/m2 in the HRC versus 0.004 fish/m2 in the

Salmonid Responses to Dam Removal 79 A migrating to the Elwha was 5,500 (<5000 – 19,800)—a large-scale reduction from historic estimates (McHenry et al. 2000). Seven of ten native salmonid stocks are at critically low levels including spring Chinook salmon, pink salmon, chum salmon (O. keta), sockeye salmon (O. nerka), sum- mer steelhead, cutthroat trout, and bull trout (Wunderlich et al. 1994, McHenry et al. 2000). Summer Chinook salmon, coho salmon and winter steelhead are currently supported by hatchery production. Estimates of relative B abundance have also shifted with the majority of salmonids in the Elwha today being coho salmon, Chinook salmon, steelhead, chum salmon, pink salmon and sockeye salmon, although it is not known if sockeye are strays or a remnant spawning population. The three most numerous species all have a significant hatchery influence (Table 1) (McHenry et al. 2000). Snorkel surveys of all mainstem and major floodplain channel habitats below the dams during the summer months of 2002 and 2003 indicated that the majority of adults were Chinook (GRP, Figure 6. Distribution by river km of (a) juvenile Chinook, trout, and coho in the personal observation). Coho lower Elwha during the summer of 2002 and (b) adult Chinook, steelhead, tended to be the dominant adult rainbow trout, and cutthroat in the summer of 2003. Based upon snorkel species during the fall, and steel- surveys. main channel). The majority of adult salmonids observed between rkm 5.0- 6.0 were associated with several large pools and glides. Reduction of salmonid populations Historic estimates of the total anadromous sal- monid population is estimated between 380,000 to 500,000 annual returns (DOI et al. 1994, DOI 1996, Munn et al. 1999). The historic relative abundance of species, in descending order, is es- timated as: pink, chum, coho, Chinook, steelhead, and sockeye salmon (DOI et al. 1994; DOI 1996; Figure 7. Juvenile salmonid density (#∙m-2 with SE) by habitat Munn et al. 1999; Gregory et al. 2002). Between type in mainstem (open) and floodplain (black) 1990 and 2000 the average number of salmonids channels of the lower Elwha river.

80 Pess et al. head was the most prevalent during the winter tions have established themselves within decades (MLM, personal observation). of glacial retreat (Milner and Bailey 1989, Milner and York 2001). Where fish ladders have been Discussion installed or culverts removed, natural colonization has led to self-sustaining populations within 1 to The Elwha River dams have disconnected the upper from the lower portion of the Elwha watershed 5 years (Bryant et al. 1999, 2002, Pess et for over 90 years. This has blocked anadromous al. 2003b). Recolonization and establishment of salmonid migration from access to the majority pink salmon in the Fraser River above Hell’s Gate of salmonid spawning and rearing habitat in the landslide required approximately 20 to 30 years to watershed. In addition the dams have altered the establish large spawning populations (Pess et al. life forms of specific salmonids such as char, 2007). Expansion of habitat area can thus allow rainbow trout, and cutthroat trout by isolating salmonids to utilize a greater diversity of habitat resident populations above the dams, and creat- types and conditions. These conditions may favor ing habitats for potamodromous life histories. increased growth and survival at key life stages, The dams have also disrupted the downstream resulting in higher population growth rates that movement of both sediment and wood, which lead to self-sustaining populations (Withler 1982). has reduced the quantity and quality of salmon Colonization can also lead to divergence of life habitat, as well as salmonid abundance and dis- history traits over decadal time frames (Kinnison tribution. Remnant populations persist below the et al. 2001). It is important to note that the success dams and are associated at the juvenile and adult of colonization is never certain and newly acces- life stage with floodplain habitats. Summarizing sible areas vary in suitability; Withler (1982) found and understanding these impacts is important only a small number of successful colonization because the factors influencing recolonization efforts, both natural and artificial, among hundreds of anadromous salmonids to the areas above the of attempts. Even though we know that salmon dams will be a function of the long-term impacts locate and utilize newly opened habitats, establish as well as the effects of dam removal. self-sustaining populations, and develop diverging life history traits in newly opened habitats, the Factors Affecting Salmonid Recolonization questions of why salmon stray and what causes successful colonizing remain unanswered. We began identifying variables affecting salmo- nid recolonization with two questions in mind. The persistence of self-sustaining populations What are the key factors that determine salmon in newly opened habitat is related to the compat- recolonization success? How do differences in ibility between specific life history adaptations salmonid species, population dynamics, and habitat and the physical and ecological characteristics conditions affect salmon recolonization success? of the new habitats (Quinn 1984, Allendorf and To answer these questions it is important to Waples 1996, Burger et al. 2000). The concept understand two alternative behaviors that affect that self-sustaining populations can be established, salmon recolonization — homing and straying or population size increased, when a sufficient (Hendry et al. 2004). Homing is the return of number of colonists have life history traits or mature salmon to the general location of their adaptations compatible with available habitats is natal site (e.g., where their parents bred) to spawn, important because it focuses on specific factors whereas straying is the return of mature salmon that can influence successful recolonization (Table to a non-natal site to spawn (Hendry et al. 2004). 2). The potential effect each of these variables The majority of salmon home to their natal sites, has on dispersal and recolonization will vary though straying is the behavior that has allowed according to species, local adaptations within salmonid populations over the course of thousands species (e.g. extent of freshwater use), and unique of years to colonize new habitats (Quinn 1984, habitat characteristics that are compatible with Hendry et al. 2004). both (Quinn 1984). Salmonids can quickly colonize new habitats Barriers are a key factor in determining the and establish self-sustaining populations (Hendry ability of salmonids to recolonize. Numerous et al. 2004). For example, in deglaciated large barriers isolate salmonids in space and over of southeast Alaska, multiple salmonid popula- time, whereas few, small barriers will allow for

Salmonid Responses to Dam Removal 81 TABLE 2. Factors affecting salmonid recolonization. non-natal habitats and reduces the probability of dispersal and recolonization. Stray rate will vary ↑ Dispersal and ↓ Dispersal and Factor Recolonization Recolonization by species (Hendry et al. 2004). For instance pink salmon stray rates average 6% and range between Barriers to movement Few, small Many, large 4 and 34%, while steelhead typically have stray Distance from source Near Far rates that average 7% and range between 5% and population 26% (Hendry et al. 2004, Keefer et al. 2005). Population Size Large Small Within a given species, run-timing and different Population Stray Rate High Low life history strategies may also result in different Habitat Area Large Small stray rates. Keefer et al. (2005) found that early Adaptation to local habitat High Low steelhead in the Columbia River system are more Habitat type1 Similar Different likely to stray into tributaries because they are typi- Habitat condition Good Poor cally exposed to high mainstem river temperatures Interaction with existing Positive Negative (e.g. > 20 ºC) for longer time periods than late fish population migrants, increasing the likelihood to temporarily 1Similarity of habitats between source and recolonized areas stray into cooler lower Columbia River tributar- ies. Population stray rates can thus either buffer or enhance the effect of population size. the exchange of individuals within and between Salmonid colonization and recolonization populations. The ability to maneuver past natural can in part be explained in terms of life-history barriers varies considerably with species and mi- characteristics such as local adaptations to habi- gration timing. For example, steelhead, coho, and tats and adjustments to changing environmental Chinook salmon combine swimming ability and appropriate flow levels to successfully maneuver conditions. Changing environmental conditions, past substantial barriers (Groot and Margolis 1991, such as turbidity levels, can play a critical role Quinn 2005). Chum salmon are not known for in the magnitude and timing of salmon coloniza- their ability to pass natural barriers (Groot and tion and recolonization. The eruption of Mt. St. Margolis 1991, Quinn 2005). Pink and sockeye Helens drastically changed habitat conditions have been known to be affected by modest barriers, that provoked an immediate straying response but can also maneuver past barriers and rapidly in returning adult salmonids. Adult Toutle River colonize habitats when flows are amenable (Roos steelhead straying rates increased from 16% to 1996). The degree to which char, cutthroat, and 45% after the eruption, with most strays moving brook trout can move past natural barriers are to watersheds with lower turbidity (Leider 1989). less understood. However, it was uncertain if these strays were productive enough to produce future spawning The theory of island biogeography (MacArthur populations (Leider 1989). Milner and Bailey and Wilson 1963) proposes that the distance from (1989) compared the density of salmonid coloniza- source population and size of newly opened habitat tion in two recently deglaciated, geomorphically area are two important factors that can determine similar, and adjacent streams in southeast Alaska. the likelihood of dispersal and colonization of new They found that turbidity was a dominant factor habitats. Habitats closer to a source population are influencing spawning density with 2.4 times the more likely to receive immigrants than those which spawning density in the stream with lower tur- are a greater distance. In addition, larger areas of bidity. Streams with lower turbidity levels were habitat increase the likelihood of recolonization. associated with a higher proportion of preferred Population size and stray rate are another set of spawning temperature range (12 to 15°C), a more factors that will influence the dispersal and ability attenuated hydrology, and greater intact riparian of salmonids to recolonize. Large population size or vegetation structure. In each case colonization high stray rates result in relatively more individu- and re-colonization occurred and the abundance als seeking new habitats, creating self-sustaining of eventual spawning populations varied as a spawning populations in other reaches of the same function of different habitat preferences among watershed or in entirely different watersheds (Pess species, local adaptations, habitat type (e.g, chan- et al. 2007). Conversely, low population size or nel slope, sediment character), and habitat quality low stray rates result in fewer individuals seeking (turbidity levels, temperature, cover).

82 Pess et al. Interactions with existing fish populations will Identifying and understanding how each of also affect salmonid recolonization potential. these variables affects species-specific salmonid Interactions between resident and anadromous recolonization provides a template for salmonid salmonids could have a positive or negative effect response in any watershed. For example, pink on the extent and rate of anadromous salmonid salmon which typically have larger population recolonization. Interspecific competition between sizes, relatively higher stray rates, minimal varia- different salmonid species is affected by fish tion in life history characteristics, and a short density and local habitat features (Harvey and freshwater residence are prime candidates for Nakamoto 1996, Volpe et al. 2001, McMillan et the colonization of newly opened habitats (Quinn al. 2007). Low levels of habitat diversity and com- 2005). Other species such as steelhead have lower plexity can lead to greater competition and result population sizes, relatively lower stray rates, in growth and survival levels being significantly greater variation in their life history, and greater less for one species relative to the other (Harvey freshwater residence time and complexity, making and Nakamoto 1996). Such competition can typi- them less likely to establish spawning populations cally result in “residents” having a competitive first (Quinn 2005). Conversely, pink salmon may advantage relative to “challengers” (Volpe et al. be limited in their spatial extent to colonize due to 2001, Glova and Field-Dodgson 1995). Interac- their relative limited ability to swim over natural tions between resident and anadromous salmonids barriers, whereas steelhead may have the greatest can also be positive. Downstream migrating spatial extent because of their ability to maneuver residents may accelerate colonization extent and past barriers. rates due to positive spawning interaction with upstream moving anadromous populations (Mc- Predicting Salmonid Response to Dam Millan et al. 2007). The downstream movement Removal in the Elwha River of upstream resident populations can also lead The Elwha River dam removal project provides to the establishment of self-sustaining spawning an interesting ecological juxtaposition of habitat populations (Roghair and Dolloff 2005), that re- expansion and degradation. Factors influencing sult in outmigrating smolts (Ruzycki et al. 2003). recolonization are a function of both the impacts of Brenkman et al. (2008) provide a more detailed the dams and the effects of dam removal (Table 3). description of resident/anadromous interactions The dams have dramatically reduced habitat avail- in the Elwha River. ability, altered habitat quality, isolated resident and

TABLE 3. Key factors that can influence salmonid recolonization in the Elwha River.

Factor Impacts of Dams Effect of Dam Removals Effect on Recolonization Anthropogenic Loss of habitat Access to spawning Attraction to specific barriers availability and rearing habitat specific habitat types Natural barriers Distance from source population Sediment Reduced spawning and Large-scale increase in Increased straying and “barrier” rearing habitat below dams sediment supply to migration due to turbidity Decreased straying due to sediment management and buffering of sediment effects due to floodplains Decrease in spawning habitat quality (short-term) Increase in spawnable area (long-term). Resident Isolation of resident and Interaction between ana- Competition and predation between populations anadromous populations dromous and resident fish anadromous and resident fish

Salmonid Responses to Dam Removal 83 anadromous populations, and altered the proportion both ocean and stream-type rearing (Beechie et of natural and hatchery fish in the watershed. Dam al. 2006). The expression of a stream-type life removal will open large stretches of river above history strategy may be particularly important the dams for the first time in nearly a century, due to lower year-round stream temperatures allowing anadromous salmonids to recolonize (Figure 2) that may limit juvenile growth rates nearly pristine freshwater habitat. Between the in the upper Elwha basin. dams there will be the simultaneous re-opening Spawning behavior above the dams should of existing salmonid habitat and a large scale mimic what currently occurs below the dams, so pulse of sediment that will change stream chan- we expect that mainstem and floodplain channel nel morphology and salmonid habitat. Changes habitats will initially be colonized by Chinook to channel morphology and salmonid habitat will salmon, as well as steelhead and coho salmon. be even more pronounced in the reservoir sections We hypothesize Chinook salmon will likely utilize and immediately below the dams. Much of the the mainstem, and to lesser extent large floodplain change to salmonid habitat will result in unstable channels similar to the HRC in the lower Elwha. channel features such as The spatial distribution of spawning Chinook and movement due to an increase in sediment salmon in the lower Elwha is currently clumped supply for the first five years, which can result in four primary locations. These include large in detrimental effects on salmon habitat capacity floodplain channels and mainstem mid-channel and survival (Beechie et al. 1996). Anadromous islands. All four sites contain significant deposits and resident populations in the Elwha will have of gravels, have flow characteristics typical of newly opened habitats to colonize and will have the Chinook salmon spawning areas, and contain opportunity to survive from deleterious sediment multiple channels. Mid-channel islands and larger impacts in existing habitats. We hypothesize that floodplain channels will thus have greater densities in general salmonids will respond to dam removal of salmonids for the spawning life stage (Cou- by establishing persistent, self-sustaining salmonid lombe-Pontbriand and Lapointe 2004). populations in the middle and upper Elwha within in one to five generations (two to twenty years) The interactions between existing resident following dam removal. populations and juvenile Chinook salmon is an unknown, however there is a potential for resi- Chinook salmon are likely candidates to colo- dent salmonids to focus their feeding efforts on nize the majority of mainstem and floodplain Chinook (Tabor et al. 2004, Kiffney et al. 2007). habitats in the Elwha River (Figure 8a). Their Trout were found to consume over 25% of the arrival time to the Elwha as returning adults in natural Chinook salmon production in nearby the late spring and summer potentially allows watersheds in the Puget Sound region (Tabor et them to migrate upstream during relatively high al. 2004). Juvenile Chinook salmon may increase flows that typify snowmelt dominated systems their exposure to predation in order to obtain ad- in Puget Sound (Beechie et al. 2006, Duda et ditional food resources relative to other salmonid al. 2008). In addition, their spawn timing in late species (Abraham and Healey 1993). In addition, summer and early fall occurs during the lowest spawning anadromous salmonids are known to average monthly flows when attract large trout because of the opportunity to is minimal (USDOI 1994), thus the large increase feed on energy-rich eggs or emerging fry (Willson in suspended sediment due to the dam removals and Halupka 1995). will have relatively less impact on their ability to migrate and find spawning areas. Distance to Coho salmon and steelhead are also likely to a source population will be short, as with most colonize the majority of mainstem, floodplain, salmonid species in the Elwha, and their popula- and tributary habitat made available to them with tion size is larger than all other species with the dam removal due to their initial population size exception of coho salmon. The type of habitat that and run timing, ability to maneuver past natural will become available to Chinook salmon also fits barriers in the canyon reaches, and their propensity well with their life history strategy of utilizing both to utilize alluvial valley bottoms and tributary mainstem and floodplain habitats for the juvenile habitats (Figure 8a). Distance to a source popula- and adult life stage (Figures 6a, 6b, and 7), as well tion for both coho salmon and steelhead is short as their diverse life history strategies that includes because both already occur in relatively larger

84 Pess et al. A

B

Figure 8. Intrinsic potential maps of (a) Chinook salmon, coho salmon, and steelhead and (b) pink salmon, chum salmon, and sockeye salmon in the Elwha River.

Salmonid Responses to Dam Removal 85 numbers below the dams (Table1). In addition, The current juvenile fish distribution below there is a self-sustaining population of resident the dams provides a natural analog to what may O. mykiss above the dams (Brenkman et al. 2008) occur above the dams. O. mykiss typically utilize which could be an important contributor to the areas with a relatively higher proportion of higher recolonization of anadromous O. mykiss due to velocity water and larger substrate habitat types, interbreeding (Seamons et al. 2004, McMillan while coho salmon dominate in habitats where et al. 2007). stream velocity is lower, habitat complexity is We hypothesize that migrating and spawn- high due to a greater amount of wood loading, ing coho salmon and steelhead will face higher variation in flow is less, and food abundance is sediment loads as their run timing occurs during high (Milner and York 2001, Pess et al. 2003a). naturally higher winter and spring flows. Higher Floodplain channels are typically critical areas for turbidity levels during that time period, whether juvenile salmonid utilization (Pess et al. 2005) and natural or related to dam removal, will thus af- such areas occur in the alluvial valley bottoms of fect migration into the middle and upper Elwha. the Elwha. Floodplain channel habitat complexity However it is uncertain whether this will result and water source are also likely to affect species in a higher proportion of colonizers due to less distribution and abundance. Similar to the lower desirable conditions in the lower Elwha or more Elwha, we hypothesize that groundwater influenced coho salmon and steelhead entirely avoiding the channels will be dominated by one or two species Elwha River. such as coho, while more complex surface water Both coho salmon and steelhead are more fresh- dominated channels will have a greater diversity water-dependent than other salmonid species thus of species. their ability to utilize the newly opened mainstem, Pink, chum, and sockeye salmon are unlikely floodplain, and tributary habitat should be strong. to colonize the majority of habitats throughout Both species also utilize mainstem margins and the Elwha for mutual and specific reasons (Figure floodplain channels below the dams which suggest 8b). Historically, the longitudinal extent of pink that the same may occur above the dams. Even and chum salmon was up to ~rkm 25, and sockeye though many Elwha tributaries will have limited were assumed to extend to Lake Sutherland (Winter spawning use due to their steepness (Munn et al. and Crain, 2008). Today all three species have low 1999), there are at least stretches of larger, low population sizes. Thus even though the distance to gradient tributaries in the uppermost portion of the nearest source population is similar to Chinook, the upper Elwha such as Hayes, Lillian, Lost, coho, and steelhead, the total number of potential and Goldie that could be utilized by both coho strays into middle and upper Elwha will likely be salmon and steelhead. The middle Elwha could small even if the stray rate is high. also have rapid tributary colonization by coho salmon and steelhead due to the greater propor- Migration timing for pink salmon coincides with tion of low gradient tributary habitat relative to periods of low sediment transport in the summer mainstem and floodplain habitat. Indian Creek is and fall. Summer and fall migration should provide likely to attract coho salmon because it has a large the greatest difficulty in passing likely natural barri- amount of rearing habitat associated with Lake ers in the canyon reaches due to low flows (Figures Sutherland and adjoining wetlands, an important 1 and 8b). However, evidence from the Fraser factor in the relative abundance of coho salmon River suggests that pink salmon can effectively throughout Puget Sound (Pess et al. 2002). Even migrate past barriers during the summer and fall if adult coho salmon do not colonize tributary and low flow time periods due to their physiological floodplain habitats first, it is possible for juvenile ability to swim and efficiently migrate to newly coho to recolonize tributary and floodplain habi- opened habitats (MacNutt et al. 2006). Minimal tats (Anderson et al. in press). The Little River, diversity in life history characteristics, a brief time a major middle Elwha river tributary, may see in freshwater, and habitats conducive to spawning steelhead play a dominant role in recolonization such as floodplain channels could positively affect because the existing rainbow trout populations are pink salmon recolonization in the Elwha River. most similar to wild Washington coastal steelhead Interactions with existing resident fish populations (Phelps et al. 1994). may initially be negative as the small founding

86 Pess et al. populations may produce limited numbers of Summary and Conclusions offspring vulnerable to predation. We identified several key aspects of salmon ecol- Existing population size of Elwha River ogy that will affect recolonization following dam chum salmon is intermediate to other salmonid removal. Barriers to migration, distance from a ­populations in the Elwha River (Table 1). Again source population, source population size, stray distance to a source population is short, however rates, the amount, quality, and type of habitat in the migration and spawn timing of chum salmon relation to specific life stage needs, and interac- in the Elwha (fall and winter) will be limited be- tions with existing fish populations will determine yond Rica and the Grand Canyon (Figure 8b). In salmonid recolonization on a species-specific basis. addition there may be temporary barriers due to Barriers to movement will affect some species such elevated sediment loads during that time period. as chum salmon, sockeye salmon, and pink salmon Habitat area and life history adaptation to local more so than others such as Chinook salmon, coho habitat characteristics should be favorable to chum salmon, and steelhead. Although distance from salmon due to the large proportion of mainstem a source population is minimal for all species, it and floodplain habitats, while interactions with is uncertain whether pink salmon, chum salmon, existing resident fish populations are similar to and sockeye salmon are currently self-sustaining. pink salmon and assumed to be minimal. Stray rates, which naturally vary among taxa, will further vary as a function of migration timing and Whether or not sockeye salmon will re-establish associated turbidity levels during and following a self-sustaining population is perhaps one of the dam removal. Habitat area, type, and condition biggest unknowns of all salmonid species in the are the most certain variables in the upper Elwha, Elwha River basin. Small numbers of sockeye are while conditions in the middle and lower Elwha seen every year in the lower Elwha (Table 1), and will also depend upon the amount, timing, and there is an established kokanee salmon population composition of sediment. Interactions with exist- in Lake Sutherland. However sockeye recoloniza- ing fish populations will likely be positive for life tion potential is unknown for several reasons. First, forms that have both a resident and anadromous distance to source population is unknown because component, but may vary for the newly reintro- sockeye in the lower Elwha could be strays from duced species such as Chinook salmon, pink another population or a small, persistent Elwha salmon, chum salmon, and coho salmon. River population. Second, resident kokanee popu- lations typically do not contribute significantly to Acknowledgements the overall anadromous population (Foerster 1947, We thank Correigh Greene, Phil Roni, Jeff Duda, Kaeriyama et al. 1992) and may produce offspring Reg Reisenbichler, and one anonymous reviewer that are maladapted to anadromous migrations for constructive comments during the peer review (Taylor and Foote 1991). Finally, there has been process. We thank Mel Elofson, Raymond Moses, alteration to the Lake Sutherland lakeshore due to Sonny Sampson, and the Lower Elwha Klallam development; potentially, habitat conditions are Tribe for field assistance, advice, and access to not as conducive to sockeye salmon spawning as Tribal Land. We thank Randall McCoy for assis- historically was the case. tance on GIS related estimates and maps.

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90 Pess et al.