V. B. 2. Salmonids |
Salmonids (family Salmonidae), which include salmon, trout, and char, are an ecologically, economically, and culturally prominent group of fishes in the Pacific Northwest (Groot and Margolis 1991; Spence et al. 1996). All are the focus of regional research, management, and conservation efforts. The eight salmonid species found in Puget Sound include chum (Oncorhynchus keta), pink (O. gorbuscha), sockeye (O. nerka), chinook (O. tshawytscha), and coho salmon (O. kisutch); as well as steelhead (rainbow trout) (O. mykiss), coastal cutthroat trout (O. clarki clarki) and bull trout (Salvelinus confluentus). All salmonids have anadromous forms, with most species undertaking extensive ocean migrations before returning to spawn in their natal stream. However, sockeye salmon (kokanee), steelhead (rainbow trout), and coastal cutthroat trout also may have non-anadromous life history cycles. The variable life-history characteristics of salmonids have allowed them to take advantage of the environmental variability of the landscapes and seascapes they have occupied over evolutionary time. As a result, salmonids have evolved into complex life-history patterns that sustain viable populations over a broad spectrum of ecosystem change at varying temporal and spatial scales (Wissmar and Simenstad 1998). Particular life-history traits and habitat requirements of each salmonid species, and relevance to Bainbridge Island nearshore habitats, are covered in greater depth later in this section.
Salmon species can be grouped into stocks, defined as groups of fish that are genetically self-sustaining and isolated geographically or temporally during reproduction. A population of fish may include a single stock or a mixture of stocks. Under the Endangered Species Act (ESA), stocks of salmonids may be grouped as Distinct Population Segments (DPSs), as is the case for bull trout under jurisdiction of the USFWS. Stocks may also belong to Evolutionarily Significant Units (ESUs), as is the case for Pacific salmon under the jurisdiction of the NMFS. Chinook salmon (within the Puget Sound ESU), summer-run chum salmon (within the Hood Canal ESU), and bull trout (within the Coastal-Puget Sound DPS) have been listed as threatened under the ESA. Coho salmon (within the Puget Sound/Strait of Georgia ESU) is a candidate species for listing.
Life History
The typical salmon life history has five main stages: (1) spawning and egg incubation, (2) freshwater rearing, (3) seaward migration, (4) ocean rearing, and (5) return migration to freshwater to spawn and the deposition of marine derived nutrients into the freshwater ecosystem (Figure V-7). We attempt here to briefly summarize some of the differences in life history and ecology for each species, although a number of references provide more extensive descriptions of the diversity and complexities of particular species (National Research Council 1996). Salmon are dependent upon freshwater habitats that are typically characterized by accessible cool, clean water with abundant woody debris, cover for shade, relatively clean spawning gravel, adequate food supply, and a balanced population of predators (Gross et al. 1988). Because freshwater stream environments in the Pacific Northwest are less productive than the ocean environment (particularly estuaries and coastal upwelling zones), salmonids have evolved an ocean feeding phase in their life history to exploit this productivity. Salmon returning to their natal spawning grounds need adequate flows, water quality, unimpeded passage, and deep pools with cover and structural complexity for resting and shelter from predators (Haring 2000). Most species have a limited time, in some cases as little as 2 to 3 weeks after entering freshwater, to migrate and spawn.
Figure V-7. Temporal phases of anadromous salmon life history (from Cederholm et al. 2000).
Chum, pink, sockeye, chinook, coho, and bull trout typically spawn sometime between August and February, a time when stream flows are increasing and water temperatures are declining. Rainbow and cutthroat spawn between January and June, when stream flows are decreasing and water temperatures are increasing. Chum, pink, sockeye, chinook, and coho salmon all die after their first and only spawning activity, a life history strategy known as semelparity. The decaying carcasses of adult salmon in turn, contributes valuable nutrients and organic matter to the stream environment, thereby enriching local productivity for their offspring. An iteroparous, or repeat spawning, strategy is more typical of steelhead, cutthroat, and bull trout.
Salmon excavate redds (spawning nests) in the clean gravel of streams, wherein eggs are deposited and fertilized. For successful development of eggs to occur, the spawning gravel must be relatively stable and not choked with fine sediments. After approximately 2 to 4 months of incubation, salmon fry emerge from their gravel nests. Certain species such as chum, pink, and some chinook salmon emerge in late winter-early spring and rapidly migrate downstream to the estuary, whereas sockeye migrate from their gravel nests to larger lake environments. Other species, such as coho, steelhead, bulltrout, cutthroat, and chinook emerge from spring to mid-summer and search for suitable rearing habitat within the stream.
For early stream-resident species (coho, steelhead, bulltrout, and some chinook), flow conditions and fish size determine patterns of habitat use. Quiet water, side margins, and off-channel sloughs are vital early rearing areas, with woody debris and overhead cover providing shelter and nutrient and food inputs. In the summer, juveniles move to deeper, faster areas of the stream as they grow and low flow conditions predominate. Declining streamflow conditions may cause some fish (i.e., chinook, coho) to emigrate to estuaries (Healey 1982; Tschaplinski 1982) where they continue to rear. Upon the first rains and high waters of fall, juvenile forms of coastal species (coho, steelhead, and cutthroat) make a directed migration to seasonally alternate rearing habitats, including side-channel swamps, riverine ponds located along river flood plains, and small “runoff” tributaries (valley-wall tributaries) of rivers. Presumably, these immigrations are designed to avoid high flows and turbidity of main rivers, as well as to take advantage of good feeding conditions during winter.
After completing their freshwater stage, juvenile salmon of all anadromous forms undergo a physiological change, called smoltification, which includes osmoregulatory adjustments that prepare them to enter saltwater. Chum and pink salmon are nearly smolts upon emergence from the gravel, migrating directly to estuaries and the ocean. Chinook and coho may either go directly to the marine environment the first spring or summer of their life or remain in freshwater for an entire year before smolting. Sockeye may rear in freshwater for one or two years before smolting, and steelhead, bull trout, and cutthroat may not smolt for two or three years or more.
Nearshore Ecology and Limiting Factors
The importance of estuarine and nearshore marine habitats to the early life-history stages of salmonids has become increasingly apparent to regional conservation and recovery efforts (Williams et al. 2001). Salmonids use the nearshore for physiological transition (adaptation from freshwater to saltwater), as migration corridors, as nursery areas, for juvenile and adult food production and feeding, and as residence and refuge (Haring 2000; Dinnel 2000). Typically cited nearshore habitat requirements of juvenile salmonids include (Simenstad 2000):
- Shallow-water, typically low-gradient habitats with fine, unconsolidated substrates
- The presence of aquatic vegetation, emergent marsh vegetation, and shrub/scrub or forested riparian vegetation
- Areas of low current and wave energy
- Concentrations of small, non-evasive invertebrates.
All juvenile salmon move along the shallows of estuaries and nearshore areas during their outmigration to the sea, and may be found in these habitats throughout the year depending on species, stock, and life-history stage (Table V-3) (Emmett et al. 1991). Shallow estuarine and nearshore habitats are structurally complex (e.g., submerged aquatic vegetation and large woody debris), highly productive, and dynamic. As such, they are critical areas for juvenile salmonids because they provide food, refuge from predators, and a transition zone to physiologically adapt to saltwater existence (Williams and Thom 2001). Juvenile salmonids behaviorally restrict their movements to shallow water (between 0.1 and 2.0 m) until they reach larger sizes that may allow them to exploit deeper channel and open water habitats and associated prey resources. Young salmon also tend to resist large changes in light intensity during migration; although they may readily move under structures that cast shadows, they strongly avoid moving under very dark pier aprons during daylight hours (Nightingale and Simenstad 2001b). While in the nearshore, young salmon are generally opportunistic feeders that prey on an array of marine benthic, epibenthic, and pelagic organisms, as well as terrestrial insects (Simenstad et al. 1979; Fresh et al. 1981; Simenstad and Cordell 2000) (J. Brennan, KCDNR, personal communication, 2002).
Table V-3: Salmonids: Summary of Nearshore and Estuarine Habitat Use and Spawning on Bainbridge Island (Adapted fromWilliams et al. 2001).
Common Name |
Scientific |
Nearshore and Estuarine Use |
Freshwater Use |
||
|
|
Juvenile Rearing |
Adult and Juvenile Migration |
Adult Residence |
Bainbridge Island Spawn |
Chinook |
Oncorhynchus tshawytscha |
‡ |
‡ |
‡ |
µ |
Chum |
Oncorhynchus keta |
‡ |
‡ |
µ |
‡ |
Coho |
Oncorhynchus kisutch |
‡ |
‡ |
† |
‡ |
Sockeye |
Oncorhynchus nerka |
µ |
‡ |
µ |
µ |
Pink |
Oncorhynchus gorbuscha |
‡ |
‡ |
µ |
µ |
Cutthroat |
Oncorhynchus clarki |
‡ |
‡ |
‡ |
‡ |
Steelhead |
Oncorhynchus mykiss |
† |
‡ |
µ |
† |
Bull Trout |
Salvelinus confluentus |
‡ |
‡ |
‡ |
µ |
Notes: ‡ - extensive use; † - some use; µ - no use or use not known in these areas.
Most young salmon enter and pass through estuaries and the nearshore environment between early March and late June, although there is wide variability in nearshore residence time depending on the species and life stage (Table V-3). Juvenile chum and chinook salmon are considered the most estuarine-dependent salmon species, feeding and rearing in these habitats for extended periods before migrating to pelagic marine habitats. Some chinook remain within Puget Sound year-round, with recent coded-wire tag information supporting extensive nearshore movements far from their natal river (J. Brennan, KCDNR, personal communication, 2002). Chum fry migrate seaward almost immediately after hatching and enter the estuary at a relatively small size (30 to 55 mm), whereas chinook fry migrate seaward either soon after yolk resorption (30 to 45 mm), as fry 60 to 150 days post-hatching, or as fingerlings. Both species prefer relatively fine-grained substrate, low gradients, and are oriented to shallow water habitats located close to shore. Because most coho spend 12 to 18 months rearing in freshwater before migrating through estuaries and into marine waters, they are generally much larger than chinook and chum juveniles in nearshore areas (Levy and Northcote 1982; Weitkamp et al. 1995) (Table V-3). However, early outmigrating coho fry (age-0 fry or pre-smolts) also may feed and rear in productive estuarine habitats for extensive periods (up to 114 days) (Miller and Sadro in press). Coho smolts are often found in intertidal and pelagic habitats in estuaries and in shallow nearshore marine habitats, including eelgrass meadows and tideflats.
Other salmon species use nearshore marine habitats to varying degrees (Table V-3). For instance, pink salmon up to 60 to 80 mm in length migrate through and rear extensively in shallow marine waters and nearshore embayments from March until June, feeding on small crustaceans and growing rapidly (Emmett et al. 1991; Levy and Northcote 1982; Hard et al. 1996). They spend little time in estuarine areas but may be abundant in estuarine tidal channels for a short time. Coastal cutthroat trout juveniles and adults can be found over a variety of substrates within nearshore marine and estuarine waters during the spring to fall (Emmett et al. 1991; Gregory and Levings 1996). Gravel beaches with upland vegetation, and nearshore habitats (<10 ft deep) with large woody debris are often used by cutthroat trout during their marine phase for feeding and migration. Coastal cutthroat trout rarely overwinter in saltwater, and can be found in tidal freshwater areas of estuaries as they await favorable conditions to go upstream (Emmett et al. 1991; Johnson et al. 1999). Ongoing research is gradually clarifying the distribution and abundance of bull trout (the anadromous form of char) in Puget Sound estuaries and nearshore waters. In the Skagit River basin, most char smolts outmigrate between April and July, rearing for the summer in estuarine and nearshore waters before moving back into freshwater to overwinter (Williams and Thom 2001). While in nearshore marine areas, char of all ages are typically associated with shallow water, especially in areas of forage fish spawning concentrations.
Other salmonid species less recogized for estuarine dependence are nonetheless reliant on the protective cover of natural nearshore habitats for migration (Table V-3). For example, sockeye salmon smolts outmigrate to the ocean under cover of darkness in the spring to early summer and usually have a shorter residence time in estuaries and nearshore areas than other salmonids (Hart 1973; Emmett et al. 1991; Gustafson et al. 1997). Adult steelhead are epipelagic (found in the upper water column) in coastal waters to a depth of 25 m (Emmett et al. 1991). Like sockeye, juvenile steelhead usually move to sea from April through June and appear to spend little time in estuaries. However, juvenile steelhead in Puget Sound are periodically collected in beach seines over shallow nearshore marine habitats, such as eelgrass meadows and tideflats.
Adult salmon pass through nearshore marine and estuarine habitats during spawning migrations that span several months, and may delay their entry into freshwater or into terminal spawning areas at the end of the marine phase of their life cycle, milling within these habitats for up to 21 days (Johnson et al. 1997) (Table V-3). Returning adults and some resident stocks use nearshore habitats as feeding areas where they consume forage fish (Penttila 1995; Brodeur 1990; Fresh et al. 1981).
The serious decline of several salmon stocks within the Puget Sound region has prompted a series of inventories and analyses to provide science-based policy direction for regional conservation and recovery planning efforts. Contributing to many of the declines are urbanization and anthropogenic activities in nearshore marine and estuarine habitats (Williams et al. 2001). More than 70% of Puget Sound’s coastal wetlands/estuaries have been lost to urban and agricultural development. In addition, the degradation or loss of shallow vegetated habitats and modification of shorelines may alter migration corridors and sheltered foraging areas. A recently published document for the Washington State Conservation Commission provides a comprehensive inventory of salmonid habitat limiting factors for Water Resource Inventory Area (WRIA) 15, which includes Bainbridge Island (Haring 2000). Key habitat impacts that limit nearshore marine productivity and likely affect salmon include shoreline armoring and nearshore fill, overwater structures, dredging and conversion of intertidal/shallow subtidal to deepwater habitat, alteration/loss of aquatic plant communities, loss/lack of functional shoreline riparian vegetation, water quality and sediment contamination, and substrate quality modification (Haring 2000).
Nearshore Management and Data Gaps
Understanding the nearshore habitat requirements of salmon in Puget Sound is a critical step in managing shoreline activities and restoring populations. Currently, all proposed shoreline construction activities are reviewed by state agencies to assess potential impacts to juvenile salmon. To this end, work windows in marine and estuarine habitats have been established by the State (WAC-220-110-271) to avoid the peak outmigration of juvenile salmon in the nearshore. The USACE follows similar work windows, the dates of which may vary somewhat depending on species of concern and lead agency (i.e., NMFS, USFWS) (R. Thurston, WDFW, personal communication, 2003) (Table V-4). It should be noted, however, that outmigration occurs during a period of time around these peaks, as well.
Table V-4. In-Water Work Windows for Salmon in Kitsap County
| Species | Work Allowed | No Work Allowed |
| Salmon (USACE) (State) |
July 15-February 28 June 15-March 14 |
March 1-July 14 March 15-June 14 |
A great deal of information is still lacking. There is a need for development of standardized methods to assess nearshore habitat quality and function for salmonids (Simenstad 2000). Limited information exists on the distribution and abundance of most salmonids in the nearshore and open waters of Puget Sound. Likewise, information is needed to determine variation in different salmonid species’ utilization of the nearshore, salmonid preference of various habitat conditions, and preferences in timing of specific habitat used by each species (Williams et al. 2001). Research needs to be conducted to assess how physical, chemical, and biological processes create and maintain properly functioning conditions in the nearshore. This information can be used to provide estimates of current nearshore carrying capacity and form the scientific basis of habitat protection and restoration programs. Few studies have assessed the shoreline characteristics and associated human modifications that affect survival of juvenile salmonids relative to predator avoidance. As previously noted, there is also a need for comprehensive annual spawning surveys and stock assessments for forage fish (surf smelt, sand lance, and herring) and other resources that serve as salmon prey along the Bainbridge Island nearshore.
Bainbridge Island Distribution
There are numerous small, perennial and intermittent streams on Bainbridge Island, most of which are thought to have average flows of less than 1 cubic feet per second (cfs) (Haring 2000). Chum, coho, cutthroat trout, and steelhead, typical species that use small lowland streams, are found within 13 Bainbridge Island subbasins (Haring 2000); Table V-5; Appendix A – Fish Occurrence Map). Coho salmon, cutthroat trout, and to a lesser extent chum salmon, utilize most of these streams, whereas steelhead have been identified in only Fletcher (Springbrook) Creek.
Table V-5. Documented or Presumed Presence of Salmonids in Bainbridge Island Subbasins (from Haring 2000).
| Stream Name | Cutthroat | Coho | Chum | Steelhead |
Unnamed 15.0319 |
l |
|||
Dripping Water Creek 15.0320 |
l |
|||
Murden Cove Creek 15.0321 |
l |
l |
l |
|
Ravine (Canyon, Winslow) Creek 15.0324 |
l |
l |
l |
|
Unnamed 15.0324A |
l |
l |
||
Sportsmen’s Club Pond Creek 15.0325 |
l |
l |
l |
|
Cooper (Head of Bay) Creek 15.0326 |
l |
l |
l |
|
Blakely Falls Creek 15.0330X |
l |
l |
l |
|
Macs Dam Creek 15.0331 |
l |
l |
||
Unnamed 15.0332 |
l |
l |
||
Schel-chelb Creek 15.0028X |
l |
l |
||
Fletcher (Springbrook) Creek 15.0340 |
l |
l |
l |
|
Mosquito Bay (Big Manzanita) Creek 15.0344 |
l |
l |
l |
Bainbridge Island’s shoreline is irregular and composed of numerous bays, harbors, and lagoons, with varied topography and slope. Juvenile salmonid use of these nearshore marine habitats is presumed to be ubiquitous, although there are few documented observations (Haring 2000). Monthly beach seine sampling at Battle Point and Point Monroe documented the seasonal presence of all five species of Pacific salmon, steelhead, and cutthroat (Fresh et al. 1981; Haring 2000). Juvenile chinook and coho have also been consistently encountered in the catches of commercial purse seine fisheries at Apple Cove Point (Haring 2000). Surveys in Blakely Harbor reported the presence of juvenile chum, pink, and chinook salmon, noting that chum and pinks used shallow protected waters for rearing and forage, while larger chinook were observed in deeper habitats feeding upon larval forage fish (Jones and Stokes Associates 1990). WDFW and the Tribes also conduct annual surveys of pink, chum, and chinook salmon fry in nearshore habitats throughout Puget Sound, including several Bainbridge Island locations, although much of this data remains unpublished (D. Hendrick, WDFW, personal communication, 2002).
| << v.b.1. forage fish |