Other Species

Ajwani (1956) reported 20 native and 15 introduced fish species in the Lake Washington watershed. Of those species, 14 are considered common or abundant in Lake Washington, including prickly sculpin, longfin smelt, juvenile sockeye salmon, three-spine stickleback (Gasterosteus aculeatus), peamouth (Mylocheilus caurinus), yellow perch, rainbow trout (O. mykiss), northern pikeminnow (Ptychocheilus oregonensis), largescale sucker (Catostomus macrocheilus), brown bullhead (Ictalurus nebulosus), cutthroat trout, smallmouth bass, largemouth bass, and common carp (Cyprinus carpio) (Beauchamp 1990). The relationships of any of the common fish species to ESA-listed salmonids would be related to the timing and duration of distributional overlaps among species. The primary zone of overlap for juvenile chinook and coho with other fish species would be the littoral zone. The expected timing of littoral zone occupation for each species is shown in Table 2 below.


Bass have been studied extensively throughout their range, including in Lakes Washington and Sammamish. Direct studies on the relationship between piers and other shorezone structures, and bass predation on salmonids are currently underway (Roger Tabor, USFWS; Kurt Fresh, WDFW; Rod Malcom and Eric Warner, Muckleshoot Tribal Fisheries). Conjecture about that relationship can be supported with information from other studies and personal communications from local scientists. Both largemouth and smallmouth bass demonstrate an affinity for structural elements, and both are piscivorous, preying on salmonids when available.

Stein (1970) found that largemouth bass in Lake Washington preferred heavy log and brush cover to all other available habitat (including docks), and considered the lack of this habitat to be a limiting factor. Largemouth bass were often found under docks in early spring in Lake Washington (Stein 1970). One third of the largemouth bass in Lake Baldwin, Florida showed a significant preference for piers in the absence of aquatic vegetation (Colle et al. 1989). Largemouth bass preferred moderate to dense vegetation and silt or sand substrate in Lake Sammamish (Pflug 1981). Nests were constructed at depths from 0.6 to 1.5 meters, in vegetated areas with soft-sediment to gravel substrates, on moderate to steep slopes (Pflug 1981). Others have noted preferences for nest locations adjacent to a structural feature such as a rock, stump, or a slope (Heidinger 1975; Allan and Romero 1975), and locations that provide cover (Vogele and Rainwater 1975). In general, largemouth bass select soft substrates; cover in the form of logs, brush, aquatic vegetation, or other structures; and utilize a variety of prey-capture tactics.

Both smallmouth and largemouth bass utilize docks and piles in addition to natural cover. However, smallmouth bass generally select hard substrates without aquatic vegetation, drop-offs or outcroppings, and cover in the form of logs or rocks, whereas largemouth bass generally prefer softer-bottom substrates and aquatic macrophytes (Coble 1975). Smallmouth bass in Lake Sammamish often selected residence areas with overhead cover such as docks, submerged logs, or overhanging vegetation, and preferred areas with cobble/gravel substrate and drop-offs, without aquatic vegetation (Pflug 1981; Pflug and Pauley 1984). Smallmouth bass were the only species that Bryan and Scarnecchia (1992) consistently found in equal or greater abundance in developed sites than in undeveloped sites in Spirit Lake, Iowa. Smallmouth bass in a Texas reservoir selected rock outcroppings more than other habitat types (Kraai et al. 1991). Male smallmouth bass in Lake Sammamish generally located nests within 7 to 20 meters of shore, on gently sloping gravel/cobble substrates, devoid of vegetation, at depths of 1 to 3 meters, and associated with a structural element such as a log, boulder, pile, or other artificial structure (Pflug and Pauley 1984; Malcom, pers. comm., 13 April 2000).

Largemouth and smallmouth bass spawned beside fallen trees in water as shallow as 80 cm in lakes of the Eastern Region national forests (Bassett 1994). Danehy and Ringler (1991) reported that smallmouth bass displayed two different foraging and habitat selection strategies: those occupying cobble/rubble shoals were strongly associated with the substrate and fed primarily on benthos (mostly crayfish), and those found over sandy substrates were piscivorous and exhibited an active hunting behavior, feeding pelagically without an association with the substrate (Danehy and Ringler 1991). Haines and Butler (1969) showed that structures that provided darkness were selected most frequently by yearling smallmouth bass. Fallen trees in less than 1.5 meters of water were generally used by juvenile smallmouth bass, but not by adults in Eastern Region national forest lakes (Bassett 1994). Bassett (1994) reported that artificial structures placed at depths of 3 to 6 meters were most effective at attracting centrarchids during summer. In Lake Joseph, Ontario, young-of-the-year smallmouth bass were the only fish group whose density was not significantly related to coarse woody debris (CWD); instead, their density was highest in areas with high concentrations of shorezone structures (Brown 1998). Helfman (1979) experimented with fish attraction to shade-producing, floating objects in Cazenovia Lake, New York, and found that smallmouth bass were not attracted to the floats (sized from 1.1-3.6 m2); largemouth bass occasionally hovered below the experimental floats, but were more common under larger swimming floats at similar depths. Helfman (1979) speculated that the response of largemouth bass might be indicative of an attraction to "more massive structure" than the experimental floats provided.

Key Predators

Table 2 illustrates that the distributions of all of the common fish species in Lake Washington overlap the distribution of juvenile chinook salmon at some point. Of primary interest is the distribution of potential predators on juvenile chinook. Information provided at a recent workshop convened to present a report on the progress of the ongoing Lake Washington Ecological Studies provided an updated perspective on the predators of juvenile salmonids. The primary native fish species identified as potential predators in the Lake Washington system were: river lamprey, cutthroat trout, rainbow trout, coho salmon, and five species of sculpin; other native species were: mountain whitefish, bull trout, longfin smelt, chinook salmon, and sockeye salmon (Lake Washington Sockeye Studies Interim Workshop 2000). The primary introduced fish species identified as potential predators in the Lake Washington system were: smallmouth bass, largemouth bass, and yellow perch; other species include: brown bullhead, black crappie, white crappie, pumpkinseed, Atlantic salmon, bluegill, and warmouth (Lake Washington Sockeye Studies Interim Workshop 2000). The most important nearshore predator of sockeye fry in Lake Washington was identified as cutthroat trout less than 250 mm; other predators noted were juvenile coho salmon, and rainbow trout (Lake Washington Sockeye Studies Interim Workshop 2000). The most important limnetic predator of juvenile salmonids was identified as cutthroat trout over 250 mm, whose diet consists of approximately 50 percent salmonids (Lake Washington Sockeye Studies Interim Workshop 2000). Prickly sculpin larger than 125 mm were also identified as the most important benthic predator (Lake Washington Sockeye Studies Interim Workshop 2000). Although the focus of the Lake Washington Sockeye Studies was on sockeye salmon, identified predators also prey on other juvenile salmonids, including chinook.

The primary predator of juvenile chinook occupying the littoral zone from January through June, and the limnetic zone for the remainder of the year, would be cutthroat trout (Warner, pers. comm., 7 July 2000). A small proportion of northern pikeminnow, yellow perch, and smallmouth bass reside in nearshore regions during winter, but the majority move inshore in the spring as temperatures in nearshore areas warm (Bartoo 1972; Olney 1975; Coutant 1975). The distributions of these fishes overlap primarily with the peak out-migration of chinook through the littoral zone, whereas the overlap of cutthroat and chinook distributions is continuous. Sculpins are present in the littoral zone year-round and are known to eat chinook (Tabor et al. 1998). In mid-summer, temperatures in the littoral zone become undesirable for juvenile chinook and coho salmon, and the majority leave the lake or seek cooler temperatures away from the littoral zone, thus segregating themselves from littoral predators, but remaining vulnerable to cutthroat trout and potentially prickly sculpin.

The magnitude of avian predation on salmonids in Lake Washington is unknown. Studies from other systems indicate that consumption rates can be substantial. Double-crested cormorants (Phalacrocorax auritus) and western grebes (Aechmophorus occidentalis) consumed more than 31 percent of the spring plant of trout fry in a Utah reservoir over a two-week period, and nearly 33,000 larger subadult trout over eight months (Modde et al. 1996). Wood (1987a) estimated that common mergansers (Mergus merganser) consumed as much as 39 percent of the potential coho smolt production from the Big Qualicum River, BC. Suter (1995) estimated that cormorants (P. carbo) consumed from 5 to 22 percent of the annual standing crop of grayling (Thymallus thymallus) in two Swiss rivers. Salmonids comprised the major dietary component of both red-breasted mergansers (M. serrator) (Feltham 1990) and common mergansers (Wood 1987b) in their respective studies. Wood (1987b) stated that "mergansers rank among the largest (in terms of appetite) and most efficient predators of juvenile salmon" and they "congregate wherever salmon density is high." Alexander (1979) was able to attribute 15 percent of annual mortality of age 0 to 1 brook trout in a Michigan River to avian predators and 58 percent to piscivorous brown trout (Salmo trutta).

Because of the presence of predatory birds in Lake Washington and Lake Sammamish, avian predation must be considered among potential threats to juvenile salmonids. Common mergansers are abundant in the spring. Double-crested cormorants are common in Lake Washington, typically perching on the log booms at Union Bay and May Creek rather than on docks and bulkheads. Cormorants also commonly perch on individual piles (Warner, pers. comm., 7 July 2000). Western grebes inhabit enclosed bays (and some marinas). Gulls are common in the lake, perching on log booms and on low docks (Warner, pers. comm., 7 July 2000). Gulls are known predators of juvenile salmonids (Ruggerone 1986).

Table 2.   The timing of the annual littoral zone occurrence of the common fish species in Lake Washington (similar data were not obtained for Lake Sammamish). Dashed black lines indicate presence, blank areas indicate absence. Footnotes appear after table.

Prickly Sculpin1


Longfin Smelt2


Sockeye Salmon3


Chinook Salmon4


Coho Salmon5


Rainbow Trout6


Cutthroat Trout7


Native Char8






*Yellow Perch11


N. Pikeminnow12


Largescale Sucker13


*Brown Bullhead14


*Smallmouth Bass15


*Largemouth Bass16


*Common Carp17



Insufficient data

Mountain Whitefish18


















* Indicates an exotic species.
1 Rickard (1978)
2 Beauchamp (1982, unpublished data), Chigbu (1993)
3 Martz (1996), Beauchamp (unpublished data)
4, 5 Fresh (unpublished data), Beauchamp (unpublished data)
6 Beauchamp (1987, 1990)
7 Beauchamp et al. (1992)
8 Beauchamp (unpublished data), USFWS (unpublished data)
9 Traynor (1973), Beauchamp (unpublished data)
10 Nishimoto (1973), Beauchamp (unpublished data)
11 Bartoo (1972), Nishimoto (1973), Nelson (1977)
12 Bartoo (1972), Olney (1975), Brocksmith (1999)
13 Beauchamp (unpublished data)
14 Beauchamp (unpublished data)
15 Beauchamp (unpublished data), Fayram (1996)
16 Stein (1970)
17-20 Beauchamp (unpublished data)