Conservation Priorities in the Squamish River Estuary To: Squamish Estuary Conservation Society

1.4 Biodiversity

Inherent (natural) edges harbour the greatest species richness and abundance because of their structural complexity. Examples of natural edges include small forest clearings, riparian borders, and wetlands containing a network of channels. The interspersion of water and cover is most conducive to high levels of biodiversity. The size of an area is also an important influence on wildlife distribution patterns because larger areas tend to have more habitat types, and can accommodate species that do not tolerate edge conditions or human disturbances.

1.4.1 Fish

Fish populations dominate the estuarine vertebrate community in terms of numerical abundance and biomass, and play a significant role in the energy flow of the system. Based on fish surveys from the 1970s, some fish species present in the Squamish estuary include Chinook (Oncorhynchus tshawytscha), pink (O. gorbuscha), chum (O. keta), and coho (O. kisutch) salmons, Dolly Varden (Salvelinus malma), cutthroat (Salmo clarki), steelhead (S. gairdneri), rainbow trout (Salmo sp.), herring (Clupea harengue), C-O Sole (Pleuronichthys coenosus), perch (Embiotoca lateralis), stickleback (Gasterosteus aculeatus), smelt (Hypomesus pretiosus), sand lance (Ammodytes hexapterus), lamprey (Lampetra sp.), cod (Gadus macrocephalus), pipefish (Syngrathus gresedeneatus), starry flounder (Platichthys stellatus), rockfish species, eelpouts (Lycodopsis pacifica), prickleback (Lumpenus sagitta), poacher (Agonopsis emmelane), and sculpin species.

Most estuarine fishes are seasonal visitors from the near shore ocean, utilizing the estuary as a migratory pathway between feeding and spawning grounds; the brackish water serves to help them transition between saline and freshwater environments. The most abundant forms of these transient species are juvenile salmonids, which use the estuary as nurseries and rearing grounds because tidal channels provide an abundance of food as well as protection from predation. The Department of Fisheries and Oceans has recently been creating spawning and rearing channels in the saltmarshes on either side of Central Channel, to increase the potential survival of juveniles until they are ready to set out for the open ocean. There are also adult salmon moving through the estuary to their spawning grounds, most of the year. Adult Chinook migrate upriver from early July to the end of October. Coho and pinks begin their upstream migrations in late summer. Whereas the migration of pinks is over by the end of October, coho continue to disperse and spawn until the end of February. Chum adults migrate between mid October and mid December (Jim Wisnia, pers. com.). Downstream juvenile migration begins in early to mid March for pinks and chums, and end in mid May. Young Chinook and coho move down river between mid March and mid June. Steelhead juveniles disperse towards the estuary from early April to mid July (Estuary Working Group 1974).
Salmon are integral to this estuary community, providing a cyclical infusion of nutrients during spawning periods, as well as a significant source of food for aquatic and riparian residents and visitors, such as the large over wintering population of bald eagles. Thus, all natural and human-made channels in the central estuary are of high ecological value because they help assure a healthy recruitment to adulthood. Commercial/recreational interests in salmon are reflected in the management guidelines for rivers and streams above the estuarine environment: the riparian guidelines of the Forest Practices Code (BC Ministries of Forest and Environment 1995a), and in the Land Development Guidelines for in-stream works (Chilibeck et al. 1993). However, these management guidelines need to be improved if long-term hydro-riparian health is to be maintained. Ecosystem integrity is compromised when one or several components (e.g., species, water quality, microclimate, important habitat attributes) are not protected.

1.4.2 Wildlife

Avifaunas are often overlooked when assessing estuarine biotic communities, but they are also dominant components of the estuarine food web, capable of controlling prey abundance and altering aquatic, as well as submergent and emergent terrestrial plant crops (Kennish 2002). The Canada Land Inventory classified this estuary as fairly significant as a migratory or wintering area for waterfowl. Two years later, the Department of the Environment similarly stated that the estuary is used by “ a great deal of waterfowl, particularly during fall and spring migrations, and the winter months” (see Estuary Working Group 1974). Moderate summer use by non-breeding water birds also occurs (Campbell et al. 1990).

Bird populations inhabiting estuaries belong to four groups: (1) seabirds such as gulls and alcids; (2) waders such as herons and sandpipers; (3) waterfowl; and (4) perching birds such as passerines, raptors and woodpeckers, in the meadow, shrub and forest margins. All groups are discussed in turn, but information on perching birds is limited because water birds have historically received research priority due to their economic value. Fortunately, recent data on both water and non-water birds are available for the Squamish estuary because of monthly bird counts, which were initiated by local citizen Jim Wisnia in 1991, and are currently spearheaded by a local birders group. Counts have been thorough and consistent throughout the years, and the data can be retrieved from Birds Studies Canada (BSC) for analysis.
Some of the water birds rely heavily on estuaries for food, and their population densities vary in response to prey availability. During wintering months, large influxes of waterfowl, diving birds and waders converge at estuaries. It is estimated that 400,000 to 500,00 water birds pass through the Puget Trough utilizing the estuaries and beaches on an annual basis, particularly the Fraser estuary (62% of all estuary water birds) (see Mahaffy et al.1994). An extensive land-based bird survey of the Squamish estuary by the Canadian Wildlife Service from the fall of 1972 to the spring of 1973, reported 42,933 bird sightings of 67 species: 90% water birds, 10% passerines (Trethewey 1985). This large biomass of water birds necessarily implies that transient and over-wintering species both play a big role in the functioning of the Squamish estuary, and thus in maintaining its health. Data from the last decade also suggest that more than 90% of the estuary visitors and inhabitants during the fall, winter and spring are water birds (BSC data).
There are 83 kinds of water birds occupying the outer estuary, deltaic channels and/or Squamish River, including ducks (27 species), loons, grebes, cormorants, herons, swans, geese, rails, shorebirds, gulls, alcids, terns, and the rare parasitic jaeger and American white pelican. Roughly 71% of these species are overwintering waterfowl or migrants. The remaining 29% represents summer breeders as well as non-breeding individuals. Although water birds make up the bulk of the birds in the Squamish estuary, 161 species of non water birds visit, breed, or inhabit its tidal meadows, shrub margins, or forest fringes (BSC data). Birds in the terrestrial zones include 22 species of raptors (hawks, falcons, owls), 10 species of swallows and swifts, five species of woodpeckers, three grouse species, three dove species, the common nighthawk, two species of hummingbirds, and 87 passerines including sparrows, finches, vireos, warblers, corvids, and others. Approximately 14% of these non water birds frequent or inhabit the estuary year-round; the remaining 86% are migrants from the south. Based on 161,552 bird sightings of 216 species in the last 12 years (excluding 2003), thorough details of bird distribution patterns in the Squamish Estuary are outlined below, with respect to overall distributions in the Puget Trough.
American widgeon and mallards are the most numerous dabblers seen in estuaries of the Strait of Georgia (see Mahaffy et al. 1994), feeding in flooded channels and inundated deltaic edges. Based on two 1973 surveys, dabbling waterfowl in the Squamish estuary include the mallard (Ana platyrhynchos), American widgeon (A. Americana), pintail (A. acuta), and green-winged teal (A. carolinensis)(Estuary Working Group 1974; Trethewey 1985). Similar results were obtained in a winter 1980 survey (Cannings 1980) and during monthly counts coordinated by local citizen Jim Wisnia from 1991 to 2002. Less common dabblers include the cinnamon teal (A. cyanoptera), northern shoveler (A. clypeata) and wood duck (Aix sponsa). Dabbler migration reaches its peak between late September and early October, and in mid April (Estuary Working Group 1974). Many mallards overwinter in the Squamish Estuary (see BSC data). Cannings (1980) reported a mean of 217 and a maximum of 337 mallards on any given census from January to March of 1980. He found dabblers to be most common in West Delta, Central Delta east of the fill site, and East Delta; they were also found at the mouth of the Stawamus River and in the upper Mamquam Blind Channel. Widgeons and shovelers favour the central delta (East of Fill), while pintails and the teal species occupy primarily the east delta (East Marsh, and likely North Field once this site is restored). Industrial development at the mouth of the Mamquam Blind Channel makes this otherwise good feeding area less favourable for waterfowl (Estuary Working Group 1974).
Based on Canadian Wildlife Service (CWS) aerial surveys in the 1980s, buffleheads were the most abundant diving duck in sheltered waters of southern BC, followed by Barrow’s goldeneyes in fjords and common goldeneyes in estuaries. Red-breasted mergansers were the second most abundant duck in coastal shores whereas common mergansers were seen more in estuaries. In accordance with this, the overwintering population of diving ducks in the Squamish estuary in the early 1970s and in 1980 was comprised primarily of buffleheads in the Central Channel, East Marsh and Bridge Pond. Given its fjord-like conditions, both goldeneyes were common in the lower Squamish River (Estuary Working Group 1974; Cannings 1980). The majority of common mergansers were found at the mouth of the Stawamus and Squamish Rivers, while most of the red-breasted mergansers were seen on the outer estuary (Estuary Working Group 1974). Smaller proportions of scaup occurred in the central channel, near East Delta from December to mid May, with the largest numbers in April in response to herring spawn (Estuary Working Group 1974). Distribution patterns have been similar in the last decade, though large populations of scaup no longer occur because the training of the Squamish River has eliminated herring breeding grounds and increasing industrial activity on Mamquam Delta may displace birds in the future. Hooded mergansers have always occurred in small numbers throughout the estuary during migration (Estuary Working Group 1974; BSC data). Diving duck numbers are at their highest from late October to the onset of the northward migration in March.
Loons and grebes occur in the outer waters of the Squamish estuary. Of all loons and grebes, western grebes are the most common in the Strait of Georgia (see Mahaffy et al. 1994). The western grebe was also the most common bird in the Squamish estuary during a 1970s Canadian Wildlife Survey; one-day counts ranged up to 772 birds, though numbers fluctuated widely (Trethewey 1985). Western Grebes populations are declining drastically (John Ryder, CWS; pers. com.). In support of this, only a total of 119 have been detected along the outer edge of the Squamish Estuary from 1992 to 2001, and aside from two large flocks reported in 1994 and 1996, most western grebes dribble in, in very small groups (< 7 birds; see BSC data) during October and November. Since 1991 there have been more than 80 sightings of four other species of grebes: red-necked, horned, pied-billed and the occasional eared grebe. A total of 48 common loons and 39 red-throated loons have been counted in this area from 1991 to 2002, and Pacific loons have been reported twice.

The trumpeter swan is the most widespread and common swan concentrated in tidal marshes of the Fraser River, and their populations have increased in the last two decades (Mahaffy et al. 1994). In the Squamish estuary, they used to be found at the mouth of the Stawamus River and in Crescent Slough (see Estuary Working Group 1974). With increasing industrial activity along the east shore of the Mamquam Blind Channel, they became confined to Crescent Slough, at the north end of Central Channel (Canning 1980; BSC data). In recent years, trumpeter swans appear to have been relying mostly on the Squamish River during their migratory stops (BSC data), particularly within eddies in the vicinity of West Delta. A total of 312 trumpeter swans have been counted in the estuary in a twelve year period (1991-2002); numbers peak from November to February.

Although Canada Geese are widespread and abundant, they did not nest around the Strait of Georgia before 1940. Small numbers were released in 1967 around the lower Fraser River valley and today the population in the same area is estimated to be between 8000 and 10000 birds (see Mahaffy et al. 1994). This species was noted in small numbers in the Squamish estuary in the early 1970s (see Estuary Working Group 1974). Today, Canada geese are very abundant throughout the estuarine environment. In a five-year period (1991-96), roughly 2500 geese were counted here (John Ryder, unpubl. data).
On a regional level, marbled murrelets are common in fjords and sheltered waters whereas common murres are the most abundant and widespread alcid along open waters and pigeon guillemots are regularly seen in low numbers in the nearshore habitat (Mahaffy et al. 1994). Whereas 233 common murres and 100 marbled murrelets were sighted in 1980, only small flocks (less than 10) were documented in the late 1980’s and early 1990’s; the last report of murres and murrelets in the Squamish outer estuary are from the 1993 Christmas bird count. The lack of sightings may in part be attributed to gradual declines in populations of schooling fish, and/or to observer bias. Cormorants occur regularly throughout the estuary; the vast majority are double-crested cormorants (>80%; n=232), followed by pelagic cormorants and the occasional Brandt cormorant (10 sightings). Declines may be associated with declines in populations of schooling fish.
The geographic isolation of Squamish Estuary causes shorebird numbers to be low here (the vast majority of shorebirds stop over in Boundary Bay). A 1973 winter census by Environment Canada noted that thirteen species of shorebirds, averaging approximately 1500 birds, frequented Howe Sound (see Estuary Working Group 1974). Based on a decade of monthly bird counts, 15 shorebird species have been reported in the Squamish Estuary since 1991, coming in singly or in very small groups. Spotted sandpipers and killdeer are the only common shorebirds here, followed by Wilson’s snipe. The presence of other species is noteworthy because shorebirds are amongst the greatest migrators, traveling up to 10,000 km in a single flight (Weidensaul 2000). East Marsh is by far the most important site in the estuary for these weary travelers, followed by Bridge Pond; the long-billed curlew, long and short-billed dowitchers, least and western sandpipers, the greater and lesser yellowlegs, solitary and spotted sandpipers, Baird and pectoral sandpipers, semi-palmated and black-bellied plovers, and killdeer have been documented there (BSC data; Trethewey 1985; Estuary Working Group 1974). Shorebirds occasionally land on the edge of the East and Mamquam Channels, and sanderlings and black turnstones were once found at the mouth of Squamish River.
Next to waterfowl, gulls are the largest group of birds on the deltas. Glaucous-winged gulls are the second most common bird in the Squamish estuary, after mallards (John Ryder, unpubl. data). Glaucous-winged gulls are the most common breeders in the estuary, as in the remainder of the Strait of Georgia (see Mahaffy et al. 1994). Glaucous-winged gull populations are on the rise likely as a result of the abundant supply of human refuse (Mahaffy et al. 1994). This species’ population is also large in Squamish because of the salmon runs. Throughout the winter, groups of them congregate at the mouth of the rivers, on the training dyke, and on the log booms in the Mamquam Channel. More than 6,000 glaucous-winged gulls were counted in the Squamish Estuary from 1991 to 1996. Other primary overwintering gulls are the mew and Thayer’s gulls. Caspian terns, as well as glaucous, ring-billed, California, Herring, western, and Bonaparte gulls are casual migrants in spring and/or fall (BSC data). The east delta appears to provide shelter for the smaller, Bonaparte gulls during strong winds (see Estuary Working Group 1974).
Herons require tall conifers near water, in relatively undisturbed situations. The great blue heron is common in the Squamish Estuary, especially in the east and central delta, and particularly during the spring and fall. Occasional green herons have been documented in the Squamish and Mamquam River floodplains in the early 1970s (Campbell 1972) and in recent years (Marcia Danielson, pers. obs.; Linda Dupuis, pers. obs.). Virginia rails breed and visit the estuary regularly, but sightings are few because rails are cryptic and have secretive habits; soras have only once been encountered, possibly for the same reasons.
Bald eagles are the most noteworthy raptor of the Squamish area as they occur in large numbers along the Squamish River during winter months. Bald eagles are abundant in the estuary in the winter, and frequent during the spring and fall. The eagles congregate to scavenge on dead salmon and prey on crows, mallards and gulls. Their numbers fluctuate from year to year. For example, the salmon run was reduced by 80% during the 1980 bird survey by Dick Cannings, and at this time a mean of 5.4 eagles (3 to 13 individuals from January to March) was reported. The eagles were concentrated at the culvert connecting Squamish River to the Central Channel, between the dredge spoils and Crescent Slough. From 1991 to 2002, eagles at the mouth of the Squamish River have ranged from 1 to 133 during the months of December and January (mean of 41 ± 12 S.E.). Fifty to 70 birds per day were documented during surveys in the early 1970s (Estuary Working Group 1974; Trethewey 1985), which indicates that the eagle population has remained relatively stable. The peregrine falcons breeding on the Stawamus Chief are also worthy of mention because they breed very rarely on the South

Coast mainland. The peregrines forage in the estuary on a regular basis. Other common raptors are the northern harrier, red-tailed hawk, Cooper’s hawk, sharp-shinned hawk, merlin and great horned owl. The northern goshawk, American kestrel, western screech owl, northern pygmy owl, short-eared owl, barred owl, and northern saw-whet owl also make an occasional appearance; barn and snowy owls are rarely seen (see Cannings 1980; BSC data). A moderate number of raptors move through the estuary in the fall. The biggest numbers are encountered in sites with inherent or established forest edges, i.e., the Squamish River riparian zone, Crescent Slough, and the forest bordering Central Channel (including Site A) and the high meadow (East marsh and North Field).

Aside from the fact that band-tailed pigeons used to migrate in the thousands in the Squamish Valley - Howe Sound Area (see Estuary Working Group 1974), no historic information is available on passerines in the area. European starlings and northwestern crows were noted as the most common songbirds by Trethewey (1985), but his report was focused on water birds. Based on the monthly bird counts initiated by Jim Wisnia, pine siskins are the most abundant passerine, followed by northwestern crows, European starlings, and red-winged blackbirds. Other common passerines are the American Robin, song sparrow, savannah sparrow, black-capped chickadee, Brewer’s blackbird, dark-eyed junco, cedar waxwing, white crowned sparrow, yellow and yellow-rumped warblers and common yellowthroat. All species of swallows make good use of the estuary during their foraging forays in the breeding season and during spring and fall migration, as does the marsh wren. Five species of woodpeckers have created holes for a variety of secondary cavity nesters, in the mature forest at the periphery of the estuary. Interior forest birds such as the brown creeper, varied thrush, red-breasted nuthatch, and winter wren are common in Site A because this site represents a large patch of contiguous forest.
The diversity and abundance of birds in various parts of the Squamish Estuary is summarized in Table 1. The results exclude West Delta because of this area’s inaccessibility and subsequent observer bias.