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

Table 1. Summary of bird abundance and biodiversity in the Squamish Estuary

Site	Mean Monthly Bird Abundance (Counts averaged across years)	Median Diversity (no. of species averaged across years)	Total Diversity (1991 to 2002)	Diversity of water birds
Squamish River	112	29	93	44
Site A	81	31	86	14
Training Dyke	105	47	115	39
Crescent Slough	120	45	119	41
Mamquam Blind Channel	229	47	112	45
North Field	117	42	104	27
Central Channel	240	48	113	63
East Marsh	111	41	124	56
East of Fill	98	39	115	41
East Channel	66	27	81	37
Bridge Pond	99	49	127	45
Outer Estuary	59	20	37	27

Bridge Pond and East Marsh host the largest diversity of birds. These areas have the highest primary productivity in the estuary. Bridge Pond receives high levels of nutrients from the town’s storm waters, and it is a structurally complex area composed of six habitat types, interspersed by tidal drainages and a slough. The 50:50 ratio of land to water in Bridge Pond is particularly optimal for waterbirds. East Marsh is naturally productive as it is least influenced by incoming freshwater. High concentrations of benthic algae at this location may explain why 73% of mud-probing shorebirds have been sighted in this area.

Mamquam and Central Channel host the largest number of birds from September to April. They host primarily overwintering and migrating water birds, which often travel in large flocks. Central Channel is most occupied in late winter and early spring (from February to April), and in late fall (November, December). Mamquam Channel seems to be particularly important in early winter (November to January), in late spring (June) and in early fall (August and September), though glaucous-winged gulls make up a significant proportion of the biomass. Crescent Slough and North Field have the next highest bird biomass likely because of the presence of multiple productive habitats, including drainage channels, low and mid level tidal saltmarshes, high shrub meadows, riparian borders, and interior floodplain forest. Squamish River has a large number of birds representing a distinct assemblage of divers in winter (especially common mergansers, and the majority of buffleheads and goldeneyes).
Very little information is available on mammals of the Squamish Estuary. Resident killer whales from Puget Sound visited Howe Sound historically; their absence in the vicinity of the estuary may in part be linked to the training of the Squamish River, and the subsequent decline in salmon stocks. Seals are the only aquatic mammals in the estuary, pursuing fish species beyond the Mamquam confluence. Large mammals that frequent the estuary during foraging forays include the American black bear (Ursus americanus), cougar (Felis concolor), blacktail deer (Odocoileus hemionus) and coyote (Canis latrans). Many medium-sized mammals are either obligate or facultative users of riparian systems at all elevations. Riparian-dependent species include beavers and mink in old river channels near the estuary, muskrats in the delta, and river otters in Squamish River, Central Channel, and upper Mamquam Blind Channel. Smaller riparian occupants include the water shrew (Sorex palustris), Pacific jumping mouse (Zapus trinotatus), and long-tailed vole (Microtus longicaudus). Bats that rely on crevices and caves within large rock outcrops may be uncommon in the estuary, but species that rely heavily on riparian zones as foraging areas or roost sites are likely plentiful. More generalist species likely to frequent/reside in the estuary or its forest borders include the raccoon (Procyon lotor), short-tailed weasel (Mustela erminea), long-tailed weasel (Mustela frenata), striped skunk (Mephitis mephitis), snowshoe hare (Lepus americanus), red squirrel (Tamiasciurus douglasi), and several species of moles, shrews, mice and voles. Mid and large sized mammals usually select cover during movement and foraging activities.
Amphibians do not breed in brackish water but northwest salamanders (Ambystoma gracile), long-toed salamanders (Ambystoma macrodactylum), western toads (Bufo boreas) and Pacific treefrogs (Hyla regilla) will breed in ephemeral freshwater depressions within the estuary. Red-legged frogs (Rana aurora) and aquatic-breeding salamanders (Ambystoma sp.) will reside in any deeper, more permanent wetlands (e.g., Site A), and slow tributary reach sections within the Squamish River riparian zone.

The western terrestrial garter (Thamnophis elegans) is an aquatic snake rarely found far from fresh or marine water (Gregory and Campbell 1984). Although the common garter (Thamnophis sirtalis) frequents many habitat types it also prefers to forage along riparian edges and shorelines, and is commonly found swimming. Even the more terrestrial northwestern garter (Thamnophis ordinoides) is known to reside in estuaries, though it does not frequent the water as the other two species do. No hibernacula (snake overwintering sites) have been reported yet in the Squamish estuary, nor are there large rock outcrops for sunning on, except on the west shore of the Squamish River across from Fisherman’s entrance, and on the bluffs beside Mamquam Blind Channel.