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

Part 2: Conservation Needs of Squamish Estuary

Prior to outlining protection priorities and management recommendations for the Squamish Estuary, a brief summary on conservation considerations is presented.

1.0 Key Conservation Tenets

To ensure the long-term persistence of species and ecological systems one must consider key landscape and habitat attributes that contribute to its high biodiversity levels, and focal fish and wildlife species or plant communities (Franklin 1993; Lambeck 1997). Focal elements include either (1) plants, plant communities, and animals that are vulnerable to human-induced change; (2) umbrella species that have a broad scale relationship to other organisms; or (3) keystone species that play a significant functional role in maintaining major ecological processes.

1.1 Important Landscape Attributes

Large reserves protect a broader spectrum of regional biodiversity because they are more resilient to isolation (extinctions and extirpations are less likely), contain greater environmental and species diversity, might capture greater intraspecific genetic diversity, have a high interior to edge ratio that safeguards against habitat destruction along their boundaries, and are more likely to maintain adequate habitats after stochastic events (e.g., flooding, channel avulsion) or in the face of global climate changes.

1.1.1 Ecotones

As estuaries represent the junction between terrestrial and aquatic environments, they contain ecotones at many different scales. Large-scale edges occur at the land-water, water-air and freshwater-saltwater interfaces. Intermediate scale edges occur at the deep-shallow water and subtidal-intertidal edges, and smaller scale edges occur at the boundaries between habitats: mudflats, seagrasses, saltmarshes, high meadows, and forest borders. The numerous ecological transition zones (ecotones) result in patchiness (e.g., horizontal and vertical foliage diversity) thereby accommodating more foraging, resting and breeding niches. Ecotones in particular, contain wildlife species from the two overlapping habitats as well as species attracted specifically to edges (Logan et al. 1985).

1.1.2 Riparian Corridors

Riparian zones are a particularly vital component of the landscape. These inherent shoreline edges offer an unusual promise of biological conservation because they are more productive and complex than upslope habitat, and their high primary productivity encourages rapid growth, large size, and abundant forage. The complexity or mix of plant taxa likewise meets diverse needs as is reflected in the high wildlife species richness associated with riparian zones (Bunnell and Dupuis 1994; see Spakman and Hughes 1994). Indeed the majority of terrestrial vertebrates in British Columbia are more abundant and reproductively successful in riparian areas than in upslope habitats because the former areas are more structurally diverse and productive (Bunnell and Dupuis 1994). Although some species such as mink, beaver, otter, the American dipper, certain amphibians, the northern water-shrew, and many waterfowl species are riparian-dependent, others rely on riparian zones for one stage in their life cycle, or simply benefit from them for nesting, roosting, foraging, traveling, or seeking safety or thermal refuge. Important elements of the riparian zone include (1) deciduous trees and shrubs; (2) rotten wood; and (3) cool, moist microclimatic conditions. Deciduous plants are a rich source of insects for many animals, an important source of nesting sites for passerines, and browse for ungulates. Because deciduous trees become moribund or die young, they also are a significant source of rotten wood and cavity sites. Riparian canopies moderate temperature and radiation regimes and precipitate humidity that would not otherwise fall as rain. The resulting microclimate within riparian zones enhances foraging and movement opportunities for amphibians, which do not tolerate desiccation from wind and sun (e.g., Dupuis et al. 1995; Rosenberg 1998; Johnston and Frid 2002). Riparian habitats are also an extremely important energy source to aquatic organisms, and their importance to fish has been well recognized (see Land Use Development Guidelines). In a large river system as much as 50% of the organic matter consumed by fish is of terrestrial origin (Cooperrider et al. 1986). In addition to being a source of food to stream organisms, riparian trees provide shade over small-order channels within the floodplain, serve to stabilize banks, control floods by storing water and reducing surface water velocity, prevent sediment infusions into the channel, and filter run-off and intercept pollutants (see Cooperrider et al. 1986). In essence then, riparian zones contribute to the sustainability of the stream and terrestrial environment.

1.1.3 Undisturbed tidal channels and mudflats

Undisturbed mudflats and tidal channels within the saltmarshes are key attributes of estuarine deltas because of their high primary productivity and the critical food base their resident phytoplankton and benthic algae support. Overwintering and migrating waterbirds rely heavily on these attributes during their stop-overs, and fish depend on the channels as transition zones between freshwater and marine environments.

1.1.4 Landscape Connectivity

Connectivity is essential to allow individuals to disperse between populations. The linear nature of riparian zones permits connectivity and travel across the landscape for many species (Naiman and Rogers 1997). For example, the Squamish and Mamquam River buffers connect the floodplain with mid and upper elevation forests, thereby providing access to the estuary, for wider ranging mammals such as dear, bear, cougars, coyotes, and weasels. At a more local scale, edges offer excellent traveling routes for small mammals, and for snakes, which rely on the warmth of the sun for foraging activities. Discontinuous blocks of riparian habitat may not fulfill the needs of many smaller ranging species, particularly those sensitive to changes in microclimate or habitat structure (Merriam and Lanoue 1990; Bauer and Bauer 1992; Rosenberg 1998). By facilitating dispersal and gene flow, continuous riparian corridors can decrease the rate of extinction of dispersal-limited species in semi-isolated populations, inflating effective population size and increasing recolonization rate in patches where such species went extinct.

1.1.5 Water

The brackish water of the estuary is highly productive, and ultimately the source of food for all overwintering waterfowl, staging migratory water birds, and marine mammals. It supports large numbers of waterfowl and shorebirds for wintering and during migration. Surveys from government agencies have shown that 350,000 waterfowl use Washington estuaries and 50,000 use Oregon estuaries during an average winter (see Gaumer et al. 1985). In 1988, the total breeding population of seabirds in the relatively sheltered waters of the Strait of Georgia alone was estimated at 36,522 birds of seven species (Mahaffy et al. 1994). Based on estimates by Trethewey (1985) for the mid 1970’s, 10 to 15% of these birds have the Squamish Estuary as their destination. Brackish water is also critical to the maintenance of salmonid and other fish populations in the region. Some freshwater fish species move downstream into upper portions of the estuary in the winter to feed and to escape from high velocity floodwaters. Anadromous fish, such as salmon and steelhead, migrate through the estuary to spawn upstream in freshwater. Juveniles of these species spend a very critical time rearing in the estuaries prior to emigration to the ocean (Gaumer et al. 1985). Some fish species such as herring, spawn, feed and rear in estuaries.

Fresh water supplies vegetation with the quantity and quality needed for the health and growth of large mammals. It is essential as ephemeral or permanent breeding habitat for amphibians, and as drinking water for all wildlife. Martin (2002) has demonstrated that bird species richness in an area is highly correlated with fresh water availability (as well as the presence of large tracts of contiguous forests, large conifers, and deciduous shrubs).