Individual Thematic Analysis [Back to TOC]
The ecosections were initially evaluated by reviewing the areal distribution for each ecounit theme. Each of the five physical ecounit themes is plotted against each ecosection using percentage of area. The following discussion examines the distribution of each theme within an ecosection (Figures 1 - 5).
The variation and distribution of depth between and within ecosections is outlined in Figure 1. The Continental Slope ecosection is a mix of abyssal, deep and shallow depths and represents a transitional zone between the abyssal Subarctic Pacific and Transitional Pacific ecosections, and the shallower ecosections of the Pacific Marine Shelf ecoregion. The Hecate Strait and Vancouver Island Shelf ecosections are the shallowest with over 20% of the Hecate Strait ecosection composed photic depth (0 - 20 m). The Johnstone Strait, Dixon Entrance and the North Coast Fjords ecosections generally comprise an equal mix of shallow and deep depths. The remaining ecosections are dominated by shallow depths with lesser amounts of deeper and photic depths. The North Coast Fjords ecosection is much deeper than the adjacent Hecate Strait and Queen Charlotte Sound ecosections.
High current environments do not account for a large portion of the areas within any of the ecosections (Figure 2). Ecosections that have the largest areas of high current include the Johnstone Strait, Queen Charlotte Strait and Juan de Fuca Strait Ecosections. A greater percentage of high currents occur in these ecosections as they are constricted (narrow) waterways that drain the inland waters of the Georgia Basin. The remaining ecosections with the exception of the offshore abyssal Subarctic and Transitional Pacific have a very low proportion of high current areas. These results can be somewhat misleading as the regional current data set was based on a threshold of three knots, which may not highlight areas with currents slightly less than 3 knots.
The Johnstone Strait and North Coast Fjords ecosections are the most protected (Figure 3). The Johnstone Strait ecosection has the lowest exposure due to its narrow channels and fjords which reduce fetches to less than 10 km in most areas. The North Coast Fjords ecosection has some moderate exposure areas as a result of the length of many fjords that comprise this area. The Strait of Georgia and Queen Charlotte Strait ecosections are composed of predominately moderate exposures with lesser amounts of low exposure and a small component of high exposure areas in the latter. Exposed ecosections include Subarctic Pacific, Transitional Pacific, Continental Slope, Dixon Entrance, Queen Charlotte Sound and Vancouver Island Shelf ecosections. The remaining ecosections, Hecate Strait and Juan de Fuca Strait are dominated by high exposures with a minor amount of moderate exposures.
The distribution of subsurface relief within the ecosections is outlined in Figure 4. The Hecate Strait and Queen Charlotte Strait ecosections have the greatest variation in relief with over 50% of their areas consisting of high relief. Ecosections with between 10 and 20% of their area made up of high relief areas include Queen Charlotte Sound, North Coast Fjords, Vancouver Island Shelf and the Strait of Georgia ecosections. The remaining ecosections have less than 10% high relief areas.
The variation and distribution of bottom substrate types between ecosections is outlined in Figure 5 and suggests that the ecosections can be categorized into five broad groups. Ecosections dominated by mud include the North Coast Fjords, Strait of Georgia and Johnstone Strait. These environments have significantly lesser amounts of sand and hard substrate. The Juan de Fuca Strait Ecosection is somewhat unique as it is the only ecosection composed of more than 80% sand. Ecosections consisting of mixes of sand and hard substrates with a minor amount of mud include the Queen Charlotte Strait, Queen Charlotte Sound, and Vancouver Island Shelf. The substrates of the Continental Shelf, Subarctic Pacific and Transitional Pacific ecosections are unknown due to a lack of information. The Dixon Entrance ecosection is dominated by hard substrate with a minor amount of sand.
The dominant characteristics of each ecosection are summarized in Table 3. Apart from the Subarctic Pacific and Transitional Pacific Ecosections, there are significant differences between ecosections. In most cases, the ecosections differ from each other by at least two or three different themes. For example, the Johnstone Strait, North Coast Fjords and Strait of Georgia ecosections have distinct current and exposure regimes but similar depth, subsurface relief and substrate. Transitional ecosections between the Strait of Georgia and the Juan de Fuca Strait, Johnstone Strait and Queen Charlotte Strait Ecosections have similar current regimes but different exposure, relief and substrate characteristics.
The homogeneity of the Pacific Shelf Ecosections was assessed by comparing the total number of ecounits within an ecosection to the total number of repetitive ecounit classes within an ecosection. The results of these comparison are outlined in Figure 6. Where there is a large difference between the number of ecounits and the number of ecounit classes, the ecosection is considered to exhibit a high degree of internal homogeneity. Those ecosections that exhibit minimal differences are thought to reflect greater internal variations.
Six of the ecosections display a high degree of internal homogeneity and include the North Coast Fjords, Queen Charlotte Sound, Strait of Georgia, Vancouver Island Shelf and Continental Slope ecosections. The Juan de Fuca Strait, Queen Charlotte Strait and Johnstone Strait ecosections demonstrate a high degree of variability and are considered to represent transitional environments. All of them are located between the inland waters of the Georgia Basin and the more open waters of the more marine ecosections. These ecosections tend to display characteristics of both their neighboring ecosections. The Dixon Entrance ecosection is more homogenous than these transitional ecosections but displays greater variability than the other ecosections. The variability within this ecosection is a function of the freshwater, marine and current influences operating within the ecosection.
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