Methods for environmental evaluation in the coastal zone: some principles and recent experience with fish habitat mapping in coastal British Columbia, Canada
M. Sarah North
and
Colin D. Levings
Fisheries and Oceans
Science Branch
West Vancouver Laboratory
4160 Marine Drive
West Vancouver, British Columbia
Canada V7V 1N6
Abstract
Environmental managers working in the coastal zone need quantitative information on the boundaries and areal extent (m2, ha, or km2) of critical fish and wildlife habitats such as wetlands and seagrass beds. These data are used in estuarine management plans, to monitor change due to industrial activity or natural processes such as sea level rise. Recent technological advances in remote sensing, positioning, and underwater acoustics enable the acquisition of these data. In coastal British Columbia, intertidal fish habitats such as seagrass beds and marshes were mapped using a combined strategy of low level aerial photography, multispectral imagery (Compact Airborne Spectrographic Imagery (Compact Airborne Spectrographic Imager (casi)), and ground-truthing using the Differential Global Positioning System (DGPS). Obtaining the data at low tide, when the habitats are exposed to air, gave the best results. In our region, the quality of conservation and land use decisions is highly dependent on accurate mapping of the habitat boundaries. Aerial photography and DGPS gave the best results in terms of boundary definition and resolving remote and ground-truthed location data. However estimation of the boundary position error is a topic that needs further research. The advantage of casi is that data may be obtained more objectively, but because of the seasonal and species variation in spectral images there is an incomplete library of signatures to use when the data are classified statistically. For high resolution, large scale mapping of fish habitat, we have found that mapping the perimeter of the habitats with a DGPS and entering the data in a Geographic Information System is an effective technique to complement visual surveys. Many important specie such as clams and sea urchins live on specific bottom substrates and acoustic techniques have been used to map habitats below zero chart datum (subtidal habitats). Acoustic methods also show promise for mapping subtidal seagrass beds. Although all the above techniques show great promise to improve the efficiency and objectivity of habitat data acquisition in the coastal zone, the work must be supervised by experienced biologists who can provide accurate ground-truthing. The data cannot be used without critical review. Significant effort must therefore be expended on field checking to ensure credibility. Criteria need to be developed on the level of effort required, perhaps scaled to the size and complexity of the habitats that need to be mapped.
A. Introduction
The coast of British Columbia (B. C. ), the west shore of Canada, encloses some of the most complex geophysical and ecological units around the Pacific Rim. Including all of the major islands and archipelagos, the total shoreline length is 27 000 km. A wide variety of marine and estuarine habitats are represented on this coast, including open ocean beaches, fjords, estuaries, rocky shores, and tidal channels. On the south portion of the coast, a brackish enclosed sea, the Strait of Georgia (SoG), is the home for the majority of B. C.'s people. Vancouver, Canada's major Pacific port, is located here, and is characterized by a rapid population growth rate of about 15% in recent years. Industrial and urban development in the SoG has led to significant losses of environmentally sensitive fish habitat, especially marshes in estuaries and seagrass beds in nearshore areas (Levings and Thom 1994). On the north coast, the human population is much parser, and habitats are generally less impacted by development. In this region, industrial forestry in river basins is the current major threat to coastal habitats, since logs removed from the forest are usually dumped into and transported through marine zones. The riparian habitats along the coast, as well as the catchment
