The use of spatial analysis for environmental assessment of shellfish aquaculture in Baynes Sound, Vancouver Island, British Columbia, Canada

Abstract

The Baynes Sound area accounts for a large proportion of shellfish aquaculture production in British Columbia. In response to non-industry concerns regarding impacts from this inter-tidal farming on bird populations in Baynes Sound, a quantitative inventory of aquaculture infrastructure, more specifically clam netting, was done. Low-level high-resolution air photos were taken during periods of extreme low tides, for all intertidal shellfish tenures in Baynes Sound. Images were geo-referenced and used to create a digital geographic file of clam netting. Geographic Information System (GIS) processing of this clam net coverage information combined with existing shore substrate data and new littoral bathymetry data for Baynes Sound resulted in an accurate enumeration of clam net coverages for each of Baynes Sound's major substrate types and for the farmed clam species' optimum habitat. The results showed shellfish tenures occupy 20.3% and clam netting 2.9% of the intertidal area of Baynes Sound as defined by the Baynes Sound Coastal Plan [British Columbia Ministry of Sustainable Resource Management, 2000. Baynes Sound Coastal Plan for Shellfish Aquaculture. http://srmwww.gov.bc.ca/rmd/coastal/planning/south_island/baynes/docs/Baynes_Plan_Dec19_2002.pdf] boundary. Of the major substrate types in Baynes Sound, none had a clam net coverage exceeding 6%. Further analysis using optimal habitat areas, based on tidal heights, for each of three clam species [ Prothaca staminae (native littleneck), Nuttallia obscurata (varnish clam), and Tapes philippinarum (manila clam)] revealed no clam net coverage exceeded 20% of a shore type (based on a major substrate) found within optimal habitat areas (with the average below 6%). These techniques offer a cost-effective method of assessing inter-tidal resource utilization and provide a basis for time-series evaluation and a useful tool for adaptive resource management in Baynes Sound. More generally, these techniques can be used in any region where a shoreline classification system is complete to quantify the extent of intertidal habitat modification and be used as a decision support tool.