Potential Exposure Zones for Proposed Newfoundland Marine Finfish Salmon Aquaculture Sites : Initial First Order Triage Scoping Calculations and Consistency Comparisons

Abstract

In this document, we describe a simple model, the Potential Exposure Zone (PEZ), that estimates the area exposed to discharges (feed, feces, in-feed drugs, and bath pesticides) resulting from finfish aquaculture activities. The PEZ provides an estimate of the spatial scale over which examination of information concerning the presence of species, habitats, and human activities should be examined for interactions of potential concern as part of an initial screening process for Fisheries and Oceans Canada aquaculture site assessments. The PEZ is a circle centred on the cage array with a radius equal to half the length scale of the cage array and a transport distance which is determined from a current speed and a transport time. PEZs are calculated for fourteen proposed Newfoundland marine finfish aquaculture sites. Benthic PEZs for waste feed, feces, and in-feed drugs are calculated using mid-depth current speeds and transport times based on the time required for particles to sink to the seabed. Pelagic PEZs for azamethiphos and hydrogen peroxide are calculated using 15 m sub-surface current speeds and a transport time based on the time required for the treatment dose concentration to dilute to a specified threshold. All calculated PEZs have radii ranging from O(100) to O(1,000) m with the exception of the PEZ associated with well-boat discharges for hydrogen peroxide which has a radius of 0 m since the assumed effective treatment concentration is less than the threshold concentration. Length scales estimated from the predicted deposition areas provided by the proponent were consistent with the length scales of the benthic PEZs estimated using mean current speeds. It should be emphasized that the entire domain within a PEZ is unlikely to be exposed but with proper selection of the input variables (i.e., current speed, sinking rate, depth, dilution rate, and threshold concentration), the PEZs should encompass all exposed areas.