Size, settling velocity and density of small suspended particles at an active salmon aquaculture site

Ba Law,I Maier,Tg Milligan,F Page,Ps Hill

doi:10.3354/aei00116

Abstract

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 6:29-42 (2014) - DOI: https://doi.org/10.3354/aei00116 Size, settling velocity and density of small suspended particles at an active salmon aquaculture site B. A. Law1,2,*, P. S. Hill2, I. Maier2, T. G. Milligan1, F. Page3 1Fisheries and Oceans Canada, Bedford Institute of Oceanography, Dartmouth, Nova Scotia B2Y 4A2, Canada 2Department of Oceanography, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada 3Fisheries and Oceans Canada, St. Andrews Biological Station, St. Andrews, New Brunswick E5B 2L9, Canada *Corresponding author: brent.law@mar.dfo-mpo.gc.ca ABSTRACT: Scientific understanding of aquaculture interactions with the environment is limited, especially concerning the far-field transport and possible impacts of particulate wastes. A pilot study was carried out in southwest New Brunswick, Canada, in November 2008 to determine the size, settling velocity, and density of suspended particles at an active salmon aquaculture cage site. The model of Khelifa & Hill (2006) was fit to size-versus-settling velocity data to estimate the fractal dimension of flocs and the density of the component particles within flocs. Flocs had a larger fractal dimension and smaller component-particle density than in other studies, suggesting that particles from the aquaculture operation may be incorporated into suspended flocs with average settling velocities of 1 mm s-1. Variability in particle size and packaging was interpreted in the context of near bed velocity, tidal stage, and wind speed and direction. This analysis indicated that advection dominated observed variations in particle size and packaging. Indicators of resuspension, aggregation, disaggregation, and deposition were not detected in the time series. Advection of flocs away from the study site provides a mechanism to transport wastes over distances greater than 1 km prior to deposition; thus a settling class of 1 mm s-1 should be considered in depositional models of aquaculture wastes. KEY WORDS: Aquaculture · Flocs · Particle size · Size-versus-settling velocity · Effective density · Waste transport Full text in pdf format PreviousNextCite this article as: Law BA, Hill PS, Maier I, Milligan TG, Page F (2014) Size, settling velocity and density of small suspended particles at an active salmon aquaculture site. Aquacult Environ Interact 6:29-42. https://doi.org/10.3354/aei00116 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 6, No. 1. Online publication date: November 11, 2014 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2014 Inter-Research.

Highlights

As of 2007, over 75% of the world’s natural fish stocks were overexploited (Food and Agriculture Organization data 2007, www.fao.org)
Dc was determined from the disaggregated inorganic grain when stress is low enough for flocs to settle from the water column, and is associated with decreases in concentration and overall particle size
Particle size and packaging are controlled in the marine environment by the processes of advection, resuspension, aggregation, disaggregation and deposition

Summary

Introduction

As of 2007, over 75% of the world’s natural fish stocks were overexploited (Food and Agriculture Organization data 2007, www.fao.org). Aquaculture operations in Canada doubled from 1996 to 2007, and by 2007 the industry was generating almost one billion dollars annually in ‘landings’ (Aquaculture Canada data 2007, www.aquaculture association.ca). With the expansion of salmon farming, environmental concerns have been raised regarding the fate of aquaculture waste materials such as feed pellets and fecal material. Research has focused primarily on the deposition of organic waste immediately under or adjacent to salmon net pens, termed the ‘near-field’. Accurate models use the settling characteristics of feed pellets and feces to map the areal extent of the near-field depositional footprint under net pens (Panchang et al 1997, Cromey et al 2002, Chamberlain & Stucchi 2007)

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Conclusion