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Biofouling of salmon-cage netting : fouling quantification, removal and prevention


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Hodson, Stephen 1997 , 'Biofouling of salmon-cage netting : fouling quantification, removal and prevention', PhD thesis, University of Tasmania.

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The quantification, removal and prevention of biofouling on salmon-cage netting
were investigated in Tasmania, Australia. Trials were aimed at identifying
environmentally-acceptable alternatives to traditional toxic antifoulants, and focussed on
three areas, viz. (1) underwater cleaning, (2) a "foul-release" silicone coating, and (3)
extruded polymers incorporating naturally-occurring compounds or a commercial shortlived
biocide. Each of these strategies was found to be applicable and effective for the
prevention and/or reduction of fouling on netting. Trials identified future directions to
improve antifouling efficacy, and potential problems such as resistant organisms. The
development of a quantification technique and the description of fouling in each trial also
provided information on the composition and variability within fouling communities on
Image analysis of close-up underwater photographs of net fouling was used to
quantify fouling removal and regrowth in terms of mesh occlusion. This enabled large
numbers of non-destructive samples to be taken and analysed quickly, which compensated
for the high degree of natural variability in the fouling communities. It also provided a
permanent record of the fouling, allowed dominant species to be identified and counted,
and permitted multiple sampling of the same area. Underwater cleaning of netting was found to be highly effective when there was
good contact between the brushes and netting, and prevented significant fouling
development over a 10 week period. However, the design of the trialed prototype cleaner
and the displacement of netting away from the cleaner, reduced the severity of scrubbing,
limiting fouling removal. This effectiveness was further compromised because residual
structures of fouling organisms and the large quantity of debris led to rapid regrowth and
recolonisation. The research identified areas for design improvement, the problems
associated with residual fouling and regrowth, and the requirements for effective in situ
net cleaning. The results demonstrate many difficulties that may limit the efficacy of in
situ cleaning, but suggest that this technology can significantly extend the immersion time
of nets during seasons of peak fouling. The application of a commercial silicone coating (Viridian 2000, International
Paints) to netting proved effective for increasing the ease of cleaning and reducing the
total mass of attached fouling. The silicone coating was particularly effective at preventing invertebrate fouling, and an absence solitary ascidians significantly reduced
total fouling biomass. However, the total algal biomass on the silicone was comparable to
uncoated netting, and some algal species were more abundant on the silicone (Ulva rigida
and Polysiphonia brodiaei). This latter effect was considered to represent effects of
surface colour, reduced competition, and differences in attachment strength. The
application of current silicone coatings to fish-cage netting was considered to be
problematic because their poor abrasion resistance and tear strength make them unsuitable
for shore-based cleaning and handling procedures. Nonetheless, the flexibility of silicone
coatings and the effective reduction of fouling adhesion make them ideal for fish cages
that will be cleaned in situ, and may provide an effective non-toxic solution to reduce the
cost of fouling removal.
Extruded polymers (plastics) incorporating either naturally-occurring compounds
or commercially-available biocides were found to prevent macrofouling development for
up to 209 days in field trials. The efficacy of polymers that incorporate either an algal
extract (Delisea pulchra or Laurencia rigida), an analog to a halogenated furanone (that
occurs in D. pulchra), or one of four commercial biocides (Busan 11-M1, Irgarol 1051,
Nopcocide N-96 and Sea-nine 211) was investigated. Fouling prevention was shown to be
a function of the polymer type and initial loading of the antifouling compound. Sea-nine
211 and the natural product analog were highly effective when incorporated into ethylenevinyl
acetate copolymers, and therefore this type of polymer may be suitable for mixtures
of these antifouling compounds. A high-density polyethylene (Shell, HET 6100) and a
copolymer of ethylene and acrylic acid (BASF, Lucalen® A) were also effective for Seanine
211. The current success with polymers that incorporate antifouling compounds, and
the many options for increasing their efficacy, are encouraging for the development of
netting which resists fouling.

Item Type: Thesis - PhD
Authors/Creators:Hodson, Stephen
Keywords: Fouling, Marine fouling organisms
Copyright Holders: The Author
Copyright Information:

Copyright 1997 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Contains 2 reprints in pocket at back. Thesis (PhD. )--University of Tasmania, 1998. Includes bibliographical references

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