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Canadian Science Advisory Secretariat
Research Document - 2006/011
Effects of Shellfish Aquaculture on Fish Habitat
By McKindsey, C.W., M.R. Anderson, P. Barnes, S. Courtenay,
T. Landry, and M. Skinner
Abstract
The purpose of this document is to provide information about the role of bivalve
culture in the ecosystem to enable habitat management to make informed
ecosystem-based management decisions with respect to the bivalve culture
industry. We do this by considering the roles of bivalves in the ecosystem under
natural conditions, describing culture methods and conditions used in Canada and
elsewhere, and subsequently evaluating whether these roles are mimicked under
aquaculture conditions.
To date, much research (and regulation) has focused on sedimentation processes
and their influence on biogeochemical and biological processes in sediments
below suspended bivalve culture operations. Similarly, much effort has been
directed to developing production carrying capacity models. Such models
typically focus on water column (phytoplankton, zooplankton, nutrients and
detritus) and benthic (nutrients) processes to ensure that harvests may be
maximized.
These approaches are quite well developed and go some distance towards allowing
for ecosystem-based management. That being said, they also provide a somewhat
truncated and negative view of the role of bivalve culture in the ecosystem. In
this document, we develop the model that many ecosystem services provided by
bivalve culture are in fact positive and may largely compensate for the more
negative effects that are often considered. We concentrate on macrofauna (macroinvertebrates
and fishes) and species directly associated with bivalves in culture and suggest
that these organisms should be considered more often and formally when decisions
are made with respect to bivalve culture operations. We also highlight some
issues that we feel need be better addressed so that true ecosystem-based
management may be practiced.
A review of the literature shows that bivalves are very important in many ways
in the way they interact with the environment. They may exert considerable
influence on planktonic communities and nutrient cycling. Through a series of
mechanisms, they also greatly promote the diversity and productivity of the
assemblages associated with them and may have cascading effects on the ecosystem
as a whole.
The main species cultured in eastern Canada are the native mussel (Mytilus
edulis and Mytilus trossulus) and the American oyster (Crassostrea
virginica). On the West Coast, the main cultivated species are the Pacific
oyster (Crassostrea gigas) and the manila clam (Venerupis
philippinarum), both of which are not native to that area. Mussels are
mostly farmed in longline systems whereas oysters in eastern Canada are mostly
in bottom or off-bottom culture. On the West Coast, oysters are culture both on
the bottom and off-bottom as well as increasingly in suspended culture. Spat on
the East Coast is almost all form wild set whereas the reverse is true on the
West Coast.
On the whole, it was found that bivalves in culture played much of the same
roles as do bivalves under natural conditions. That being said, the greater
concentration of bivalves in culture does lead to some negative effects on the
ecosystem due to increased organic loading in the vicinity of the farms and to
harvesting in bottom and off-bottom culture. On the other hand, bivalve culture
operations also function more or less as do artificial reefs. In suspended
bivalve culture, the abundance of fouling organisms and large mobile species
that are associated with these fouling organisms and the abundance of
macroinvertebrates and fishes directly under culture operations was, when
evaluated, consistently great. Some work has shown that the presence of these
species may compensate for any losses directly below suspended culture
operations. Similar increases in associated species have also been observed in
off-bottom culture operations. Interactions between bivalve culture and birds
and marine mammals are variable.
A number of methods are discussed to address sampling strategies for the suite
of organisms that we feel should be included in the evaluation of the influence
of bivalve culture in the ecosystem. We also briefly outline issues concerning
aquatic invasive species in bivalve culture. We finish up by highlighting
certain knowledge gaps and make recommendations for future research.
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(93 pages; 590K)
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