GENERAL BACKGROUND
After repeated introductions of exotic salmonids since the mid 19th century, their
successful acclimation to Chilean ecosystems did not occur until the late 20th century
(Camus and Jaksic 2009). Since then, Chile has been the world’s second largest producer of
farmed salmon and trout (mainly Atlantic salmon Salmo salar, coho salmon Oncorhynchus
kisutch, and rainbow trout O. mykiss, nearly 100% for export), accounting for nearly 40%
of the world production in some years (Buschmann and Fortt 2005; Bjørndal 2002;
Wigodsky and Herdener 2009). Such a growth took place at high environmental costs due
to the use of intensive production systems without ecosystem management, linked to the
widespread occurrence of farming centers in landscapes and seascapes all across southern
Chile (Buschmann et al. 2006; Camus and Jaksic 2009). However, the activity is heavily
concentrated in the Los Lagos District (“the lakes region”, ~20% of southern Chile), which
a decade ago reached a saturation level by occupying 100% of the “usable” lakes (i.e.,
appropriate for aquaculture), and holding 85% of the country’s salmon farms. The high
demands and the need for increasing salmon production prompted the industry to expand its
geographical range southwards (Soto et al. 2001; Camus and Jaksic 2009; Liberona and
Furci 2008). Currently, the lakes at the Los Lagos District are still saturated, and up until
2008 the district still held 474 marine concessions, representing 49% (~ 6,200 ha; Liberona
and Furci 2008) of the inshore waters dedicated to salmon aquaculture in southern Chile.
DESCRIPTION OF STUDY SITES
The marine localities of Metri and Calbuco were both located in relatively open
bays of low slope and sandy shores of ca. 120-180 m, delimited by rocky reefs or
sand/gravel. All plots were in inland bays, and thus calm and protected from the ocean.
Control and experimental sites at Calbuco were phisiognomically very similar among each
other. At Metri, the salmon farm bay was less extended, somewhat closer and protected
than the corresponding control site. The latter also had some small boulders. All sites had a
native forest vegetation cover that separated the shore from the prevailing agricultural and
dairy-dominated landscape in the region. The lakes Rupanco and Llanquihue were both
oligotrophic and surrounded by remnants of native forest vegetation. Again, control and
treatment plots were located in semi-open bays, with sand and gravel shores of ca. 150-200
m in length, 4-12 m wide, and delimited by rocky outcrops at their ends. All sites had a
strip of native forest vegetation cover that separated the shores from the prevailing
agricultural and dairy farms-dominated landscape in the region.
Salmon farms were run in similar ways as these are semi-industrial and standardized
operations. Salmon were kept in mesh pens, with either round or square frames, generaly in
groups of up to 40 units of varying sizes. The structures of the pens constituted a major
element in the landscape at salmon farms. Pens are floating structures of metal or plastic.
They emerge up to 1.5 m over the surface and have structures that hold the nets in place. In
all salmon farms, every pen was covered by a mesh to avoid direct access of birds to the
fishes. Still, occationally birds such as egrets and herons could congregate at pens, land on
the net, lowering it up to the water level and thus, had access to the captive fishes. We
could confirm that if not for the netting over the surface of the pens, birds would cause
major damage to the salmon industry. Often birds such as cormorants and night herons
were persecuted and killed with shotguns.
Normally, in lake farms salmons were kept up to the smolt size (18-25 cm) and then
were moved to marine farms where fishes reached their harvesting size (50-70 cm). Birds
could use the structures provided by the pens to land, perch, and feed. Often, birds
remained in the pens for several hours and several species congregate. Small passerines
such as Cinclodes spp. used the plastic pipes with open ends for nesting.
Bird assemblages are important components of the above ecosystems as they
represent the highest trophic level at the local community level. Also, the high
heterogeneity of freshwater and marine systems habitats results in high levels of
biodiversity (Victoriano et al. 2006).
REFERENCES
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salmonid farming on marine coastal ecosystems in the southeast Pacific. ICES J
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ambiental (1856-2008). Pontificia Universidad Católica de Chile, Santiago de Chile
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