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AQUACULTURE ENVIRONMENT INTERACTIONS
Aquacult Environ Interact
Vol. 4: 273–283, 2013
doi: 10.3354/aei00089 Published online December 19
INTRODUCTION
Farming of salmon and trout (hereafter salmonids)
has experienced an exponential growth during re -
cent decades, with Chile and Norway accounting for
over 80% of the global salmonid aquaculture pro-
duction (Fig. 1; FAO 2011). In 2006, Chilean salmo nid
aquaculture reached its highest production, with
nearly 640 000 t valued at US $3.8 billion (FAO 2011).
This production corresponded mostly to Atlantic
salmon Salmo salar (60.3%), coho salmon Oncorhyn-
chus kisutch (17.5%), and rainbow trout O. mykiss
© The authors 2013. Open Access under Creative Commons by
Attribution Licence. Use, distribution and reproduction are un -
restricted. Authors and original publication must be credited.
Publisher: Inter-Research · www.int-res.com
*Email: maritza.sepulveda@uv.cl
REVIEW
Escaped farmed salmon and trout in Chile: incidence,
impacts, and the need for an ecosystem view
Maritza Sepúlveda1,*, Ivan Arismendi2, Doris Soto3, Fernando Jara4,
Francisca Farias5
1Centro de Investigación y Gestión de los Recursos Naturales (CIGREN), Instituto de Biología, Facultad de Ciencias,
Universidad de Valparaíso, Gran Bretaña 1111, Playa Ancha, Valparaíso, Chile
2Department of Fisheries and Wildlife, Oregon State University, Nash Hall, Room 104, Corvallis, Oregon 97331, USA
3Aquaculture Management and Conservation Service (FIMA), Fisheries and Aquaculture Department, FAO of UN,
Via delle Terme di Caracalla, 00153 Rome, Italy
4Statistics and Information Service (FIPS), Fisheries and Aquaculture Department, FAO of UN, Via delle Terme di Caracalla,
00153 Rome, Italy
5Oficina OCDE y Foros Internacionales, Ministerio del Medio Ambiente, Teatinos 258, Santiago, Chile
ABSTRACT: The exponential growth of the salmonid farming industry during the last 3 decades
has created conditions for massive escapes of these exotic species into natural environments in
southern Chile. Here, we review and update information about salmonid escapes from 1993 to
2012 and examine their potential environmental, social, and economic consequences. We estimate
that more than 1 million salmonids escape each year from marine farms, mainly due to weather
conditions and technical and operational failures of net-pens. While a decrease in the magnitude
of escaped Atlantic and coho salmon has occurred during the last several years, escaped rainbow
trout have not followed the same pattern. Rainbow trout have become a greater threat to native
ecosystems due to their greater potential to establish self-sustaining naturalized populations. The
main ecological effects of escapees are related to short-term predatory effects upon native fish,
long-term effects linked to the likelihood of farmed salmon establishing self-sustainable popula-
tions, and disease and pathogen transfer to native fauna. More research is needed to identify and
develop reliable indicators to estimate the impact of escapees at the ecosystem level in both mar-
ine and freshwater systems. An understanding of the mechanisms of coexistence between native
fishes and introduced non-native salmonids may be useful to design effective management strate-
gies aimed at protecting native fish from salmonid introductions. A precautionary approach that
encourages local artisanal and recreational fisheries to counteract colonization and naturalization
of salmon species in southern Chile may constitute another management option.
KEY WORDS: Fish farming · Salmo salar · Oncorhynchus kisutch · Oncorhynchus mykiss ·
Exotic species
O
PEN
PEN
A
CCESS
CCESS
Aquacult Environ Interact 4: 273–283, 2013
(22.2%). Salmonids were initially introduced in the
Southern Hemisphere for recreational purposes in
the early 1900s (e.g. rainbow trout and brown trout S.
trutta), and additional introductions (mostly Pacific
salmon species) occurred during the 1970s when
they were farmed in hatcheries for ranching and
aquaculture-fishery purposes (Basulto 2003). The ex -
pansion of the aquaculture industry in Chile began in
the 1980s with salmonids grown to commercial size
in net-pens in the inner seas and fjords of the Chiloe
Archipelago in the Lakes Region (41− 43° S; Fig. 2).
Currently the aquaculture industry, both in size and
in the number of farming facilities (>1150), is rapidly
expanding farther south (Aysen Region; 44− 46° S;
Fig. 2) (Buschmann et al. 2009, Nik lit schek et al. 2013).
Salmonid farming phases mirror the cycles used by
salmonids during their natural lives. Salmonids in-
habit both fresh and marine waters, with freshwater
systems playing a key role during early developmen-
tal stages. In Chile, the main growth of stocks takes
place in the sea (Soto et al. 2001, Rojas & Wadsworth
2007) where they are reared in either square or circu-
lar floating net-pens until they attain commercial size
(at 1−3 yr of age). The current density of salmonids in
each net-pen is 16 to 20 kg m−3, although higher den-
sities (~30 kg m−3) were re corded in some facilities
before 2008 (X. Rojas pers. comm.). It has been
shown that as the magnitude and number of sites
where salmonid farming occurs increases, the poten-
tial consequences due to net-pen or farm failure in-
crease, resulting in a higher probability of exotic es-
capees in the environment (Arismendi et al. 2009,
Jensen et al. 2010, Niklitschek et al. 2013).
Here, we review and update information about
salmonid escapes in Chile during the period from
1993 to 2012, and examine their po-
tential environmental and economic
consequences. We also provide a sum-
mary of the main factors that influence
escapees, and discuss mitigation and
prevention alternatives. We propose
actions to diminish escape risks and
highlight some management practices
to mitigate negative impacts and en-
hance those which appear to be posi-
tive. This information is fundamental
to understand the trade-off between
the negative effects of biological inva-
sions upon natural ecosystems and the
high economic value of salmonids for
aquaculture and recreational purposes
in Chile and elsewhere.
274
0
500
1000
150 0
2000
2500
199 0 19 92 1994 19 96 1998 200 0 20 02 2 00 4 20 06 2 00 8 2010
Production (×1000 t)
Year
Others
Canada
Faroe Islands
United Kingdom
Chile
Norway
Fig. 1. Oncorhynchus mykiss, O. kisutch, and Salmo salar. World production
(thousands of tonnes) of salmonid species including rainbow trout and coho
and Atlantic salmon between 1990 and 2011 (main producers are shown).
Source: FAO aquaculture statistics (www.fao.org/fishery/statistics/en)
Fig. 2. Salmonid farm locations (black dots) in the Lakes and
Aysen regions of Chile
Sepúlveda et al.: Escaped farmed salmonids in Chile
CAUSES OF SALMONID ESCAPES
Several factors can explain the escapes of salmo -
nids from facilities in coastal, marine, and freshwater
environments, including those of external and inter-
nal origins. Among these, external factors include
attacks by predators (e.g. Sepúlveda & Oliva 2005,
Vilata et al. 2010), theft or vandalism (intentional
damage of nets to let salmon escape and then steal
the fish), and adverse weather conditions, whereas
internal factors are directly related to and under the
responsibility of the fish farmer and include failure or
neglect during routine fish handling procedures and
site maintenance as well as accidental boat collisions
(Sepúlveda et al. 2009). Reports by salmonid farm
companies during the period 2004 to 2009 indicate
that, considering both regions together, escape events
were primarily caused by severe weather conditions
(29%), theft (21%), and structural failure of net-
pens and deficient handling incidents (18%; Fig. 3).
Storms lead to stronger waves and currents, resulting
in ripping of the net-pen tethering ropes, breaking of
the net-pen mesh, or tipping over of the net-pens
(Jensen et al. 2010). Unfortunately, due to the high
demand for new farming sites, often the selection of a
new location does not include proper consideration of
potentially adverse environmental conditions (i.e.
water currents, winds), in creasing the risk of fish es-
capes during extreme adverse weather conditions.
Overall, the causes of sal mo nid escapes are similar
to those reported by producers in other salmonid-
producing countries such as Norway, Canada, and
Scotland (Thorstad et al. 2008), but there the respon-
sibility for fish escapes lies mainly with the farmer
and/or providers of the equipment and services, in-
cluding routine site maintenance and fish handling
(Melo et al. 2005). Routine net-pen maintenance and
fish handling procedures carried out at the farms also
pose escape risks, from holes in the nets or trans-
portation of fish among cages. Moreover, carelessness
when changing fish or predator nets may result in the
escape of fish. The sorting of fish into 2 or more net-
pens through a tube can also lead to the involuntary
re lease of species if the tube is poorly mounted.
Moreover, collisions from boats used during opera-
tional activities, predator attacks (e.g. sea lions and
birds), inadequate manufacturing materials, and poor
net maintenance in crease the probability of escapes
(Robles 2002). Lastly, although it is difficult to quan-
tify, intentional damage of nets attributable to fisher-
men or farmers seeking to benefit from the subsequent
captures of escaped salmonids or insurance policies
are also factors that may increase escape risks.
QUANTIFYING SALMON AND TROUT ESCAPES
The real magnitude of salmonid escapes is most
likely underestimated, mainly due to the fact that not
all escapes are detected or reported. Numbers of
escaped salmonids in Chile have mostly been re -
ported or estimated after large and/or catastrophic
events (Soto et al. 2001, Thorstad et al. 2008, Nik lit -
schek et al. 2013). In addition to escapes caused by
harsh weather conditions, farmed salmon may
escape from marine net-pens through persistent low-
level leakage (Buschmann et al. 2009, Schröder &
García de Leaniz 2011). Unfortunately, information
on the number of salmonids that escape from regular
leakages in Chile remains poorly documented. Soto
et al. (2001) estimated that 1 to 5% of escapees come
from leakages. However, this estimate has not been
evaluated directly and remains somewhat specula-
tive, as the threat of leakages remains insufficiently
recognized (Sepúlveda et al. 2009).
By consulting insurance companies, Soto et al.
(2001) reported an important number of escapes after
major storms during 1994 and 1995 (Fig. 4, Table 1).
Since 2004, the salmon industry in Chile must inform
government institutions about every escape event at
their facility, but there are no official records of
escapes available for the period 1997 to 2003. A total
of 58 escape events were reported during the period
2004 to 2012 (data from Soto et al. 1997 and from
the National Fisheries Service; Fig. 4), accounting
for almost 6.5 million salmonid escapees, although it
is estimated that more than 1 million salmonids may
275
0
10
20
30
40
50
60
Thefts Weather Handlin
g
Unknown
Frequency (%)
The Lakes
Aysen
Fig. 3. Main technical issues associated with salmonid es-
capes, according to reports by salmonid farm companies in
the Lakes (filled bars) and Aysen (open bars) regions of Chile
(see Fig. 2) during the period 2004 to 2009. Source: National
Fisheries Services and Chilean Navy (unpubl. data)
Aquacult Environ Interact 4: 273–283, 2013
escape each year in Chilean marine systems (Thor -
stad et al. 2008).
During the 13 years for which escape reports are
available (1993 to 1996 and 2004 to 2012) a total of
3.7 million Atlantic salmon (289 600 yr−1), 3.1 million
coho salmon (239 954 yr−1), and 4.0 million rainbow
trout (313 892 yr−1) were reported to have escaped
from salmon farms located in both the Lakes and
Aysen regions. These amounts of escaped salmonids
appear to be similar to those reported in other coun-
tries such as Norway and Scotland (440 000 and
216 000 yr−1, respectively; Thorstad et al. 2008, Jen -
sen et al. 2010) and within an estimated range of
escapes in Chile (1 to 2% of the total production;
Niklitschek et al. 2006). However, when considering
total salmonid production, the proportion of escaped
fish in Chile was double that of Norway and similar
to that of Scotland.
Overall, the number of salmon and trout reported
to escape relative to the total production varies
greatly among the 3 species analyzed; it was lowest
for Atlantic salmon and highest for coho salmon and
rainbow trout. The average escape proportions (i.e.
total no. of escaped fish reported divided by the total
no. of fish produced, by species) covering both the
1993 to 1996 and 2004 to 2012 period were 1.2 t
for Atlantic salmon, 2.4 t for rainbow trout, and 2.5 t
for coho sal mon. Comparing the 2 time periods
(1993− 1996 versus 2004− 2012), the escapes of Atlan -
tic salmon and coho salmon decreased in the second
period (Atlantic salmon: from 374 349 to 251 933 yr−1;
coho salmon: from 512 413 to 118 860 yr−1) despite a
marked in crease in production during the second
period, especially for Atlantic salmon. In contrast, the
escapes of rainbow trout increased during the second
time pe riod (from 211 669 to 359 324 yr−1). This ten-
dency in rainbow trout escapes is likely due to large-
scale escape events in the Aysen Region during
2004, 2007, and 2008. The largest escape event in
2004 corresponded to a specific incident when about
1.8 million rainbow trout and coho salmon escaped
due to bad weather conditions. The largest event in
2007 was mainly associated with the tsunami that
took place in April, when more than 1.5 million spec-
imens were reported as escaped from net-pens. For
2008, Thor stad et al. (2008) estimated that about 5
million specimens had escaped, which could account
for one of the largest escape events documented both
at national and international levels.
In freshwater systems, the information regarding
salmon escapes is even more scarce, with a total of 11
events reported from 2004 to 2012 accounting for a
total of 613 586 salmonid escapees, principally from
lakes (75% rainbow trout and 25% Atlantic salmon).
A positive and strong relationship between the mag-
nitude of salmon production in freshwater facilities
and the relative abundance of free-living salmonids
including coho, Atlantic, rainbow trout, and Chinook
salmon has been described in lakes of southern Chile
(Arismendi et al. 2009, Young et al. 2009, 2010, Gar-
cía de Leaniz et al. 2010, Vanhaecke et al. 2012a). In
fact, exotic salmonids have been reported as the most
abundant fishes in freshwater systems of Chile (Soto
et al. 2006). Since there is no documented evidence
of successful natural reproduction of Atlantic and
coho salmon in Chile, individuals from these species
inhabiting freshwater systems appear to have exclu-
sively originated from aquaculture escapes (Soto et
al. 2001, 2006, Arismendi et al. 2009, Schröder & Gar-
cía de Leaniz 2011). Also, because no massive escape
events have been reported in freshwater systems, the
276
Production (×1000 t)
0
100
200
300
400
No. of fish escaped (×1000)
0
500
1000
150 0
0
100
200
300
400
0
500
1000
150 0
Year
1995 2000 20 05 2010
0
100
200
300
400
0
500
1000
150 0
Production
No. of fish escaped
Atlantic salmon
Coho salmon
Rainbow trout
Fig. 4. Total salmonid production and reported escapes. Es-
cape data for 1993 to 1996 from Soto et al. (1997) and for
2004 to 2012 from the National Fisheries Service (unpubl. in-
formation). Production data for 1993 to 2012 from FAO aqua-
culture statistics (www.fao.org/fishery/statistics/en)
Sepúlveda et al.: Escaped farmed salmonids in Chile
recurrent presence of salmonids in freshwater sys-
tems could be explained by frequent operational
leakages from salmon farms.
ECOLOGICAL CONSEQUENCES OF ESCAPES
There is a general consensus among scientists that
introduced species directly or indirectly alter the
structure and diversity of natural ecosystems (Gros -
holz 2002, Naylor et al. 2005). Among freshwater
introductions, salmonids are considered to be among
the most pervasive exotic species in the world (Pas-
cual et al. 2009). In Chile, the environmental con-
cerns from salmonid escapes have focused on short-
term predatory effects upon native fish, long-term
effects linked to the probability of farmed salmon
establishing self-sustainable populations, and dis-
ease and pathogen transfer (Young et al. 2010, Aris-
mendi et al. 2012, Niklitschek et al. 2013).
Displacement of native fishes due to ecological
interactions
Freshwater systems, including rivers and lakes,
and marine systems have been invaded by salmo -
nids, and it is possible that their ecosystem-level pro-
cesses may be affected through trophic cascade
effects (Carpenter et al. 1996). Unfortunately, there is
scarce information about the state of native fishes be -
fore salmonid introductions, which makes an under-
standing of their impacts more difficult to ob tain
(García de Leaniz et al. 2010). Based on stomach and
stable isotope analyses, several studies conducted in
Chile have shown negative effects from salmonid
species on native fishes due to predatory and inter-
ference competition (Soto et al. 2001, 2006, Aris-
mendi et al. 2009, 2012, Penaluna et al. 2009, Young
et al. 2009, 2010, García de Leaniz et al. 2010). Col-
lectively, the evidence suggests that salmonid spe-
cies have detrimental impacts on native fishes in all
types of ecosystems, including lakes (Soto et al. 2006,
Arismendi et al. 2009, García de Leaniz et al. 2010,
Habit et al. 2010, Correa & Hendry 2012), rivers (Soto
et al. 2006, Penaluna et al. 2009, Arismendi et al.
2012, Vanhaecke et al. 2012a,b), and inner seas (Soto
et al. 2001). Lakes in particular, where most of the
freshwater phase of salmonid aquaculture occurs,
could be particularly sensitive to the impacts of
escapes because top predator species may produce a
detrimental impact to aquatic biodiversity and spe-
cies richness (Moyle & Light 1996, García de Leaniz
et al. 2010, Vanhaecke et al. 2012a,b). However, a
more complete evaluation of the effects of predation
and competition on native fauna is prevented by the
277
Year Production (×1000 t) Number of fish escaped (×1000)
S. salar O. kisutch O. mykiss Total S. salar O. kisutch O. mykiss Total
1993 29.2 25.2 22.3 76.6 425.0 43.8 0 468.8
1994 34.2 34.5 32.9 101.6 1023.1 1288.8 646.4 2958.3
1995 54.3 44.0 42.7 141.0 27.4 392.1 168.5 588.0
1996 77.3 67.0 54.4 198.7 21.9 324.9 31.8 378.6
1997 96.7 73.4 77.1 247.2 – – – –
1998 107.1 76.9 75.1 259.1 – – – –
1999 103.2 76.3 50.4 229.9 – – – –
2000 166.9 93.4 79.6 339.9 – – – –
2001 253.9 136.9 109.9 500.7 – – – –
2002 265.7 102.5 111.7 479.9 – – – –
2003 280.3 91.8 114.6 486.7 – – – –
2004 349.1 90.3 126.6 566.0 12.4 896.5 949.5 1857.4
2005 385.8 102.5 123.0 611.3 190.3 31.4 – 221.7
2006 376.5 118.2 150.6 645.3 95.8 80.0 89.1 268.9
2007 331.0 105.5 162.4 598.9 1119.2 26.3 573.6 1719.1
2008 388.8 92.3 149.4 630.5 447.4 12.9 1137.1 1597.4
2009 204.0 120.0 149.6 473.6 312.0 22.3 484.7 819.0
2010 123.2 122.7 220.2 466.1 – 0.4 – 0.4
2011 264.4 159.6 224.5 648.5 15.5 – – 15.5
2012 398.3 161.3 262.7 822.3 70.9 – – 70.9
Table 1. Salmo salar, Oncorhynchus kisutch, and O. mykiss. Total salmonid production and reported escapes by species from
1993 to 2012. Escape data for 1993 to 1996 from Soto et al. (1997) and for 2004 to 2012 from the National Fisheries Service
(unpubl. information). Production data for 1993 to 2012 from FAO aquaculture statistics (www.fao.org/fishery/statistics/en)
Aquacult Environ Interact 4: 273–283, 2013
278
fact that the basic biology and ecology of native
aquatic communities in freshwater, inner seas, and
fjords of southern Chile remains poorly understood.
Spreading of pathogens and diseases
Animal health, especially in response to disease, is
another issue to consider when discussing the ecolog-
ical impacts of salmonid escapes, because exotic
salmonids can introduce new pathogens, alter disease
patterns, and even act synergistically to in crease the
impact of other stressors (García de Leaniz et al. 2010,
Habit et al. 2010). During the past few years, several
aquaculture facilities have been affected by epidemic
outbreaks of diseases, favored by the conditions of
fish being confined at high densities and the short
distance among farms (Asche et al. 2010). In addition,
escaped salmonids can travel large distances (Melo et
al. 2005, Whoriskey et al. 2006, Skilbrei et al. 2009),
and hence they become potential vectors for parasites
and diseases at a broad scale (Thorstad et al. 2008).
Epidemiological studies conducted in the Northern
Hemisphere (i.e. Ireland, Scotland, Norway, and
Canada) suggest that the occurrence of diseases such
as rickettsial septicemia and sea lice (Caligus spp.) in
both salmonids and native fishes are directly related
to higher concentrations of farmed fishes (Krkosek et
al. 2005, Naylor et al. 2005). Also, a virus that regu-
larly affects salmon farms in different countries in -
cluding Chile is the infectious pancreatic necrosis
virus, which has been detected in all salmon species
at all developmental stages (freshwater and ocean
phase of aquaculture) as well as in native fishes, mol-
lusks, and crustaceans (Rodríguez Saint Jean et al.
2003, Asche et al. 2010). The infectious salmon ane-
mia virus has also been documented in salmon farms
in Norway, Canada, Scotland, the USA, and recently
in Chile, causing enormous damage to the industry
and the local and national economy (Niklitschek et al.
2013). In Chile, the potential transmission of diseases
from farmed salmonids to other taxa such as marine
birds and mammals is yet unknown. However, pre-
liminary evidence of skin lesions in dolphins has sug-
gested a potential link to the salmonid aquaculture
industry (S. Heinrich pers. comm.).
Threats from escapees establishing self-sustaining
populations
Rainbow trout and Chinook salmon escapees may
pose the greatest threat to native ecosystems be -
cause they have a greater potential to establish natu-
ralized populations compared to both Atlantic and
coho salmon. Thus, the magnitude of their ecological
impacts may increase when they can establish self-
sustaining populations (Soto et al. 2006, 2007, Correa
& Gross 2008, Arismendi et al. 2009, 2011a,b). The
successful establishment of self-sustainable popula-
tions could be related to a relatively high plasticity of
these species (i.e. the ability to feed on a broad range
of organisms; Becker et al. 2007). Coho, Chinook
salmon, and rainbow trout have also been part of
ranching programs in the past which eventually may
also play a role in their establishment, especially in
the case of Chinook salmon (Astorga et al. 2008). It is
also possible that salmonid escapees might increase
the probability of establishing self-sustaining popu-
lations when those escapes are greater than from
slow leakages or ‘silent’ escapes (Consuegra et al.
2011). According to Consuegra et al. (2011), invasion
success may also de pend on pro pagule pressure. For
example, rainbow trout may have achieved high
establishment success and expanded more rapidly
than other anadromous species (such as brown trout)
because their spread is aided by rainbow trout
escaped from fish farms (Ciancio et al. 2008).
For Atlantic salmon, there is no evidence for the
establishment of naturalized populations (Soto et al.
2001, 2006, Schröder & García de Leaniz 2011). Indi-
rect evidence suggests that this species fails to estab-
lish because escaped individuals do not feed or grow
very well in the wild (Soto et al. 2001). This is similar
to other systems where efforts to establish Atlantic
salmon as a game fish species have failed (Naylor
et al. 2005). Considering that Atlantic salmon have
tradi tionally represented the highest proportion of
farmed salmonids in Chile, the risk of establishment
is an ongoing, unresolved question. Similarly to
Atlan tic salmon, there is no evidence suggesting that
coho salmon may successfully reproduce in the
Aysen Region, although some evidence of reproduc-
tive individuals migrating upstream has been re -
ported (Becker et al. 2007, Soto et al. 2007). Hence,
the possibilities for management and mitigation of
any adverse effects of escapes in these species may
be greater than for the other salmonids.
SOCIAL AND ECONOMIC EFFECTS OF ESCAPES
The conflict between the salmon industry and the
artisanal fishing sector is one of the most relevant
socio-economical impacts arising from salmon
escapes in Chile. Small-scale fishing of escaped
Sepúlveda et al.: Escaped farmed salmonids in Chile
salmon could have an important social and economic
effect, providing food security and extra income for
rural people and low-income families (Arismendi
1997, Soto et al. 2001). For example, during the
massive escapes of 1994–95 a large number of local
fishers, often women and children, were fishing for
salmonids (mostly with gillnets), which were then
sold in local markets (Soto et al. 2001). The practice is
still quite common in communities near salmon farm-
ing locations in the inland seas and lakes. It is impor-
tant to note, however, that the application of large
quantities of antibiotics in the salmon aquaculture in
Chile has environmental implications that potentially
impact the health of humans and wildlife (Fortt et
al. 1997).
Currently salmonids are the property of farm own-
ers even after they have escaped, so the capture and
marketing of escaped salmon by artisanal fishermen
is considered an illegal practice. During the previ-
ously mentioned massive escapes, fishermen created
considerable turmoil requesting fishing rights to
these escaped salmon, in addition to claiming that
native fish resources were affected (Soto et al. 2001).
The possibility of an artisanal fishery is somewhat
feared by salmon farmers, as legalization of a salmon
fishery could generate competing products whose
standards may not be at the level of those adopted by
the farmers’ organizations (Niklitschek et al. 2013). It
is clear however, that products from the salmon fish-
ery could be oriented to local markets for domestic
consumption, whereas production from salmon aqua -
culture is aimed for export to international markets.
However, for salmon farmers, opening a fishery of
escaped salmon could enhance vandalism and/or
theft at the farms. If some of the escaped salmon spe-
cies are indeed able to develop and establish natural-
ized populations, we predict a new ‘battleground’ in
the marine environment between artisanal fishery
and salmon farming.
In addition, sport fishing entities are debating the
pros and cons of this new species for tourism and
business. Hence this creates conflict between those
who want to fish and those who would like to elimi-
nate these returning exotic salmon runs.
PREVENTION AND MITIGATION OF ESCAPES
Preventing salmonid escapes
Considering that many escapes are due to human
mistakes, preventive measures can be effective in a
number of cases. A prevention system utilized in
aqua culture facilities located in streams is the use of
physical barriers to prevent fish from escaping. The
barriers are strategically located in critical connec-
tion points throughout the facilities, such as pools or
tanks containing the fish in water inlets and outflows.
Some companies have more efficient systems that
minimize the risk of escapes by using recirculation
tanks. In these closed and independent systems,
salmo nids do not come into contact with the outside
environment.
Ocean grow-out farms pose the largest challenges
for the industry. Although anti-predator nets protect
against external attacks and may also serve as con-
tainment when fish nets tear, there are no actual
physical barriers in place. Instead, fish farmers have
developed maintenance practices to prevent nets
from breaking and releasing fish into the environ-
ment. The proper tension of fish and anti-predator
nets through anchoring and mooring systems re -
duces friction between materials and prevents nets
from sticking to one another, thereby preventing sea
lions from approaching the fish. Other typical prac-
tices to reduce escape risks include replacing and
maintaining nets and monitoring by divers or the use
of video cameras.
Mitigating salmonid escapes
The aquaculture regulatory framework in Chile in -
cludes environmental regulations (the Environmen-
tal Impacts Assessment System, SEIA) established
in 1997, and the executive decree on environmental
norms for aquaculture (RAMA). These regulatory
tools and their operational norms affect both licens-
ing and operation of fish farms. The SEIA includes
the establishment of contingency plans for escaped
salmonids and, according to the RAMA, these plans
must follow special guidelines. These guidelines
have information about operational procedures and
devices to recover escaped salmonids, as well as the
obligation to provide immediate de tailed information
to authorities about escapees. Mandatory reporting
of escape incidents was introduced to Chile in 2001,
with a national statistics database since 2004. This
has enabled a gross assessment of the overall status
of the escape problem at an industry-wide scale
from year to year, and an evaluation of the causes
of escapes.
Different and non-exclusive techniques are used to
capture free-living salmonids that have escaped from
marine grow-out farms. The most popular technique
is to try to capture the escaped salmonids with nets
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Aquacult Environ Interact 4: 273–283, 2013
or mobile empty cages, often using pellets to attract
escaped salmonids to a particular location (Melo et
al. 2005). All aquaculture staff is required to work
following an escape event, but often the employees
do not have training in how to manage or respond to
such events.
No quantitative information is available on how
effective these prevention techniques and recapture
systems are. The background information collected
in other producer countries reveals a low success rate
for recapture efforts (recaptures amount to < 3 %;
Thorstad et al. 2008). This is likely the case in Chile,
because current recapture systems reflect mitigation
measures taken by the industry which are both inef-
ficient and insufficient (Melo et al. 2005). The RAMA
does not detail specific mitigation and recapture pro-
tocols, and producers have to define their own action
plan to deal with escaped fish. According to Melo et
al. (2005), salmonids do not remain in the vicinity of
the cages but are actually highly mobile and can
move up to 3 km in 10 h. In fact, molecular analyses
on rainbow trout indicated that the incidence of
escapees is widespread (Consuegra et al. 2011). Be -
cause large-scale escape events often occur under
bad weather conditions, time becomes a critical fac-
tor and recapture tasks are extremely complex,
which further reduces the success of such operations.
Additionally, action plans are not always enforced
because of the limited capacity of local and regional
government institutions. An improved knowledge of
patterns of movements, behavior, and survival rates
of escapees would be useful to inform natural re -
source managers and the fish farming industry.
To reinforce action plans and also regulation by
government institutions, it would be useful to deter-
mine the specific origin of escaped salmon. Re cently,
some tools have been developed to differentiate
potentially escaped from free-living fish, including
the detection of manganese concentration from
scales (Adey et al. 2009) and stable isotopes of car-
bon and nitrogen (Schröder & García de Leaniz
2011). Furthermore, some approaches with molecu-
lar markers have been used in Chile to distinguish
whether salmonids in rivers and lakes are descended
from specimens introduced for ranching or from
individuals which have escaped from salmon farms
(Astorga et al. 2008), or whether a genetic admixture
occurs be tween individuals escaping from fish farms
and ‘naturalized’ salmonids (Consuegra et al. 2011).
Using this approach as a baseline, in the future it
might be possible for each aquaculture facility to
have a unique and registered genetic marker stored
in a database, allowing a posterior cross-comparison
with escaped fish and thus allowing the determina-
tion of their specific origin.
Soto et al. (2001) proposed that a mitigation proce-
dure could be that artisanal fishers try to control
escaped salmonids by capturing escapees, especially
considering that artisanal fishing commonly occurs
around fish farm locations. In addition, there is poten-
tial for developing a recreational fishery especially
following an escape (Arismendi & Nahuelhual 2007).
Such fish could be allowed in a take quota (assuming
that the fish are safe to eat), complementing the
current catch and release approach for trout. Sport
fishing could be improved and facilitated around
farms to collect and control escaped fish and to pro-
vide additional income to local people and fishermen.
It is clear that such a fishery must be well organized to
be sure it does not conflict with the industry and/or
facilitate more escapes. The promotion of both arti-
sanal and recreational fisheries should be considered
only as a mitigation procedure. Although all species of
salmonids introduced for aquaculture purposes are
already present in both freshwater and marine envi-
ronments, some of them are not yet reproducing on
their own (Soto et al. 2001, 2006, Arismendi et al.
2009). The removal of these potential new invasive
species through a salmonid-based fishery could cer-
tainly decrease the likelihood of new establishments.
Artisanal fisheries based on salmonids should be of
limited access and highly regulated in order to dis-
courage the promotion of further releases.
It is important that artisanal and recreational fish-
eries should not impact native species. Fortunately,
in freshwater systems of southern Chile there are no
native fish that could be potentially affected by arti-
sanal or recreational fisheries. Native fish are smaller
in size than salmonids and thus have a low potential
for incidental capture. In general, salmonid-based
artisanal fisheries use gillnets, which are highly size-
selective. Anglers tend to use a catch-release ap -
proach, avoiding negative effects on native fish. In
marine environments, however, the potential for inci-
dental capture of na tive species is greater than in
freshwater, but these native fish already have pre-
existing historical fisheries and thus an established
commercial value (Soto et al. 2001).
Local and regional natural resource managers
should be involved to assess free-living and self-
sustaining salmonid populations, and should begin
discussions with interest groups on the use and man-
agement of such populations. To inform these man-
agers, investigators need to evaluate social and eco-
nomic scenarios involving these potential fisheries. If
a monetary value is given to these escaped salmo -
280
Sepúlveda et al.: Escaped farmed salmonids in Chile
nids, then the industry could be held accountable to
compensate the local and regional governments.
RESEARCH NEEDS
As has been identified in this review, there are still
several gaps in the knowledge of the impacts and
consequences of escaped salmonids in Chile. Thus,
considering that salmonid aquaculture is expected to
continue to grow, different research needs should be
identified including biological, social, and economic
aspects that could generate useful information for
decision makers. One of the most important research
needs is to implement a monitoring program to
evaluate the frequency, abundance and impact of
escaped sal mo nids. For example, the establishment
of long-term field surveys would allow estimation
of the relative importance of escaped and self-
sustaining salmonid populations. It is also important
to evaluate and develop reliable indicators to esti-
mate their impact on native species and ecosystems,
as well as their social and economic impact in both
marine and freshwater ecosystems (Velásquez et al.
2011). For example, to test broad-scale hypo theses
about taxonomic homogenization and expansion of
introduced species, a paired comparison be tween
historical and current presence/ absence of both na -
tive and introduced species appears to be a useful
tool (Marr et al. 2010, 2013).
While additional work is needed to increase our
knowledge of the processes underlying the patterns
described in this review, more data could improve
management of non-native salmonids in areas where
they impact native fishes negatively. For example,
patterns of apparent coexistence of non-native trout
and native fishes in some streams could provide clues
for managing invasions in more heavily impacted
streams (see conservation status in Campos et al.
1998, Habit et al. 2006). Thus, understanding mecha-
nisms of coexistence between native fishes and intro-
duced non-native salmonids may help in designing
effective management strategies that protect both
native fishes and important recreational fisheries.
Coexistence may also improve our knowledge of the
functioning of pelagic and benthic communities in
lakes and inner seas of southern Chile, maintaining
areas without salmonid farming as reference sites to
understand more completely the effects of free-rang-
ing salmonids. Even more important is to monitor
lakes without salmon farming, especially lakes with-
out trout, which seem to be very scarce (Soto et al.
2006, Correa & Hendry 2012).
CONCLUSIONS
Aquaculture is continuing to grow and expand
worldwide, as is salmonid farming probably every-
where, including the major producing countries
such as Norway and Chile. Effects of escaped
salmonids in regions where they are not native are
quite different from where they are native such as
Norway, because there, major impacts are related
to genetic modification of natural populations of
Atlantic salmon (Fleming et al. 2000, Thorstad et
al. 2008). In Chile, the effects are mostly related to
direct impacts of escaped individuals on native
fishes and the local environment, including impor-
tant social and economic effects related to artisanal
and recreational fisheries. The establishment of
new salmonid species such as Atlantic and coho
salmon, with their potential long-term effects due
to naturalized populations, requires urgent action
by decision makers.
In such a complex situation, with ecological, social,
health-related, political, and economic implications,
all stakeholders must assume their responsibilities.
Government agencies must ensure the ecological
balance of water systems, minimum escape levels
and effective mitigation measures, including regula-
tions to help manage these values. Salmonid farmers
must undertake a more proactive prevention role,
which includes (1) identifing critical issues in every
stage of salmon farming, so as to establish protocols
to prevent salmon escapes; (2) conducting an ade-
quate se lection of fish farm sites; (3) designing opti-
mal structures for the area’s oceanographic conditions;
(4) de veloping and implementing special technolo-
gies and materials to prevent escapes; and (5)
preparing more effective procedures and guidelines
for the recapture of escaped fish. In this context, the
coupling of aquaculture with fisheries (artisanal and
recreational) could help manage the natural re -
sources which both of these activities require, and
thus the management of escaped salmonids should
be addressed accordingly.
Acknowledgements. We thank all those who helped us to
compile the information presented in this work, particularly
people from the salmon farming industry, academics,
Undersecretary of Fisheries (Subsecretaría de Pesca),
National Fisheries Service (Servicio Nacional de Pesca,
SERNAPESCA), and the Chilean Navy. We also acknowl-
edge P. Moreno, B. Penaluna, and 3 anonymous reviewers
for their valuable comments and suggestions in the prepara-
tion of this manuscript, and L. Eaton for language correc-
tions. This study was supported by WWF-Chile.
281
Aquacult Environ Interact 4: 273–283, 2013
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Submitted: May 3, 2013; Accepted: October 31, 2013
Proofs received from author(s): December 13, 2013
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