Establishment of Chinook salmon (Oncorhynchus tshawytscha) in Pacific basins of southern South America and its potential ecosystem implications

Abstract

Salmon and trout species are not native to the southern hemisphere, however rainbow and brown trout have been established a century in southern South America. Yet most attempts to introduce anadromous salmon failed until the onset of aquaculture by 1980. Escapes of Oncorhynchus tshawytscha (Chinook salmon) from aquaculture after 1990 have apparently produced increasingly important reproductive returns "naturalized", to upper basins in Chile and Argentina south of 390 S. In this paper we show data on the historic and spatial occurrence of chinook salmon in four Pacific basins during the past decade. Our objective is to establish the progress of the settlement forecasting some ecosystem disruptions in order to project and manage potential impacts. In Chile, sampling took place from 1995 to 2005 including rivers Petrohue, Poicas, and Rio Negro-Hornopiren, and Lake Puyehue, in the X Region. In Argentina sampled rivers were Futaleufu, Carrenleufu and Pico. In Chile and Argentina reproductive Chinooks ranged in size between 73 and 130 cm total length, being the smallest sizes those of Lake Puyehue where the population is apparently landlocked. In Rio Petrohue, the size of the runs varied from year to year reaching in the peak season of 1996 and 2004 up to 500 kg of fish along 100 m of riverbank. Temporal distribution of juvenile Chinooks suggested mainly a typical ocean type as they are gone to sea within the first year of age. As seen in Petrohue, reproductive populations could import significant quantities of marine derived nutrients as they do in their original habitats thus disturbing natural cycles and balances. Chinook establishment in these pristine watersheds in southern South America poses new challenges for decision makers and fishermen since they may develop a fishery in the Pacific Ocean with consequences to other fishery resources. Additionally they also become a resource for sport fishing. Therefore there is the need of developing management tools and approaches to control the populations avoiding irreversible ecosystem disruptions and social conflicts.

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CHINOOK SALMON IN SOUTHERN SOUTH AMERICA
Revista Chilena de Historia Natural
80: 81-98, 2007
Establishment of Chinook salmon (Oncorhynchus tshawytscha)
in Pacific basins of southern South America and its
potential ecosystem implications
Establecimiento del salmón Chinook (Oncorhynchus tshawytscha) en cuencas del Pacífico
sur de Sudamérica y sus potenciales implicancias ecosistémicas
DORIS SOTO1, 2, IVÁN ARISMENDI1, CECILIA DI PRINZIO3 & FERNANDO JARA4
1 Laboratorio de Ecología Acuática, Instituto de Acuicultura, Universidad Austral de Chile,
Campus Puerto Montt y Núcleo Milenio FORECOS
2 Present address: Inland Water Resources and Aquaculture Service (FIRI), Fisheries Department, FAO of
United Nations, Via delle Terme di Caracalla, 00100, Rome, Italy
3 Laboratorio de Investigaciones en Ecología y Sistemática Animal (UNPAT)-CONICET Esquel (Chubut), Argentina
4 Universidad San Sebastián, Puerto Montt, Chile
ABSTRACT
Salmon and trout species are not native to the southern hemisphere, however rainbow and brown trout have
been established a century in southern South America. Yet most attempts to introduce anadromous salmon
failed until the onset of aquaculture by 1980. Escapes of Oncorhynchus tshawytscha (Chinook salmon) from
aquaculture after 1990 have apparently produced increasingly important reproductive returns “naturalized”, to
upper basins in Chile and Argentina south of 39o S. In this paper we show data on the historic and spatial
occurrence of chinook salmon in four Pacific basins during the past decade. Our objective is to establish the
progress of the settlement forecasting some ecosystem disruptions in order to project and manage potential
impacts. In Chile, sampling took place from 1995 to 2005 including rivers Petrohué, Poicas, and Río Negro-
Hornopiren, and Lake Puyehue, in the X Region. In Argentina sampled rivers were Futaleufú, Carrenleufú and
Pico. In Chile and Argentina reproductive Chinooks ranged in size between 73 and 130 cm total length, being
the smallest sizes those of Lake Puyehue where the population is apparently landlocked. In Río Petrohué, the
size of the runs varied from year to year reaching in the peak season of 1996 and 2004 up to 500 kg of fish
along 100 m of riverbank. Temporal distribution of juvenile Chinooks suggested mainly a typical ocean type
as they are gone to sea within the first year of age. As seen in Petrohue, reproductive populations could
import significant quantities of marine derived nutrients as they do in their original habitats thus disturbing
natural cycles and balances. Chinook establishment in these pristine watersheds in southern South America
poses new challenges for decision makers and fishermen since they may develop a fishery in the Pacific
Ocean with consequences to other fishery resources. Additionally they also become a resource for sport
fishing. Therefore there is the need of developing management tools and approaches to control the
populations avoiding irreversible ecosystem disruptions and social conflicts.
Key words: salmon invasion, naturalized populations, nutrients uploads, sport fishing potential.
RESUMEN
Los salmonídeos no son nativos del hemisferio sur, y es así que las truchas (arcoiris y café) se establecieron
en el sur de Sudamérica hace un siglo. La mayoría de los intentos por introducir salmones anádromos falló
hasta el establecimiento de la acuicultura en los años ochenta. A partir de 1990, aparentemente debido a
escapes de Oncorhynchus tshawytscha (salmón Chinook) de cultivo, se están produciendo retornos
reproductivos de esta especie en cuencas chilenas y argentinas al sur de los 39o S. En este trabajo se muestra
la ocurrencia histórica y espacial de salmón chinook en cuatro cuencas de vertiente Pacífica durante la última
década. Nuestro objetivo es establecer el progreso de su establecimiento al tiempo que se proyectan algunos
impactos así como alternativas de manejo. En Chile, el muestreo se realizó entre 1995 y 2005 incluyendo los
ríos Petrohué, Poicas, Río Negro-Hornopirén, y el Lago Puyehue, en la X Región. En Argentina los ríos
muestreados incluyen al Futaleufú, Carrenleufú y Pico. En las cuencas chilenas y argentinas los Chinook
reproductivos alcanzaban 73 a 130 cm de largo total encontrándose los más pequeños en el Lago Puyehue
donde la población estaría encerrada. En el Río Petrohué, los retornos variaron de año en año alcanzando
máximos en 1996 y en el 2004 de hasta 500 kg de pescado en una extensión de 100 m de río. La distribución

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SOTO ET AL.
temporal de juveniles sugiere que principalmente se trata del tipo chinook oceánico ya que migrarían al mar
durante el primer año de vida. Como se observa en Petrohué, poblaciones reproductivas de la especie
aportarían cantidades relevantes de nutrientes de origen marino tal como ocurre en sus hábitats naturales,
produciendo así una importante perturbación a los balances y ciclos naturales en estos sitios. El
establecimiento de poblaciones de Chinook en el sur de Sudamérica, genera nuevos desafíos a pescadores y
autoridades ya que se podría desarrollar una pesquería de la especie en el océano Pacífico con consecuencias
sobre otros recursos pesqueros. Adicionalmente también se transforman en un recuso para la pesca deportiva.
Por ello se hace necesario desarrollar herramientas de manejo y control sobre la población para evitar
perturbaciones ecológicas y ecosistémicas irreversibles.
Palabras clave: invasión de salmonídeos, poblaciones naturalizadas, ingreso de nutrientes, potencial de pesca
deportiva.
INTRODUCTION
The Pacific salmon (Oncorhynchus spp.) from
North America has been introduced to several
areas in the world because of its high
nutritional value and as a prized sport fishing
catch. Introduction purposes have aimed at
ranching, sport and commercial fisheries, and
aquaculture (Soto et al. 2001b, Basulto 2003).
In the Patagonian waterways of Argentina
and Chile, native fish fauna is poor in
diversity (Ringuelet et al. 1967, Campos 1974,
Campos et al. 1998), and with almost no
sports fishery value due to the small body size
of the fish and/or to the fact that they are not
as attractive as the more popular introduced
trout. Around 1900, with sport fishing as a
target, the first salmon eggs were brought to
Chile (Basulto 2003) and to Argentina from
the Northern Hemisphere. In 1924, eggs of
Chinook salmon (Oncorhynchus tshawytscha)
were imported from the United States and
were sown in the river basins of Maullín,
Cochamó and Puelo in the Los Lagos region
(Fig. 1). In 1930, eggs of sockeye (O. nerka)
and coho (O. kisutch) were also introduced
from the United States. However, of all the
salmonid species introduced to Argentina (10
species) and Chile (11 species) only a few
have established self-sustaining populations
(Mendez & Munita 1989, Pascual et al. 2002).
Rainbow trout (O. mykiss), brown trout
(Salmo trutta) and brook trout (Salvelinus
fontinalis) became established in almost all
Patagonian basins in Argentina, whereas only
the first two have been truly successful in
Chile (Soto et al. 2006).
Chile has pioneered the development of
salmon aquaculture in America; the great
majority of it taking place in the 10th and 11th
administrative geographic regions (Soto et al.
2001b, Basulto 2003). The initiative, started
by Domsea Farms in the 1970’s, set a
landmark in Chilean aquaculture by
developing coho (O. kisutch) and Chinook
salmon (O. tshawytscha) “ocean ranching”.
The first returns of this “ranching” were
obtained in 1979; returns continued
intermittently until 1991 when they disappeared
(Mendez & Munita 1989). More recently, and
due to Chilean salmon farming, escapees of
Chinook have run into Patagonian rivers of
Pacific outlet in Chile and Argentina, spawning
in many of these areas (Soto et al. 2001b). In
their natural habitats in the northern
hemisphere, chinook return to their natal rivers
after spending about 3 to 8 years in the ocean;
the return to fresh water marks the end of their
life cycle as semelparous fish that reproduce
once and then die (Healey 1991).
In most lakes, fjords, and channels with
salmon farming in southern Chile (39-44o S)
there have been escapees, which include
rainbow trout, coho, Chinook, and Atlantic
salmon. However, massive returns have been
reported only for Chinook. Indeed, massive
reproductive runs were recorded from Petrohué
(41°12’ S) in Chile starting 1995 (Soto et al.
2001b). Previously, Grossman (1991, 1992)
had reported the presence of chinook in the Río
Futaleufú in Argentina. From available records
we can infer regular returns during the Austral
summer and fall in at least three Pacific slope
basins of the Chubut province in Argentina
(Futaleufú, Corcovado, and Pico), and in the
Petrohué and Negro basins in Chile (Fig. 1).
Of all the Pacific salmon species, Chinook
is the one attaining the largest sizes and the one
that performs the longest migrations (Healey
1991). In addition, it requires large alluvial
rivers for its reproduction (Geist & Dauble
1998).

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CHINOOK SALMON IN SOUTHERN SOUTH AMERICA
Fig. 1: Study sites: 1 = Río Toltén, 2 = Río Valdivia, 3 = Río Bueno, 4 = Río Pilmaiquén, 5 = Lago
Puyehue, 6 = Lago Todos los Santos, 7 = Laguna Los Patos, 8 = Río Petrohué, 9 = Río Maullín, 10
= Cochamó, 11 = Estuario del Reloncaví, 12 = Río Poicas, 13 = Río Puelo, 14 = Calbuco, 15 = Río
Negro, 16 = Río Futaleufú en Argentina, 17 = Lago Yelcho, 18 = Río Futaleufú, 19 = Río Palena,
20 = Río Carrenleufu, 21 = Río Pico, 22 = Río Vargas, 23 = Río Jaramillo, 24 = Río Pascua, 25 =
Puerto Natales.
Sitios de estudio: 1 = Río Toltén, 2 = Río Valdivia, 3 = Río Bueno, 4 = Río Pilmaiquén, 5 = Lago Puyehue, 6 = Lago Todos
los Santos, 7 = Laguna Los Patos, 8 = Río Petrohué, 9 = Río Maullín, 10 = Cochamó, 11 = Estuario del Reloncaví, 12 =
Río Poicas, 13 = Río Puelo, 14 = Calbuco, 15 = Río Negro, 16 = Río Futaleufú en Argentina, 17 = Lago Yelcho, 18 = Río
Futaleufú, 19 = Río Palena, 20 = Río Carrenleufu, 21 = Río Pico, 22 = Río Vargas, 23 = Río Jaramillo, 24 = Río Pascua, 25
= Puerto Natales.

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SOTO ET AL.
Many attempts have bee made worldwide to
establish populations of anadromous species,
but few have been successful (Mendez &
Munita 1989). One such case was the
introduction of Chinook salmon in New
Zealand at the beginning of the 20th century
(Waugh 1980, McDowall 1990). A more recent
“potential” settlement of Chinook in southern
South America is the one referred to in this
study. Factors that may determine successful
settlements are of interest particularly when, in
its native habitat, the species is deemed
“endangered” and cited under the Endangered
Species Act (ESA) of North America
(Lichatowich 1999, Willson 2003).
Impacts of introduced anadromous species
on native populations could result from direct,
indirect, or cascade effects both in the ocean
and in freshwater habitats. A significant such
impact may result from the transport of
nutrients to the river basins from the ocean
(Kline et al. 1993, Naiman et al. 2002) when
salmon return and later die and decompose or
are eaten in reproductive areas. This issue
merits attention in the case of southern Chile,
since Chinook are invading mostly pristine
areas that nutrient-wise may resemble pre-
industrial northern hemisphere salmon country.
Another issue we raise in this paper deals
with the difficult dilemma about conservation
of native biodiversity and foreign species
introductions, especially when the alien species
is considered valuable from a commercial and
recreational perspective.
In this paper we show data on the historic
and spatial occurrence of O. tshawytscha
(chinook salmon) in four Pacific basins (three
of them trans-Andean) during the past decade.
Our objective is to establish the spatial and
numeric progress of Chinook settlement in
southern South America forecasting some
ecosystem disruptions in order to project and
manage potential impacts.
MATERIAL AND METHODS
Study area
In Chile, main hydrographic watersheds are
born from the Andes mountains and flow
towards the Pacific Ocean, in an east to west
direction. South to 40º S there are trans-Andean
basins (Niemeyer & Cereceda 1984) that also
flow in an east-west direction from Argentina
to Chile (Fig. 1); these are also known as
“Pacific slope Argentinean basins”. Most of the
basins studied here originate in Andean or pre-
Andean lakes.
Watersheds from the 10th Region, in Chile,
were extensively sampled including all the
great lakes (Soto et al. 2006). However, the
present study includes only those basins where
Chinook specimens were found. This was also
the case with the Chubut Province in
Argentina. Table 1 presents data including river
discharge and length of main rivers, of all the
watersheds sampled. Sites included correspond
to the Argentinean basins of Pacific slope
Futaleufú, and the sub-basins Carrenleufú and
Pico (Fig. 1), and the Pacific basins of the
rivers Petrohué and Hornopirén. Information is
also included for Lago Puyehue in Chile (Fig.
1) as part of the Río Bueno basin where there
would be a partially “landlocked” Chinook
population.
Sampling of Chilean rivers and lakes
Sampled rivers included in the study are,
Petrohué, Poicas, and Rio Negro-Hornopiren,
additionally, as mentioned above, we include
information on Lake Puyehue within Rio Bueno
watershed (Table 1). The most intensely
evaluated river has been Río Petrohué, an
effluent from Lago Todos Los Santos and
tributary to the Reloncaví estuary (Fig. 1),
because the most conspicuous runs were
initially observed here. The main reproductive
activity is found in a river branch of
approximately 1,200 m long by 30 m wide and
an average depth of 1.1 m (range 0.6-1.8 m),
with lower water velocity (70 to 110 cm seg-1),
and lower water depth (55 to 120 cm) than the
main course of the Río Petrohué (Table 1). This
site named “Los Patos lagoon” is located
approximately 500 m down the Petrohué Falls
(of approximately 20 m high). The substratum
at the spawning area corresponds to clastic
rocks or volcanic ashes of spherical to
semispherical type, dark in color, which cover
the whole range from sands and gravel up to
boulders. Measured redd material resulting in
highly spherical gravel of 0.6 cm average
diameter (size range 0.6-7.7 cm). The canal bed
is covered by clumps of fine foliage aquatic

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CHINOOK SALMON IN SOUTHERN SOUTH AMERICA
plants (Myriophyllum sp.). Most of this
watercourse runs within the Vicente Perez
Rosales National Park, on its banks vegetation
is abundant and essentially pristine. Between
2002 and 2005, water temperature at “Los
Patos site varied between 8 and 15 oC being the
lowest during August, coinciding with Lago
Todos Los Santos thermal regime (Campos et
al. 1990).
Sampling at Los Patos started in April 1995
when direct visual estimates of fish density
were made of returning specimens (including
the recently dead) along a 150 m stretch.
Starting in the fall of 1996 (April) and
thereafter every fall until 2005, and whenever
possible, we used monofilament nets, diving,
and underwater video recording which allowed
counting/ measuring individuals and redds.
When river conditions did not allow evaluation
of alive individuals we made estimates of the
size distribution based upon spawned-out
fishes. Total egg counts were completed for
captured mature females recently arriving to
the spawning grounds.
To estimate potential nutrient contributions
in the form of dissolved nutrients (PO4 and
DIN = NO2 +NO3 + NH4) due to decomposing
spawned-out Chinook salmon, duplicate water
samples were taken before and on the spawning
site (temporal comparisons) on each sampling
visit between 2003 and 2005. Additionally, on
three occasions (April, September 2003 and
April 2005) samples were also taken of the
same river in a nearby area (spatial
comparisons), above the spawning site close to
the riverhead water at lake Todos los Santos.
This area should be unaffected by spawning
due to a high water fall in between (“Saltos del
Petrohué”) and indeed no spawners have been
observed there. In addition, we compared
dissolved nutrient data from similar rivers in
the region, obtained from the literature and
from our own team (Soto et al. 2006). All
nutrient analyses have been carried out
following methods described by Wetzel &
Likens (2000) except for NO3-N, which was
analyzed spectrophotometrically after sodium
salicylate treatment (Soto 2002).
TABLE 1
Information and capture techniques of main watersheds where Chinook salmon populations have
been evaluated within this study or have been reported by fisherman
Información y técnicas de captura en las principales cuencas donde se han evaluado poblaciones de salmón Chinook en el
marco de este estudio o donde han sido reportadas por los pescadores
Watershed LatitudeOrigin Area of
basin (km2)
Length Altitude
(m)
Average Q
(m3s-1)
Evaluation
method* of river** (km)
Toltén
Valdivia
Pilmaiquen
(Lago Puyehue)#
Bueno
Maullín
Petrohué
Poicas
Negro Hornopirén
Futaleufú
Carrenlelfu/
Corcovado
Pico-Palena
39°05’ S
40°10’ S
Chile
Chile / Argentina
8,040
11,320
23
55
134
50
323
600
FMR
FMR
40°37’ S
40°10’ S
40°33’ S
41º12‘ S
41º33‘ S
41°57’ S
42°15’ S
Chile
Chile
Chile
Chile
Chile
Chile
Chile/Argentina
2,680
17,210
4,298
2,644
24
200
11,600
68
130
85
36
10
23
246
184
50
50
189
30
50
6
176
372
100
278
5
60
363
GN
FMR
GN
EF
EF
GN – EF
SF - GN
43°54’ S
44º20’ S
Chile / Argentina
Chile / Argentina
880
12,887
60
240
850
500
47
700
SF
SF - GN
* Electrofishing (EF), gillnet (GN), sport fishing (SF), fisherman reports (FMR)
** Approximate distance to the ocean except for Carrenlelfu which drains to Palena (inner seas of Chiloe, Fig. 1); # data on
Lake Puyehue from Soto et al. (2001a)

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SOTO ET AL.
The presence of juveniles and the potential
impact of the spawning Chinook on other fish
species at Los Patos site was evaluated using
electro fishing gear (Smith and Root Model
12B Power electro fisher); four to six sampling
events were carried out every year between
July 1999 and January 2005. Electro fishing
was carried out repeatedly covering each time a
stretch of the river approximately 300 m long
by 3 m wide for 30 minutes or more, until the
catch of 90 % or more of the fish in the area
was secured. All fish specimens caught were
identified and counted, thus obtaining
abundance (fishes m-2) according to the
methodology described in Soto et al. (2006).
All fishes were measured, weighed, and then
released.
The two lesser rivers where juvenile
Chinooks have been recorded are the Río
Poicas tributary to the large Río Puelo which
flows into the Reloncaví Estuary, and a
tributary to the Río Negro Hornopirén which
runs into the inner sea in continental Chiloé
(Fig. 1). These are shorter rivers closer to the
sea, both drain first to second order mountain
streams, and have very transparent waters with
an estimated average discharge of 1.6 and 6 m3
sec-1, respectively. Their beds have pebbly
bottoms where rocks 10 to 20 cm in diameter
prevail with average depths of 50-70 cm. In
both cases, the riparian vegetation is abundant,
with scarce human intervention. During the
sampling period temperatures varied from 4.5
oC in July to 15.2 oC in January at Río Poicas,
while at Río Negro the variation was from 6 oC
in July to 9 oC in February. Similar sampling
methodology to that described for Petrohué was
applied in the later two rivers between 1999
and 2003, where we made two samples in the
summer (January-February) and one in winter
(July).
For rivers Pilmaiquén, Petrohué, and Negro
Hornopirén, data on annual water discharge
were obtained from official records (DGA,
Dirección Nacional de Aguas, Gobierno de
Chile). The flow speed, river bottom features,
and morphometric parameters were measured
directly with a Hydro-Bios Kiel (catalog
number 445 500-033) flow meter (Germany).
At Lago Puyehue we used information on
chinook “population” reported by Soto et al.
(2001a), and Soto et al. (2006). Data from this
lake were obtained from gillnetting near the
lake shore between August 1999 and November
2001. Lago Puyehue, is one of many lakes of
glacial origin, within the Araucanian Lakes
district; it is considered oligotrophic to
mesotrophic, temperate monomictic (Soto
2002). The only outlet of the lake is the Río
Pilmaiquén with a small hydropower plant and
waterfall of 17 m in height, less than 10 km
from its origin; this river connects with the Río
Bueno which in turn reaches the sea (Fig. 1).
This lake had a Chinook cage aquaculture
facility, one of the few sites in Chile where the
species was cultured.
In total, by using gill nets and electrofishing
we measured 122 adult individuals in Lago
Puyehue, 68 adults in Petrohué during
reproductive season and three individuals in
Hornopirén. We were not able to find
reproductive returns in Río Poicas. With
electrofishing we identified and measured at
least 20 juvenile individuals per species per
sample on each sampling trip.
Argentinean rivers
The rivers sampled were Futaleufú, Carrenleufú
and Pico, their geographic position and main
watershed are shown in Table 1, all of them
located east from the Andes range. Río
Futaleufú belonging to a large trans-Andean
basin (Table 1) originates in the southern zone
of Los Alerces National Park in Argentina (Fig.
1), and crosses to Chile reaching the Pacific
Ocean through the Lago Yelcho and river of the
same name (Fig. 1).
The Río Carrenleufú basin drains towards
the Pacific slope, taking the Rio Pico inflow,
through the Río Corcovado, and after flowing
52.8 km it reaches the Pacific Ocean through
the Río Palena in Chile (Fig. 1, Table 1).
Maximum temperatures reported for the
Futaleufú, Carrenleufú and Pico rivers were
usually in January, being respectively 15.9,
15.8, and 13.1 oC, while annual reported
averages are 11.4, 11.3, and 10.8 oC (Coronato
& Del Valle 1988).
The two spawning sites at Carreleufú river,
Argentina, corresponded to areas of old
riverbeds and deep pools, with arboreal and
bushy vegetation on both banks. The
substratum was made of spherical and
semispherical gravel black to gray in color,
interspersed with sandy areas and larger

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CHINOOK SALMON IN SOUTHERN SOUTH AMERICA
boulders and rocks. The average width of the
river is approximately 80 m, with a mean depth
of 1.5 m. In the Río Futaleufú (Argentina side),
the observed spawning site was a branch of 200
to 300 m in length, with an average width of 20
m, an approximate depth of 1.2 m and similar
substrate to that described above, which was
also the case in Río Pico. A common feature to
riparian zones in all the rivers both in Chile and
in Argentina, is the relatively pristine condition
of the vegetation and land use in the
catchments.
The collection of biological data from the
Argentinean basins was carried out during the
sport fishery seasons in 1999-2000 (October
through March), and 2000-2001 (November
through April). Fish samples were collected by
sport fishing, in addition to the use of
multifilament gillnets in Río Pico in March
2000 and in April 2001 in Río Futaleufú. Data
from Río Carrenleufú was provided by
fishermen and villagers only. In Argentina 35
adult individuals were measured, considering
19 in Río Corcovado, 10 in Río Futaleufú, and
six in Río Pico.
All fish disregarding the capture method,
were measured, weighed, and sexed. In
Argentina it was not possible to do electro
fishing for collection of juvenile specimens.
RESULTS
Assessment of reproductive conditions and
spawning events
At Los Patos in Río Petrohué, massive spawning
returns were observed in 1995, 1996, 2000, and
then again in 2004 (Table 2). Also, there have
been local reports of Chinook runs in this area
before 1995, but the magnitude is unknown. The
peak season for the Chinook spawning includes
mid March through mid May (Fig. 2). Direct
observations made at the site indicated pairs of
chinook salmon near their redds or in holding
groups of 5-12 individuals. Similar returns were
observed in March 2004 and April 2005 at Río
Hueñu Hueñu, another tributary to the Río
Petrohué, which runs into it about 2 km below
Los Patos. However, we have not systematically
sampled Río Hueñu Hueñu.
Captured of Chinooks at Los Patos in Río
Petrohué, since April 1995, ranged in size
between 73 and 130 cm total length (Fig. 3),
with a modal size at 95 cm and a weight
distribution between 5 and 13.4 kg. Using the
information for the years with highest returns it
is thus possible to estimate a biomass of
approximately 200-600 kg along 100 m of river
area (Table 2).
TABLE 2
Estimates (density/biomass on 100 m of lineal river shore) of spawning salmon at “Los Patos, Río
Petrohué” between 1995 and 2004 and prevalent climatic conditions prior to the spawning
Estimaciones (densidad/biomasa a lo largo de 100 m de línea de costa) de salmones chinook desovantes en el sector Los
Patos, Río Petrohué, entre 1995 y 2004 y condiciones climáticas prevalentes previas a la etapa reproductiva
Year Accumulated precipitation
(Jan-April) (mm)
Average river discharge
(Jan-April) (m3 seg-1)
Density/biomass
(kg salmon in 100 m)
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
732
785
909
455
440
718
688
780
581
541
411.6
406.1
399.6
314.9
240.4
343.2
677.1
446.8
501.7
361.8
200-300
450-500
< 10
< 10
< 10
80
None*
10
< 10
500 - 600
* No salmon spotted during sampling visits

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SOTO ET AL.
Fig. 2: Biomass per species in Petrohué-Los Patos site (all sampling methods combined). For O.
tshawytscha, biomass over 10 g m-2 corresponds solely to spawners, the bars have been cut to
facilitate graphical comparison but the total values are indicated above each.
Biomasa por especie en el Río Petrohué- sector Los Patos (todos los métodos de muestreo combinados). Aquellas biomasas
de O. tshawytscha sobre 10 g m-2 corresponden solamente a desovantes, las barras han sido cortadas en su parte superior
para facilitar la comparación gráfica pero los valores totales aparecen junto a cada una.
Fig. 3: Size classes of spawning chinook at Los Patos site, Río Petrohué (1995, 1996, 2000 and
2004).
Clases de talla de los chinook desovantes en el sector Los Patos, Río Petrohué (1995, 1996, 2000 y 2004).

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CHINOOK SALMON IN SOUTHERN SOUTH AMERICA
Based on the number of chinook redds
counted in a subsection of the river, we
estimated around 420 to 560 as the total
number of redds in this secondary river channel
used as spawning site. In 1996 an estimated
total of 800 individuals reached this part of the
river. The evaluation of gonads of un-spawned
females, between 85 to 95 cm total lengths,
ranged between 4,180 to 4,950 mature eggs. A
fraction of the spawned eggs is eaten by other
fish (brown and rainbow trout, coho salmon
and brook trout, Salvelinus fontinalis) as was
attested by the stomachs packed with eggs, and
by freshwater crabs (Aegla sp.) which
congregated to feed on the eggs among the
cobbles at each redd.
The intensity of the returns has varied from
year to year. Evaluations at the same site in
1999 and again in 2000 showed either so few
individuals that were virtually impossible to
sample (1999) or a much lesser return (2000)
that did not exceed 80 kg along 100 m of the
river (Table 2). In 2004, a massive spawning
even larger than the one reported in 1996, took
place (Table 2). This allowed for a more
complete sampling from March to May 2004;
in this case, returning Chinooks were rather
larger than in previous years, total length
ranged from 67 to 130 cm and the average was
94.9 cm (Fig. 3). Further, the largest fish
biomass was recorded in the river during
March, April and May, corresponding to
spawning Chinook (between 60 and 130 cm
total length) reaching more than 1000 g m-2
during spawning in May 2004. Over the same
months, increases in the biomass of rainbow
trout and brown trout were reported (Fig. 2).
Table 2 indicates Chinook estimated
biomass density for every 100 m along the river
in the area of Los Patos lagoon, over the past
10 years. Accumulated rainfall and average
river discharge are also shown for the period
January-April, the preceding and actual months
of the spawning. Though the accumulated
precipitation per se might not have a direct
effect probably due to the regulating effect of
Lago Todos Los Santos, average river
discharge seems to affect the intensity of the
returns. On the one hand, either too little a
discharge would not allow for strong enough
signals or sufficient water for the upward
return, or on the other hand, too much a
discharge would wash away fish from the
spawning grounds. The fact is that the greatest
return years took place when the average river
discharge was between 362 to 412 m3 seg-1
(Table 2).
At Lago Puyehue, the evaluation of
population structure showed individuals
ranging from 20 to 90 cm in total length, 90 %
of the individuals over 40 cm had mature
gonads by the end of April both in 2000 and
2001 when population density increased by the
lake shore (Soto et al. 2001a). However, there
is no information on massive reproductive runs
in tributaries to the lake and we have no
samples (nor other reports) that include
juvenile Chinook in the streams (Soto &
Arismendi 2005).
Specimens caught in basins of Argentinean
origin were between 50 and 130 cm of total
length; most of the individuals ranging from 80
to 100 cm (Fig. 4), unfortunately we could not
obtain reliable information on the size of
returns or about inter-annual variability.
Length-weight relationships varied for the
different environments in Chile and Argentina.
Lago Puyehue had adult individuals of the
smallest sizes, while returns in Argentina
showed slightly larger sizes than those in Chile,
though average size were not statistically
different (Mann-Whitney U-test, P = 0.058). In
addition, for those Chinook with similar
lengths in Chilean and Argentinean basins, the
latter had larger weights (Fig. 4).
Juvenile population features
In the Río Petrohué a total of 16 samplings
with electro fishing were made from 1999 to
January 2005, covering all four seasons. Brown
trout (Salmo trutta) was the prevailing species
(Fig. 2), followed by rainbow trout
(Oncorhynchus mykiss) and chinook (O.
tshawytscha); all of them with abundance
generally below 0.2 individuals m-2 (Fig. 5).
Rainbow and brown trout were captured in all
the samplings, and were within the range 0.2 to
36 g m-2 (Fig. 2). Juvenile Chinook captured by
our method reached highest density between
September and October especially in 2004 (Fig.
6) while they were mostly absent in the fall
months, February to June (Fig. 6).
At rivers Poicas and Negro-Hornopirén
average density of juveniles were 0.35 and 0.03
individuals m-2 respectively although variability

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SOTO ET AL.
Fig. 4: Total length versus total weight for Chinook salmon. All sites, (accumulated data - all
fishing methods).
Longitud total versus peso total para el salmón chinook. Se incluyen todos los sitios (datos acumulados-todos los métodos
de pesca).
Fig. 5: Average abundance of each salmon-trout species in the sampled Chilean rivers (electrofis-
hing). Error bars represent standard error. In the white column for Chinook (O. tshawytscha) the
number (5.5) represent the top value with the error bar.
Abundancia promedio de cada especie de salmón-trucha en los ríos chilenos muestreados (pesca eléctrica). Las barras de
error representan error estándar. En la columna blanca correspondiente a Chinook (O. tshawytscha) el número (5.5)
representa el valor incluyendo la barra de error.
´
´
´
´

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CHINOOK SALMON IN SOUTHERN SOUTH AMERICA
among sampling dates was much higher in Río
Negro-Hornopirén (Fig. 5). Here the largest
density was observed in May (1.3 individuals
m-2) when average total length of individuals
was 12.3 cm, while in August we observed the
largest size (Fig. 7); in Río Poicas the largest
individuals (8-11 cm) were observed in July
(Fig. 7) and January (7.6-9.3 cm).
Dissolved inorganic nitrogen (DIN)
concentrations measured on spawning grounds
water were not much different from those in the
same river above the latter, or from those
measured on comparable Andean rivers of the
region (Soto et al. 2006). Yet the highest values
on the spawning area were observed at the time
or right after maximum spawning (Fig. 8). On
the other hand, dissolved inorganic phosphorus,
values were much higher than those up river or
on other comparable rivers. Concentrations also
showed temporal fluctuations with the highest
values on the peak spawning (Fig. 8).
DISCUSSION
Under the US Species Act (ESA), different
populations of chinook salmon are at present
cited as threatened or endangered. The decline
of these populations along with the other
Pacific salmon species have been caused by a
mixture of factors including habitat destruction,
over harvesting and hydropower dams
(Lichatowich 1999, Willson 2003). Quite a
different situation seems to be taking place in
southern South America, where chinook salmon
is conquering new environments.
Anadromous salmon play an important role
in their natural environments particularly
supplying marine derived nutrients to head
waters. The decline of Pacific salmon in North
America, including that of Chinook populations,
is producing and impoverishment of the upper
basins and there is a disruption of a normal
ocean-land connection (Gresh et al. 2000,
Naiman et al. 2002). The opposite situation is
taking place in southern South America where
apparently the accidental escapes of chinook
salmon from aquaculture have produced
increasingly important reproductive returns,
“escapements”, to upper basins in Chile and
Argentina. This could be in turn, an ecosystemic
disruption since no such connection existed
within evolutionary scales in these southern
ecosystems.
Origin and success of the reproductive
populations
Attempts to introduce populations of
anadromous species in different places in the
world have mostly failed. The exception can be
found in New Zealand where successful returns
Fig. 6: Density of juvenile chinook at Los Patos-Río Petrohué. Only sampled months are shown.
Densidad de juveniles de chinook el sector los Patos-Río Petrohué. Solo se indican los meses muestreados.

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SOTO ET AL.
of chinook (after seeding eggs and juveniles)
were already observed between 1901 to 1907.
Today there are numerous reproductive
populations in that country (McDowall 1990).
However, in Chile early chinook
introduction attempts (before 1970) with eggs
were apparently not successful and persistent
returns were not observed until the 1990s.
These could have originated in the ranching
attempt carried out in 1975 (Basulto 2003) but
most likely they resulted from salmon farming
accidental escapes since 1980 (Soto et al.
2001b). Accidentally farm escaped juvenile and
adult salmon should have higher survival
probabilities than eggs.
It is surprising that this species, which
accounts for a very small proportion of the
salmon farming (less than 2 %) and the
smallest proportion of escapees, could be
successful in establishing feral populations.
Total salmon escaped from farming in the inner
seas of southern Chile between 1994 and 1996
amounted to more than 3 million individuals,
including coho salmon, rainbow trout, Atlantic
salmon and chinook. The latter could have
reached up to 50 thousand individuals
corresponding to the 1+ age class or older, and
with an individual mass around 1 kg (Soto et al.
2001b). However, the first large reported
Fig. 7: Monthly average length of juvenile chinook at Los Patos, Río Petrohué.
Longitud promedio mensual de juveniles de chinook en el sector Los Patos, Río Petrohué.
reproductive run in Petrohué occurred in April
1995 (Table 2) and perhaps these individuals
originated in previous escapes to those reported
in 1994. The size distribution of the
reproductive individuals (Fig. 3), according to
the length-age relationship proposed by Healy
(1991) for Alaskan chinook populations, should
correspond to individuals of 6 to 8 years old.
There were only two sites in the inner seas
of Chiloé (Fig. 1) where Chinook salmon were
farmed, one in Hornopirén and other near
Calbuco (Fig. 1), localities which could have
originated straying populations moving slightly
north to Reloncavi Estuary and Río Petrohué,
eventually to Río Puelo and south to Futaleufú
basin and to Chubut Province in Argentina.
Accordingly, Grosman (1992) reported the first
noticeable chinook runs near Esquel, Argentina
(Fig. 1) by 1990, suggesting that reproductive
returns became more frequent during that
decade and reinforcing the hypothesis that they
might have originated from farming escapees
after 1980. Individuals reaching Argentina
basins are slightly larger than those
reproducing in Petrohué (Fig. 4). On the other
hand the farm escaped individuals in Lago
Puyehue, although can reach sexual maturity,
they do not seem to be able to reach the ocean
and there are no observations of successful
´

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CHINOOK SALMON IN SOUTHERN SOUTH AMERICA
reproductions in the affluent streams to the lake
either (Soto & Arismendi 2005). Probably the
presence of the Pilmaiquén hydroelectric dam
in the outlet of the lake is the main barrier to
outgoing fish and for returning reproductive
individuals. Nevertheless there are reports of
reproductive returns to a tributary below the
dam (Javier Marín, personal communication).
The presence of hydropower and irrigation
dams have been one of the most important
damaging factors blamed to cause the decline
of chinook populations in the Pacific coast of
Oregon and British Columbia (Willson 2003).
The reproductive population in Petrohué
seems to be the typical ocean type according to
the characteristics mentioned by Haley (1991)
and Brannon et al. (2004). These are individuals
which run in late summer/early fall (late March-
Fig. 8: Above; concentration of dissolved inorganic nitrogen (DIN = NO2+ NO3+ NH4) in other
similar Andean rivers and in Rio Petrohué above spawning grounds (SPW) and on the spawning
site (black bars) on different sampling occasions. Error bars are standard errors for duplicate
samples.
Arriba, concentración de nitrógeno inorgánico disuelto (DIN = NO2+ NO3+ NH4) en otros ríos Andinos similares y en el
Río Petrohué más arriba del lugar de desove (SPW) y en el área de desove (barras negras) en diferentes momentos de
muestreo. Las barras de error corresponden a error estándar para muestras duplicadas.
early May, Fig. 2), juveniles with short stream
residence since their hatching probably takes
place within three to four months after spawning
(July-August) and youngsters are apparently
gone to sea within the first year of age. We
conclude this since we observed the last juvenile
individual at Los Patos in February (at 10 cm of
total length) but the largest proportion of the
juvenile population was gone from the
reproduction area after November (Fig. 6) when
they had reached 5 to 7 cm of TL (Fig. 7). Since
the river is rather short (30 km, Table 1), these
juveniles could reach the fjord marine waters
within the 0-age. Río Petrohué as the lake outlet
has small temperature variation with the lowest
of 8 oC in August increasing to 14 oC in
February (Campos et al. 1990). Such conditions
offer comparatively high temperatures possibly

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SOTO ET AL.
shortening hatching time, facilitating fast growth
and early ocean migration as suggested by
Brannon et al. (2004). Most chinook rivers in
North America, for example those in the
Columbia basin, have much lower winter
temperatures usually below 5 oC. Although we
have been able to check few females with
complete gonads, fecundity seems lower (around
4500 eggs) than expected for ocean type (Healey
1991), yet this could be a sampling bias.
It is likely that chinook ocean type is very
common at more southern latitudes, because
rivers with present reproductive populations are
also connected to head water lakes as in
Petrohué, such is the case of Futaleufú basin
and Carrenleufú basins. Most lakes in southern
Chile and Argentina are monomictic, and
lowest circulation temperatures in winter rarely
fall below 8 oC and for a very short period
(Soto 2002). Thus average rearing temperatures
should be over 9 oC.
However, rivers born directly from wet
precipitation and or from snow usually have
lower temperatures as is the case in rivers Poicas
and
temperatures can fall below 5 oC. There it could
be possible to find stream type chinook as seems
to be the case at Poicas where we found the
largest size individuals in July (Fig. 7).
Yet another factor, which we were not able
to consider here, is the distance young fish have
to go through to reach the ocean. This is the
shortest in Petrohué and Negro rivers while is
much longer for the trans-Andean basins which
may force the juvenile fish to remain in the
stream condition until they reach 1+ years of
age. Indeed, according to Brannon et al. (2004)
it could be possible to find a mixture of ocean
type and stream type chinook populations.
Negro-Hornopirén where winter
Why are Chinook so successful?
It is intriguing that Chinook could be so
successful, since it is the less cultured species
while the more common cultured species (coho
and Atlantic salmon) which have also escaped
in greater numbers have not been that
successful (Soto et al. 2001b).
Possible the most general and comprehensive
explanation relates to the much greater plasticity
and the diversity of life history modes of this
species as compared with other salmonids
(Healey 1991, Brennan et al. 2004). The
possibility of going earlier or later to the marine
environment, the variation in maturity, variation
in the time to return to the natal stream are all
characteristics which would make this species
more successful because the possibility to adapt
to different situations.
Another important reason is that these
salmon apparently do not remain in the inner
seas but could go to the open Pacific Ocean,
thus escaping from artisanal fishing pressure in
the inner seas. The latter has been the main
factor controlling the spread of other salmon
species escaped from aquaculture (Soto et al.
2001b).
Additional evidence pointing to salmon
farming as the main recent source of Chinook
is based on the increasing number of runs
reported after 1990 (Fig. 1). Besides those
shown here, there are numerous recent reports
by fishermen catching chinook in a much wider
latitudinal range from the Río Tolten watershed
from the north (39°05’ S, 72°30’ W) to Río
Pascua in the south (48°15’ S, 73°03’ W). The
rivers Vargas and Jaramillo (47°41’ S, 73°00’
W) are apparently becoming popular among
fisherman due to the large size of Chinook (N.
Sanchez personal communication). On the
other hand, Ciancio et al. (2005) have been
reporting chinooks in the Río Santa Cruz in the
Atlantic basin in Argentina which the authors
suggest as originating in a ranching activity
near Puerto Natales in southern Chile (51°40’
S, 73°32’ W). Thus, it is evident that this
salmon species is establishing numerous
reproductive populations and the migrating
individuals could develop large marine
populations as well. The pristine environmental
conditions of rivers in southern Chile and
Argentina seem indeed ideal for the species.
Unfortunately we still have limited data in
order to propose explanations for inter annual
spawning variability of returns even at Los
Patos site in Petrohué (Table 2). There is some
evidence that long term climatic trends or
regime shifts affect Chinook populations in
North America (Tolimeri & Levin 2004). Thus,
it is likely that El Niño Southern Oscillation
may have some effect on Chinook salmon
establishment in southern Chile and Argentina,
particularly because this species could go to the
open ocean and its growth may be affected by
variation in the upwelling which sustains
productivity in the central-southern Chile coast.

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CHINOOK SALMON IN SOUTHERN SOUTH AMERICA
Potential ecosystem disruptions: nutrient enri-
chment
Along one km of river at the Los Patos site in
Petrohué, the input of biomass during a given
reproductive run can reach about 2,000 to 6,000
kg wet weight (Table 2). According to Larkin
and Slaney (1997) estimates of marine derived
nutrients (MDN) from salmon carcasses, a run
of Chinook salmon such as that observed in
2004 could contribute about 8 kg of N and 0.3
kg of P on 100 m of river bed. Considering the
Los Patos spawning area of approximately
15,000 m2, the supply of N and P could amount
to 4.8 g of N m-2 and 0.4 of P m-2. These
estimated values are comparable to some
historical nutrient supplies such as those
reported by Suzumoto (1992) in a 100 m stretch
of Willapa River in the coast of Washington
(Table 3). However according to this author,
the present values at that site are much lower
due to the decline of salmon populations.
TABLE 3
Comparative fish biomass and potential loads
of N and P (kg in 100 m of river length) for a
North American typical river in pre industrial
and present times (Willapa Bay Drainage basin,
redrawn from Suzumoto 1992) and at Los Patos
area in Río Petrohué
Comparación de la biomasa de peces y aportes estimados
de N y P (kg en 100 m de río) en un típico río
norteamericano, en una época preindustrial y actual
(Cuenca de la Bahía del Río Willapa, adaptado de
Suzumoto 1992) y en el sector Los Patos del Río Petrohué
VariableWillapa
Historical
Willapa
Present
Los Patos*
Biomass
Nitrogen
Phosphorus
82-140
8-14
0.3- 0.5
8.6
0.9
0.03
144
13.8
0.57
*Average 1995-2004
We have not been able yet to demonstrate
the effect of these MDN in food webs from
southern South America, while such effects
have been widely explored for the Pacific coast
of North America (Naiman et al. 2002).
However our measurements of dissolved
inorganic nutrients at the site show a strong
effect particularly on dissolved phosphorus
(Fig. 8). Since there is a short distance (less
than 5 km) from the origin of Río Petrohué at
the outlet of Lago Todos Los Santos and the
spawning site at Los Patos, with no other
potential nutrient sources in between, it is
reasonable to blame salmon carcasses for the
PO4 and DIN increases. This is more striking
for PO4 since values are usually very low in
most Andean streams and rivers including Río
Petrohué at its origin (Fig. 8).
Because there is no natural removal of
carcasses in our streams, such as bears do in the
Chinook native environments (Naiman et al.
2002), it is likely that the impact of MDN
would be more concentrated in immediate
surroundings of streams and rivers. Although
there is some consumption of carcasses by
large scavenger birds such as the “tiuque”
Milvago chimango, and the “caracara”
Polyborus plancus whom could play de role in
spreading nutrients to other parts of the basins.
Effects on aquatic biodiversity
There is no evidence for a negative effect on
trout population as it has been suggested by
sport fishermen, on the contrary trout biomass
of both species seem to increase with chinook
spawning events (Fig. 2). This is not surprising
since Chinook are subsidizing the river with
additional food including eggs and carcasses.
McDowall (1990) describes similar effects after
introduced chinook spawning in New Zealand,
when trout populations were eventually
benefited by Chinook. Soto et al. (2006) have
shown that rainbow trout and brown trout are
the most common fish in most rivers of
Southern Chile while native fish species are
rare and often absent from Andean streams and
rivers such those reported here (Fig. 5).
Therefore the most likely chinook interactions
will be with both trout species.
The impact of growing adults at sea remains
to be evaluated, yet their feeding behavior and
predacious nature as described in North
America (Healey 1991) implies a potential
effect on some marine resources particularly
pelagic organisms. Since the Chilean Ocean
coast is very productive it is likely that
Chinook populations will grow well as they are
likely to be successful as well in some areas of
the Patagonia Atlantic as proposed by Ciancio
et al. (2005) therefore establishing populations