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Global Status of Trout and Char: Conservation
Challenges in the Twenty-First Century
Clint C. Muhlfeld, Daniel C. Dauwalter, Vincent S. D’Angelo,
Andrew Ferguson, J. Joseph Giersch, Dean Impson,
Itsuro Koizumi, Ryan Kovach, Phil McGinnity,
Johannes Schöffmann, Leif Asbjørn Vøllestad, and John Epifanio
Introduction
Freshwater ecosystems are among the most threatened ecosystems in the world (Richter
et al. 1997; Strayer and Dudgeon 2010), and freshwater fishes may now be the most
threatened group of vertebrates (Ricciardi and Rasmussen 1999; Vörösmarty et al. 2010;
Darwall and Freyhof 2016). Of the 7,300 freshwater fish species globally assessed by the
International Union for Conservation of Nature (IUCN; www.iucnredlist.org) in 2013,
nearly one of every three species was threatened with extinction (Darwall and Freyhof
2016). Growing pressures from a multitude of direct and indirect human stressors (e.g.,
habitat loss and degradation, pollution, invasive species, overexploitation, diversion or al-
teration of biological flows, climate change, and others) threaten the persistence of many
freshwater fish species and entire aquatic communities around the globe (Limburg et al.
2011). is pattern is particularly true for salmonid fishes (family Salmonidae, subfamily
Salmoninae, belonging to the genera Oncorhynchus, Salvelinus, Salmo, Hucho, Parahucho,
Brachymystax, and Salvethymus). Salmonids are globally distributed coldwater species
with life cycles restricted entirely to freshwater ecosystems (typically referred to as trout
and char), but also include species that migrate from the ocean to freshwater to spawn
(e.g., Atlantic Salmon Salmo salar and Pacific salmon Oncorhynchus spp.).
Trout and char are one of the most culturally, economically, and ecologically impor-
tant taxonomic groups of freshwater fishes worldwide (Prosek 2013). ese coldwater
specialists provide recreation and food to millions of people and play important roles in
ecosystem functioning and health in both their native and nonnative ranges (Holmlund
and Hammer 1999). ey are also extremely sensitive to human disturbances because
they require cold, clean, complex, and connected habitats for survival and persistence—
all attributes that humans have substantially altered and degraded (Gresswell et al. 1997;
Haak and Williams 2013; Hauer et al. 2016). Despite their broad importance as societal
icons and as indicators of biodiversity, many of the world’s trout and char species and lin-
chapter 21718
eages are endangered and some require immediate conservation efforts to reverse their
precarious decline (Muhlfeld et al. 2018). However, a thorough understanding of their
status, threats, and conservation challenges at a global scale is currently lacking.
Native to all continents in the Northern Hemisphere—including North America,
Asia, Europe, and Mediterranean Africa—and distributed across 52 countries, trout
and char have adapted to and persist in the face of environmental change (Figures 1
and 2). Present-day species evolved over the past 50 million years, with most lineages
tracing back to the Eocene and early Oligocene (Crête-Lafrenière et al. 2012; Penalu-
na et al. 2016). During this lengthy period, trout and char survived and evolved in tan-
dem with the advances and retreats of continental glaciers, major volcanic eruptions,
enormous floods, extreme droughts, and massive geotectonic movements that have
reorganized freshwater habitats and shaped the course of present-day river systems.
Figure 1. Global trout and char species richness by continent and genus (top panel), and total
richness, numbers of species assessed, and numbers of species threatened with global extinc-
tion by continent (bottom panel) from the International Union for Conservation of Nature
(IUCN 2018).
global status of freshwater trout and char 719
Figure 2. Global trout and char species richness, distributions (by country), and the per-
centage of species assessed and threatened with extinction by genus (Salmo, Salvelinus, On-
corhynchus, Parahucho, Salvethymus, and Brachymystax). The bars along each map show the
percent of species that have been assessed by the International Union for Conservation of
Nature and the percent of species threatened with global extinction (IUCN 2018).
chapter 21720
Contemporary patterns of taxonomic and ecological diversity reflect this complex evo-
lutionary history because of the repeated cycles of isolation, colonization, and dispersal
in freshwater habitats (Box 1). Many trout and char species also display a wide variety
of life history strategies at the population level within freshwater environments while
others have populations that migrate between freshwater and marine environments
to complete their life cycle (e.g., Rainbow Trout Oncorhynchus mykiss, Cutthroat Trout
O. clarkii, Brown Trout Salmo trutta, and all char; Jonsson 1985; Northcote 1997), in
addition to species-level divergence and radiation. eir genetic, phenotypic, and life
history diversity coupled with their ability to migrate long distances over diverse habi-
tats has allowed trout and char to persist through major climatic fluctuations and en-
vironmental change (Behnke 1992). Conserving the portfolio of natural evolutionary
and ecological characteristics of trout and char is integral to ensuring their persistence
in changing environments (Hilborn et al. 2003; Schindler et al. 2010).
Conservation of native trout and char and their freshwater habitats is a growing
challenge in the face of accelerating anthropogenic changes in the 21st century. Many
freshwater trout and char species face increasing risks of decline and extinction due to
numerous human activities. Moreover, climate change often acts in synergy with other
stressors to further endanger species and populations within species (Vitousek et al.
1997; Vörösmarty et al. 2000; McGinnity et al. 2009). Some trout and char species will
be resilient to these future changes while others will not. While genomic diversity—
both within and among populations—is often presented as improving the chances for
such resilience, a better understanding of the current diversity, status, and threat to the
world’s trout and char species is crucial to inform effective conservation management
strategies to protect, restore, and conserve these iconic species in the coming decades.
Distribution and Status
In this chapter, we describe the global conservation status of freshwater trout and char
species as of January 2018. Using FishBase (www.fishbase.org), we assembled a global
catalog of all described freshwater species of trout and char within the subfamily Sal-
moninae (char, trout, huchen, taimen, lenok, Pacific salmon, and Atlantic Salmon) in the
genera Oncorhynchus, Salvelinus, Salmo, Hucho, Parahucho, Brachymystax, and Salvethy-
mus. For the purposes of this assessment, we defined “freshwater” as those species that
spend their entire life history in freshwater or those that migrate between freshwater
and marine habitats (i.e., anadromous). We also limited the assessment to species of
trout and char within their native ranges and did not consider taxa at the subspecies
level (Appendix), acknowledging that the accepted within-species taxonomy in trout
and char continues to evolve even for well-studied species (see Chapter 5; Box 1).
As of 2018, there were 124 described species of freshwater trout and char within
Salmoninae belonging to the genera Salvelinus (N = 51, 41%), Salmo (N = 48, 39%),
Oncorhynchus (N = 16, 13%), Hucho (N = 4, 3%), Brachymystax (N = 3, 2%), Parahucho
(N = 1), and Salvethymus (N = 1) distributed across 52 countries (Figures 1 and 2;
global status of freshwater trout and char 721
Box 1. e ever-evolving taxonomy of trout and char
Trout and char are a diverse taxon of freshwater fishes across the globe. ere
are currently 124 species designated in the subfamily Salmoninae across seven
genera (see also Chapter 5). However, diversity at the species level does not
begin to describe the genetic diversity of this group of fishes, and recognition
of this diversity continues to evolve, as illustrated by the Cutthroat Trout On-
corhynchus clarkii and Softmouth Trout Salmo obtusirostris. Both species have
recognized subspecies, but new genetic lineages continue to be found and sub-
species classifications refined, including some unique genetic variants yet to be
formally described (Chapter 5).
e Cutthroat Trout is a polytypic species of Pacific trout native to much
of western North America. Until recently, it was generally accepted that Cut-
throat Trout had four major lineages and 14 subspecies, 2 of which are extinct
(Alvord Cutthroat Trout O. c. alvordensis and Yellowfin Cutthroat Trout O. c.
macdonaldi; Behnke 1992). Some recognized subspecies even have (or have
had) specific restoration programs under the U.S. Endangered Species Act
(Chapter 5). Despite a preponderance of phylogenetic evidence for the com-
monly used classification of Cutthroat Trout subspecies attributed largely to
Robert J. Behnke (1992, 2002), even Behnke himself suggested that Colo-
rado River Cutthroat Trout O. c. pleuriticus and Greenback Cutthroat Trout O.
c. stomias—as recognized at the time—may not deserve recognition as sepa-
rate subspecies, but he maintained those subspecies descriptions because they
were recognized by fisheries management agencies. Recent studies of Cut-
throat Trout across the species’ range have shed new light on genetic rela-
tionships that now suggest multiple colonization and recolonization events in
western U.S. river basins, sometimes by different genetic lineages (Loxterman
and Keeley 2012). Additionally, some populations in one drainage basin may
represent two different lineages, even though those populations are currently
recognized as a single subspecies under commonly used classifications. More
than a century of interbasin stocking practices has also clouded understanding
of the pre-European settlement distribution of some Cutthroat Trout genetic
lineages, and much recent work has been done to clarify genetic diversity, ori-
gin, and relatedness of Cutthroat Trout populations (Penaluna et al. 2016). In
short, the taxonomy of Cutthroat Trout continues to evolve.
Similarly, the genus Salmo contains multiple lineages across Eurasia due
to colonization and isolation dynamics during glacial–interglacial periods
Box continues
chapter 21722
Box 1. Continued
(see Chapter 5), but like Cutthroat Trout, the taxonomy of species like the
Softmouth Trout is not fully resolved. Softmouth Trout occupies a small geo-
graphic range in four river systems on the Balkan Peninsula in Europe that is
considered a diversity hotspot for freshwater fishes. e karst geology of this
region results in subsurface and spring-fed rivers that have isolated river seg-
ments and, thus, isolated and genetically divergent populations of Softmouth
Trout. is isolation had led to evolution of four recognized subspecies: Salmo
obtusirostris krkensis from the Krka River, S. o. salonitana from the River Jadro,
S. o. oxyrhynchus from Neretva River, and S. o. zetensis from the River Zeta.
Last, the Vrlijika Softmouth Trout has yet to be formally described as a sub-
species but occupies the River Vrlijika, which is connected to the River Neret-
va through an underground karst passage, and this population is most closely
related to S. o. oxyrhynchus in the Neretva River (Snoj et al. 2008; Chapter 13).
e Vrlijika population has been studied little, and future research will resolve
this last remaining piece of the taxonomy for Softmouth Trout.
Suffice it to say that the species level of biological classification is conven-
tional and necessary, but it does not fully capture the breadth of trout and char
diversity across the world. Rand et al. (2012b) used e International Union for
Conservation of Nature’s Red List of reatened Species criteria to show how
population-level extinction risk of Sockeye Salmon Oncorhynchus nerka con-
veys a greater risk of biodiversity loss than does assessment at the species level.
Unique subspecies, genetic lineages, and life forms exist for many trout and char
taxa. is full suite of diversity will play key roles in trout and char conservation
given the myriad threats faced globally. As an old conservation adage suggests,
it is worthwhile to save all of the pieces of diversity, and importantly, we are still
revealing the full suite of diversity for many trout and char species.
Table 1) of which four species (Salmo pallaryi, Salvelinus neocomensis, S. profundus,
and Silver Trout S. agassizii) are now considered to be globally extinct (IUCN 2018).
Using the IUCN Red List of reatened Species search (hereafter, IUCN Red List;
www.iucnredlist.org), we searched for each of the species found in FishBase to de-
scribe the global conservation status and threats to these species. e IUCN Red List
is widely recognized as the most comprehensive global inventory of the conservation
status of plant and animal species on the international scale. e assessment requires
Box continues
global status of freshwater trout and char 723
Box 1. Continued
Figure. Map showing the global distribution of subspecies for Cutthroat Trout and
Softmouth Trout.
a comprehensive evaluation of each species’ distribution, threats, and risk of global
extinction. Species assessed and classified by IUCN as critically endangered, endan-
gered, or vulnerable are herein classified as threatened with extinction.
Alarmingly, as of 2018, only 54% of the total described species of trout and char
have been assessed by the IUCN. Of the 67 species assessed, an estimated 73% are
threatened with global extinction, and of those, 36 are listed as vulnerable, endangered,
or critically endangered. is percentage estimate does not include the 4 species deter-
mined to be extinct and the 14 species for which there was inadequate information to
assess extinction risk (data deficient). We determined this percentage estimate using
the following equation (IUCN 2018):
% threatened
CE EN VU
total assessed EX DD
=
++
−−
,
chapter 21724
Table 1. Genera of the subfamily Salmoninae with the number of species, documented native
ranges, and number of species in each International Union for Conservation of Nature (IUCN)
status category. EX = extinct; CE = critically endangered; EN = endangered; VU = vulnerable;
NT = near threatened; LC = least concern; DD = data deficient; NE = not evaluated (see Ap-
pendix for individual species detail).
Number of
Number species in each
of Documented IUCN status
Genus species native ranges Continent category
Salvethymus 1 Russia Asia VU = 1
Salvelinus 51 Austria, Canada, China, Asia, Europe, EX = 3; CE = 3;
Denmark, Finland, North America VU = 10; NT =
France, Germany, 1; LC = 7; DD
Great Britain, Iceland, = 1; NE = 24
Ireland, Italy, Japan,
Kuril Islands, North
Korea, Norway, Russia,
South Korea, Sweden,
Switzerland, USA
Salmo 48 Albania, Algeria, Africa, Asia, EX = 1; CE = 3;
Armenia, Azerbaijan, Europe, EN = 2; VU =
Bosnia, Bulgaria, North America 6; NT = 1; LC
Canada, Croatia, = 4; DD = 12;
Czech Republic, France, NE = 20
Georgia, Great Britain,
Greece, Herzegovina,
Iran, Ireland, Italy,
Macedonia, Montenegro,
Morocco, Russia, Serbia,
Slovenia, Spain,
Switzerland, Turkey,
Ukraine, USA
Oncorhynchus 16 Armenia, Canada, China, Asia, North CE = 2; EN = 1;
Japan, Kuril Islands, America VU = 1; LC = 1;
Mexico, North Korea, DD = 1; NE =
South Korea, Taiwan, 10
Russia, USA
Hucho/ 5 China, Europe-wide, Asia, Europe CE = 2; EN = 1;
Parahucho Japan, Kazakhstan, VU = 1; DD = 1
Kuril Islands,
Mongolia, North
Korea, Russia, South
Korea
Brachymystax 3 China, North Korea, Asia NE = 3
South Korea,
Kazakhstan, Mongolia,
Russia
global status of freshwater trout and char 725
where CE is critically endangered, EN is endangered, VU is vulnerable, EX is extinct,
and DD is data deficient (classifications for the total number of species assessed by
the IUCN).
e IUCN classifies a taxon as extinct when there is no reasonable doubt that the
last individual has died or when extensive surveys failed to document an individual
within its historical range (IUCN 2018). Currently, the four trout and char species
classified as globally extinct include three species within the genus Salvelinus and one
species within the genus Salmo. Salmo pallaryi was restricted to Lake (Aguelmam)
Sidi Ali in the Atlas Mountains in northern Morocco and disappeared in the late
1930s (Crivelli 2006), probably due to the introduction of Common Carp Cyprinus
carpio. Salvelinus neocomensis, known locally as jaunet, was only documented in Lake
Neuchâtel, Switzerland and was last recorded in 1904 (Freyhof and Kottelat 2005).
e Deepwater Char S. profundus was only documented from Lake Constance (Aus-
tria, Switzerland, and Germany) and was a commercial species in the 1960s but is
thought to have gone extinct in the 1970s due to eutrophication (Freyhof and Kottelat
2008b). e Silver Trout was native to a few lakes in the northeastern United States
(New Hampshire) prior to 1939. is species was first published as extinct in 1986
(World Conservation Monitoring Centre 1996).
Most of the 36 threatened trout and char species are currently classified as vulnerable
(N = 19, 53%) while 7 (19%) are listed as endangered and 10 (28%) are classified as criti-
cally endangered (Figure 3A, 3B). An additional 11 species are categorized as of least
concern and 2 as near threatened. Most threatened species are imperiled due to having
small, restricted populations (42%), due to limited geographic ranges (36%), or due to
reductions in population size (22%). e proportion of trout and char threatened with
extinction is highest in Europe (64%) followed by Asia (22%), North America (11%),
and Africa (3%) (Figure 3A). Across genera, Salvelinus and Salmo contain the majority
of IUCN Red List species, 44% and 31%, respectively, followed by Oncorhynchus (11%),
Hucho (8%), Parahucho (3%), and Salvethymus (3%); none of the three species within the
genus Brachymystax (N = 3) have been assessed (Figure 3B).
Salvelinus
e genus Salvelinus, often called char (or more colloquially, charr), has a northern
circumpolar distribution that encompasses North America, Europe, and Asia (Figure
1). Currently, there are 51 designated species, three of which are determined to be
extinct. Of the 24 extant species within this genus that have been evaluated by the
IUCN, 16 (67%) are listed as threatened: 10 are vulnerable, 3 are endangered, and 3
are determined to be critically endangered (Figure 3B); one species is data deficient.
Salmo
e genus Salmo contains the European species of trout and salmon, including the
well-known Brown Trout and Atlantic Salmon. e distribution of Salmo extends
chapter 21726
Figure 3. Global International Union for Conservation of Nature (IUCN) status of trout and
char species by continent and genus (A, B) and the numbers of species classified to each
of the main threat categories as coded in the IUCN Red List (C, D) (IUCN 2018). IUCN clas-
sifications are as follows: EX = extinct, CE = critically endangered, EN = endangered, VU =
vulnerable, NT = near threatened, LC = least concern, DD = data deficient, and NE = not
evaluated.
throughout Europe, Asia (including the Black Sea basin in western Asia), and
Mediterranean Africa, with a single species in Atlantic North America, Atlantic
Salmon (Figure 1). Presently, Salmo contains 48 designated species, and 28 (58%)
of these species have been assessed by the IUCN, with one listed as extinct (S.
pallaryi). Of the 27 extant species, 11 (41%) are listed as threatened with extinc-
tion: 3 are critically endangered, 2 endangered, and 6 are classified as vulnerable
(Figure 3B).
Oncorhynchus
Spanning western North America and East Asia, the genus Oncorhynchus (mean-
ing hooked snout) contains 16 designated species of Pacific salmon and Pacific
trout. Four of these species are threatened with extinction (IUCN 2018): 2 are
listed as critically endangered (O. formosanus and Apache Trout O. apache), 1 as
endangered (Gila Trout O. gilae), and 1 as vulnerable (Mexican Golden Trout O.
chrysogaster) (Figure 3B). Oncorhynchus formosanus is endemic to Taiwan, whereas
the three threatened species of Pacific trout are native to southwestern North
America (USA and Mexico)—Apache Trout, Gila Trout, and Mexican Golden
Trout.
global status of freshwater trout and char 727
Hucho
Hucho is a genus containing four species of relatively large salmonid fishes that occur
throughout Asia and portions of Europe (Figure 1). ree Hucho species are currently
listed as threatened with extinction (1 critically endangered, 1 endangered, and 1 vul-
nerable; Figure 3B; Rand 2013). e Sichuan Taimen H. bleekeri is native to China
and is listed as critically endangered (Ding and Qing 1994; Yue and Chen 1998). e
Danube Salmon (also known as Huchen) H. hucho is an endangered species native
only to the Danube drainage in Europe, where it presently occupies a very restricted
(<500 km2) and fragmented distribution (Freyhof and Kottelat 2008a). e Siberian
Taimen (also known as Taimen) Hucho taimen is listed as vulnerable and is native to
parts of Europe and Asia, including the Caspian and Arctic drainages in Eurasia and
portions of the Pacific drainage in Mongolia, Russia, and China.
Parahucho
Parahucho is a genus containing one species (Crête-Lafrenière et al. 2012), the Sakha-
lin Taimen (also known as Japanese Huchen) P. pe r r y i, which is critically endangered
and is restricted to Far Eastern Russia and Hokkaido, Japan (Figures 1 and 2). e
International Union for Conservation of Nature recognizes the Sakhalin Taimen
as H. perryi. However, several morphological and molecular studies (Matveev et al.
2007; Fukushima et al. 2011) have concurred with the placement of Parahucho as a
monotypic genus, so we treat it as such in this chapter (see Chapter 5 for details).
Brachymystax
Brachymystax is a genus of primitive salmonid fishes, called lenok, that contains three
species, Lenok B. lenok, B. savinovi, and B. tumensis, native to rivers and lakes in Mon-
golia, Kazakhstan, Siberia, Far East Russia, northern China, and Korea (Froufe et al.
2008). None of these species have been evaluated for the IUCN Red List (IUCN
2018), but independent conservation assessments list subspecies as threatened; B. le-
nok tsinlingensis, for example, is protected in China (Zhao and Zhang 2010).
Salvethymus
e Long-finned Char Salvethymus svetovidovi is the only recognized species with-
in the monotypic genus Salvethymus. e Long-finned Char is endemic to Lake
El’gygytgyn in the Chukchi Peninsula in Far East Russia and is listed as vulnerable to
extinction (Kottelat 1996) (Figures 1 and 3B).
Regional Comparisons
Europe and Mediterranean Africa
e European continent and Mediterranean Africa—primarily Morocco, Algeria,
and Madeira Island—hosts a diverse array of trout and char species (Figures 1 and
chapter 21728
2; Table 1). Fifty-seven species across three genera account for this diversity, including
Hucho (N = 1), Salmo (N = 34), and Salvelinus (N = 22). Several of these species, such
as Brown Trout, Atlantic Salmon, Arctic Char Salvelinus alpinus, and Danube Salmon,
have an iconic status in part because of their continent-wide or pan-Atlantic ranges.
Conversely, 12 are considered endemic to a single ecosystem while many others have
been reported within multiple waterways in a single nation. Almost half (N = 24) of the
51 European and Mediterranean African species that have been assessed for the IUCN
Red List as of 2018 are threatened with extinction; 10 are classified as of least concern
and 12 as data deficient. ree species, Salvelinus neocomensis, Deepwater Char (Europe),
and Salmo pallaryi (Morocco), are extinct while species such as Salmo carpio (endemic to
Lake Garda, Italy), Salmo ezenami (Russia), and Salvelinus lonsdalii (England) are con-
sidered critically endangered by the IUCN. Moreover, Black Sea Salmon Salmo labrax is
considered locally extirpated from Ukraine tributaries of the Black Sea, although other
tributaries continue to support populations. e diverse native assemblage of trout and
char species in Europe are facing significant challenges to their persistence and viability
due to a suite of anthropogenic threats facing salmonids around the globe.
Asia
e Asian continent contains the highest level of native trout (including salmon) and
char diversity that is represented by 58 species from all seven known genera: Brachy-
mystax (N = 3), Hucho (N = 3), Parahucho (N = 1), Salmo (N = 16), Salvelinus (N = 23),
Salvethymus (N = 1), and Oncorhynchus (N = 11) (Figures 1 and 3; Table 1). Only 15
of these species (26%) have been assessed by the IUCN. An estimated 67% of the 15
Asian trout and char species that have been assessed for the IUCN Red List as of
2018 are threatened with extinction. As noted for Europe and Mediterranean Africa,
several species occur on two or more continents; however, a key feature of distribution
in Asia is that native Salmo occur primarily in the west, Oncorhynchus occur exclusively
in the east, and Salvelinus occur throughout the continent. Like the other continents,
Asia has instances of endemism. ree genera occur nowhere else (Brachymystax, Sal-
vethymus, and Parahucho). Species like Flathead Trout Salmo platycephalus in Turkey or
Salvelinus neiva in Russia are endemic to a few streams or lakes in a single ecosystem.
No recent Asian species of trout and char are known to have gone extinct based on
IUCN data; however, 43 of the 58 Asian species are listed as not evaluated, especially
in Russia, while 2 additional species are listed as being data deficient. Five species—
namely those that are continental in distribution—are listed as least concern. Only
eight species are listed as threatened with extinction. Salvelinus tolmachoffi is listed as
endangered owing, in part, to its restricted distribution in four lakes in the Taymyr
region of Russia. Flathead Trout is also listed as endangered because it is only found
in a few streams in Turkey. While species on this continent are threatened by myriad
factors common to other regions globally, a key and worrying feature of this Asian as-
semblage is that not much is known or reported about the majority of species.
global status of freshwater trout and char 729
North America
e continent of North America hosts 20 designated species of trout and char with-
in the genera Oncorhynchus (N = 11), Salvelinus (N = 8), and Salmo (N = 1) (Figures 2
and 3; Table 1). e distribution of Oncorhynchus spp. spans western North America
from Mexico to Alaska and into East Asia. Salvelinus occurs throughout the north-
ern portions of the continent while the only native species within Salmo, Atlantic
Salmon, occurs along the northeastern coast of North America. Half of the extant
trout and char species in North America occur on other continents, including East
Asia (e.g., Pacific salmon and Dolly Varden Salvelinus malma) and Europe (Atlantic
Salmon and Arctic Char).
Only eight trout and char species native to North America have been assessed by
the IUCN as of 2018, four of which are currently classified as threatened (one criti-
cally endangered, one endangered, and two vulnerable), three of least concern, and
one extinct (Silver Trout) (Figure 3A). Of the eight assessed species, four are threat-
ened with extinction. e three threatened species of Pacific trout inhabit limited
geographic distributions within arid regions of Mexico (Mexican Golden Trout)
and the southwestern United States (Apache Trout and Gila Trout). e Bull Trout
(char) Salvelinus confluentus—one of North America’s most cold-adapted fishes—is
listed as a vulnerable species that is native to the Pacific Northwest of the United
States and Canada.
Factors that Threaten Trout and Char Populations
e alarming declines in native trout and char diversity throughout the world reflect
numerous human impacts on freshwater habitats and populations identified in the
IUCN assessments, including invasive species (69% of species), overfishing (47%),
pollution (33%), and dams (28%) (Figure 3C, 3D). Other threats, such as deforesta-
tion, agriculture, grazing, water abstraction, roads, and extractive industries (i.e., min-
ing), were listed to affect 6% to 22% of trout and char species, along with emerging
threats of climate change and disease outbreaks. Trout and char are exceptionally sen-
sitive to anthropogenic stressors and climate change, which often act in synergy to
exacerbate population declines and extinction risk (Kovach et al. 2017).
Invasive species
Anthropogenic introductions of invasive species have resulted in rapid and widespread
declines of native trout and char populations across the globe. is includes trout
species such as Rainbow Trout, Brook Trout, and Brown Trout that have been intro-
duced globally for food, culture, and recreation (Figure 4). e ecological impacts of
invasive species are often irreversible and far-reaching, often causing reductions in the
distribution, abundance, and diversity of native species, trophic cascade effects, and
increases in the prevalence of disease outbreaks (Simberloff et al. 2013). Moreover, in-
vasive species also have significant impacts on local and regional economies via losses
chapter 21730
in recreational value and the enormous costs to manage and mitigate negative impacts
(Sepulveda et al. 2012).
Extensive introductions of nonnative fishes for aquaculture and recreational fishing
have been particularly detrimental (Gozlan et al. 2010) and have led to the decline and
local extirpation of many trout and char populations via competition, predation, hy-
bridization, and disease transfer (Moyle 1986; Allendorf 1991; Elvira and Almodóvar
2001). For example, widespread stocking and invasion of Rainbow Trout in many wa-
ters throughout western North America have resulted in extensive introgression and
homogenization among historically allopatric lineages and subspecies of Cutthroat
Trout (Allendorf and Leary 1988). Elsewhere, the introduction of nonnative conspe-
cifics, such as domesticated farm-reared Brown Trout, and congeners, such as Brown
Trout into native Marble Trout Salmo marmoratus watersheds, has led to widespread
introgression (Ferguson 2007; Berrebi et al. 2017), putting the native gene pool at
risk of “genomic extinction” (Epifanio and Philipp 2000). Widespread introductions
of nonnative eastern Brook Trout have also caused declines in native Cutthroat Trout
Figure 4. Global distribution of Rainbow Trout, Brown Trout, and Brook Trout by country
within their native and introduced (nonnative) ranges.
global status of freshwater trout and char 731
and Bull Trout populations throughout western North America (Peterson et al. 2004).
In eastern North America, introductions of nonnative species (e.g., Smallmouth Bass
Micropterus dolomieu) into watersheds that support native Brook Trout have caused dra-
matic declines via competition and predation, particularly in main-stem rivers (Vander
Zanden et al. 2004; Dunham et al. 2008). Ongoing habitat loss, increased transportation
paths, and climate change will facilitate further expansion of invasive species in many
freshwater systems in the coming decades (Sorte et al. 2013).
Over the past few decades, the widespread release of hatchery-produced trout has
been considered a conservation threat in addition to its use as a resource manage-
ment tool. In cases where the ranges of trout have been extended—such as European
Brown Trout to the Americas, Australia, and southern Africa—the hazard may be
to local (nonsalmonid) biodiversity. Perhaps more insidious, however, is the threat
of more localized translocation of congeners and even supplementation of the same
species. A widespread example is the high levels of escapes from salmon farms and
the detrimental genetic and ecological effects on wild populations (McGinnity et al.
2003; Glover et al. 2017). e long-term consequences of introgression from escaped
farm salmon are expected to lead to changes in life history traits (Bolstad et al. 2017),
reduced population productivity, and decreased resilience in recipient wild populations
to future challenges. Several of the chapters in this volume (e.g., Chapters 6 and 12)
discuss these issues in greater detail. While the majority of this chapter focuses on
species-level threats to conservation, trout stocking with nonnatives as well as intro-
ductions of native trout that have been captive bred for one or more generations is also
a potential population-level hazard within species.
Stocking is not a single, uniform action practiced globally. Rather, stocking ought
be viewed as a suite of activities with multiple goals that range from an extreme biodi-
versity conservation purpose to the alternate extreme that focus solely on recreation-
al and commercial purposes (Rand et al. 2012a). reats to native biodiversity may
emerge in the form of ecological, disease, or genetic risks among others. Ecological
risks may be recognized as the alteration of the structure of native aquatic communi-
ties. Releases of large numbers of trout, which occupy only a narrow trophic niche, can
have profound effects (competition and predation) on the broader trophic structure
by surpassing the ecosystem’s carrying capacity. Disease risks result from the emer-
gence of novel pathogens or parasites carried from the hatchery environment out to
recipient watersheds (Coughlan et al. 2006; de Eyto et al. 2007; de Eyto et al. 2011)
and are likely to substantially change the selective environment. Even where these
disease-causing agents exist in a watershed, pathogen or parasite loads can be elevated
if not treated sufficiently. ere is evidence to link salmon farm-intensive areas and
the spread of salmon lice to wild Atlantic Salmon and sea trout (anadromous Brown
Trout), and the effects of salmon lice from fish farms on wild salmon and sea trout
populations can be severe (orstad and Finstad 2018). Finally, genetic risks may be
expressed where brood sources are derived or mixed from divergent lineages or distant
chapter 21732
sources. ey may also emerge from hatchery operations that lead to domestication
or inbreeding. Paradoxically, while it may be possible to address and minimize one or
few of the risk classes, it generally may not be feasible to eliminate simultaneously all
of the risks (Meffe 1992; Waples 1999; Epifanio and Waples 2016).
Habitat loss and pollution
On a landscape scale, the loss of functionally intact and connected ecosystems is likely
the most pervasive threat facing trout and char worldwide (Figure 3C). Habitat loss
may be realized in a number of ways, including habitat degradation, fragmentation,
modification, simplification, homogenization, or degradation of the full suite of physi-
cochemical attributes of watersheds that result in quality trout and char habitat. Such
losses may be associated with landscape alterations through urbanization and agricul-
tural or grazing practices (Wang et al. 2003; Nusslé et al. 2017), water diversions for
industry or irrigation (Vörösmarty et al. 2010), impoundment by dams (Brown et al.
2013), surface or tunnel mining (Griffith et al. 2012), timber harvest and related forest
management practices (Rieman et al. 2010), recreational activities, and road construc-
tion or culvert placement (Wheeler et al. 2005)—to name a few.
Overfishing
Overexploitation of fisheries is commonplace globally, and this is true for trout and
char as well. Of all trout and char listed as threatened by the IUCN, overfishing
was listed as the second leading threat to extinction (Figure 3C). Trout and char are
harvested as food to sustain livelihoods, generate income, and provide recreation
(Cooke et al. 2016). Historically, fish were caught from local waters for subsistence,
and certain salmonids have always been sought specifically because of their flesh
qualities and taste. Eventually, some fisheries become commercial or intensively
prosecuted over time as detailed for Atlantic Salmon and other species in medieval
Europe (Hoffmann 2005). More recently, Arctic Char were commercially harvested
in Lake Vättern, Sweden, to the point where there are only low numbers of small
fish and the fishery has shifted towards littoral and nonsalmonid species (Degerman
et al. 2001). e Ohrid Trout Salmo letnica, one of the oldest lineages of Salmo liv-
ing in one of the oldest lakes in the world, Lake Ohrid, has been overfished because
of its large size and reputation as a local delicacy; the species is also threatened by
pollution. Other examples are Lake Trout Salvelinus namaycush in the Laurentian
Great Lakes of North America (Cooke et al. 2016) and Siberian Taimen in the Bai-
kal watershed on the Russia–Mongolia border and in Far East Russian (Matveyev
et al. 1998; Rand 2013). Recreational fishing can also lead to declines in trout and
char populations where harvest is allowed (Post et al. 2002) and, in some recorded
instances, can change their biological character (Consuegra et al. 2005; Quinn et
al. 2006). Even in a no-kill or catch-and-release setting, angling poses some risks
to individuals and populations due to direct release mortality, cumulative mortality
global status of freshwater trout and char 733
from multiple hooking and release events, and sublethal effects that can reduce fit-
ness (Bartholomew and Bohnsack 2005).
Climate change
ere is growing empirical evidence that climate change is already impacting many
freshwater trout and char populations through increases in water temperature, shifts
in streamflow regimes, and increases in the frequency and magnitude of disturbance
events (e.g., flood, wildfire, and drought; Comte et al. 2013; Kovach et al. 2016). ese
changes are shifting the distribution, abundance, and phenology of many trout and
char species (Otero et al. 2014; Kovach et al. 2016), particularly in the southerly por-
tions of species’ ranges or lower elevations (Almodóvar et al. 2012; Eby et al. 2014).
Species models generally predict substantial reductions in trout and char distributions
as snowpacks and resulting summer streamflows continue to decline and water tem-
peratures warm and exceed physiological thresholds of native populations over the
21st century (Keleher and Rahel 1996; Ayllón et al. 2010; Mantua et al. 2010; Wenger
et al. 2011). Trout and char species with limited geographic distributions and genetic
and life history diversity are highly vulnerable to shifting climatic conditions and are
expected to be most vulnerable to a changing climate.
Climate warming is also indirectly impacting native trout and char through en-
hanced interactions with invasive species (Rahel and Olden 2008; Al-Chokhachy et
al. 2017). For example, climate warming is increasing hybridization between native
and nonnative trout in western North America through induced increases in stream
temperature and reductions in spring flow (Muhlfeld et al. 2014, 2017). Climate
change will also influence disease dynamics and virulence, especially novel diseases
and emergence of novel pathogens to which trout and char are naive (Mitro 2016).
Although some species may cope with these changes by adapting in situ or migrating
to more suitable conditions in connected headwater areas, many populations are al-
ready at risk of climate-induced extirpation due to physiological requirements for cold
temperatures (Almodóvar et al. 2012). Although climate change will pose significant
challenges to the persistence of trout and char over the next century, the response of
affected species will not be uniform given their broad geographic distribution and
adaptations to a wide variety of historical environmental conditions.
Information and Data Gaps
Freshwater trout and char is a group of coldwater fishes with enormous genetic, life his-
tory, and phenotypic diversity. Pioneering taxonomic work by Robert J. Behnke (1992)
serves as the foundational starting point for classifying this enormous evolutionary and
ecological diversity. However, recent advances in molecular genetic techniques and phy-
logenetic analyses have led to increased understanding and, in some cases, revision of
taxonomic relationships among species and have expanded our understanding of di-
versity below the species level (subspecies, phylogeographic units, and evolutionary sig-
chapter 21734
nificant units [ESUs] or other defensible taxonomic units such as populations). Using
the IUCN Red List and FishBase global databases, we report 124 species of trout and
char across seven genera (not including subspecies). is global taxonomic list is likely
outdated and inaccurate as some of the species are likely subspecies, lineages, or distinct
ecotypes. For example, some species tend to be overly designated (too many unwar-
ranted species), some of which are based only on a few characters with little scientific
evaluation (Box 2). Further rigorous phylogenetic analyses using both morphological
and molecular data sets are needed to revisit genus, species, and subspecies level tax-
onomy. Also, in some cases, the IUCN database information is not updated with current
knowledge. For example, Sakhalin Taimen, a highly divergent and independent lineage,
is still placed within the genus Hucho in the IUCN Red List. Nevertheless, no equivalent
information is available to evaluate the status and conservation of this group of fishes at
a global scale. erefore, in this chapter, we follow the databases and assessment while
keeping the uncertainties and potential biases in mind. ere is an urgent need to rigor-
ously maintain and update a globally consistent and quantitatively comprehensive and
standardized approach to assess species’ diversity and status.
Although some of the trout and char species are likely to be subspecies, lineages,
or distinct ecotypes, an estimated 73% of these are classified as being threatened with
global extinction (IUCN 2018). is is exceptionally high compared with other ver-
tebrate groups assessed by the IUCN: 31% of freshwater fishes (Darwall and Freyhof
2016), 13% of birds, 25% of mammals (25%), and 42% of amphibians (IUCN 2018).
However, this estimate contains some uncertainty and reporting bias for several rea-
sons. First, as noted previously, there is insufficient information for some species (N
= 14, 21% were data deficient), and this percentage estimate can only be applied to
species assessed by the IUCN (54% of described species). As a very conservative (op-
timistic) estimate, if we assume that all the 57 unassessed species are species of least
concern (i.e., not threatened), then the percentage threatened becomes 39%, for ex-
ample. Second, many assessments were for species that were known or perceived to be
threatened, which triggered a formal IUCN status assessment. ird, the designated
species list that we used probably includes subspecies or local populations (see Chap-
ter 5; Box 2). However, if we use the 27 species proposed in Chapter 6, of which 12
were evaluated by IUCN, the threatened estimate is 75%. If we include somewhat
controversial species, the percent threatened is again 75% (a total of 39 species, ex-
cluding unresolved species complexes, of which 20 were evaluated). ese estimates
are almost identical to our estimate based on the 124 currently recognized species.
erefore, our overall estimate is probably reasonable given the uncertainties and that
the level of threat is substantially high in freshwater trout and char as compared to
other vertebrate groups assessed by the IUCN (IUCN 2018).
Comprehensive IUCN status assessments have been completed for only 54% (67
species) of all described trout and char species (IUCN 2018). Status assessments have
been completed for a majority of described species in Europe (83%) and Africa (67%).
global status of freshwater trout and char 735
Box 2. A population-based approach as an alternative to species designations.
Given colonization by multiple lineages, differential hybridization/reproduc-
tive isolation of lineages, natal homing, population isolation, natural selection
and local adaptation, genetic drift, and so on, most populations of salmonids
are genetically differentiated and thus differ in many aspects of their morphol-
ogy, life history, and so forth. e evolutionary species concept (ESC) was
adopted by Kottelat and Freyhof (2007), and their work forms the basis of the
IUCN European salmonid species lists. Under the ESC, differences in a single
character, often subjective, between spatially separated populations can result
in separate species designation since subspecies are generally not recognized.
e potential of the supposed diagnostic character(s) to identify individuals is
often low due to few specimens having formed the basis of the species descrip-
tion and due to phenotypic plasticity (Etheridge et al. 2012). e ESC also
takes into account reproductive isolation in sympatry but as a result of natal
homing, which is ubiquitous in salmonids and is dependent on the precise
definition of sympatry (Mayden and Wood 1995). us, with the ESC, po-
tentially many thousands of species of salmonids could be described. However,
species designated to date represent only a small fraction of potential ones and
are generally restricted to populations where appropriate descriptions exist or
where museum specimens are available. For example, 14 species of Salvelinus
have been described from Britain and Ireland, with each species generally rep-
resented by a single or at most a few populations (Kottelat and Freyhof 2007).
us, these species encompass only a small number of the populations present
in the estimated 246 lakes where char are thought to be extant (Chapter 11).
Twelve out of the 14 species are based on descriptions from more than 100
years ago when many later-to-be-discovered populations were unknown (Ad-
ams and Maitland 2007). e widespread occurrence of sympatric char popu-
lations within lakes were also not known at that time. us, the described spe-
cies greatly underestimate the considerable diversity of char, with many unique
populations not represented. All 14 species are currently extant. However, out
of 399 lakes in Britain and Ireland known previously to have char, they are
considered to be extinct in 38% of these. us, the species approach totally un-
derestimates the extent to which char have declined in the region, albeit most
of the species are assessed as at least vulnerable (Appendix). Brown Trout is
regarded as of least concern. However, in south and southeast England, Brown
Trout is no longer present in 66% of river length where it likely previously
Box continues
chapter 21736
Box 2. Continued
occurred. Similarly, it is absent from 50% of river catchments in England and
Wales (Chapter 11). Many lacustrine Brown Trout populations have also be-
come extinct especially in lowland areas adjacent to major centers of human
habitation. Given the high genetic diversity distributed among populations,
loss of a population is just as serious whether that population has been de-
scribed as a distinct species or not.
Effective conservation of trout and char should be independent of classifi-
cation and based on the genetic differences among populations irrespective of
whether they are designated as species, subspecies or simply populations. Each
population can then be assessed as to its biological significance, and this taken
together with potential threats to its continued survival results in a priority
ranking (e.g., Allendorf et al. 1997; IUCN 2012). Such a priority ranking can
assist in allocating limited resources for conservation and ensuring that this is
carried out in a focused way. Assessment of biological significance has been
discussed by Allendorf et al. (1997) for prioritizing Pacific salmon Oncorhyn-
chus spp., and for Brown Trout by Laikre et al. (1999). General aspects of pri-
oritization have been discussed widely, including, for example, by Bonin et al.
(2007), Funk et al. (2012), Vøllestad et al. (2014), and Volkmann et al. (2014).
Biological significance of a population can be based on, for example, phy-
logenetic relations; genetic diversity as determined by molecular techniques,
especially where this is of adaptive significance; genetically based tolerance of
extreme environmental conditions; unusual life history traits; unusual mor-
phology, where this has a genetic basis; geographical isolation, especially where
adjacent populations are extinct; lack of introgression from nonnative conspe-
cifics; occurrence as a member of an unusual or rare native species community;
and cultural, economic, and recreational importance. e problem with the
population approach is that in many countries, conservation legislation is pri-
marily species, and sometimes subspecies, based and there is no equivalent of
distinct population segments under the U.S. Endangered Species Act or desig-
natable units in Canada’s Species at Risk Act, which could be used to protect
significant population-level diversity in salmonids.
is level of attention is largely a result of recent status assessments published by
IUCN. In contrast, the IUCN database points to significant information gaps that
exist in North America (33%) and Asia (16%) in spite of a sizeable publication record
in both areas (Figure 3A). Status assessments for many North American species, and
global status of freshwater trout and char 737
even subspecies, have been completed (Hudy et al. 2008; Muhlfeld et al. 2015), but no
group has undertaken the IUCN assessment process. In general, species that have not
been evaluated tend to be widespread in distribution and are probably not of conserva-
tion concern. In contrast, many of the assessed species that were deemed data deficient
may be threatened. As such, there are potential assessment biases towards species that
are likely imperiled or occupy restricted ranges (i.e., endemics), but at present, it is un-
clear and will remain so until the unassessed are assessed and more data are available
to assess data deficient species.
Because of the kinds of data included in the IUCN and FishBase databases, it is
somewhat problematic to identify exact causes for species listing. For example, the
described threats—where presented—are at a general level (e.g., deforestation, over-
harvest, watershed impoundments, etc.). erefore, identifying the most important
threats or the patterns in reductions or distribution is rather tenuous. Ultimately, the
unevenness in coverage begs for a coordinated and perhaps standardized effort on a
global scale to get a more complete contemporary snapshot of salmonid biodiversity,
including standardized methods for threat assessments.
Global Conservation Actions Needed in the 21st Century
In spite of the incomplete status of and potential bias in IUCN data and information,
it is clear that many trout and char species are in decline—and some are threatened
with extinction—as are freshwater fishes globally. is then begs question: what can
we do about it? Conservation has been practiced for centuries, and efforts have in-
creased in modern times, but many freshwater species, including trout and char, still
have a downward-trending status within their native ranges. is suggests that while
many of the more traditional conservation actions, such as harvest restrictions, local
habitat rehabilitation, and fish passage—to name but a few—are still relevant, we also
need new approaches and forward thinking in the 21st century.
Given the magnitude of habitat loss and fragmentation, watershed, stream habitat,
and connectivity restoration will play a prominent role in protecting and restoring
trout and char diversity across their native ranges. Billions of dollars are spent annually
in the United States on stream and river restoration (Bernhardt et al. 2005), a figure
that is likely to increase through this century. In the Republic of Ireland, for example,
more than 500 km of salmonid river habitat has been enhanced since 1980 with sig-
nificant increases in Brown Trout numbers. In-channel actions such as channel resto-
ration, removal of impassable road culverts, and providing passage over water diversion
structures will continue to be necessary to facilitate access to critical habitats. Ripar-
ian restoration through vegetation plantings, livestock exclosures, and road removal
will still be needed to promote streambank stability and reduce fine sediment inputs
(Gornish et al. 2017). Agriculture, urban, and ex-urban development must be done
strategically to minimize negative impacts to aquatic systems, and any existing land
use impacts must be mitigated. All restoration efforts should directly address threats
chapter 21738
and their root causes over the long term. Simply put, the focus needs to be on healthy
watersheds with habitats that are more resilient to environmental variation and cata-
strophic events, such as floods, wildfires, and severe droughts, which are increasing in
frequency and severity as the climate changes (Westerling et al. 2006). is, in turn,
will lead to more-resilient trout and char populations (Williams et al. 2015).
On-the-ground conservation actions will also need to be strategic in the future.
Restoration efforts will need to be undertaken at larger watershed scales, engage local
communities and partners, and have clear measurable goals and objectives, something
that many past restoration projects have lacked (Roni et al. 2002; Bernhardt et al.
2007; Beechie et al. 2008). To ensure that species have the best chance at adapting
to novel habitats and environmental change, strategic conservation actions will need
to account for the full suite of genetic and life history diversity for any given species,
ESU, or ecotype (Haak and Williams 2012). Strategic land management will need to
integrate concepts such as native fish conservation areas where management is focused
on natural watershed function and healthy habitats that meet all life history needs of
threatened trout, char, and other aquatic species (e.g., Donner Und Blitzen Redband
Trout Refuge in southeast Oregon; Williams et al. 2011). Since trout and char have
both inherent and recreational values, they can often be used to leverage conservation
efforts for imperiled nongame species and jumpstart broader conservation planning
efforts (Haak and Williams 2013). Climate change is also going to make some his-
torical habitats unsuitable, therefore forcing conservationists to use novel approaches
to identify climate refugia where conservation efforts might be prioritized (Isaak et
al. 2015). Recent analyses suggest that protected land designations are often, but not
completely, based on physical features (prominent landscape features) and terrestrial
animals, largely ignoring the conservation needs of freshwater fishes (Pinsky et al.
2009; Grantham et al. 2016). However, new analytical tools now exist to assist conser-
vationists in identifying sets of key watersheds across broad landscapes to most stra-
tegically and efficiently conserve threated aquatic species (Ferrier and Wintle 2009;
Dauwalter et al. 2011).
Conservation and protection of the world’s freshwater habitats require addressing
threats over a range of scales from local to global (Lapointe et al. 2013). Landscape-
scale planning processes need to account explicitly for watershed function and threat-
ened species, as was done for the U.S. Northwest Forest Plan (Reeves et al. 2006).
Formal land designations (wilderness areas, national parks, international peace parks,
native trout biosphere reserves, special areas of conservation, sites of special scientific
interest, etc.) are required to guide or even prohibit human development in sensitive
watersheds. Multijurisdictional and transnational water compacts for large river ba-
sins will be needed to not only ensure equitable sharing among different jurisdictions
(Bennett et al. 2000), but also ensure that streams and rivers have adequate ecological
flows required by threatened aquatic organisms, even when water availability changes
in future climates (Christensen et al. 2004). Overall, working beyond watersheds and
global status of freshwater trout and char 739
across large landscapes will require interagency coordination and collaboration with
policymakers across multiple jurisdictions and globally.
As it is the most commonly cited extinction threat to trout and char (Figure 3C),
in addition to protecting and restoring watersheds and habitat, the control or eradi-
cation of nonnatives will be paramount to trout and char conservation. is includes
other trout species that have been introduced across the globe for food and recreation
(Figure 4). Nonnative species pose competition, predation, and hybridization threats
to native trout and char and need to be removed using physical or chemical methods,
where feasible (Buktenica et al. 2013; Al-Chokhachy et al. 2014; Fredenberg et al.
2017). Invasive species are likely to continue to spread via intentional, accidental, and
illegal introductions or through more natural colonization processes (Rahel 2004), and
new invasion pathways are likely arise as the Earth’s climate continues to change and
as human demands for protein continue to grow (Rahel and Olden 2008; Sorte et al.
2013).
Several countries now have legislation to protect natural populations from in-
trogression as a result of stocking with long-term domesticated hatchery strains of
trout, which can result in loss of genetic diversity and, thus, life history diversity. For
example, in England and Wales, only stocking with sterile (triploid) Brown Trout, or
offspring of local broodstock (same population) produced to a strict protocol, has been
permitted since 2015, except in reservoirs and other still-waters with little or no natu-
ral recruitment and where they are closed from movement of fish to natural waters.
Isolation management with artificial barriers to prevent upstream invasion of non-
native fishes is often used as a conservation strategy for native trout and char in small
headwater streams (Fausch et al. 2009). is approach, however, may increase the
threat of local extinction because individuals are restricted to small stream habitats,
which are susceptible to natural disturbances such as flooding, wildfire and drought,
and small populations are inherently vulnerable to demographic and genetic stochas-
ticity (Hilderbrand and Kershner 2000; Peterson et al. 2008). Conservationists are
increasingly confronted with a double-edged sword: protect native genetic integrity
via isolation management at the cost of losing genetic and life history diversity or
maintain connectivity that can ultimately facilitate nonnative invasion. is manage-
ment conundrum will require difficult and context-specific decisions to protect criti-
cal populations and species adaptations—from local population to metapopulation
scales—across the landscape (Peterson et al. 2008; Muhlfeld et al. 2012). In some
cases, human-assisted migration may be a solution to resolve this conundrum.
Conservation translocations are increasingly becoming an important tool for trout
and char populations threatened by accelerating human stressors (Olden et al. 2011;
Vincenzi et al. 2012). Imperiled species are commonly moved above natural barriers,
such as waterfalls, to re-establish populations to their historical habitat (Harig and
Fausch 2002) or to establish new conservation populations outside their historical dis-
tribution in response to climate change (Galloway et al. 2016). In Scotland, conserva-
chapter 21740
tion populations of Loch Doon Arctic Char have been successfully established in two
artificial water storage reservoirs. Also, in several lakes where trout had become extinct
due to acidification and where waterfalls prevented natural colonization, trout popu-
lations have been re-established by stocking with offspring from a population with
increase tolerance of low pH. Genetic rescue is also a conservation translocation tool
that is becoming increasingly useful to increase the fitness of small, imperiled popula-
tions via migration (Whiteley et al. 2015). Recent IUCN guidelines (IUCN 2013)
draw attention to the risks and uncertainties that are implicit in translocation. De-
cision-making frameworks are being developed to assist managers in applying more
standardized approaches for assessing the feasibility of conservation translocations to
maximize success and avoid detrimental impacts to native biodiversity (Dunham et al.
2011; Galloway et al. 2016). Recommendations for managed translocations are that
they should occur within the historical ranges of, and ideally the same watersheds as,
the source populations and in localities where long-term population viability is maxi-
mized and impacts to receiving ecosystems are minimized.
Long-term monitoring will be critical to determine whether conservation efforts
are successful and to understand, predict, and mitigate the severe and chronic effects
of human activities on trout and char populations (Dauwalter et al. 2010; Kovach et
al. 2017). While most restoration projects are not monitored (Bernhardt et al. 2005),
monitoring long-term watershed-scale restoration efforts will be most fruitful in
terms of documenting population-level demographic and genetic responses by trout
and char populations to environmental and human stressors across broad landscapes
(Beechie et al. 2013; Pierce et al. 2013; Neville et al. 2016). New molecular monitor-
ing techniques, such as environmental DNA, are now being used to develop spatially
intensive monitoring programs for native trout and char that occur over large geo-
graphic areas and to detect nonnative species invasions (Blanchet 2012; Deiner et al.
2017). Each of these monitoring applications should be focused on objectively evalu-
ating progress towards eliminating the threats to and improving the status of target
populations and species.
New technologies will transform future trout and char conservation. Remote sens-
ing and geographic information systems have revolutionized our ability to visualize
and understand spatial patterns in aquatic ecosystems and species distributions across
the globe, especially how humans have been a major driver of those patterns (Fisher
and Rahel 2004; Dauwalter et al. 2015). Hydrography databases that have unique
information for every stream segment are now routinely used to archive informa-
tion on aquatic ecosystem attributes (soils, land use, and water quality) important for
conservation applications (e.g., U.S. Geological Survey National Hydrology Dataset).
Likewise, archives of satellite data are now available for free and are easily accessible
through new cloud computing platforms like Google Earth Engine (Dauwalter et al.
2017). Use of satellite archives will vastly improve understanding of how environmen-
tal stochasticity influences the population dynamics, and thus population viability, of
global status of freshwater trout and char 741
endemic trout and char, which, in turn, can be used to mitigate threats and inform con-
servation planning efforts (Wenger et al. 2017). ese new spaceborne and airborne
technologies (including unmanned aerial vehicles) will broaden our understanding of
trout and char ecology across larger landscapes and provide the big picture to trout
and char conservation across the globe in the 21st century (Dauwalter et al. 2017).
More exciting still, the greatest advances in biological sciences are in the rapidly
growing field of population genomics. Population genetics has long played a crucial role
in salmonid conservation, especially for trout (e.g., Allendorf and Leary 1988). Genom-
ics offers a number of tremendous advances that will further broaden the impact of
molecular data in trout conservation (e.g., Ali et al. 2016). is new technology provides
cost-effective, powerful data that can address a wide swath of issues in trout and char
conservation, including taxonomy and systematics, demography; inbreeding depression,
outbreeding depression, adaptation to captivity, hybridization and introgression, and the
genetic basis of local adaptation itself (Allendorf et al. 2010).
Anglers will play a pivotal role in trout and char conservation in the coming de-
cades. ere is a growing body of literature indicating that catch-and-release fishing
can reduce impacts on individuals and populations. Angler-based organizations are
using social media and other communication channels to disseminate best practices
for catch and release in recreational angling communities (Danylchuk et al. 2018).
Angler-based organizations have also become engaged in citizen science monitoring
programs centered on aquatic environments. As highlighted by Williams et al. (2016),
anglers have participated in stream temperature monitoring to determine baseline
conditions for extant populations of native trout, as well as provide information on
the thermal suitability of streams for native trout reintroductions. ey have also par-
ticipated in monitoring programs aimed at early identification of water-quality pollu-
tion to enhance the limited capacity of agencies charged with compliance monitoring.
Anglers can also be advocates for native species conservation, bringing awareness of
native species to anglers through programs like the Cutt-Slam in Wyoming (USA)
that recognizes anglers that catch the four subspecies of Cutthroat Trout occurring
in that state. Educated anglers will better appreciate native trout and char diversity,
understand basic requirements for species viability, and advocate for trout and char
conservation when opportunities arise. is is true even on continents with no native
trout but where global processes, such as climate change, impact coldwater habitats
and where changes to policy related to global processes can affect change across the
globe where trout and char are native (Chapter 22).
Conclusions
is review is the first global assessment of the status of freshwater trout and char
and represents a call to action to scientists, anglers, and conservation practitioners
to preserve these unique fishes over the next century. Freshwater trout and char have
enormous ecological, social, economic, and cultural significance worldwide. ey are
chapter 21742
key components of freshwater biodiversity, play important roles in the structure and
functioning of coldwater ecosystems, act as indicators of ecosystem stress, and provide
numerous services to societies and cultures as food security, recreation, and esthetic
values. Currently, there are 124 designated trout and char species in seven genera
distributed across all continents in the Northern Hemisphere (see also Chapter 5).
However, only 54% of these species have been assessed and some lack sufficient data
to determine their global conservation status. Alarmingly, ~73% of the world’s trout
and char species that have been assessed by the IUCN are classified as threatened with
global extinction due to escalating human pressures (IUCN 2018). A global response
is urgently needed to fill these critical information gaps and to reverse the declines and
extinction threats facing many of the world’s trout and char species.
Escalating human pressures have and will continue to pose serious challenges to
native trout and char diversity in the 21st century (Muhlfeld et al. 2018). However,
we are optimistic that population declines can be reversed through progressive con-
servation efforts to protect native trout diversity and ameliorate ongoing and future
threats at local and global scales. To preserve these unique fishes, we must protect
ecological and genetic diversity, which are critical for long-term resiliency, viability,
and adaptation in the face of rapid environmental change. Innovative conservation
approaches include reconnecting rivers with floodplains, establishing native fish ref-
uges, restoring habitat diversity, and reducing invasive species, including nonnative
trout stocking programs. Moreover, comprehensive, coordinated, and comparable
approaches are needed immediately to assess conservation status and to delineate
conservation units across the globe, particularly for data-poor species. Only by first
identifying and subsequently addressing threats at their root causes can we accom-
plish these conservation goals to ensure that these valuable fishes will remain on the
landscape into the 22nd century and beyond.
Acknowledgments
We thank Jeff Kershner and two anonymous reviewers for comments that improved
the manuscript. We thank M. Mayfield for assistance with the maps. is chapter was
funded by the U.S. Geological Survey Fisheries Program (Ecosystems Mission Area),
Trout Unlimited’s Coldwater Conservation Fund, and the Illinois Natural History
Sur ve y.
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Appendix: Described Species of Freshwater Trout and Char
Table A.1. Trout and char species in the subfamily Salmoninae used in this assessment, includ-
ing documented native ranges and International Union for Conservation of Nature status
category and threats (IUCN 2018). EX = extinct; CE = critically endangered; EN = endangered;
VU = vulnerable; NT = near threatened; LC = least concern; DD = data deficient; NE = not
evaluated.
Documented
Species native range Continent Status reats
Lenok China, North Korea, Asia NE
Brachymystax South Korea,
lenok Kazakhstan,
Mongolia, Russia
B. savinovi China, Kazakhstan, Asia NE
Russia
B. tumensis North Korea, Russia Asia NE
Sichuan Taiman China Asia CE Dams, deforestation,
Hucho bleekeri road construction,
illegal fishing
Danube Salmon Europe-wide Europe EN Overfishing, pollution,
(also Huchen) dams
H. hucho
Korean Taimen China, North Korea, Asia DD
H. ishikawae South Korea
Siberian Taimen China, Kazakhstan, Asia VU Pollution, illegal sport
(also Taimen) Mongolia, Russia angling, dams,
H. taimen mining, road
construction,
climate change
Golden Trout USA (endemic to North NE
Oncorhynchus Kern River) America
aguabonita
Apache Trout USA (endemic to North CE Dams, deforestation,
O. apache Colorado River) America grazing, overfishing,
introduced species,
habitat destruction/
loss
Mexican Golden Mexico North VU Overfishing,
Trout America introduced species
O. chrysogaster (hybridization)
chapter 21754
Table A.1. Continued.
Documented
Species native range Continent Status reats
Cutthroat Trout Canada, USA North NE
Oncorhynchus America
clarkii
O. formosanus Taiwan Asia CE Deforestation, dams,
agriculture,
overfishing
Gila Trout O. gilae USA (endemic to Gila North EN Grazing,
River America deforestation,
overfishing,
introduced species
Pink Salmon Canada, China, Japan, North NE
O. gorbuscha Kuril islands, North America,
Korea, Russia, USA Asia
Iwame Trout Japan Asia DD
O. iwame
O. kawamurae Japan Asia NE
Chum Salmon Canada, China, Japan, North NE
O. keta Kuril Islands, America,
North Korea, Asia
Russia, South
Korea, USA
Coho Salmon Canada, Japan, Kuril North NE
O. kisutch Islands, Mexico, America,
Russia, USA Asia NE
Cherry Salmon China, Japan, Kuril Asia NE
O. masou Islands, North
Korea, Russia,
South Korea
Rainbow Trout Canada, Mexico, North NE
O. mykiss Russia, Armenia, America,
USA Asia
Sockeye Salmon Canada, Kuril Islands, North LC Overfishing, global
O. nerka Japan, Russia, USA America, climate change
Asia
Japanese Amago Japan (endemic to Asia NE
O. rhodurus Lake Biwa)
Chinook Salmon Canada, Japan, Russia, North
O. tshawytscha USA America, NE
Asia
Sakhalin Taimen Japan, Kuril Islands, Asia CE Overfishing, logging,
(also Japanese Russia gas and oil
Huchen) development, dams,
Parahucho perryi agriculture
Salmo abanticus Turkey Asia NE
global status of freshwater trout and char 755
Table A.1. Continued.
Documented
Species native range Continent Status reats
Salmo akairos Morocco (endemic to Af rica VU Introduced species,
Lake Infi) water abstraction
S. aphelios Albania, Macedonia Europe DD
(endemic to Lake
Ohrid)
S. balcanicus Albania, Macedonia Europe DD
(endemic to Lake
Ohrid)
S. carpio Italy (endemic to Lake Europe CE Overfishing, habitat
Garda) destruction, water
pollution,
introduced species
S. caspius Iran, Turkey, Armenia, Asia NE
Azerbaijan
(Kura-Aras
drainage)
S. cenerinus Italy, Slovenia, Europe NE
Switzerland
S. cettii Italy, France Europe NT Water abstraction,
overfishing,
introduced species
S. chilo Turkey (endemic to Asia NE
Ceyhan River)
S. ciscaucasicus Azerbaijan, Russia Asia NE
S. coruhensis Turkey Asia NE
S. dentex Albania, Bosnia Europe DD
Herzegovina,
Croatia, Greece,
Macedonia,
Montenegro
S. euphrataeus Turkey (endemic to Asia NE
Euphrates River)
S. ezenami Russia Europe CE Introduced species
S. farioides Albania, Bosnia Europe NE
Herzegovina,
Croatia, Greece,
Italy, Macedonia,
Montenegro,
Kosovo
S. ferox UK (Wales, England, Europe DD
Scotland, Northern
Ireland), Republic
of Ireland
chapter 21756
Table A.1. Continued.
Documented
Species native range Continent Status reats
Salmo fibreni Italy (endemic to Lake Europe VU Introduced species,
Posta Fibreno and pollution
tributaries)
Sevan Trout Armenia (endemic to Asia NE
S. ischchan Lake Sevan)
Antalya Trout Turkey Asia NE
S. kottelati
Seyhan Trout Turkey (endemic to Asia NE
S. labecula Seyhan River)
Black Sea Salmon Austria, Bulgaria, Europe, LC
S. labrax Hungary, Asia
Macedonia,
Romania, Russia,
Serbia, Turkey,
Ukraine (extirpated
from Czech
Republic)
Ohrid Trout Macedonia (endemic Europe DD Water pollution,
S. letnica to Lake Ohrid) hybridization
S. lourosensis Greece (endemic to Europe NE
Louros River)
S. lumi Albania, Macedonia Europe DD Destruction of
(endemic to Lake spawning areas,
Ohrid) water pollution,
overfishing
S. macedonicus Macedonia, Greece Europe DD
(questionable)
Mediterranean Algeria, Morocco Africa DD Hybridization with
Trout introduced trout
S. macrostigma
Marble Trout Albania, Europe LC Hybridization, water
S. marmoratus Bosnia-Herzegovina, extraction, pollution
Croatia, Italy,
Kosovo, Macedonia,
Montenegro,
Slovenia
S. montenigrinus Bosnia-Herzegovina, Europe NE
Montenegro
S. multipunctata Morocco Africa NE
S. nigripinnis UK (Northern Ireland), Europe VU Eutrophication,
Republic of Ireland introduced species
Softmouth Trout Bosnia-Herzegovina, Europe EN Overfishing
S. obtusirostris Croatia, introduced species
Montenegro (hybridization),
dams, pollution
global status of freshwater trout and char 757
Table A.1. Continued.
Documented
Species native range Continent Status reats
Salmo ohridanus Albania, Macedonia Europe VU Introduced species
(endemic to Lake (hybridization),
Ohrid) overfishing,
pollution
Okumus Trout Turkey Asia NE
S. okumusi
Opimus Trout Turkey Asia NE
S. opimus
S. pallaryi Morocco Africa EX Introduced species
S. pelagonicus Greece, Macedonia Europe VU Overfishing, illegal
fishing, introduced
species
(hybridization)
S. peristericus Albania, Greece, Europe EN Water extraction,
Macedonia grazing, poaching,
pollution, dams
Flathead Trout Turkey Asia CE Illegal fishing,
S. platycephalus introduced species
Rhône Trout France, Italy, Europe DD Hybridization with
S. rhodanensis Switzerland Brown Trout
S. trutta
Rize Trout Georgia, Turkey Asia NE
S. rizeensis
Atlantic Salmon Europe, North Europe, LC
S. salar America North
America
S. schiefermuelleri Austria Europe DD
S. stomachicus UK (Northern Ireland), Europe VU Eutrophication,
Republic of Ireland introduced species
S. taleri Montenegro, Europe DD Introduced species
Bosnia-Herzegovina (hybridization)
(Sava drainage),
Croatia, Slovenia
Tigris Trout Turkey (endemic to Asia NE
S. tigridis Tigris River)
Brown Trout Asia, Europe, Africa Asia, LC Water pollution and
S. trutta (Madeira Islands) Europe, impacts from
Africa salmon farming
(sea lice etc.)
S. visovacensis Croatia Europe NE
S. zrmanjaensis Croatia Europe NE
Silver Trout USA North EX Unknown
Salvelinus America
agassizii
chapter 21758
Table A.1. Continued.
Documented
Species native range Continent Status reats
White Char Russia Asia NE
Salvelinus albus
Arctic Char Europe, North Europe, LC
S. alpinus America North
America,
Asia
Angayukaksurak USA North NE
Char America
S. anaktuvukensis
Chukot Char Russia Asia NE
S. andriashevi
Boganida Char Russia Asia LC Overfishing, habitat
S. boganidae degradation from
drilling/boring
S. colii Republic of Ireland Europe NT Eutrophication,
introduced species,
acidification
Bull Trout Canada, USA North VU Invasive species,
S. confluentus America deforestation, dams
S. curilus Japan, Russia Asia NE
S. czerskii Russia Asia NE
Dryanin’s Char Russia Asia NE
S. drjagini
S. elgyticus Russia Asia NE
S. evasus Germany (endemic to Europe VU Introduced species,
Ammersee Lake) pollution,
overfishing
S. faroensis Denmark (Faeroe Europe NE
Islands)
S. fimbriatus Republic of Ireland Europe VU Eutrophication,
(endemic to Lough introduced species
Coomasaharn)
Brook Trout Canada, USA North America NE
S. fontinalis
S. gracillimus UK (Scotland Europe VU Introduced species
S. grayi UK (Northern Ireland), Europe CE Introduced species,
Republic of Ireland eutrophication
(endemic to Lough
Melvin)
S. gritzenkoi Russia Asia NE
S. inframundus UK (Scotland) Europe DD
Yacutian Char Russia Asia NE
Salvelinus
jacuticus
global status of freshwater trout and char 759
Table A.1. Continued.
Documented
Species native range Continent Status reats
Salvelinus japonicus Japan (endemic Asia EN Unknown
Totsukowa River)
S. killinensis UK (Scotland) Europe VU Introduced species
S. krogiusae Russia Asia NE
S. kronocius Russia (endemic to Asia NE
Kamchatka)
S. kuznetzovi Russia (endemic to Asia NE
Kamchatka)
S. lepechini Finland, Norway, Europe LC
Russia, Sweden
Whitespotted China, Japan, Kuril Asia, NE
Char Islands, North Korea, North
S. leucomaenis Russia, South Korea, America
USA (Alaska)
S. levanidovi Russia Asia NE
S. lonsdalii UK (England) Europe CE Avian predation
S. mallochi UK (Scotland) Europe VU Introduced species,
angling
Dolly Varden Canada, China, Japan, North NE
S. malma North Korea, Kuril America,
Islands, Russia, USA Asia
S. maxillaris UK (Scotland) Europe VU Introduced species
S. murta Iceland (endemic to Europe LC
Lake ingvalla)
Lake Trout Canada, USA North NE
S. namaycush America
S. neiva Russia (endemic to Asia NE
Okhota River)
S. neocomensis Switzerland (endemic Europe EX Unknown
to Lake Neuchâtel)
S. obtusus Republic of Ireland Europe CE Eutrophication,
pollution,
afforestation
S. perisii UK (Wales) Europe VU Dams, angling,
eutrophication,
climate change
Deepwater Char Austria, Germany, Europe EX Eutrophication
S. profundus Switzerland
(endemic to Lake
Constance)
Bear Island Charr Norway (endemic to Europe NE
S. salvelinoinsularis Bear Island)
S. schmidti Russia (endemic to Asia NE
Lake Kronotskoe)
chapter 21760
Table A.1. Continued.
Documented
Species native range Continent Status reats
Salvelinus UK (Scotland) Europe VU Introduced species
struanensis
S. taimyricus Russia (endemic to Asia NE
Lake Taimyr)
S. taranetzi Russia (endemic to Asia NE
Chukchi Peninsula)
S. thingvallensis Iceland (endemic to Europe LC
Lake ingvalla)
S. tolmachoffi Russia (endemic to Asia EN Pollution from
Khatanga River) mining
Lake Char S. umbla Austria, France, Italy, Europe LC Eutrophication,
Germany, Sweden, habitat destruction
Switzerland
Sakhalinian Char Russia Asia NE
S. vasiljevae
S. willoughbii UK (England) Europe EN Introduced species,
eutrophication
Golden Charr UK (Scotland) Europe VU Introduced species
S. youngeri
Long-finned Char Russia (endemic to Asia VU Unknown
Salvethymus Chukchi Peninsula)
svetovidovi
