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General effects of climate change on Arctic fishes and fish populations.

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General Effects of Climate Change on Arctic Fishes and Fish Populations
Author(s): James D. Reist, Frederick J. Wrona, Terry D. Prowse, Michael Power, J. Brian Dempson,
Richard J. Beamish, Jacquelynne R. King, Theresa J. Carmichael, and Chantelle D. Sawatzky
Source: AMBIO: A Journal of the Human Environment, 35(7):370-380.
Published By: Royal Swedish Academy of Sciences
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James D. Reist, Frederick J. Wrona, Terry D. Prowse, Michael Power, J. Brian Dempson, Richard J. Beamish,
Jacquelynne R. King, Theresa J. Carmichael and Chantelle D. Sawatzky
General Effects of Climate Change on Arctic
Fishes and Fish Populations
Projected shifts in climate forcing variables such as
temperature and precipitation are of great relevance to
arctic freshwater ecosystems and biota. These will result
in many direct and indirect effects upon the ecosystems
and fish present therein. Shifts projected for fish popu-
lations will range from positive to negative in overall
effect, differ among species and also among populations
within species depending upon their biology and toler-
ances, and will be integrated by the fish within their local
aquascapes. This results in a wide range of future
possibilities for arctic freshwater and diadromous fishes.
Owing to a dearth of basic knowledge regarding fish
biology and habitat interactions in the north, complicated
by scaling issues and uncertainty in future climate
projections, only qualitative scenarios can be developed
in most cases. This limits preparedness to meet chal-
lenges of climate change in the Arctic with respect to fish
and fisheries.
Fishes and wildlife intimately associated with arctic freshwater
and estuarine systems are of great significance to local human
populations (1) as well as significant keystone components of
the ecosystems (2). Accordingly, interest in understanding the
impacts of climate change on these components is very high.
However, in addition to the problems outlined elsewhere in this
issue (2), detailed understanding of climate change impacts on
higher-order biota is complicated by a number of factors.
Firstly, fishes and wildlife will experience first-order effects of
climate change (e.g., increased growth in arctic taxa due to
warmer conditions and higher productivity). Large numbers of
second-order effects will also occur (e.g., increased competition
with species extending their distribution northward). The
responses of fishes will integrate these effects in complex and
not readily discernible ways; further, responses to climate
change will be embedded within effects resulting from other
impacts such as exploitation and habitat alteration, and it may
be impossible to differentiate these. These multiple impacts are
likely to act cumulatively or synergistically to affect arctic taxa.
Secondly, higher-level ecosystem components affect lower levels
in the ecosystem (i.e., top-down control) and in turn are affected
by changes in those levels (i.e., bottom-up control) (2). The
balance between such controlling influences may shift in
indiscernible ways in response to climate change, and this, in
turn, will affect fish populations. Thirdly, higher-level ecosys-
tem components typically migrate seasonally and/or annually
between habitats or areas key to their life histories—arctic
freshwater and diadromous (i.e., sea-run) fishes and aquatic
mammals may do so locally, and aquatic birds tend to do so
globally between arctic and non-arctic areas. Thus, the effects of
climate change on such organisms will represent the integrated
impacts across numerous habitats that indirectly affect the
species of interest. These biotic circumstances increase the
uncertainty associated with developing understanding of
species-specific responses to climate change, particularly for
key fish (Table 1-Box 1) and other aquatic species that are of
economic and ecological importance to arctic freshwater
ecosystems and the communities of northern residents that
depend on them.
This contribution provides an overview summary of fresh-
water and diadromous (primarily anadromous) fishes of the
Arctic, develops information needs required to project respons-
es of arctic fishes to climate change, and examines some general
effects of climate change on physical habitat in the context of
their relevance to fishes. Finally, to promote future research a
short review is given of various approaches relevant for
projecting climate change effects on arctic fish populations.
This treatment is not exhaustive but rather is developed for
particular important arctic freshwater and diadromous fishes as
examples of the types of changes to be expected.
There are approximately 99 species in 48 genera of freshwater
and diadromous (i.e., anadromous or catadromous forms
moving between fresh and marine waters) fishes present in the
Arctic as used here (2). These represent 17 families (Table 1).
Ninety-nine species is a conservative estimate because some
groups (e.g., chars and whitefishes) in fact contain complexes of
incompletely resolved species. Many species are also represented
by local polymorphic forms that biologically act as species (e.g.,
four morphs of Arctic char, Salvelinus alpinus, in Thingvalla-
vatn, Iceland) (6). The most species-rich family is the
Salmonidae with more than 33 species present, most of which
are important in various fisheries. The next most species-rich
family is the Cyprinidae with 23 species, few of which are fished
generally, although some may be fished locally. All remaining
families have six or fewer species, and five families are
represented in the Arctic by a single species. These generalities
hold true for the individual ACIA regions as well (Table 1). All
of the families represented in the Arctic are also present in
lower-latitude temperate and subtemperate regions. Most have
370 Ambio Vol. 35, No. 7, November 2006ÓRoyal Swedish Academy of Sciences 2006
Box 1.
Freshwater and diadromous fishes of the Arctic.
There are approximately 99 species in 48 genera of freshwater and diadromous (i.e., anadromous or catadromous forms moving between fresh
and marine waters) fish present in the Arctic as defined by ACIA (2).These represent 17 families (see table). Ninety-nine species is a
conservative estimate because some groups (e.g., chars and whitefishes) in fact contain complexes of incompletely resolved species. Many
species are also represented by local polymorphic forms that biologically act as species (e.g., four morphs of Arctic char in Thingvallavatn,
Iceland).The most species-rich family is the Salmonidae with more than 33 species present, most of which are important in fisheries.The next
most species-rich family is the Cyprinidae with 23 species, few of which are fished generally, although some may be fished locally. All remaining
families have six or fewer species, and five families are represented in the Arctic by a single species.These generalities hold true for the individual
ACIA regions as well. All of the families represented in the Arctic are also present in lower-latitude temperate and subtemperate regions. Most
have a southern center of distribution, as do many of their associated species (3). Individual species may be confined to the Arctic, or may
penetrate northward from subarctic areas to varying degrees.
Substantive differences in the number of species present are apparent between the ACIA regions. Region 3 (unglaciated Beringia and the
western Canadian Arctic) contains 58 named taxa, followed by Region 1 (Arctic Europe and Russia) with 38, while Regions 2 (Siberia) and 4
(eastern North America) are about equal at 29 and 32, respectively. This probably represents a combination of historical effects (e.g., glacial
events, postglacial recolonization routes and access) as well as present-day influences such as local climate, habitat diversity, and ecological
processes (e.g., competition and predation). Arctic char is the only species that is truly holarctic, being present on all landmasses in all ACIA
regions, occurring the farthest north to the extremes of land distribution (;848N), and also exhibiting the widest latitudinal range (about 40
degrees) of all true arctic species (i.e., south in suitable lakes to ;458N). A few additional species are distributed almost completely across the
Holarctic but are absent from one or more areas within an ACIA region (e.g., burbot with ;75%of a complete circumpolar distribution; northern
pike with ;85%; lake whitefish, European whitefish, and Siberian whitefish (Coregonus pidschian) with ;85%; and ninespine stickleback with
;90%). With the exception of the stickleback, all are fished extensively where they occur, representing the mainstays of food fisheries for
northern peoples and supporting significant commercial fisheries in most areas.These species are often the only ones present in extremely
remote areas, inland areas, and higher-latitude areas, and thus are vital for local fisheries. Where they are regionally present, many other species
are exploited to a greater or lesser degree.
Table 1. Freshwater and diadromous fish present in the Arctic.
Family Name
Number of
arctic forms
in ACIA area
Number of
species in
ACIA regions
Exploitation in
ACIA regions CommentsGenera Species 1 2 3 4
2 5 4 2 2 1 Cool Some in Region 1
1 5 2 2 1 1 Warm/Cool Region 1, some in
Region 4
1 1 0 0 1 0 Warm Region 3 where they
occur and are abundant
Goldeye (Hiodon alosoides), in North
America only
(freshwater eels)
1 2 1 0 0 1 Warm Region 1, eastern Region
Mostly in southern areas only
1 3 2 0 1 0 Warm/Cool Region 1, limited in
Region 3
Southern areas in interior; also in
northern coastal areas influenced by
warm currents
14 23 11 4 13 1 Warm Some species in Regions
1 and 2; not exploited or
limited elsewhere
Most species only occur in southern
ACIA area
2 3 0 1 2 3 Warm/Cool/
Limited in Region 2 and
western Region 4
1 1 1 0 0 0 Warm Not fished Stone loach (Noemacheilus barbatulus)
only. Subarctic only; very southern
edge of Region 1
1 1 1 1 1 1 Cool/Cold Extensively fished in all
four Regions
Northern pike (Esox lucius) only, and
widely distributed
1 2 0 0 2 0 Cold/Arctic Limited at most, where
they occur
Blackfishes (Dallia spp.) only
2 3 0 0 2 0 Cool/Cold Limited at most, where
they occur
(salmon, char,
10 33þ9 14 22 14 Cool/Cold/
Most species extensively
fished in all four Regions
Salmonids are the most widely
distributed and abundant arctic group
and fisheries mainstay
1 1 0 0 1 1 Cool/Cold Not fished Trout perch (Percopsis omiscomaycus)
Gadidae (cods) 1 1 1 1 1 1 Cool/Cold Extensively fished in all
four Regions
Burbot (Lota lota) only, and widely
3 3 2 1 3 2 Warm/Cool/
Not fished
Cottidae (sculpins) 2 6 2 2 4 3 Cool/Cold Not fished
Percidae (perches) 4 6 2 1 3 3 Warm/Cool Fished where they occur,
especially Region 1
Mostly temperate species, but enter the
Arctic via warmer northward-flowing rivers
Totals 48 99 38 29 58 32
Total families 17 - 12 10 14 12
Notes: a) see references 4 and 5 for guild definition; b) only Alosinae (shads) are arctic representatives; c) only Dallia (blackfish) are arctic representatives.
Ambio Vol. 35, No. 7, November 2006 371ÓRoyal Swedish Academy of Sciences 2006
a southern center of distribution, as do many of their associated
species (3). Individual species may be confined to the Arctic, or
may penetrate northwards from subarctic areas to varying
Substantive differences in the number of species present are
apparent between the ACIA regions (Table 1). Region 3
(unglaciated Beringia and the western Canadian Arctic)
contains 58 named taxa, followed by Region 1 (Arctic Europe
and Russia) with 38, while Regions 2 (Siberia) and 4 (eastern
North America) are about equal at 29 and 32, respectively. This
probably represents a combination of historical effects (e.g.,
glacial events, postglacial recolonization routes and access) as
well as present-day influences such as local climate, habitat
diversity, and ecological processes (e.g., competition and
predation). These regional fauna differences of course will
result in variation in the local significance of climate change on
arctic fishes and on fisheries based upon them. Arctic char is the
only species that is truly Holarctic, being present on all
landmasses in all ACIA regions, occurring the farthest north
to the extremes of land distribution (;848N), and also
exhibiting the widest latitudinal range (about 40 degrees) of
all true arctic species (i.e., south in suitable lakes to ;458N
latitude). A few additional species are distributed almost
completely across the Holarctic but are absent from one or
more areas within an ACIA region (e.g., burbot Lota lota with
;75%of a complete circumpolar distribution; northern pike
Esox lucius with ;85%; lake whitefish, European whitefish, and
Siberian whitefish (Coregonus clupeaformis/lavaretus/pidschian)
with ;85%; and, ninespine stickleback Pungitius pungitius with
;90%). With the exception of the stickleback, all are fished
extensively where they occur (Table 1), representing the
mainstays of food fisheries for northern peoples and supporting
significant commercial fisheries in most areas. These species are
often the only ones present in extremely remote areas, inland
areas, and higher latitude areas, and thus are vital for local
fisheries. Where they are regionally present (e.g., lake trout,
Salvelinus namaycush, in North America), many other species
are also exploited to a greater or lesser degree.
Implicit in this and other papers in this issue is the linkage
between atmospheric climate parameters and habitat parame-
ters present in aquatic ecosystems, and the linkage of these to
effects manifested in organisms and populations. It follows
from this logic that changes in climate regimes, however they
may be manifested, will only indirectly affect aquatic organisms
of interest. That is, the aquatic environment itself will be
directly affected by changes in climate, but will modify and then
transmit the influences in some fashion. For example, substan-
tive shifts in atmospheric temperature regimes will affect water
temperatures but given the density differences between water
and air and the influence of hydrodynamic factors, the effects
on aquatic systems will be modified to some degree. In turn,
changes in atmospheric parameters will have indirect effects on
biota present in aquatic systems and thus may be ameliorated or
partially buffered (e.g., thermal extremes or seasonal timing
shifted). In some instances, however, climate change effects may
be magnified or exacerbated, increasing the multiplicity of
possible outcomes resulting from these changes. For example,
stream networks amplify many environmental signals that occur
at the watershed level, and that are concentrated in the stream
(7). This added level of complexity and uncertainty in the
magnitude and direction of climate change manifestations in
arctic freshwater ecosystems is not as acute for terrestrial
environments. It does however result in greater uncertainty in
projecting potential impacts on aquatic organisms. This is
especially relevant for arctic anadromous fishes such as
whitefishes, ciscoes and chars which occupy many habitats
during life history. Figure 1 provides an example of the logical
associations and both direct and indirect effects of climate
parameters on anadromous fish and the various aquatic
environments used. In addition to effects on freshwater habitats
used, climate change will affect estuarine, nearshore and marine
habitats and their contained biota. Both habitat effects and
effects on biota will in turn influence how sea-run fish species
conduct their life histories. For example, effects on nearshore
marine ecosystems will likely alter local trophic structure and
transfer rates. This, in turn, will alter feeding opportunities for
sea-run fish and ultimately affect fisheries based upon these
populations. Compounded effects are almost certain, for
example, in addition to marine shifts, habitat impacts in
freshwater (e.g., altered timing, nature and amounts of
precipitation) may combine to affect routes, timing and success
of key life functions such as survival and migrations. In most
cases our understanding of the dynamics of arctic aquatic
ecosystems and of the ways in which climate change may
possibly be manifested is so rudimentary that even the potential
direction of effect (i.e., positive or negative relative to a process
or organism) can not be projected. In other cases, the same
proximate climate change effect on the local habitat may differ
in its ultimate effect upon particular fish species because of, for
example, differences in life history, feeding modes and
sensitivities to environmental parameters.
Fish and Climate Parameters
The Arctic includes high-, low-, and sub-arctic areas defined by
climate, geography, and physical characteristics (2). In addition,
many areas included in this assessment (e.g., southern Alaska,
the southern Northwest Territories, northern Scandinavia, and
Russia) are significantly influenced by nearby southern mari-
time environments and/or large northward-flowing rivers. This
proximity ameliorates local climatic regimes, resulting in more
northerly distributions of aquatic taxa than would otherwise
occur based strictly on latitudinal position. In some areas (e.g.,
Labrador, Canada) the opposite is true due to southern
transport of colder waters by coastal marine currents. More-
over, the Arctic includes many different climatological zones.
Given that the distribution of many freshwater and anadro-
mous fish species is controlled or significantly influenced either
directly or indirectly by climate variables (particularly temper-
ature), it follows that primary associations of fish distribution
with climate variables will be important.
Fish are ectotherms, thus, for the most part, their body
temperature is governed by that of the surrounding waters. In
addition, fish species and individuals can behaviorally choose
specific thermal preferenda (preferred optimal temperatures) (8)
at which physiological processes are optimal (i.e., greatest net
benefit is achieved for the individual). This is typically a thermal
range that may be fairly narrow; temperatures outside this are
suboptimal (i.e., net benefit is still attained but it is not the
greatest possible), grading to detrimental (i.e., non-lethal but
net energy is expended while in such conditions) and ultimately
to lethal conditions (i.e., death ensues after some level of
exposure). Furthermore, within a species, local northern
populations often have such preferenda set lower than do
southern representatives, which presumably represents differ-
ential adaptation to local conditions. In addition, individual life
stages (e.g., egg, alevin, juvenile, adult) differ in their thermal
preferenda linked to optimizing criteria specific to their
developmental stage. For most species, only limited under-
standing of such thermal optima is available, and typically only
372 Ambio Vol. 35, No. 7, November 2006ÓRoyal Swedish Academy of Sciences 2006
for some life stages of southern species. Fish control body
temperatures behaviorally, sensing and moving into appropri-
ate, or from inappropriate, zones (9). Aquatic thermal regimes
are spatially and temporally heterogeneous and availability of
water at the preferred temperature may be limited, making it an
important resource for which competition may ensue. This may
be particularly important in species found in Alaskan and
Yukon north slope rivers (e.g., Dolly Varden Salvelinus malma
and Arctic grayling Thymallus arcticus) during winter, when
physical habitat is limited due to rivers freezing to the bottom
over long reaches (10). Thus, the thermal niche of individual
fish species can be defined.
Temperate species have been grouped into three thermal
guilds defined by thermal niches (4): Warmwater (preferred
summer temperatures centered upon 27 to 31 8C), Coolwater
(21 to 25 8C), and Coldwater (11 to 15 8C). Following this
approach, an Arctic Guild was defined (11) as fish distributed
wholly or primarily in northern areas and adapted to relatively
colder waters (,10 8C) and related aspects of the habitat such as
short growing seasons, extensive ice presence, and long periods
of darkness. Freshwater and most diadromous fishes occurring
within the geographic definition of the Arctic as used here
represent all of these guilds (Table 1), however, those of the
Warmwater Guild tend to be present only along the southern
margins of arctic waters, often associated with local climatic
amelioration resulting from inputs from nearby maritime areas
or northward-flowing rivers. Some of these guilds can be further
subdivided based upon the nature of the fish distribution.
Within the generalities discussed below, the impacts of climate
change will be species- and ecosystem-specific, thus the
following should be viewed as a range of possibilities only. In
addition, although thermal regimes are emphasized in this
discussion, the influence of other climate parameters may be
equally or more important to specific species in particular areas
or at particular times during life.
Species of the Arctic Guild have their center of distribution
in the Arctic with the southern limits defined by, for example,
high temperatures and associated ecological factors including
competition from southern fish species. Fish such as broad
whitefish (Coregonus nasus) or Arctic cisco (Coregonus autum-
nalis), and many char taxa are examples of Arctic Guild species.
The pervasive and ultimate impacts of climate change upon
such species are likely to be negative. These impacts generally
will appear as range contractions northwards driven by thermal
warming that exceeds preferences or tolerances; related habitat
changes; and/or increased competition, predation, or disease
resulting from southern taxa extending their range northwards,
possibly preceded by local reductions in growth, productivity,
and perhaps abundance. Many of these effects will possibly be
driven or exacerbated by shifts in the life history of some species
(e.g., from anadromy to freshwater only). Other than concep-
tual summaries, no detailed research has been conducted to
outline such impacts for most fish species of this guild.
Fish that have distributions in the southern Arctic are
northern members of the Coldwater Guild. This group includes
species such as the lake/European/Siberian whitefish complex
and lake trout, which have narrow thermal tolerances but
usually are widely distributed due to the availability of colder
habitats in water bodies (e.g., deeper layers in lakes; higher-
elevation reaches in streams) (12). Two distributional subtypes
can be differentiated: those exhibiting a wide thermal tolerance
(eurythermal) as implied, for example, by a wide latitudinal
distribution often extending well outside the Arctic (e.g., lake
whitefish Coregonus clupeaformis); and those exhibiting a
narrow thermal tolerance (stenothermal) implied by occupation
of very narrow microhabitats (e.g., lake trout occupy deep lakes
Figure 1. A stylized portrayal of some potential direct effects of climate parameters on arctic aquatic environments and some potential
indirect effects on aquatic organisms such as anadromous fish. The complexity of interactive effects raises great difficulties in projecting
climate change effects on these fishes. For wholly freshwater fishes, similar complex patterns are likely especially if these involve use of
many habitats during life (e.g., both lacustrine and riverine habitats).
Ambio Vol. 35, No. 7, November 2006 373ÓRoyal Swedish Academy of Sciences 2006
below thermoclines in the south but a much wider variety of
coldwater habitats in the north) and/or narrow latitudinal
distribution centered in northern areas (e.g., pond smelt
Hypomesus olidus). The overall impacts of arctic climate change
on these two distributional subtypes are likely to be quite
different. Thus, eurythermal species are likely to have the
capacity for reasonably quick adaptation to changing climate
and, all other things being equal, are likely to exhibit increases
in growth, reproduction, and overall productivity. Such species
are also likely to extend the northern edge of their distribution
further northwards where this is at present thermally limited,
but this is likely to be a secondary, relatively small response.
Conversely, stenothermal coldwater species are likely to
experience generally negative impacts. Lake trout in northern
lakes, for example, will possibly be forced into smaller volumes
of suitable summer habitat below deeper lake thermoclines and
will possibly have to enter such areas earlier in the season than
at present. Subsequent impacts on such species are very likely to
be negative as well. To some degree, northern members of the
Coldwater Guild are likely to experience the same general
impacts as described for arctic-guild species in the previous
paragraph (i.e., reductions in productivity characteristics,
increased stress, local extirpation, and/or range contractions).
Similar to the arctic-guild species, little or no detailed research
assessing impacts on northern coldwater-guild fishes has been
conducted to date.
Coolwater-guild species (such as perches Perca spp.) have
southern, temperate centers of distribution but range northward
to the southern areas of the Arctic as used here (2); these include
northern pike, walleye (Sander vitreus), and yellow perch (Perca
flavescens) (12). Like those of the Coldwater Guild, these species
can also be differentiated into eurythermal and stenothermal
species. For example, the perches have a wide latitudinal range
and occupy a number of ecological situations extending outside
temperate regions, and hence can be described as eurythermal.
Assuming waters are accessible, northward range extensions of
approximately 2 to 8 degrees of latitude are projected for yellow
perch in North America under a climate-change scenario where
annual mean temperatures increase by 4 8C (Figure 2) (13). The
linkage between perch distribution and climate was indirect;
that is, the first-order linkage was the direct dependency of
overwinter survival (and related size at the end of the first
summer of life) on food supply, which limited growth (13). The
food supply, in turn, was dependent upon climate parameters.
Alternatively, many northern minnows (e.g., northern red-
belly dace Chrosomus eos in North America) and some
coregonines (e.g., vendace Coregonus albula in Europe) are
probably stenothermal, as implied by their limited latitudinal
range and habitat associations. Range contraction along
southern boundaries is likely for these species, initially
manifested as contraction of distribution within the local
landscapes, followed by northward retraction of the southern
range limit. Because of their stenothermal tolerances, however,
their northward extension is not likely to be as dramatic as that
described for perch. To some degree, the presence of many of
these species in the large northward-flowing arctic rivers such as
the Lena, Mackenzie, Ob, and Yenisey is very likely to promote
their northward penetration. The associated effects of heat
transfer by such river systems will facilitate northward
colonization by these species as well as eurythermal species
also present in the systems. Knowledge of the association of
ecological processes with climate parameters and research
quantifying the potential impacts of climate change on cool-
water-guild species, although inadequate overall, generally
tends to be more comprehensive than for the previous two
guilds, but, it is often focused upon southern populations.
Hence, its applicability to arctic populations of the species may
be limited.
Warmwater-guild species have their center of distribution
well south of the Arctic. Those present in the Arctic are few in
number (Table 1) and with few exceptions (some cyprinid
species) are generally distributed only in the extreme southern
portions of the ACIA region. In many areas of the Arctic, a
number of species of this guild are present in southerly areas
immediately outside the Arctic boundary used here (2).
Presumably, their northward limit is in most cases deter-
mined by present thermal and ecological regimes, especially in
the large northward-flowing rivers of Siberia and the western
Figure 2. Present and projected future distributional limits of yellow
perch in North America. Northward displacements are based on
overwinter survival assuming a 48C increase in mean annual
temperature (adapted from reference 13). Similar shifts in distribu-
tions of other freshwater species are likely throughout the Arctic
especially where present limits are determined thermally (or by
some similar climatic parameter likely to change in the future) and
where suitable colonization pathways (e.g., large northward flowing
rivers) exist.
Figure 3. Growth rates of fish species at varying temperatures
determined from laboratory studies. Stenothermic northern species
(e.g., A, B, C and F) are grouped towards the lower temperatures on
the left, whereas mesothermic southern species (e.g., G, I, and J) are
grouped towards the right. Stenothermic species tend to have a
more peaked curve indicating only narrow and typically lower
temperature ranges over which optimal growth is achieved. Wide-
ranging eurythermic species (e.g., D, E, and H) probably exhibit the
greatest possibilities for adapting rapidly to shifting thermal regimes
driven by climate change. Scientific names of most species are
given in the text; Bluegill ¼Lepomis macrochirus, Brook Trout ¼
Salvelinus fontinalis.
374 Ambio Vol. 35, No. 7, November 2006ÓRoyal Swedish Academy of Sciences 2006
Northwest Territories. As the effects of climate change
increasingly ameliorate local limiting factors, species of this
guild are very likely to extend their geographic ranges into the
Arctic or, if already there, to more northerly locales.
Thermal preferenda presumably optimize all internal phys-
iological processes (i.e., benefits outweighs costs) in individual
fish associated with digestion, growth, muscle (hence swim-
ming) efficiency, gas exchange across gills, cellular respiration,
reproduction, and so on. The relationship of temperature to
such processes is perhaps most easily seen with respect to
growth (e.g., increase in size or weight over time) (Figure 3). In
addition to exhibiting higher growth rates at lower tempera-
tures, arctic fish species also exhibit narrower ranges of
temperature preference and tolerance (i.e., they are stenother-
mic; Figure 3), which has profound effects on productivity.
Stenothermic tolerances also imply that the species may have
little capacity to accommodate thermal impacts of climate
change. Conversely, species exhibiting eurythermic or wide
thermal tolerances or responses are likely to have a much wider
capacity to accommodate climate changes (see above and Table
Population-level influences of thermal regimes are also
apparent. Effects on individuals, such as temperature effects
on mortality, feeding, parasitism, and predation, are integrated
into consequences for fish populations through the various
processes that connect fish populations to their ecosystems
(Figure 4). As noted previously, environmental parameters such
as temperature may affect various life stages differently and
thus can be modeled separately, but it is important to remember
that the ultimate effects of all these influences are integrated
throughout the fish population of interest.
Similarly, environmental changes also have specific effects on
other organisms relevant to fish, such as predators, parasites,
and food organisms. Therefore, a single environmental param-
eter may exert both indirect and direct effects at many levels
that influence the fish population, but the actual effect of this
may be indiscernible from the effects of other natural and
anthropogenic influences. Figure 4 provides examples of
linkages between environmental parameters that affect key
processes at the fish population level. Migratory aspects of life
history are not shown in the figure, but will also (especially in
anadromous fish) be significantly affected by abiotic processes.
Salinity will also be a factor for sea-run phases of adult life
history. Climate change and increased variability in climate
parameters will drive changes in aquatic abiotic parameters.
Such changes will affect the fish directly as well as indirectly via
impacts on their prey, predators, and parasites. This cascade of
effects, and synergies and antagonisms among effects, greatly
complicates the projection of climate change impacts on valued
northern fish populations. In addition, other parameters not
shown in Figure 4, such as groundwater inflows to spawning
beds, will affect the survival of various life-history stages. The
ultimate effects of all these interacting factors will in turn affect
sustainability of the populations and human uses in a fishery
Temperature effects on individual fish and fish populations
are perhaps the most easily understood ones, however, other
climate parameters such as precipitation (amount and type) will
directly affect particular aquatic environmental parameters such
as productivity (e.g., see elsewhere in this issue (16)), and flow
regimes (amounts and timing). For example, flattening hydro-
graphs and shifts in water sources (17) are very likely to alter the
availability of arctic rivers as migratory routes for anadromous
fish and shift timing of migratory runs. Increased and earlier
vernal flows are very likely to enhance fish survival during out-
migration and lengthen the potential summer feeding period at
sea (both positive effects at the levels of the individual fish and
the population).
Figure 4. The major biotic process-
es affecting the dynamics of a
freshwater or anadromous arctic
fish population and some of the
aquatic abiotic environmental pa-
rameters that affect these process-
es. The tan ovals refer to the four
major processes controlling fish
production (predation, transport/
migration, starvation, spawning/re-
cruitment); these will shift as a
result of climate change effects on
the various components of the
ecosystem (15).
Ambio Vol. 35, No. 7, November 2006 375ÓRoyal Swedish Academy of Sciences 2006
However, autumnal flows are required in many smaller rivers
to provide access to returning fish (18); reduction in amounts
and shifts in timing of these flows are very likely to have
negative effects. Environmental factors, particularly local
temperature effects on flow regimes, influence migrations of
Arctic char with consequences for fish population abundance
and structure (19).
Additional secondary environmental factors that may
change in response to direct changes in basic climate parameters
will also have important effects on aquatic biota. These include
the nature and duration of freeze-up, ice types, ice-cover
periods, and breakup, and the nature and penetration of
incident radiation into aquatic systems. Similarly, terrestrial
impacts of climate change may influence aquatic habitat and
indirectly affect its biota (e.g., permafrost alteration and runoff
influences on sediment loads, pH and related water chemistry,
etc.). Another potential class of indirect effects of climate
change includes those affecting the behavior of aquatic biota.
For example, fish use thermal regimes and spatiotemporal shifts
in these regimes, at least in part, as behavioral cues or
thresholds to trigger critical life history functions. Water mass
boundaries defined by temperature act as barriers to movement
and may define feeding areas (9). Final gametic maturation in
autumn-spawning species is probably triggered by decreasing
water temperatures and perhaps also photoperiod in arctic
whitefishes (Coregonus spp.). There is anecdotal evidence that
decreased sediment loads resulting from freezing of riverbanks
trigger final upstream movements by broad whitefish from
holding areas to spawning sites (20), an adaptation to ensure
eggs are not smothered. Water temperature integrated over time
(e.g., as degree-days) affects the rate of egg development. Thus,
aquatic thermal regimes affect ectotherms such as fish in two
basic ways: by influencing physiology and as cues for behavioral
changes. Although typically less understood, similar effects
probably result from other physical (e.g., currents, flows,
turbidity, ice dynamics) and chemical (e.g., pH, oxygen)
parameters in the aquatic habitat (e.g., see 15). Climate-induced
alteration of these habitat characteristics is very likely to
significantly affect arctic fish populations, although substantive
research is required to quantify such effects.
Freshwater and diadromous fishes of the Arctic exhibit high
diversity in the way that climate parameters affect their
distributions, physiology, and ecology. These factors, together
with the more complex indirect effects that climate may have
upon their habitats, implies a wide range of possible responses
to climate change. Other than logical extrapolations, most
responses to climate change are impossible to quantify due to
the absence of basic physiological information for most arctic
fish species and the incomplete understanding of the overall
associations of ecological processes with present-day climate
Effects of Climate-induced Changes on Physical Habitat
Physical changes in aquatic habitats will very probably affect
arctic fishes as climate changes in the north. This section provides
some examples to illustrate the linkages and various potential
effects on biota, but the underlying absence of data precludes
quantification of causal linkages in most cases. Rectifying these
and similar knowledge gaps is a major future challenge.
Groundwater and fish. Groundwater flows sustain fish
habitat and are extremely important during periods of low
flow in many arctic rivers (19) and perhaps some lakes (17). For
stream-dwelling salmonids, inflows along stream bottoms clear
fine-grained sediments from spawning areas, supply thermally
regulated and oxygenated water to developing eggs and larval
fish, and in many cases provide physical living space for juvenile
and adult fish. In highly channeled shallow arctic rivers that
characterize many areas of the North American Arctic and
Chukotka, groundwater inputs are critical to fish migrations
and stranding prevention (21). In winter, many Alaskan and
western Canadian north slope rivers cease flowing and freeze to
the bottom over large stretches, and groundwater provides
refugia that support entire populations of Arctic grayling and
Dolly Varden as well as any co-occurring species (10).
Overwintering mortality, especially of adults weakened from
spawning activities, is suspected as a primary regulator of the
populations of Dolly Varden in this area and a major factor in
such mortality is the quality and amount of winter habitat
maintained by groundwater. Possible increases in groundwater
flows resulting from climate change are likely to positively affect
overwinter survival, especially if coupled with shorter duration
and thinner ice cover. However, increased nutrient loadings in
groundwater will possibly have more complex impacts (e.g.,
increases in in-stream primary and secondary productivity are
likely to promote growth and survival of larval fish, but
increases in winter oxygen demand associated with vegetation
decomposition will possibly decrease overwinter survival of
larger fish). How these various effects will balance in specific
situations to result in an overall net effect on particular fish
populations is unknown.
In summer, ground and surface water inflows ameliorate
summer temperatures and provide thermal refugia, especially
along southern distributional margins (21). This is probably
especially relevant for fish belonging to the arctic and coldwater
thermal guilds. However, even the small increases in water
temperatures (2 to 4 8C) that are likely to result from climate
change (e.g., warmer surface flows) will possibly preclude some
species from specific aquatic habitats (e.g., temperature in
higher-elevation cold-water stream reaches determines habitat
occupancy of bull trout Salvelinus confluentus) (22). Increased
ambient conditions above physiological thermal optima are
very likely to further stress populations and combined with
other possible effects such as competition from colonizing
southern taxa, such impacts are likely to exacerbate range
contractions for arctic species.
Ice and fish. The influence of ice on arctic fish and fish
habitat is significant, especially in smaller lotic systems
important to salmonids (10, 21, 23, 24, 25). Effects include
possible physical damage (e.g., from frazil ice), limitation of
access to habitat (e.g., decreasing water volumes in winter due
to ice growth), and annual recharge of habitat structure during
dynamic breakup (e.g., cleansing of interstitial spaces in gravel).
Shifts in the timing and duration of ice-related events are very
likely to affect the survival and success of fish, with some effects
being advantageous and others disadvantageous. In the north,
these effects will be superimposed upon a poorly known but
complex biological and environmental situation. Limited
knowledge precludes accurate forecasting of many of these
potential effects, and novel approaches are required to redress
this (23).
Decoupling of Environmental Cues Due to Differential Effects
Of Climate Change
A speculative issue, which may present surprises and unantic-
ipated effects, is the potential for decoupling of various types of
environmental drivers due to climate change affecting them
differentially. Fish and other organisms use progressive and/or
cusp-like changes in environmental parameters as cues to trigger
key life-history functions such as migration, reproduction, and
development. For example, although quantitative linkages are
lacking, change in photoperiod (e.g., declining light period) is
probably coupled with declining water temperatures in the
376 Ambio Vol. 35, No. 7, November 2006ÓRoyal Swedish Academy of Sciences 2006
autumn and together these trigger final gonadal maturation and
reproductive activities in many northern fishes (especially
salmonids). Environmental cues that drive major life-history
events are especially critical for migratory species, and in the
Arctic, particularly for anadromous species. This coupling is
probably especially strong in the north where both parameters
change rapidly on a seasonal basis. Although not explored to
date in a climate-change context, as seasonal photoperiod shifts
remain unchanged but coincident cues such as declining
temperatures occur later in the autumn, such decoupling will
possibly have profound impacts on population processes. The
initial impact of such decoupling may be quite subtle (e.g.,
lowered fecundity, fertilization success, and/or egg survival in
the previous example), not readily discernible, and almost
certainly not directly attributable to climate change. However, a
critical threshold is likely to be reached when impacts become
significant (e.g., total reproductive failure in one year resulting
in a failed year class, ultimately leading to population
extirpation if it occurs over successive years approaching the
generation time of the population). Investigation of coupling
between cues, their influence upon population processes in fish
and other aquatic organisms, and their potential for decoupling
due to climate change in the Arctic should be a priority.
These are but a few examples of likely influences of physical
habitat on fish populations and the potential effects of climate-
induced change on them that will have cascading effects on the
integrity, sustainability, and future productivity of northern
fishes. These serve to illustrate the general lack of knowledge
that exists regarding associations between physical habitat and
biology in northern aquatic biota, and thus how the impacts of
climate change will be manifested. Redress of this knowledge
gap is required on a community- and/or species-specific basis to
account for local and historical influences and filters, which
greatly affect the present-day structure and function of these
aquatic ecosystems (26).
Issues at the Level of Fish Populations
As implied previously, projecting climate change impacts at the
population level for most species is complex and fraught with
uncertainty, especially for arctic species for which there is a
dearth of fundamental biological information. A variety of
approaches to address this problem are available (see below)
and most have been applied in one way or another to develop
some understanding of climate change impacts on northern fish
In North America, much of the research focus on climate
change effects on freshwater fish populations and communities
has been in the south, for example, in the Great Lakes region
and associated fisheries (e.g., 12, 14, 27, 28, 29, 30, 31). In that
region, climate change is projected to result in effects similar to
those projected for the Arctic (e.g., significant reductions in the
duration and extent of ice cover, an earlier seasonal disappear-
ance of the 4 8C depth isotherm, measurable declines in
dissolved oxygen, and slight hypolimnetic anoxia in shallower
basins) (32, 33). Loss of suitable cool-water habitat associated
with lake warming is also projected, which will very probably
differentially affect species within lacustrine fish communities
(e.g., promote growth and survival in lake whitefish but
negatively affect these in lake trout) (29).
Preliminary consideration of northern areas has occurred for
European systems (34). Relatively less attention has been paid
to the possible effects of climate change on resident fish
communities in other ecosystems, particularly those in the
Arctic. With respect to freshwater fish populations, the
Intergovernmental Panel on Climate Change (35) concluded
that fish populations in streams and rivers on the margins of
their geographic distributions (e.g., arctic and subarctic species)
will be the first to respond to the effects of climate change
because these systems have a high rate of heat transfer from the
air. Some of these effects include the following.
Nutrient level and mean summer discharge explained 56%of
the variation in adult Arctic grayling growth over a 12-year
period in two Alaskan rivers (36). Summer temperature
added to these variables explained 66%of variation in
young-of-the-year growth. Correlation with discharge was
positive for adults and negative for young, thus grayling life
history appears able to respond to variability in the arctic
environment by balancing adult growth with year-class
strength. How this balance will shift under climate change
is uncertain at present.
Temperature effects on growth appear to be greatest at the
extremes of the geographic range of the species (37), and
local effects will be species-specific (38). Generally, young-of-
the-year fish appear to grow better in warmer summers and
reach relatively larger sizes, predisposing them to higher
overwinter survival, which determines year-class strength
and population abundance (39); potentially a positive result
of climate change assuming food is not a limiting factor.
Northern lake cisco (Coregonus artedi) populations along the
coast of Hudson Bay exhibited reduced growth and later
maturity due to lower temperatures and shorter growing
seasons (40). Individual fecundity did not change, but the
most northerly populations skipped reproduction more
frequently (hence overall population productivity was
lower). This latitudinal gradient represents responses to
temperature stresses whereby further trade-offs in energy
allocation between reproduction and growth currently are
not possible (40); a common circumstance for most arctic
fish populations and one that will probably be ameliorated
under scenarios of increased temperature, potentially result-
ing in increased population abundances.
Counter-gradient variation (41), whereby genetic influences
on growth in species such as brown trout (Salmo trutta) vary
inversely with mean annual water temperatures (42), suggest
that trout in the coldest rivers are specifically adapted to low
temperatures and short growing seasons. Thus, increased
temperatures are likely to negatively affect growth rates, age/
size structure, and abundances of northern populations.
Uncertainty in projections of future temperature, hydrology,
and precipitation, and their associated consequences for
vegetation and nutrient patterns in arctic aquatic ecosystems,
makes projecting the specific effects of climate change on a fish
species difficult. To date, fisheries literature has documented
three approaches to this problem:
i) the use of regionally specific climate projections that can be
coupled directly to knowledge of the physiological limits of
the species;
ii) the use of empirical relationships relating local climate
(weather) to measurements of species or stock dynamics
(e.g., abundance, size, growth rate, fecundity) and compar-
ison of population success temporally (e.g., from a period of
climatically variable years) or spatially (e.g., locales
representing the extremes of variation in weather conditions
such as latitudinal clines); and,
iii) the use of current distributional data and known or inferred
thermal preferences to shift ecological residency zones into
geographic positions that reflect probable future climate
Ambio Vol. 35, No. 7, November 2006 377ÓRoyal Swedish Academy of Sciences 2006
Physiological Approaches
Temperature is typically regarded as a factor affecting
individual physiological and behavioral processes, but it is also
a key characteristic of the habitat of an organism.
The niche of an animal is defined as the complete range of
environmental variables to which it must be adapted for
survival (43). At the fringes of the distributional range, abiotic
parameters associated with particular niche axes are likely to
exert a greater influence over the physiological responses (e.g.,
growth) of the species to its environment than elsewhere.
Growth rates and population dynamics of fish living at the
limits of their distribution usually differ from those of the same
species living in the optimum temperature range (44). For
example, studies of northern populations of yellow perch have
shown that although heterogeneous thermal environments
allow fish opportunities to compensate for temperature
fluctuations by selecting for preferred temperatures, such
opportunities are limited in the portion of the geographic range
where temperatures do not typically exceed those that define the
optimum scope for growth (37). Accordingly, unless future
temperatures increase above the point where the maximum
scope for growth is realized, northern fish will be limited in their
abilities to select for optimal growth temperatures and,
consequently, are very likely to more strongly reflect the
influence of temperature on growth than southern populations.
This also suggests that analogues derived from lower-latitude
populations will not be accurate guides to the probable impacts
of temperature increases on subarctic and arctic fishes.
Nevertheless, the effects of climate change in the north are
very likely to include faster, temperature-driven growth and
maturation rates, reductions in winter mortality, and expanded
habitat availability for many species (45). However, somatic
gains will possibly be offset by increased maintenance-ration
demands to support temperature-induced increases in metabo-
lism. Ration demands for lacustrine fish are likely to be met as
temperatures increase, since warm-water lakes are generally
more productive than cold-water lakes (45). Basic knowledge of
temperature-growth relationships and temperature-dependent
energy demands is lacking for many key arctic fish species,
particularly those exhibiting primarily riverine life histories,
thus accurate physiologically based projections of climate
change impacts cannot be generally made.
Empirical Approaches
Empirical approaches to projecting the possible effects of
climate change on fish populations can be subdivided into two
groups. The first group examines the integrated responses of a
population measured by yield or production over time. The
second group examines the population characteristics spatially
and uses inherent latitudinal variability to make inferences
about how they will change under climate change scenarios.
Temporal Yield/Production Projections – There are numer-
ous models for projecting freshwater fish production in lakes
(see 46). However, disagreement exists among researchers as to
which lake characteristics most significantly influence produc-
tivity. Comparative studies based on lakes covering a wide
range of geographic areas and trophic status, however, have
suggested that fish production in oligotrophic to hyper-
eutrophic lakes of moderate depth is better correlated with
primary production than the morphoedaphic index (47).
Limitations surrounding such modeling center on the deficien-
cies in fish distribution data and knowledge of the interactive
effects of climate-induced changes in key environmental
variables (30). Together with limited fishery databases of
sufficient length, these limitations in most cases preclude this
approach for projecting productivity changes in arctic popula-
Latitudinal Projections - Organism life-history characteris-
tics often vary with latitude because of predictable changes in
important environmental factors (48, 49, 50). Among the most
important environmental factors which may vary with latitude
is temperature, which is known to influence growth rate in fish
populations (44, 51) and thereby indirectly affect life-history
attributes that determine population dynamics (e.g., longevity,
age-at-maturity, and fecundity). In salmonids, temperature has
been shown to influence movement and migration (18), habitat
occupancy (22), migration timing (52), smolting (53, 54), growth
rate (42, 55), age-at-maturity (49, 54, 56), fecundity (48), and the
proportion of repeat spawners (50). Many studies have
demonstrated latitudinally separated disparate populations of
the same species with distinctive metabolic rates, thermal
tolerances, egg development rates, and spawning temperature
requirements consistent with a compensatory adaptation to
maximize growth rates at a given temperature (57). Animals
living in low-temperature, high-latitude locales would therefore
be expected to compensate by increasing metabolic and growth
rates at a given temperature relative to animals in high-
temperature, low-latitude locales. There are two generalizations
which may be made from studies on latitudinal variation in
growth rates: high-latitude fish populations often attain larger
maximum body size than conspecifics at lower latitudes; and,
although lower temperatures often reduce activity and constrain
individuals to grow more slowly, they compensate by acceler-
ating growth rate or larval development time relative to low-
latitude conspecifics when raised at identical temperatures.
Although adaptation to low temperature probably entails a
form of compensation involving relative growth acceleration of
high-latitude forms at low temperature, the shift in metabolism
increases metabolic costs at higher temperatures, leaving cold-
adapted forms with an energetic disadvantage in the higher-
temperature environments (57) that are likely to result from
climate change. Accordingly, fish populations are likely to be
locally adapted for maximum growth rate and sacrifice
metabolic efficiency at rarely experienced temperatures to
maximize growth efficiency at commonly experienced temper-
atures. This suggests that the possible effects of temperature
increases on northern fish will possibly include decreased
growth efficiency and associated declines in size-dependent
reproductive success. Therefore, particular responses to tem-
perature increases are likely to be population-specific rather
than species-specific, which greatly complicates the ability to
project future situations for particular species over large areas
of the Arctic.
Distributional Approaches
Many attempts to project biological responses to climate change
rely on the climate-envelope approach, whereby present-day
species distributions are mapped with respect to key climate
variables (e.g., temperature, precipitation) and the distributions
shifted in accordance with climate change projections (30). For
example, weight-specific basal metabolism is suggested to
increase as size decreases with no associated increase in energy
storage capacity, resulting in smaller fish being less tolerant of
the starvation conditions typically associated with overwinter-
ing (13). Size-dependent starvation endurance requires that
young-of-the-year fish complete a minimum amount of growth
during their first season of life. Growth opportunity, however, is
increasingly restricted on a south-north gradient and the
constraint has been demonstrated to effectively explain the
northern distributional limit of yellow perch in central and
western North America (Figure 2), European perch (Perca
378 Ambio Vol. 35, No. 7, November 2006ÓRoyal Swedish Academy of Sciences 2006
fluviatilis) in Eurasia, and the smallmouth bass (Micropterus
dolomieui) in central North America. If winter starvation does
form the basis for the geographic distributions of many fishes
(e.g., 11 families and 25 genera of fish within Canadian waters)
(13), climate-induced changes in growing-season length, and
consequent reductions in the period of winter starvation, are
very likely to be associated with significant range extensions of
many species. Species already well established within low-arctic
watersheds are likely to show the greatest potential for range
extensions. Associated changes in species assemblages are likely
to shift patterns of energy flow in many aquatic systems. For
example, increasing the number of cyprinids that consume
plankton (e.g., emerald shiner Notropis atherinoides, lake chub
Couesius plumbeus) in northern waters will possibly divert
energy from existing planktivores (e.g., ciscoes; Coregonus spp.)
and reduce their population abundances. In turn, top predators
(e.g., lake trout) are likely to have altered diets, and changes in
the ratio of pelagic and benthic sources of carbon in piscivore
diets are likely, in turn, to alter tissue mercury concentrations
(58, 59), thus linking general climate change impacts with local
contaminant loadings.
The dominant result of simulations used to project the
impact of climate change on the distribution and thermal
habitat of fish in north temperate lakes is an increase in
available warmer habitat. Temperature influences on thermal
habitat use are strong enough to develop measures of thermal
habitat volume during the summer period by weighting the
amount of lake-bottom area and pelagic volume with water
temperatures within species’ optimal thermal niches (60).
Thermal habitat volume explained variations in total sustained
yield of four commercially important species: lake trout, lake
whitefish, walleye, and northern pike.
Although distributional changes provide a convenient and
easy means of assessing possible range extensions, the flaw in
the approach is that species’ distributions often reflect the
influence of interactions with other species (61) or historical
effects (26). Projections based on changes in single-species
climate envelopes will therefore be misleading if interactions
between species are not considered when projections are made.
Microcosm experiments on simple assemblages showed that
as the spatial distribution of interdependent populations
changed as a result of temperature increases, the pattern and
intensity of dispersal also changed. Thus, climate change will
possibly produce unexpected changes in range and abundance in
situations incorporating dispersal and species interaction (e.g.,
competition and predator-prey dynamics). Feedbacks between
species are likely to be even more complex than simple
experiments allow (61); for example, distributions of stream-
resident salmonids are not simple functions of either temperature
or altitude (62). Accordingly, whenever dispersal and interac-
tions operate in natural populations, climate change is likely to
provoke similar phenomena, and projections based on extrap-
olation of the climate envelope may lead to serious errors (61).
In theory, the temperature signal should be strong enough to
project long-term changes in the availability of fish thermal
habitat and to use available empirical relationships to project
sustainable yields. However, until the results of such research
are available for arctic fishes, interannual variability and
latitudinal differences in climate will provide the best tests for
hypotheses about the importance and effects of climate change
on arctic fish species (63).
Although relatively depauperate in comparison to lower
latitudes, the diversity of arctic freshwater and diadromous
fishes is relatively high including about 99 species, a large
number of which are used in commercial, subsistence and
recreational fisheries throughout the area. Many of these are
also found in areas south of the Arctic. The complexity of
pathways by which climate change will directly and indirectly
influence arctic fishes, coupled with widespread variability in
potential response envelopes reduces our predictive ability. To
this is added a very limited understanding of the interactions of
fish and climate, particularly as this applies within species to
northern populations which may differ from southern counter-
parts. In concert these factors in most cases presently preclude
quantitative estimation of climate change effects on most
northern fish populations. Rather, loose qualitative generaliza-
tions are all that are possible at present, a factor that generally
reduces preparedness to meet challenges and opportunities
associated with climate change in the Arctic. A short review of
the approaches available to redress this gap suggests that studies
relating interannual variation in fish population parameters to
putative environmental drivers and/or those examining latitu-
dinal variation as a proxy measure of potential responses to
climate change will provide the best information about future
climate change effects on arctic freshwater and diadromous
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983 5032, Fax: 204 984 2403.,
Frederick J. Wrona, National Water Research Institute of
Environment Canada, Department of Geography, University of
Victoria, PO Box 1700 STN CSC, Victoria, BC, V8W 2Y2.
Terry D. Prowse, Water and Climate Impacts Research
Centre, National Water Research Institute of Environment
Canada, Department of Geography, University of Victoria, PO
Box 1700 STN CSC, Victoria, BC, V8W 2Y2, Canada.
Michael Power, Department of Biology, University of Waterloo,
200 University Avenue West, Waterloo, ON, N2L 3G1,
J. Brian Dempson, Fisheries and Oceans Canada, 80 East
White Hills Road, PO Box 5667, St. John’s, NL, A1C 5X1,
Richard J. Beamish, Fisheries and Oceans Canada, 3190
Hammond Bay Road, Nanaimo, BC, V9T 6N7, Canada.
Jacquelynne R. King, Fisheries and Oceans Canada, 3190
Hammond Bay Road, Nanaimo, BC, V9T 6N7, Canada.
Theresa J. Carmichael, Fisheries and Oceans Canada, 501
University Crescent, Winnipeg, Manitoba, R3T 2N6, Canada.
Chantelle D. Sawatsky, Fisheries and Oceans Canada, 501
University Crescent, Winnipeg, Manitoba, R3T 2N6, Canada.
380 Ambio Vol. 35, No. 7, November 2006ÓRoyal Swedish Academy of Sciences 2006
... Overall, this study found changes in fish species composition were associated with changes in environmental conditions in Prudhoe Bay and favored species that were more generalist in physiological tolerance. We identified 31 unique species in this study, representing 10% of the approximately 310 fish species known to inhabit the Arctic Ocean (Mecklenburg et al. 2011;Reist et al. 2006). Our study found that species richness increased significantly from 2001 to 2018 around Prudhoe Bay, Alaska, at a rate of approximately one additional species per decade. ...
... In contrast, Humpback Whitefish were negatively associated with water temperature. Although several species were positively associated with water temperature, continued warming could push fish past optimal metabolic conditions or cause species interactions such as increased trophic competition for limited resources (Reist et al. 2006). ...
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Nearshore fish communities comprise a fundamental component of Arctic marine ecosystems and serve as an important subsistence resource. As changing climate conditions affect Arctic waters, nearshore fish communities may also shift; however, how these communities will respond to climate change is not well understood. This study summarizes trends from a long-term (2001–2018) nearshore fish sampling program near Prudhoe Bay, Alaska, in the central Beaufort Sea. Abundance data (n = 1.78 million fish) from daily sampling (July–August) at four fixed sampling locations showed distinct shifts in fish community metrics. Since 2001, annual species richness has significantly increased by approximately one species per decade (p = 0.0167) while water temperature has warmed by approximately 1.4 °C. Results from non-metric multidimensional scaling (nMDS) and Permutational Analysis of Variance (PERMANOVA) models indicated that species composition based on biweekly catch data has significantly changed across years with distinct variations among sample locations and throughout the season. Salinity and water temperature were significantly related to multivariate species composition; specifically, the abundances of five species changed significantly over time. The species that increased in response to observed changes in the aquatic environment appear to be eurythermic and/or euryhaline generalist species such as Broad Whitefish Coregonus nasus and Saffron Cod Eleginus gracilis. Such patterns of altered species compositions demonstrate that continued long-term changes in environmental conditions will likely favor generalist species, potentially causing substantial shifts within the Arctic nearshore ecosystem with impacts on important subsistence resources.
... Marine waters below sea ice consistently plummet to subzero winter temperatures just above the freezing point of saltwater [9] and are too cold for fishes like salmonids that lack antifreeze proteins [10,11]. The lack of aquatic habitat is so severe that liquid water persisting through the winter, "overwinter habitat", is considered an important limitation on the presence and abundance of Arctic amphidromous, anadromous, and freshwater fishes [7,12,13]. The Arctic migration strategies of fish are unique when compared with confamilial species from elsewhere. ...
... To illustrate the information needs, we focus on Dolly Varden in the Canning River, AK (Figure 2), where the foremost questions are related to juvenile habitat use during winter and migration to those areas. Survival at the juvenile stage is an important bottleneck for fish population size and overwinter survival is a key determinant of juvenile survival to the adult stage [12]. Juvenile Dolly Varden occupy the lower Canning River and the extensive delta region during summer and fall, and the area experiences large aufeis (overflow ice from successive groundwater releases) accumulation during winter (Figure 3 E, F). ...
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Amphidromous fish such as Dolly Varden (S alvelinus malma ) and Arctic Cisco ( Coregonus autumnalis ) have distinct life histories that facilitate their success in Arctic environments. Both species spawn in freshwater and make annual migrations between marine, brackish, or freshwater environments. Dolly Varden rear for one or more years in freshwater before migrating to sea whereas Arctic Cisco migrate to sea during their first summer. By contrast, Pacific salmon ( Oncorhynchus spp.) spawn in freshwater, but once they smolt and go to sea they remain there until they mature and return to spawn. Salmon migrate at variable ages depending on species. Arctic marine environments offer productive food resources during summer, but during winter they are too cold for salmonids that lack antifreeze proteins. To avoid the cold sea during winter, Dolly Varden return to freshwater while Arctic Cisco overwinter in brackish estuaries. The lack of migration back to freshwater for overwintering helps explain why Pacific salmon success is limited in Arctic waters and suggests major increases in success will not be realized until Arctic seas provide suitable overwinter conditions. In this paper we contrast these migration strategies, discuss potential changes in a warming Arctic, and highlight information needs especially for juvenile fish.
... At high latitudes, warming rates are two to three times faster than global levels, leading to complex direct and indirect effects on freshwater ecosystems (IPCC, 2021;Meredith et al. 2019;Wrona et al., 2013). Much of the climate change research on northern aquatic biodiversity to-date has focused on anticipated changes in available thermal habitat, and it is expected that there will be a net loss of habitat for Arctic specialists whereas cold and cool water species will gradually expand their northern range limits as new habitats become thermally suitable (Lynch et al., 2016;Poesch et al., 2016;Reist et al., 2006). In addition to warmer lakes, climate change can produce marked changes in water quality including the eutrophication (greening) and brownification (browning) of subarctic lakes (Hayden et al., 2019), mirroring what has been observed for thousands of lakes at lower latitudes (Leech et al., 2018;Mahdiyan et al., 2020). ...
... Together, these results highlight the potential vulnerability of freshwater fish diversity within the rapidly changing lower Mackenzie River landscape as lakes may become increasingly degraded with additional warming, permafrost loss, and human development. Our finding that water quality effects may be driving northern fish diversity has important implications for guiding future research at the global scale, as much of the work on climate change to-date has focused on thermal habitat limitations alone rather than incorporating a more comprehensive view of possible outcomes (e.g., Reist et al. 2006;Lynch et al. 2016;Poesch et al. 2016). ...
• Rapid environmental change occurring in northern permafrost regions may have profound implications for fish biodiversity but remains poorly understood. Climate change, increasing human development, and resultant permafrost thaw may combine to alter the quality and quantity of fish habitat including reductions in preferred thermal habitat, changes in water quality, and modified drainage patterns. • Our study objective was to understand how lake fish communities residing on permafrost landscapes may be responding to climate change and land use disturbance. We investigated the drivers of freshwater fish community health in lakes of the lower Mackenzie River basin, an ice-rich permafrost region that is experiencing substantial warming, permafrost thaw, and new major highway development. We collected lake morphometry, water quality, and fish community data from 50 lakes and derived several indicators of aquatic health including fish species richness, relative abundance, and the occurrence of three culturally important fish species. • We found that water quality and lake size were significant co-drivers of fish community health whereas relationships with summer thermal habitat, as represented by July air temperature, were relatively negligible. Dissolved organic carbon (an indicator for lake browning) emerged as a particularly important driver of fish community structure, and fish community health steeply declined when dissolved organic carbon concentrations exceeded 17–18 mg/L. We suggest potential mechanisms for these declines including light inhibition during summer and a reduced capacity for overwintering in smaller and murkier lakes that may experience faster oxygen depletion rates. • Using a more expansive regional water quality database of 203 lakes, we observed potential supporting evidence that warming and new road development increased dissolved organic carbon and total phosphorus concentrations, possibly reducing fish habitat quality in this region. • Together, these results highlight how fishes relying on the numerous small and shallow lakes that dominate permafrost landscapes may be vulnerable to the combined effects of rapid warming and new infrastructure.
... Climate change will exacerbate issues of habitat alteration and potentially leave fish in thermally unsuitable habitats (Pandit et al. 2017). In particular, water temperature is a defining habitat characteristic for aquatic organisms and can affect the physiology and behavior of individuals (Reist et al. 2006a). Stream fish use both thermal and hydrologic regimes as behavioral cues to trigger critical life history functions (Cassie 2006;Schlosser 1985;Taylor and Cooke 2012). ...
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Northern aquatic ecosystems face increasing pressures from climate change and natural resource development. The Arctic grayling (Thymallus arcticus) is a widely distributed, northern freshwater fish which can be vulnerable to such pressures. There remains a paucity of information on life stage requirements through most of the species’ range to reliably map and manage habitat to protect populations into the future. We sought to characterize fluvial Arctic grayling distribution among mountain streams and determine habitat characteristics and habitat use across life stages. Sampling was conducted at 183 sites across the Little Nahanni River watershed to collect information on fish distribution and reach-scale habitat parameters. Arctic graylings were collected for biological analyses of age, size, weight, and reproductive development. Based on age and size classes, there were four distinct post-emergence life stages: YOY, juvenile, sub-adult, and adult. YOY Arctic graylings were found exclusively in low elevation (< 1000 m) streams, flat-water habitat dominated by silty-sand substrate with average water temperatures > 10 °C. Similarly, juvenile Arctic graylings occupied low elevation, warm water stream habitat, but associated strongly with run habitats. Sub-adult Arctic graylings, the most widely distributed life stage, were found associated with riffle, pool, and cascade-boulder habitats. Adults occupied high-elevation (> 1200 m) habitats that were cold (mean stream temperature = 7 °C) and had higher proportions of pool and boulder habitats. The dynamic nature of Arctic grayling habitat use in mountain streams highlights the need to consider habitat complexes at the watershed scale when defining species life stage requirements, managing habitats, monitoring populations, and assessing potential impacts.
... Dans un exemple ult erieur, il a et e d emontr e que le r echauffement des cours d'eau d ependant de l'altitude a un effet mineur sur la quantit e de perte d'habitat thermique par rapport a l'augmentation moyenne de la temp erature de l'eau dans un r eseau de rivi eres de montagne. Nous concluons que les pr evisions des effets du Introduction Global climate change is warming Earth's rivers and streams (Arora, Tockner, and Venohr 2016;Chen et al. 2016;Isaak et al. 2018a;Michel et al. 2020) and poses risks to cold-water species, fisheries, and biodiversity that society values (Reist et al. 2006;Heino et al. 2009;Myers et al. 2017; Barbarossa et al. 2021). In mountainous regions, headwater areas have emerged as important climate refugia for many native aquatic species because of their perennially cold environments and slow rates at which isotherms shift upstream to affect the distribution of thermal habitats (Loarie et al. 2009;Isaak et al. 2016). ...
Full-text available
Climate change is warming stream temperatures with significant implications for species that require cold temperatures to persist. These species often rely on headwater habitats in mountainous regions where elevation gradients in hydroclimatic conditions may induce differential patterns of long-term warming that affect the resistance of refugia. Forecasts from mechanistic and statistical stream temperature models diverge regarding whether this elevation dependence will cause above- or below-average warming in headwaters during warm summer periods, so we examined monitoring records for stream temperature (n = 271), air temperature (n = 690), and stream discharge (n = 131) across broad elevation gradients in a mountainous region of western North America to better understand potential future trends. Over a 40-year period characterized by rapid climate change from 1976–2015, air temperature stations exhibited below-average warming rates at high elevations while stream discharge declined at above average rates. Between climatically extreme years that involved summer air temperature increases >5 °C and discharge declines >70%, temperatures in high-elevation streams exhibited below average increases but otherwise showed negligible elevation dependence during intermediate climate years. In a subsequent example, it was demonstrated that elevation dependent stream warming has a minor effect on the amount of thermal habitat loss relative to the average water temperature increase within a mountain river network. We conclude that predictions of above average warming effects on headwater organisms for this region may be overly pessimistic and discuss reasons why different types of temperature models make divergent forecasts. Several research areas warrant greater attention, including descriptions of elevation-dependent patterns in other regions for comparative purposes, examination of long-term stream temperature records to understand how sensitivity to climate forcing may be evolving, use of new data sources to better represent key processes in temperature models across broad areas, and development of hybrid models that integrate the best attributes of mechanistic and statistical approaches.
... Steigende Temperaturen beschleunigen bei ausreichender Ressourcenverfügbarkeit im Allgemeinen das Wachstum und die Entwicklung einzelner Organismen, obwohl Änderungen der absoluten Abundanzen tendenziell artspezifisch sind (Adrian et al. 2006, Reist et al. 2006, Blenckner et al. 2007 ). ...
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Gewässer und deren Management stehen im Hinblick auf den prognostizierten Klimawandel vor großen Herausforderungen. Intensiver werdende Extremereignisse, wie Hochwasser, Starkregen oder lang anhaltende Trockenphasen mit hohen Temperaturen werden zukünftig verstärkt das sensible ökologische Gleichgewicht der Oberflächengewässer mit deren Flora und Fauna beeinträchtigen. Für eine Aufrechterhaltung der Lebensgrundlage "Wasser" und "biologischen Vielfalt" in Fließgewässern und Seen werden wirksame Anpassungsmaßnahmen benötigt. Demnach stehen sämtliche Akteure der Wasserwirtschaft vor der Herausforderung, die komplexen Wirkungszusammenhänge der vom Menschen beeinflussten Ökosysteme besser zu verstehen und gezielt die Anpassungsfähigkeit aquatischer Ökosysteme zu verbessern. Auf Seiten der Fachinstrumente ist auf EU-Ebene für die Wasserrahmenrichtlinie (EG-WRRL) zu hinterfragen, inwieweit sich deren Methoden und Bewertungssysteme unter sich ändernden klimatischen Randbedingungen als nutzbar erweisen. Zur Untersuchung der Auswirkungen der prognostizierbaren klimatischen Entwicklungen auf die ökologische Beschaffenheit von Oberflächengewässern wurden im Forschungsvorhaben anhand einer umfassenden Literaturrecherche und ergänzenden Expert*inneninterviews zunächst der derzeitige Wissensstandes und bestehende Wissenslücken ermittelt. Anschließend wurde die EG-WRRL als Handlungsinstrument auf ihre künftige Anwendbarkeit überprüft und Vorschläge hinsichtlich einer Anpassung des Methoden- und Bewertungssystems der EG-WRRL abgeleitet. Für die analysierten Wirkungszusammenhänge wurden zudem Verfahrensschritte und derzeitige Umsetzungsgrenzen eines Modellierungskonzeptes beschrieben. Weiterhin erfolgt eine Zuarbeit zur Ermittlung des Indikators "Wasserstress" gemäß der Ziele für nachhaltige Entwicklung der Vereinten Nationen für die Bundesrepublik Deutschland. Im Fokus standen hier die methodischen Ansätze zur Untersuchung des sogenannten "ökologischen Mindestwasserbedarfs" bzw. „Gesamtumweltwasserbedarfs“ für Deutschland. Sämtliche (Zwischen-)Ergebnisse wurden ausgewählten Expert*innen im Rahmen eines Fachworkshops vorgestellt und diskutiert. Die somit identifizierten Kernaussagen und Erfordernisse wurden in Handlungsempfehlungen zusammengefasst und werden über den vorliegenden Bericht Akteuren der Forschung, Verwaltungs- und Fachbehörden, sowie der Planungspraxis bereitgestellt.
... Temperature is also an important determinant of the phenology of bull trout life history events, such as hatching and emergence timing, as well as growth rates that may reflect either local phenotypic adjustments, or adaptations to unique thermal regimes that act to maximize individual fitness (Sparks et al. 2017;Austin et al. 2019;Campbell et al. 2019). Moreover, the timing of phenological events varies across the species' range because both climate and the length of development and growing seasons differ across latitude-i.e., winter begins earlier and is longer in the north than it is in the south (Reist et al. 2006b;Shuter et al. 2012). Once eggs are deposited in the gravel, the rate and magnitude of thermal units that accumulate throughout the incubation and initial growth period determine when hatching occurs and juveniles emerge-i.e., where the yolk sac is absorbed and juveniles can swim on their own (Neuheimer and Taggart 2007; Fuiman and Werner 2009). ...
Full-text available
Maintaining natural thermal regimes in montane stream networks is critical for many species, but as climate warms, thermal regimes will undoubtedly change. Mitigating impacts of changing thermal regimes on freshwater biodiversity requires knowledge of which elements of the thermal regime are limiting factors for aquatic biota. We used full-year stream temperature records sampled across a broad latitudinal gradient to describe the diversity of the thermal landscapes that bull trout (Salvelinus confluentus) occupy and identify potential divergences from thermal regimes where this species has been studied previously. Populations of bull trout occupied stenothermic, cold thermal niches in streams that exhibited low to moderate thermal sensitivity throughout the species' range. However, winter thermal regimes in the central and northernmost streams were colder and more stable than in the southernmost streams, reflecting differences in sensitivity to air temperature variation and contributions of perennial groundwater to baseflow. In the southernmost streams, bull trout distributions appeared to be regulated by warm summer temperatures, whereas in northern streams, unsuitably cold temperatures may be more limiting. Our results also suggest that local differences in the extent of complete freezing during winter among northern streams may further limit the distributions of suitable habitats. Contrasts in limiting factors at bull trout range extents would suggest differential responses to climate warming wherein northern populations extend their range while southern populations contract, and an overall change in species status that is less dire than previously anticipated.
... Artificial dams are the only major barriers to fish movement in the Mackenzie and Yukon drainage basins. Fish communities at high latitudes are changing as some species extend their range northward (McLeod and O'Neil 1983), although the complexities of interactions among multiple factors make the net effect of climate change on fish communities difficult to predict (Reist et al. 2006). ...
Large rivers of the North American arctic and subarctic remain among the least‐altered large rivers in the world, and thus provide opportunities that no longer exist within temperate latitudes to investigate and understand large‐river process and form in the absence of human manipulations. The Mackenzie and Yukon Rivers are the largest arctic/subarctic rivers in North America. Although the large arctic and subarctic rivers of North America have historically experienced much less alteration by humans than the large arctic and subarctic rivers of Eurasia, there have been anthropogenic impacts on the Yukon and Mackenzie drainage basins. The Yukon and the Mackenzie share distinctive physical traits related to the presence of permanently frozen ground and seasonal freezing of the river surface. Their differences reflect the geological structure and glacial history of each river basin.
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While the sentinel nature of freshwater systems is now well-recognized, widespread integration of freshwater processes and patterns into our understanding of broader climate-driven Arctic terrestrial ecosystem change has been slow. We review the current understanding across Arctic freshwater systems of key sentinel responses to climate, which are attributes of these systems with demonstrated and sensitive responses to climate forcing. These include ice regimes, temperature and thermal structure, river baseflow, lake area and water level, permafrost-derived dissolved ions and nutrients, carbon mobilization (dissolved organic carbon, greenhouse gases, and radiocarbon), dissolved oxygen concentrations, lake trophic state, various aquatic organisms and their traits, and invasive species. For each sentinel, our objectives are to clarify linkages to climate, describe key insights already gained, and provide suggestions for future research based on current knowledge gaps. We suggest that tracking key responses in Arctic freshwater systems will expand understanding of the breadth and depth of climate-driven Arctic ecosystem changes, provide early indicators of looming, broader changes across the landscape, and improve protection of freshwater biodiversity and resources.
Freshwater fish are one of the most diverse groups of vertebrates, but are also amongst the most threatened. With contributions from leaders in the field, this is the first assessment of the global state of freshwater fish diversity, synthesising the opportunities, challenges and barriers facing the conservation of freshwater fish biodiversity. The book includes the first global assessment of the number, type and distribution of threatened freshwater fish species, discussing the features of freshwater fish biology and ecology that render so many species vulnerable to extinction. Introductory chapters on why freshwater fish are so sensitive to environmental change and disturbance lead into chapters providing detailed reviews of the key threatening processes and potential solutions. A concluding chapter summarises the key issues and looks to the future for opportunities and challenges for the conservation and management of freshwater fish.
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We examined the influence of river discharge and temperature on growth of adult and age-0 Arctic grayling Thymallus arcticus in the Kuparuk River (1985-1996) and Oksrukuyik Creek (1990-1996) during the Arctic growing season (late June to mid-August). Grayling growth was compared against six physical variables (river, nutrient level, mean summer discharge, mean summer temperature, consecutive days with extreme low flow, and total days with extreme high flow) using stepwise regression analysis. Fifty-six percent of the variance in adult grayling growth rate in both rivers was associated with nutrient level and mean summer discharge. Sixty percent of the variance in age-0 grayling weight at 40 d was associated with nutrient level, mean summer discharge, mean summer temperature, and river. The correlation with discharge was positive for adult grayling growth but negative for age-0 grayling weight. This study suggests that river discharge and water temperature may influence long-term survival and population dynamics of grayling in Arctic tundra streams.
A coupled hydrodynamic and water quality model was used to examine the response of dissolved oxygen concentrations to warming of the central basin of Lake Erie. An area-averaged hydrodynamic model was used to estimate the lake temperatures and thermocline variability as forced by surface heating and winds. Vertical turbulence mixing processes were incorporated by a second-moment, turbulence closure submodel. The water quality model comprised a set of 15 mass balance equations that predicted distributions of phytoplankton biomass, nutrient concentration, and dissolved oxygen. A synthesis of the results from the coupled model forced by climate warming scenarios from three atmospheric general circulation models suggested that there will be a substantial decline in oxygen concentrations in the central basin. Although forecasts of future conditions that are beyond established experiences are uncertain, it appears likely that climate warming will lead to such a decline regardless of details in changes of lake stratification dynamics. Losses of 1 mg/L of dissolved oxygen in the upper layers and of 1-2 mg/L in the lower layers of Lake Erie’s central basin can be expected, along with an increase in the area of the lake that is anoxic. The decline in dissolved oxygen is predicted to be due to warmer lake temperatures, which increase the rate of bacterial activity in the hypolimnion waters and sediment, rather than to thermocline location and volume of water below the thermocline.
How a water body's temperature characteristics constrain organisms ecologically has been a continuing focus of interest in limnology and aquatic ecology for over a century now. A number of complementary scientific approaches are reviewed briefly. Progress in assessment of climate change is hampered by the still fragmentary and scattered scientific literature. A number of tentative generalizations are sketched. We expect that climate change of a type consistent with currently available scenarios will have severe consequences for Great Lakes fish and fisheries: in rivers that flow south, east or west and which contain isolated endemic species at the northerly edge of their ranges and which have no opportunity to migrate northwards; and where effects on the aquatic ecosystem of climate change interact synergistically and harmfully, as seems likely, with bad effects of other cultural stresses such as damming and nutrient loading.
Revelle and Suess (1957) pointed out that human enterprise throughout our planet could yield “far-reaching insight into the processes determining weather and climate.” Today, scientists worldwide continue to search intensively for this insight into global weather and climate as the rate of emission of radiatively significant trace gases continues to increase. Much has been learned about the processes that determine weather and climate, but substantial uncertainty remains as predictions are made relative to future global warming and climate change.
Competition is an interaction between individuals in which one or more of the participants suffers a net loss of fitness and none show a net gain compared with values in the absence of the competitive interaction. In terms of Table 8.1, competition is defined as - 0 or - -. The competition is asymmetrical if the loss in fitness suffered by some participants is much greater than that suffered by others. Mutualism is classified as + 0 or + + in Table 8.1. Some or all of the participants in the interaction show a net gain in fitness and none shows a net loss.