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Journal of Environmental Management 91 (2010) 2771e2780
Contents lists available at ScienceDirect
Journal of Environmental Management
journal homepage: www.elsevier.com/locate/jenvman
Vulnerability of Fraser River sockeye salmon to climate change: A life cycle
perspective using expert judgments
Tim McDaniels a, *, Sarah Wilmot b, Michael Healey c,1, Scott Hinch d, 2
a
Institute for Resources, Environment and Sustainability at the University of British Columbia, Lasserre Building, 433 e 6333 Memorial Road, Vancouver, BC Canada V6T 1Z4
School of Community & Regional Planning at the University of British Columbia, 433-6333 Memorial Road, Vancouver, BC Canada V6T 1Z2
c
Institute for Resources, Environment and Sustainability at the University of British Columbia, Aquatic Ecosystem Research Laboratory, 432 e 2202 Main Mall,
Vancouver, BC Canada V6T 1Z4
d
Institute for Resources, Environment and Sustainability, University of British Columbia, 1933 West Mall Vancouver, BC Canada V6T 1Z4
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 June 2009
Received in revised form
12 July 2010
Accepted 7 August 2010
Fraser River sockeye salmon have been the basis for a major commercial fishery shared by Canada and
the United States, and an important cultural foundation for many aboriginal groups; they are also of huge
ecological significance throughout the Fraser Basin. The potential for altered aquatic habitat and
temperature regimes due to climate change is an important concern for Fraser River sockeye salmon. This
paper characterizes the vulnerability of Fraser River sockeye salmon to future climate change using an
approach that is novel on three counts. First, previous efforts to assess the vulnerability of salmon to
climate change have largely focused on only part of the life cycle, whereas we consider climate
vulnerability at all stages in the life cycle. Second, we use the available scientific literature to provide
a basis for structuring and eliciting judgments from fisheries science and management experts who
research and manage these systems. Third, we consider prospects for mitigating the effects of climate
change on sockeye salmon. Tests showed that participants’ judgments differentiated in statistically
significant ways among questions that varied in terms of life stages, spawning regions and climate
scenarios. The consensus among participants was that Fraser River sockeye are most vulnerable to
climate change during the egg and returning adult stages of the life cycle. A high temperature scenario
was seen as imposing the greatest risk on sockeye stocks, particularly those that migrate to the upper
reaches of the Fraser River system and spawn earlier in the summer. The inability to alter water
temperature and the highly constrained nature of sockeye management, with competing gear types and
sequential fisheries over a long distance, suggest the potential to mitigate adverse effects is limited.
Fraser River sockeye already demonstrate a great deal of adaptive capacity in utilizing heterogeneous
habitats in different river sub-basins. This adaptability points to the potential value of policies to make
stocks more resilient to uncertain futures.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Climate change
Sockeye salmon
Characterizing vulnerability
Life cycle stages
Participant judgments
1. Introduction
The Fraser River has been described as the most important
salmonine-producing river system in North America (Northcote
and Larkin, 1989). Sockeye salmon (Oncorhynchus nerka) are the
second most abundant salmon species in the Fraser River, after pink
salmon (O. gorbusha), which have a much lower economic value.
* Corresponding author. Tel.: þ1 604 822 9288; fax: þ1 604 822 3787.
E-mail addresses: timmcd@interchange.ubc.ca (T. McDaniels), healey@
interchange.ubc.ca (M. Healey), shinch@interchange.ubc.ca (S. Hinch).
1
Tel.: þ1 604-822-4705; fax: þ1 604-822-9250.
2
Tel.: þ1 604-822-9377; fax: þ1 604-822-9102.
0301-4797/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jenvman.2010.08.004
The fishery for Fraser River sockeye salmon has been the most
economically valuable commercial salmon fishery in Canada,
shared with fishers from the United States under the Pacific Salmon
Treaty (Williams, 2007). Aboriginal communities depend on the
sockeye runs to provide salmon for food and ceremonial purposes
(Jones et al., 2004). Sockeye salmon migrate to spawning beds
distributed from near the river mouth to more than 1000 km
upstream in important tributaries in the Fraser system (Northcote
and Larkin, 1989), providing protein and nutrients through much
of the 230,000 km2 of the Fraser basin (Finney et al., 2000; Helfield
and Naiman, 2001; Johnston et al., 2004).
In recent years, production of Fraser sockeye has declined
precipitously and it was recently classified as ‘endangered’ by the
IUCN in the first ever global endangerment assessment on
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T. McDaniels et al. / Journal of Environmental Management 91 (2010) 2771e2780
a salmonid (IUCN-SSG, 2009). There are many hypotheses for the
causes of this decline, including freshwater and ocean habitat
changes, over-fishing, diseases, and other factors, all of which were
recently evaluated by a ‘think tank of sockeye experts’ (STTS, 2009).
In 2010, the issue is being evaluated by a federal judicial inquiry
(the ‘Cohen Inquiry’). Global climate change is likely playing a large
role in this decline. Various authors have examined the potential
impact of global climate change on particular life stages of sockeye
salmon, with many of the analyses done on Fraser sockeye stocks
(e.g., Henderson et al., 1992; Hinch et al., 1995a, 1995b; Swansburg
et al., 2002; Rand et al., 2006; Farrell et al., 2008; Hague et al., in
press; Martins et al., in press), as well as on overall production
rates (e.g., Klyashtorin, 1998; Levin, 2003), and concluded that
Fraser sockeye salmon would experience declining production
based on recent changes in climate, and production would continue
to decline as climates continue to change.
The objective of this paper is to characterize the vulnerability of
Fraser River sockeye salmon to future climate change. Its approach
is novel on three counts. First, previous efforts to consider vulnerability of sockeye salmon to climate change have generally only
focused on part of the life cycle (e.g., Hinch et al., 1995b; Henderson
et al., 1992; Rand et al., 2006), although numerous studies have
considered Chinook, Atlantic salmon, and steelhead (e.g., Crozier
et al., 2008; Mangel, 1994). Pacific salmon are anadromous, occupying various fresh water and marine environments at different life
stages. Hence, over their life cycle, sockeye salmon integrate the
effects of climate change on fresh water and marine ecosystems,
and the consequences for one generation can carry forward to
influence reproductive success, abundance and ecological fitness in
subsequent generations. To date, no study has examined the way
changes at one life stage propagate through the life cycle to affect
other stages or accumulate across generations (Healey, submitted
for publication). Here we consider the effects of climate change
on the vulnerability of sockeye salmon to changing habitat at all life
stages. Second, while expert judgments are used extensively in risk
and decision analysis, often in the form of elicited probabilities of
specific events, the approach adapted here is novel in considering
vulnerability over life cycle stages, climate scenarios and regions of
the Fraser River system. Third, we also consider prospects for
mitigating the effects of climate change on sockeye salmon.
2. Scientific understanding regarding climate
change and Fraser sockeye
2.1. Sockeye salmon abundance cycles and recent changes
Fraser River sockeye populations are characterized by a 4-year
cycle of abundance with one or two years in four having much
greater abundance than others (Burgner, 1991). The causes of this
cycle remain unknown (Ricker, 1997). Fraser sockeye also fluctuate
in abundance in relation to decades-long cycles in ocean environmental conditions (Mantua et al., 1997 discusses this pattern for
Pacific salmon in general). Presumably in response to one of these
oceanic regime changes, Fraser River sockeye began increasing in
abundance dramatically at the end of the 1970s, reaching historic
high abundance in the mid 1990s. After 1995, abundance in terms
of annual harvest surplus began to decline, in coincidence with
changes in ocean conditions (M. Lapointe, pers. comm.).
Pacific salmon populations, living near the southern extent of
their range in the Columbia River and Fraser River, have all experienced significant increases in summer freshwater temperatures
since the 1950s (Patterson et al., 2007; Crozier et al., 2008) and such
increases during spawning migrations have been identified as
a major threat to the future viability of salmon populations in both
the Columbia and Fraser River systems (Rand et al., 2006; Farrell
et al., 2008). Indeed, several studies have quantified a negative
relationship between episodes of unusually warm river temperatures and salmon health and mortality (Naughton et al., 2005;
Young et al., 2006; Patterson et al., 2007; Crossin et al., 2008;
Mathes et al., 2010).
Most of the 150 stocks (i.e. populations) in the Fraser River
initiate adult river migrations between July and October, encountering a range of temperatures. The 40-year average daily temperature is lowest in July and October (w15 C), and highest in August
(w19 C; Patterson et al., 2007). The Fraser River has experienced
an average increase in peak summer water temperature of >1.5 C
over the past 40 years. Eight of the past 10 summers (as of 2009)
have been the warmest on record (Morrison et al., 2002). Thus, all
stocks now encounter warmer river temperatures than they once
did, and, one group of stocks, the Late-runs, which includes the
world-famous Adams run, encounter temperatures 3e6 C warmer
than historic. This has occurred because, since 1994, Late-runs have
begun entering the Fraser River 2e6 weeks earlier than normal
(Cooke et al., 2004). While the causes of this phenomenon are not
clear, evidence suggests that changes in ocean environments and
endogenous migratory cues are responsible (Hinch and Gardner,
2009).
Early migrating Late-run adult sockeye experience 50e95%
mortality prior to spawning (Cooke et al., 2004; Hinch and Gardner,
2009) and the causes of mortality have been shown to be related to
the higher migratory temperatures encountered (Crossin et al.,
2008; Mathes et al., 2010). Other Fraser runs of sockeye are also
perishing at relatively high levels when river temperatures are
relatively warm (Martins et al., in press). Because Late-runs have
changed their river entry timing, and because the Fraser River
is much warmer in summer now than in the past, segments
of all Fraser River sockeye stocks now encounter river
temperatures >19 C during a portion of upstream migration. This
change has profound evolutionary significance because no sockeye
stock anywhere in the world is known to have initiated river
migration at 20 C (Hodgson and Quinn, 2002). River temperature
is therefore an important factor in the search for causes of the
current declines in stock abundance (Crossin et al., 2008).
2.2. Sockeye salmon life cycle
Sockeye salmon are anadromous and semelparous. Young spend
one to several years in freshwater before migrating to sea where
they grow to adult size and return to their natal stream to spawn
(Burgner, 1991). For the purposes of this paper, we distinguish
among eight stages in the sockeye life cycle. The rationale for eight
stages rather than the more traditional five is to address migrational
life stages (Hinch et al., 2006). Different stages require different
habitat, as shown in Table 1. Details on life-stage specific movements and migrations for sockeye salmon can be found in Hinch
et al. (2006).
Table 1
Life cycle stages of Sockeye salmon.
Life cycle stage
Habitat
Egg
Fry e emergence to
lake entry
Fry e lake entry to
first winter
Fry e first winter
Fry e smolt
Post smolts
Immatures
Returning adults
Fresh water (lakes and rivers)
Fresh water (lakes and rivers)
Fresh water (lakes and rivers)
Fresh water (lakes and rivers)
Fresh water, moving towards ocean
Estuary and coastal ocean
Ocean
Ocean, coastal, estuary, and fresh
water rivers and lakes
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T. McDaniels et al. / Journal of Environmental Management 91 (2010) 2771e2780
For this study we grouped Fraser River sockeye stocks into three
broad categories based on the location of their spawning grounds
along the Fraser River: upper (northern), middle, and lower
(southern). These three groups of stocks generally return to the
river at different times, have different cycles of abundance, and
occupy different habitats during the fresh water life cycle stages
shown in Table 1. Our classification scheme creates some
unavoidable overlap among groups in some of these variables.
2.3. Environmental changes caused by climate change
that may affect Fraser River sockeye
Global climate change is expected to result in higher average
temperatures and altered precipitation patterns in the Fraser River
basin, which will alter the habitat for sockeye salmon throughout
their life cycle stages. The Pacific Climate Impacts Consortium
provides access to a range of climate change scenarios for the Fraser
Basin, drawing on various global circulation models (GCMs) and
future greenhouse gas emission scenarios. There is a high level of
uncertainty within and among the scenarios and models, although
all indicate warmer air temperatures and changes in precipitation
patterns. Over all scenarios of emissions and economic activities,
and over all models, estimates of average annual increase in air
temperature for the Fraser Basin by 2070 range from about 2.5 C to
about 5.5 C compared to the average for 1980 to 1999 (PCIC, 2008).
Hydrological models for the Fraser River predict earlier peak
summer water temperatures with a 2e4 C average warming of the
Fraser River over the next few decades, relative to temperatures
experienced in the 1990s (Morrison et al., 2002; Rand et al., 2006;
Ferrari et al., 2007; Hague et al., in press).
Detailed analyses have been conducted to assess likely changes
in Fraser River flow and temperature patterns. Morrison et al.
(2002), using historic data from the past 50 years, found that
summer temperatures have been increasing and peak flows
decreasing. Based on GCM predictions, these trends are expected to
continue. Specifically, for the period 2070e2099, the flow model
predicted a modest 5% (150 m3/s) average flow increase but
a decrease in the average peak flow of about 18% (1600 m3/s). These
peaks would occur, on average, 24 days earlier in the year, even
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though for 13% of the years, the peak flow would occur much later
as a result of summer or fall rain, instead of the currently normal
spring freshet. In the same period, the summer mean water
temperature is predicted to increase by 1.9 C.
As a result of these changes in flow, freshwater spawning and
rearing areas are expected to change. Using output from GCMs in
conjunction with empirical time-series analyses of hydrologic data,
Moore (1991) and Levy (1992) argued that within the next 80e100
years, the streams, lakes and groundwater in the Fraser Basin will
warm by 1e4 C; there will be an increase in stream velocities in
winter and spring though a decrease in summer and fall precipitation, and earlier spring freshets. Altered runoff patterns are
predicted to make the Fraser River drainage more oligotrophic,
resulting in a reduction in the abundance and availability of food for
juvenile sockeye, which are reared in lakes (Henderson et al., 1992).
Key environmental features in the North Pacific Ocean are also
expected to change. Simulation results from GCMs, coupled with
a simplified mixed-layer ocean model, predict that within the next
80e100 years sea surface temperatures will warm 2e4 C, and
north-south air pressure gradients will weaken, leading to reductions in surface winds and wind-driven upwelling, as well as
a 5e9% decrease in zooplankton biomass food production for ocean
sockeye (Hinch et al., 1995b).
The broad potential impacts of climate change on sockeye
habitat in the Fraser Basin are summarized in Table 2.
3. Method
3.1. Role of judgments from scientific and management specialists
Any method for assessing and managing risks will necessarily
rely on the informed judgments of technical specialists and scientists to some extent. Methods have been developed and applied to
characterize judgments about uncertainties in the form of probabilities for specific well-defined events (Keeney and von
Winterfeldt, 1986, 1989; Morgan and Henrion, 1990). Probability
elicitation has been employed in various climate change contexts,
including, for example, changes in ocean circulation patterns
(Zickfeld et al., 2007). However, these methods are time intensive,
Table 2
Broad potential impacts of climate change on fraser basin sockeye habitat.
Habitat
Spawning streams during
spawning and incubation
Nursery lakes
Coastal marine habitats
Gulf of Alaska
Sources: See details and references in Healey (2010).
Impact of climate change
Spawning streams will be warmer during the normal late
summer/autumn spawning time and through the incubation period.
Spring freshet will be earlier and may be of shorter duration
due to the decrease in snow pack.
Discharge may be somewhat lower in later summer/autumn but
may remain higher over the winter if more winter precipitation falls as rain.
Coastal spawning streams will be warmer and may be subject to stronger
winter freshet if winter storms intensify.
Temperatures in summer will be higher, particularly in smaller streams,
which may cause stress for stream resident species like coho (Oncorhynchus kisutch)
and Chinook (Oncorhynchus tschawytscha) but may be less important for migratory
species such as sockeye.
Interior lakes will lose ice cover earlier in the year (or may not be ice covered at all),
may stratify thermally earlier and remain stratified longer and will have higher summer
epilimnion temperatures.
Coastal nursery lakes may also stratify longer and have higher summer temperatures.
Coastal waters of British Columbia will be warmer and productivity will probably be higher.
Spring plankton blooms will probably occur earlier.
Along the coast of Alaska, where downwelling conditions occur, there may be nutrient limitation
due to reduced upwelling in the central Gulf of Alaska.
Surface temperatures will be warmer and gyre circulation may be slower due to
weakening of the Aleutian low.
Upwelling may be reduced and production lower.
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require extensive commitment from those who provide the judgments, and typically only focus on one variable at a time. Other
approaches to eliciting judgments include seeking consensus
among a nominated group through iterative responses to specific
questions (e.g., the Delphi method) (Linstone and Turoff, 1975), or
consensus reports derived through negotiation and review, such as
the Intergovernmental Panel on Climate Change (IPCC, 2007). In the
present study the concern is with interactions over a wide range of
variables (eight different life stages, three regions, and two climate
regimes). Hence, a judgment-based approach was used to characterize vulnerability to climate change, but not in probabilistic
terms. Unlike some of the approaches noted above, we also saw no
reason to force a consensus in the judgment process, through
iteration or negotiation, because previous studies have shown that
consensus approaches narrow the range of differences among
expert views (Morgan and Henrion, 1990). Hence, we sought an
approach that could be implemented in a group context, allowing
for individual expression of views, followed by interpretation over
the opinions of recognized experts on Fraser River sockeye salmon
and climate change.
3.2. Characterizing scientific knowledge
Three approaches were used in this research to structure
scientific knowledge and thus provide the basis for the judgmental
assessment of vulnerability. First, interviews were conducted with
scientific specialists, including two of the authors of this paper
(Authors’ names deleted), to confirm that considering sockeye
salmon vulnerability to climate change throughout their whole life
cycle is sensible and relevant as a basis for structuring vulnerability
judgments, and that managers and scientists would want to
consider the vulnerability of specific geographic groups of Fraser
River sockeye stocks. Second, an extensive background paper was
prepared summarizing available scientific information regarding
the effects of climate change on sockeye (Author’s name deleted).
The information was structured in terms of a conceptual model that
considers how changes to sockeye due to climate change at one life
stage may propagate through the life cycle to affect other stages or
accumulate across generations. The paper also included a series of
influence diagrams (Howard, 1989; Clemen and Reilly, 2000)
illustrating possible linkages among variables that could influence
the possible effects of climate change on each life cycle stage (Fig. 1
provides one example). The figures are not deterministic, nor do
they imply the linkages necessarily hold. They are representations
of beliefs in the form of a model on paper. The third step was the
creation and testing of a survey instrument that was meaningful for
the participants, and workable in terms of the tasks required. This
survey instrument is described below.
3.3. Participants
Selecting participants for an expert elicitation is not a matter of
random sampling within a sampling frame. Rather it is a process of
recruiting the most knowledgeable people about the technical
issues at hand, while recognizing the range of thinking about these
issues. We had a two-stage process to select participants. First, the
fisheries specialists on the study team nominated individuals
recognized as highly knowledgeable about sockeye salmon and
climate issues. Second, some of those individuals nominated other
participants. A one-day workshop was held in December 2006 to
obtain judgments regarding sockeye vulnerability. Participants
included academic scientists, federal and provincial government
staff members, and non-government organization staff members
knowledgeable about Fraser River sockeye and climate change.
Confirmed attendees were sent the background paper so they could
become familiar with the available literature prior to the workshop.
Thirteen experts participated in the workshop (seven categorized
themselves as biologists, four as policy makers, one as “both”, and
one as “neither”).1 The mean number of years of experience was
over 16, with the biologists having more experience (20 years) on
average than the policy-makers (7 years).
3.4. Structure and survey instrument design
The workshop began with brief presentations on key topics
(including an overview of the literature on likely environmental
trends given climate changes) to ensure participants understood
the tasks. Vulnerability was defined as “.the extent to which
a natural or social system is susceptible to sustaining damage from
climate change. Vulnerability is a function of the sensitivity of
a system to changes in climate and the ability to adapt the system to
changes in climate. Under this framework, a highly vulnerable
system would be one that is highly sensitive to modest changes in
climate.” (IPCC 1997 definition cited by The Vulnerability Network,
http://www.vulnerabilitynet.org/)
For the first half of the workshop, participants used a workbook
to rate: 1) the vulnerability of sockeye at each life stage, 2) the
vulnerability of sockeye over their entire life cycle (overall vulnerability); and 3) the participant’s knowledge and confidence
regarding the previous two exercises. Participants were given the
opportunity to discuss their responses and adjust their answers if
their opinions changed as a result of the discussion.
The questions were designed so that responses could be
analyzed for differences between the life cycle stages, between the
individual stages, and overall. Pre-defined scales were used to
describe various levels of vulnerability and the same scale was used
for all questions. A sample question is shown in Fig. 2 for one
geographic area.
3.5. Structuring the judgments
The questions elicited judgments of vulnerability in relation to
life stage, spawning region, and climate forecast. The first set of
questions asked participants to rate the vulnerability of sockeye at
each life stage under two different climate change scenarios (2 C
and 4 C average air temperature increases), and for three separate
spawning regions (upper, mid and lower Fraser River). This created
a total of six combinations. The two scenarios were cast as a relatively low and relatively high temperature increase, reflecting
a likely minimum and maximum range based on the available
literature for the Fraser Basin and North East Pacific Ocean (Moore,
1991; Henderson et al., 1992; Levy, 1992; Hinch et al., 1995b;
Morrison et al., 2002; PCIC, 2008). Clearly, there are many environmental changes associated with these temperature changes
(e.g., a rise in river temperature is associated with a decrease in
river discharge; a rise in ocean temperature is associated with
a decrease in wind strengths and upwelling). Overall, the more
extreme the change in temperature, the more extreme would be
the expected change in the associated environmental features. We
asked participants to consider the temperature change as an indicator of the myriad of environmental changes that may occur
simultaneously with temperature changes. Nonetheless, temperature changes are expected to have some of the most direct and
dramatic effects on salmonids. The accuracy of the 2 C and 4 C
scenarios was not the concern of this workshop, which focused
1
The individual self-identified as neither a biologist nor a manager is a former
federal Minister of Fisheries, and a knowledgeable member of non-governmental
organizations regarding fisheries issues.
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Fig. 1. Sample influence diagram (returning adults life cycle stage).
instead on how vulnerable sockeye were to adverse effects given
these two reasonably understandable scenarios.
Participants were asked to consider the effects over a 60-year
time frame (15 cycles of sockeye salmon), and to consider the
effects summarized in Table 2 all together. The questions were
organized by life cycle stage and the issue of vulnerability focused
on the ability of the sockeye to move on to the next stage of their
life cycle in good state (i.e. considering both quantity and quality)
under each climate scenario. Participants circled a number between
1 and 5, where 1 indicated no vulnerability (i.e. no different from
the status quo) and 5 indicated a high degree of vulnerability (i.e.
reproductive capacity is severely disrupted). The second exercise
asked the participants to rank the overall vulnerability of sockeye
salmon (on the same 1e5 vulnerability scale) to 2 C or 4 C climate
warming in each of the three regions over the same 60-year time
frame. Answers to this question were later compared to the
answers for individual life cycle stages. Finally, participants were
asked to rate their knowledge of and confidence in their responses
to each question.
3.6. Eliciting and revising judgments
All judgments for a particular life stage were elicited together,
for both temperature scenarios and for the three spawning
regions. Before each life stage was considered we reviewed the
structure of the influence diagram and content of the background
paper relevant for that question. After all participants had
completed their judgments for a given set of questions, we
encouraged participants to discuss their answers. For some life
cycle stages, lively discussion ensued, and for others, little was
said. Participants were permitted to revise their judgments at any
time. A review of the workbooks showed that 11 of the 13
participants had revised at least one answer; some had made
many revisions.
3.7. Statistical approach
After the workshop was completed, responses to the questions
were compiled in a database. We used the non-parametric
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Fry Emergence to Lake Entry
As described above, the faster development of embryos may lead to early emergence of smaller fry. This
early emergence may result in a mismatched timing with the spring bloom of zooplankton. This mismatch
may limit feeding and growth opportunities for sockeye.
When the nursery lake is upstream, fry must migrate against the current. Smaller fry may be less able to
make such an upstream migration successfully.
As a result, the quantity and/or quality of sockeye at the end of this lifecycle stage would be
impaired.
How vulnerable are fry, from their emergence to lake entry, to this reduction in quantity and/or
quality?
Sockeye the spawn in the upper Fraser system
Vulnerability with 2ºC average temperature increase
1
2
3
4
Not vulnerable
(not affected at all
or status quo)
5
Highly vulnerable
(reproductive capacity
severely disrupted)
Vulnerability with 4ºC average temperature increase
1
2
3
4
Not vulnerable
(not affected at all
or status quo)
5
Highly vulnerable
(reproductive capacity
severely disrupted)
Fig. 2. Sample question for one life cycle stage and one spawning region.
ManneWhitney U rank sum test to compare the distribution of
responses for pairs of questions or question sets assuming a null
hypothesis of no difference in the ranks (n ¼ 13)2. We conducted
three sets of ManneWhitney tests.
To investigate differences between life cycle stages when other
variables were held constant, we compared vulnerability estimates for three life cycle stages (eggs, fry-first winter and
returning adults) within all six temperature-region combinations.3 For example, we compared the vulnerability of the eggs
life cycle stage in the upper Fraser region under a 2 C temperature increase scenario with the vulnerability of the fry-first
winter life stage and the returning adults life cycle stage in the
same region and at the same temperature increase. This analysis
involved a total of 18 ManneWhitney tests (three for each of the
six temperature-region combinations). To investigate differences
between temperature scenarios and regions, we compared overall
vulnerability estimates for the six combinations of spawning
region and temperature increase. The overall vulnerability estimates for a particular temperature scenario and region were
compared to the overall vulnerability estimates for the same
region but at the other temperature. The overall vulnerability for
a particular temperature and region was also compared to the
same temperature in different regions. These tests investigated
the impact of changing the location and temperature scenario on
overall vulnerability.
The third set of ManneWhitney tests investigated differences in
knowledge and confidence of the participants for three life stages
(eggs, fry-first winter, and returning adults).
2
A total of 63 data points out of the potential total of 936 were missing because
some participants did not answer certain questions. Of these, 46 were left blank by
one individual, who self-identified as a policy maker and not a fisheries expert. We
handled these missing responses by replacing them with the mode response for
that question, in keeping with the ordinal, categorical data structure.
3
We selected these three life stages for comparison because, a priori, they
seemed to have the most potential to be affected by climate change.
4. Results
4.1. Histograms of the responses for each question
Fig. 3 shows the histograms of responses for all questions. The
histograms are all unimodal. The variation ranged from questions
for which responses were in two adjacent categories (indicating
high agreement) to questions for which responses were spread
over four categories.4 The judgments showing high agreement
(varying over only two categories) and high vulnerability of stocks
were (i) eggs in the mid-Fraser under the 4 C scenario, and (ii)
upper Fraser stocks over the whole life cycle under the 4 C
scenario.
Visual inspection of the histograms does not show that participants were more confident regarding the impact of a 4 C increase
than of a 2 C increase, nor do they appear to be more confident
about vulnerability over the entire life cycle than for any specific
stage.
4.2. Life cycle vulnerability ratings
Participants rated sockeye as most vulnerable to climate change
during egg and returning adult life stages. Eggs had a mean score of
3.67 and returning adults had a mean score of 3.82 (for all regions
and temperature scenarios). Mid-life cycle stages such as fry-first
winter had, in contrast, lower vulnerability means (range
2.58e3.13). The means for each life cycle stage are shown in Table 3,
broken out by location and temperature scenario, and shown for
each life stage overall.
The difference in vulnerability between eggs and fry-first winter
was statistically significant (p < 0.01) for all six combinations of
spawning region and temperature increase. None of the differences
4
In the two judgment sets for returning adults spawning in the Middle Fraser
region, one participant judged vulnerability much lower than the other participants
(Fig. 3, centre two histograms for returning adults).
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T. McDaniels et al. / Journal of Environmental Management 91 (2010) 2771e2780
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Fig. 3. Histograms of responses for each question.
in vulnerability between egg and other life stages were statistically
significant.
Likewise, the difference in vulnerability between the returning
adults and fry-first winter stages was statistically significant
(p < 0.01) for all six regionetemperature combinations. The
difference in vulnerability between returning adults and fry-smolt
was significant for the upper Fraser at 2 C and 4 C, and the lower
Fraser at 2 C. None of the other differences in vulnerability were
statistically significant.
The mean vulnerability scores of the most vulnerable life stages
(eggs and returning adults) were not statistically different from the
mean score for the overall life cycle.
4.3. Overall vulnerability ratings
Table 4 shows the mean ratings for overall vulnerability. Sockeye
were viewed as substantially more vulnerable to climate change
under the 4 C temperature scenario compared to the 2 C scenario.
Table 3
Vulnerability (on a scale of 1e5) of upper, mid, and lower sockeye salmon at different temperatures and by life cycle stage.
Life cycle stage
Eggs
Fry e emergence to lake entry
Fry e lake entry to first winter
Fry e first winter
Fry e smolt
Post smolts
Immature sockeye in ocean
Returning adults
Means for all life cycle stages
Mean vulnerability scores for each region and temperature increase
Upper e 2 C
Upper e 4 C
Mid e 2 C
Mid e 4 C
Lower e 2 C
Lower e 4 C
3.17
2.42
2.42
2.36
2.45
2.46
3.04
3.69
2.75
4.21
3.54
3.75
3.18
3.27
3.46
3.96
4.58
3.74
3.17
2.67
2.67
2.27
2.55
2.63
2.96
3.35
2.78
4.13
3.79
3.75
3.18
3.36
3.63
3.88
4.27
3.75
3.25
2.67
2.42
1.91
2.36
3.04
2.95
3.12
2.71
4.13
3.71
3.67
2.55
3.09
3.79
3.95
3.92
3.60
Means for all regions
and temperatures
3.67
3.13
3.11
2.58
2.85
3.17
3.46
3.82
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Table 4
Mean overall vulnerability (on a scale of 1e5) of upper, mid, and lower sockeye
salmon stocks at different temperatures.
Temperature
Overall
vulnerability mean
Upper fraser
spawning
grounds
Mid fraser
spawning
grounds
Lower fraser
spawning
grounds
2 C
3.58
2 C
3.42
2 C
3.27
4 C
4.73
4 C
4.50
4 C
4.19
Table 5
Mean ratings of own knowledge and confidence regarding sockeye vulnerability
issues, by life cycle stage and overall.
Life cycle stage
Mean knowledge rating Mean confidence rating
Eggs
Fry e emergence to lake entry
Fry e lake entry to first winter
Fry e first winter
Fry e smolt
Post smolts
Immature sockeye in ocean
Returning adults
Means for all life cycle stages
As reported overall
2.54
2.54
2.62
2.46
2.54
2.46
2.69
3.62
2.68
3.13
2.54
2.42
2.42
2.17
2.42
2.29
2.54
3.23
2.50
2.42
The vulnerability of Fraser River sockeye to climate change
increases from the lower to the upper Fraser River spawning
regions, but the differences in vulnerability between regions was
statistically significant only for the upper Fraser compared to the
lower Fraser at 4 C. The difference between the 2 and 4 C
temperature scenarios within each region was statistically significant (p < 0.01) for all regions.
4.4. Uncertainty
Participants rated their overall knowledge of the workshop
topics and confidence regarding workbook responses on a scale of
1e5 (5 being highly knowledgeable or confident and 1 not confident). The mean knowledge rating was 3.13 and mean confidence
was 2.42, suggesting the participants did not have high confidence
in either their knowledge or their judgments. This is despite the
fact that the participants were among the best-informed technical
and management specialists in the world regarding these fish
resources. Participants were roughly equally uncertain about their
judgments regarding each life stage except for returning adults,
where they felt more knowledgeable and confident. Differences
between the knowledge ratings for the returning adult stage
and every other stage were statistically significant (p < 0.01) and
differences in confidence between the returning adult stage and
others were statistically significant (p < 0.05 for immature sockeye
in ocean and eggs; p < 0.01 for the other life cycle stages). Note that
participants’ self-assessment of their overall knowledge was higher
than the mean of reported knowledge over all life cycle stages.
Table 5 shows participants’ knowledge and confidence ratings
for each life cycle stage.
4.5. Mitigation
The second major task was to elicit the participants’ views
regarding the potential to mitigate adverse effects of climate
change on reproductive capacity of Fraser River sockeye salmon.
We addressed two broad questions in a facilitated discussion: (i)
what options are available to mitigate the effects of climate change
on Fraser River sockeye stocks, and (ii) how practical are these
options?
The discussion began with the adult stage of the salmon life
cycle, as participants explained that the ability of adults to reach
spawning grounds was crucial to every other stage. Each life cycle
stage was then examined in reverse sequential order. Participants
were asked to discuss two kinds of options: (i) mitigation measures
that involve changes in how fisheries are managed, and (ii) mitigation measures that involve the use of infrastructure of some kind.
Table 6 summarizes the results. In general terms, the kinds of
policy measures that could be pursued for returning adults are
similar to those now being considered or implemented by fisheries
managers in the Department of Fisheries and Oceans. Policy
measures for other life cycle stages are unclear, except for perhaps
predator management for the stage from lake entry to smolts. The
only infrastructure measures that were viewed as practical were
construction of additional spawning channels to aid returning
adults and eggs. Investments in temperature management and flow
augmentation were suggested as prospects in systems without lake
influence. Importantly, temperature management in the mainstem
of the Fraser River through construction of low level outlets on the
Table 6
Climate change mitigation options for Fraser River sockeye.
Life cycle stage
Returning adults
Immatures in ocean
Post smolts, estuary, and coastal
Fry: lake entry to Smolts
Eggs
Policy measures to assist with mitigation
Adopt a balanced “fish friendly” approach that fostered adaptive
management and policy coordination across species.
Alternative fishing strategies to achieve escapement goals
(thereby conserving genetic diversity) including: quota
management, limited harvest and removal rates, more
efficient fishing strategies,and an increased number
of smaller fisheries.
Not clear. At this stage the fish are widely dispersed and
not necessarily \within Canadian jurisdiction.
None suggested
Participants argued for a multi-species monitoring program that
could help identify predators early on, before they became
established in a new ecosystem.
Predator management to stop the spread and distribution
of predators (e.g., preventing fishermen from moving
bass from lake to lake or preventing the natural migration
of predators).
None suggested
Infrastructure to assist with mitigation
Create additional spawning channels,
Cold-water release (to lower the temperature of the
Fraser main stem or spawning streams) is not a viable
option, given the volumes of water that would be required.
None suggested
Measures to aid in recovery of estuary ecosystems
None suggested
Constructing spawning channels and off-channel
spawning places can best assist eggs. Investments in
temperature and flow management should be made
in systems without lake influence.
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T. McDaniels et al. / Journal of Environmental Management 91 (2010) 2771e2780
existing Kenny Dam, or construction of dams on other tributaries
were viewed as impractical and likely ineffective, given the
volumes of water needed to alter temperature regimes in the
mainstem of the Fraser River system.
In sum, there are relatively few alternatives available to mitigate
the effects of climate change on sockeye salmon in the Fraser River
system. These fisheries are already tightly managed and nearly fully
committed to various user groups. There are few or no new structural alternatives and little in terms of new management directions
that could help mitigate the vulnerability of Fraser River sockeye to
climate change.
On the other hand, Fraser River sockeye already demonstrate
a great deal of adaptive capacity in utilizing heterogeneous habitats
in different river basins. Hence, this adaptability points to the
potential value of policies that seek to make stocks more resilient to
uncertain futures. Some authors have discussed the potential for
future adaptation of salmon to climate changes (Crozier et al.,
2008). Healey (2009) considers the resilience attributes of salmon
and measures to enhance them.
5. Conclusions
Participants clearly thought that sockeye salmon in the Fraser
River system are vulnerable to climate change to the extent that
reproductive capacity could be substantially impaired. This was
particularly true for climate scenarios that predict greater
temperature increase and for stocks spawning in the upper Fraser
River system. Participants believed that returning adults and eggs
were the life stages most vulnerable to climate change. The
returning adults life stage was rated as the most vulnerable, and
was also the life stage for which the participants had the highest
knowledge and confidence ratings. Overall, participants stressed
the many uncertainties regarding vulnerability estimates and the
difficulty of predicting specific levels of impact.
Finally, sockeye in the Fraser River system are highly adapted to
specialized habitat conditions, which differ greatly from one river
system to the next. Hence it is possible that the adaptive capacity
they have demonstrated in the past may lead to spontaneous
adaptation of warmer conditions through behaviour changes. For
example, delayed run timing for stocks spawning in the upper
portion of the system have been recorded in recent years.
Mitigation of the impacts of climate change on sockeye salmon
may be difficult because the resource management systems are
already highly constrained, with overlapping demands on the
resource from multiple gear types and sequential fisheries. Participants believed that efforts should be concentrated on fostering
resiliency to climate change impacts instead of predicting specific
levels of change. To facilitate adaptation, participants suggested
improved information collection and strategic science-based
learning to improve understanding of current system functions.
This new information could help experts develop robust policies
that are better able to cope with the irreducible uncertainties of
climate change.
Turning to the process developed and applied here, this is to our
knowledge the first use of a structured process to elicit expert
judgments of vulnerability to climate change for a specific species,
in a specific habitat system, over its life cycle, differentiating among
sub-groups. Ecological vulnerability to climate change has largely
been addressed over large geographic areas (e.g., such as the Pacific
Northwest states, as in Miles et al., 2007) or over many species (e.g.,
Walther et al., 2002; Parmesan and Yohe, 2003). These assessments
have largely considered impacts of climate change to the present,
without considering vulnerability of specific species to future
change in particular locations. Here we used approaches informed
by methods of probability elicitation (Morgan and Henrion, 1990),
2779
but within a more direct and less complex judgment task, to obtain
judgments of vulnerability that integrate over many variables and
scenarios. We sought the individual judgments of each participant,
rather than attempting to create a consensus within the elicitation
process, because of the importance of understanding the range of
views (Morgan and Henrion, 1990). Based on this experience, the
method appears promising for similar judgment tasks regarding
vulnerability and climate change. The method could benefit from
further applications and critical examination, as well as experimental testing of the kind that is sometimes employed for probability assessment. Any experimental tests would, however, face
methodological hurdles similar to that arising for probability elicitation, such as the difficulty of judging calibration without rapid
feedback on the results (Clemen and Winkler, 1999).
Some might wonder whether the role of eliciting scientific
judgments is as a contribution to science or more policy-relevant
research. We do not claim that eliciting judgments creates new
scientific knowledge. We do believe that synthesis of viewpoints
regarding vulnerability of an ecologically-important species to
climate change, based on existing scientific knowledge and the
informed judgments of recognized experts, is an important
contribution, as both meta-science and as a contribution to policy.
Indeed, the whole IPCC enterprise addresses such a meta-analysis,
but with a different method. The approach adopted here is a step
toward more focused science that addresses key issues, such as the
linkages among vulnerability among life stages of sockeye. But no
matter how much research is devoted to these issues, the vulnerabilities summarized here will remain significant but uncertain
threats to Fraser River sockeye salmon.
Acknowledgements
This research was made possible through support from the
Climate Decision Making Center (CDMC) located in the Department
of Engineering and Public Policy. This Center has been created
through a cooperative agreement between the National Science
Foundation (SES-0345798) and Carnegie Mellon University. The
CDMC provided a sub-grant to the University of British Columbia
for these efforts. The contributions by M. Healey were supported by
an NSERC Discovery grant.
We thank the expert participants who spent time working with
us to provide their judgments and insights for this research project.
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