Proceedings from the
Nutrients and Salmon Production Workshop
Thursday November 21, 2002
Please note that many of the figures included in this volume were
prepared for electronic display and do not transfer to the best
black and white print quality.
SALMON NUTRIENTS: CLOSING THE CIRCLE
John Stockner, Limnologist, Fisheries Centre,
University of British Columbia and Eco-Logic Ltd.
Report from the Nutrients and Salmon Production
workshop held at Simon Fraser University on November 21, 2002.
Summarized from Stockner, J. and K. Ashley. 2003.
Salmon Nutrients in Aquatic Ecosystems: Closing the
Circle in Stockner, J.G., editor. 2003. Nutrients in
Salmonid Ecosystems: Sustaining Production and
Biodiversity. American Fisheries Society, Symposium
34, Bethesda, Maryland.
Facilitator: Craig Orr, Associate Director, Centre for
Coastal Studies, Simon Fraser University
Editors: Deirdre Dobson, Masters Candidate,Centre
for Coastal Studies, Simon Fraser University
Jennifer Penikett, Program Assistant, Centre for
Coastal Studies, Simon Fraser University
Patricia Gallaugher, Director, Continuing Studies in
Science, Simon Fraser University
The consequences of nutrient loss (oligotrophication)
and attendant low productivity on ecosystem
biodiversity and fish production have only recently
piqued the interest of aquatic researchers.
Conversely, research into the causes and
consequences of eutrophication has been a major
focus of aquatic research over the last few decades.
Oligotrophication is the process where plant nutrients
are removed from a system and the subsequent
reduction in ecosystem biodiversity. Various
anthropogenic processes lead to oligotrophication:
dams and reservoirs trap nutrients, acidification,
drainage of wetlands, logging, liming, climate change
and the simple reduction of fish (through blocked
passage or over-fishing). In these situations, the
phosphorous that is present ultimately sinks to the
bottom of lakes and oceans, taking it out of the
working ecosystem.
Sponsored by the Centre for Coastal Studies, Simon
Fraser University through a grant from the Vancouver
Foundation.
BACKGROUND
The idea for the topic of this Speaking for the Salmon
workshop evolved from a conversation that Patricia
Gallaugher had with Rudy North,President, North
Growth Management Ltd., early in Fall 2002, where
Rudy asked the question: “In lakes where salmon are
not returning in the numbers they once were, is it
possible to increase productivity by adding fertiliser?”
The purpose of this workshop was to seek a better
understanding of the relationship between nutrients
and salmon production.
Within an aquatic ecosystem there are a number of
important nutrients. Hydrogen, sodium, potassium,
1
nutrients) of lakes. Now in the 21st century there is a
renewed realisation of the importance of nutrients and
the value of human wastes. Presently, societies have
an extremely high use of phosphorous and the
depletion of reserves is greater than the return. With
phosphorous consumption reaching an all time high,
soils are becoming worn out. With this rate of use
and without the addition of phosphorous back into the
ecosystem there is the risk of running out. It is
important to re-learn how to close this circle.
magnesium and calcium are among the essential ones,
though these are required in lesser amounts than
nitrogen, phosphorous and carbon; all are essential for
life. Most plants need nutrients in amounts described
by the Redfield Ratio of 1P: 16N: 106C. Phosphorous
is the limiting element in this ratio because it is
unique. Lacking a gas phase (unlike carbon and
nitrogen) it cannot be removed by biogenic
assimilation. Therefore, if phosphorous runs out, the
ecosystem can no longer support life. The loss of
nutrients, such as phosphorous, occurs when the
cycling of nutrients is interrupted, such as in British
Columbia where a decline in nutrients is a result of a
decline in salmon populations.
With respect to salmon, the decline of phosphorous
nutrients began in 1850-1930 during times of overfishing. In the time of first contact with the First
Nations people, the settlers built canneries where the
seine fleets from the Fraser River would package their
chinook. During that time all the nutrients were being
put into tin cans and were not available to replenish
the environment. In addition, there was increased
habitat degradation, logging, agriculture, and loss of
other species, all exacerbating the decline of lake
nutrients. The primary reduction of phosphorous and
other nutrients in streams, lakes and estuaries can thus
be attributed to the decline of fish populations (Figure
1). As smolts, young salmon migrate to the Pacific
Ocean taking some of their natal lake or stream’s
nutrients with them. As adults migrating back to their
natal ecosystem, they return much larger quantities of
marine nutrients from their oceanic rearing grounds to
their aquatic and estuarine ecosystems. The
harvesting of adult salmon, since the turn of the
The resultant loss of nutrients in the environment was
not always the case and only recently became an issue
because of modern perspectives. Historically,
phosphorous was continually cycled through the
ecosystem regardless of the amount of demand placed
upon the ecosystem. For instance, in Tokyo from
1720-1820, the city’s population grew from 20,000 to
1 million without sewage systems and without disease.
The “recycling” of human excreta facilitated this
growth, as this source of essential nutrients was fed
back into the land, used as fertiliser. This practise
closed the circle from extraction to replacement from
the earth’s resources. However, in the 20th century
there was no such recycling: human waste was viewed
as having no value. This led to the wastes being
dumped, resulting in eutrophication (too much
1200
Catc h (tons x 102)
1000
P (tons)
800
600
400
200
0
1875
1900
1925
1950
1 975
Figure 1. British Columbia salmon catch expressed in biomass and phosphorous
equivalents (Fisheries and Oceans Canada, Vancouver, BC, unpublished data)
2
2000
Given the evidence of the importance of salmon
nutrients in maintaining productivity in salmonid
ecosystems, it is clearly time for a major paradigm
shift in fisheries, forestry and river basin
management. The problem is that the amount of
phosphorous in the world is finite and usable
phosphorous is running out. We need to re-learn how
to close the circle through better nutrient
management, especially for phosphorous. This can be
accomplished through nutrient addition to low
productivity wetlands, forests, streams (i.e. apply
increased phosphorous sludge), public education
about nutrient cycles in water systems and a change in
public perception of nutrient enrichment from
“pollution” to one of habitat restoration.
Implementation will require good limnological
knowledge and a better understanding of the
importance of maintaining a balanced nutrient supply
and suitable habitat to optimize potential productivity.
More importantly, this will require the education and
need to re-engineer management of water bodies,
wetlands, dams, and treatment plants, stressing the
importance of phosphorous replacement.
century, has led to an average loss of 225-275 tons of
phosphorous per year (Figure 1). This equates to
enough phosphorous to produce greater than 100,000
tons of living autotrophic plant biomass.
There are consequences to this process of
oligotrophication. The obvious one is an ecosystem
lacking sufficient primary productivity. There needs
to be a balance for if the fishery is lost, so too is the
biodiversity. This loss will be reflected up through the
food chain as the ecosystem relies on the carcasses
and fish for food.
Replacement of these lost nutrients is now required by
means of lake and stream fertilisation. One such
method is the of dumping liquid nutrients into the
lakes from planes or helicopters. This is effective but
very expensive, and therefore the BC Ministry of
Water Land and Air Protection has used an alternate
barge method, such as on Chilko Lake. For nearly a
century, adult sockeye escapements to Chilko Lake
have been less than 15% of estimated historic levels.
In recent years (1990-2000) however this improved to
just over 20% of total returns as a result of
implementation of lake fertilisation in the late 1980s
and early 1990s and to restricted harvest in the 1990s
(Figure 2). Results of this fertilisation project showed
fish production to be a product of the amount of total
phosphorous.
Discussion
A participant asked what happens to the waste
product from treatment plants? John Stockner replied
that the treatment plants are not recycling and that
wastes are simply dumped into the ocean or sludge
dumps. The iron and nitrogen results in a high boost
250
Chilko Escapement
200
150
100
1990
1980
1970
1960
1950
1940
1930
1920
1910
1900
0
Year
Figure 2. Chilko sockeye escapement from 1890 to present (from J. Hume, Fisheries and Oceans Canada, Cultus
Lake Laboratory, Cultus Lake, BC, unpublished data).
3
2000
50
1890
mgP/m2
300
to productivity in the ocean but better engineering is
required for treatment of wastes in order to recycle the
nutrients for use in lakes and streams.
of practical and applied components of lake
fertilisation.
Four nutrient assessment techniques are:
1. Bioassays to determine nutrient limitations;
add N and P in different amounts to see
which is the limiting nutrient; or
2. Synoptic surveys of biota to determine if the
system is oligo, meso, or eutrophic;
3. Low-level water chemical analysis; and
4. Qualitative assessment.
Questions were raised regarding the cost of the
fertilisation projects and who should cover the costs.
The methods used by the BC Ministry of Water, Land
and Air Protection were effective and relatively
inexpensive, costing approximately $2.2 million,
using a plane (low cost/unit growth and the number of
adults produced). It was suggested that perhaps
revenues brought in by recreational fishers could be
directed towards financing future fertilisation projects.
Prior to proceeding, it is important to realise that
adding nutrients is controversial in some areas,
and illegal in others (e.g., USA). Therefore, you
must ensure that all regulatory agencies are
notified in advance. Fisheries and Oceans
Canada is presently developing draft guidelines
for nutrification. In addition, the BC Water Act
requires that you have a downstream license.
PROTOCOL FOR APPLYING LIMITING NUTRIENTS TO
INLAND WATERS
Ken Ashley, Aquatic Ecosystem Science Section, BC
Ministry of Water Land and Air Protection
Summarized from Ashley, K. and J. Stockner. 2003.
Protocol for Applying Limiting Nutrients to Inland
Waters in Stockner, J.G., editor. 2003. Nutrients in
Salmonid Ecosystems: Sustaining Production and
Biodiversity. American Fisheries Society, Symposim
34, Bethesda Maryland.
In aquatic ecosystems, phosphorous is typically
the limiting factor when TDP (total dissolved
phosphorous) is <2-3µgL -1and SRP (soluble
reactive phosphorous) is <1µgL-1. In streams
nitrogen is limiting when DIN (dissolved
inorganic nitrogen NO3-N+NO2-N+NH3-N) is
<20µgL-1. Nitrogen is the limiting nutrient in
lakes and reservoirs when the epilimnetic DIN
is <30 ugL-1. Therefore, before proceeding it is
There are logistical and practical aspects that need to
be addressed when considering fertilisation programs.
BC has taken a lead in the research and development
Figure 1. Response of algal weight per square metre to nitrogen and phosphorous addition.
4
important to determine the nutrient status by collecting
a minimum of one-year pre-enrichment data.
although this is not fully researched in oligotrophic
systems. Nitrogen levels vary with season and in
response to water sources (e.g., melt water vs.
groundwater) as well as land cover and geologic
ground composition. It is difficult to identify the
sources of nitrogen because they are often masked by
point and non-point pollution. It is also possible for
an ecosystem to shift from being P limited to being N
limited during enrichment.
The nutrients not only affect the immediate area in
which they are added but also the downstream areas.
Unidirectional flow of water displaces nutrients
considerable distances downstream, and the amount of
distance varies in accordance with stream size (the
greater the stream, the greater the distance).
Examination of stream ecology shows that the amount
of phosphorous has greater affects on primary
productivity than does nitrogen (Figure 1). However,
this is not a “more is better” scenario, for even low
concentrations of phosphorous can lead to increased
algal growth. In the first year of study (1983)
described in Figure 2, a lot of phosphorous was added,
and resulted in excess algae growth. While the
Project planing requires 1-2 years, with a minimum of
one-year pre-enrichment data. This involves the
collection and analysis of stream discharge, water
chemistry, biota, residence time, stratification depth,
water licenses and escapement trends.
There are seven key components to any project:
1. Desired concentration of nutrients
Streams: You need to be able to list the nutrient
components of the system and the concentrations.
invertebrates eventually graze the excess algae down,
it takes time (a few years) for the grazers to catch up to
Figure 2. Responses of algae downstream to nutrient additions
The target load is 3-5 µgL-1 SRP and 30-50 µgL-1
DIN for phosphorous and nitrogen respectively in
streams. For streams, salmon carcasses are the
most effective method of adding nutrients (as is
used in the State of Washington, USA) (Figure 3).
the increased nutrients. Therefore, starting the
fertilisation off slowly will enable the grazer to keep
up with algal production.
When planning a project, it is important to realise that
nitrogen limitations do occur in aquatic ecosystems
5
Phosphorous will rarely be detected, so it is
important to not over apply this element. The
number of carcasses that should be added can be
estimated from tree ring data, sediment cores,
historic run numbers in addition to salmon
estimate curves.
Lakes and Reservoirs: The nutrient loading
method for lakes and reservoirs is derived from the
Vollenweider-type loading model, which
incorporates mean depth and residence time.
There is a need to apply the N and P within the
oligotrophic range and ensure that the epilimnetic
N:P ratio is > 10:1 (wt:wt) during the growing
season.
2. Type of nutrients. Salmon carcasses are the best
type of nutrient, although liquid or granule
inorganic or slow release methods can also be
used. There are storage and handling problems
April through to September (Figure 4). Nitrogen
uptake takes place mostly in the summer months
over a 20-22 week period (Figure 4). By frontend loading the timing, the addition mimics a
“run” or the spring freshet, thereby enabling the
system to keep above the N-limiting situation
(Figure 5).
4. Frequency. For both lakes and streams nutrients
can be added as often as technically and
economically feasible. Within lakes, more
frequent pulses favour smaller sized
phytoplankton due to higher surface area to
volume ratio. Flow proportional injection systems
can be used for continual loading as can slow
release fertiliser or carcasses. An alternative is to
use pre-programmed injectors that can be used for
loading so many times per hour.
5. Location of application. For streams, the location
of application depends on the type of
nutrients that are used as well as the
presence of large woody debris (which
can improve carcass retention). Site
selection should also consider
accessibility and nutrient spiraling
distance. For lakes, it is best to dump
the nutrients in the middle of the lake,
as they will be carried through by
natural circulation.
6. N:P ratio. The nitrogen:phosphrous
ratio depends on the geology of the
watershed, season, biological uptake
and run-off sources. Coastal BC is
Figure 3. Nutrient enrichment as a function of carcass availability.
typically phosphorous-limited while the interior of
BC is nitrogen or nitrogen-phosphorous counique to each type of nutrient used, for instance,
limited.
solid fertilisers absorb moisture, which causes
7. Application technique. It is important to mimic
caking; liquid fertilisers will salt out under certain
nature whenever possible.
conditions; ammonium nitrate is extremely
explosive; and salmon carcasses have a limited
Conclusions
shelf life.
Nutrient enrichment programs should mimic the
3. Seasonality of application. For streams this would “nutrient pump” whenever possible, ensuring that
depend on the type of nutrients used and can
treatment produces edible phytoplankton and
reflect salmon runs with carcasses or snowmelt.
periphyton and avoids the occurrence of nuisance
For lakes, fertilisation can take place from late
algae. Treatment needs to be adequately monitored,
6
Figure 4. Seasonality of fertilisation in Upper Arrow reservoir.
Keogh River for a one-time application that equalled
one tonne of slow release fertiliser. Therefore, when
considering all prior techniques for increasing salmon
numbers, this is the most cost effective when looking
at the cost per salmon. However it is important to
note that fertilisation is not a solution for declining
stocks.
and should be viewed as an interim measure that is
most effective if all components of ecosystem
recovery (e.g. habitat loss) and key external factors
(e.g. over-fishing) are conducted in a co-ordinated
program.
Discussion
The main concern raised with regard to this technique
is cost. However, it was pointed out that hatcheries
are also very expensive. While hatcheries might cost
millions of dollars, fertilisation for a whole river can
be accomplished for $1,000, as was the case for the
The question with regard to the effectiveness of
fertilisation in glacial waters also sparked discussion.
One response was that phosphorous absorption would
occur at a higher rate during the times when glacial
7
NIMPKISH WATERSHED SOCKEYE ENHANCEMENT USING
LAKE FERTILISATION
Don McQueen, Adjunct Professor, Department of
Biological Sciences, Simon Fraser University
When the number of salmon present in a lake
increases, there is a decrease in individual size of the
salmon when they leave the lake. This is because the
salmon are limited by food as in the example of Woss
Lake in the Nimpkish Watershed in BC (Figure 1).
However, when there is a high density of fish, there is
an increased chance for returning adults. On the other
hand, larger individual fish will have an increased
ability to survive and also to return as adults. Thus, it
is possible to achieve the more desirable outcome of
larger fish with increased survivability by increasing
the food source within the lake by adding nutrients.
The efficacy of using lake fertilisation to enhance
juvenile sockeye salmon growth rates and to improve
subsequent rates of marine survival were tested within
the Nimpkish Watershed (Vancouver Island). The
Nimpkish Watershed has characteristically
experienced catastrophic declines in salmon in recent
years, including the disappearance of whole year
classes (Figure 2). There are three lakes within the
Figure 5. Vertical profiles of nitrate and silicic acid in the North
Arm and South Arm in 2001.
flour is at its greatest. Glacier flour, the fine silts and
muds that are deposited in a lake that has formed at
the base of a retreating glacier, are the finest sediments
of the glacial outwash material, and the last to settle
out from the material deposited in the lakes. On the
other hand, it was suggested that the more glacial flour
there is the less effective the fertilisation and the
system could turn to a bacterial run system.
Figure 1. Correlation between number of sockeye and
average weight of individual fish.
8
watershed, Nimpkish Lake, Woss Lake and Vernon
Lake, that are still producing sockeye.
weights (Figure 7). The second and third years also
saw large diatom blooms, although the species were
There was a need to know that the fertiliser mixing
method was effective in this study. In the first attempt
to fertilise Woss Lake in 2000, there was no build-up
of phosphorous and there was a 10-fold increase in
algae (Bacillariophyceae) (see Figure 3), and therefore
it was assumed that the phosphorous was being taken
up. However, after one year, this increase in nutrients
Figure 3. Algae species in Woss Lake in 2000.
Figure 2. Estimated escapement of spawning sockeye salmon
into the Nimpkish River.
resulted in an increase in Daphnia with no change in
zooplankton. This meant that there was no increase in
sockeye growth rate. This was the result of nutrients
being used by diatoms (Rhizosolenia eriensis), an alga
not eaten by zooplankton, and therefore the extra
nutrients were not available to sockeye (Figure 4). As
a result of these findings the method was changed in
the second year. In 2001/02 we fertilised Woss Lake
and used Vernon Lake as the control (Figure 5). This
time fertiliser was added earlier, which possibly drove
the lake from being phosphorous driven to nitrogen
limited.
The results of this study are described in Figures 6 and
7. Woss Lake had a greater concentration of the
desired zooplankton in 2001 compared with Vernon
Lake (Figure 6) and as a result the sockeye responded
in the second year and third year with increased
Figure 4. Nutrient pathway in Woss Lake, 2000.
9
Figure 5. Woss Lake and Vernon Lake within the Nimpkish Watershed system.
different than in Year 1 and were an edible species
(Figure 8).
Vernon Lake was not as successful in increasing the
sockeye run size (data not shown), possibly due to the
increased steelhead competition that was present.
After the three years of treatment, Vernon Lake still
had few diatoms with no increase in sockeye while
Woss Lake was very successful with the production of
sockeye in greater numbers. Therefore nutrification
Figure 6. Zooplankton concentrations (µgL-1 dw) in Vernon and Woss Lakes.
10
Figure 7. Fish weight (mean +/- SD) for Woss (O) and Vernon (∆) years 2000-2002.
Figure 8. Pytoplanktonbiovolume mm3m-3 in Vernon and Woss Lakes, 2000-2002.
of Woss Lake has shown that increased sockeye
populations can be attained.
However, increasing the size of stocks is not the sole
objective of this research. The next objective is to
obtain a balance between big fish while at the same
time maintaining the density. An initial examination
of the 2001-2002 data shows there is an increase in
Woss Lake sockeye weights compared with sockeye
from Vernon Lake (Figure 7). However, there is also
the goal of trying to rebuild the stocks, as the
population is still low relative to historical data. If
and when the desired population level is reached, then
the fertilisation of the lakes may be ceased.
What can we expect from nutrient additions? There
are costs and benefits to this process. Overall with
the addition of 732 g of phosphorous per hectare of
11
Woss Lake equates to 12g of phosphorous per juvenile
sockeye in the fall, as shown in Table 1. You need to
add significant amounts of phosphorous to the system
since you lose 80-90% at each step through the food
web (Table 2). In this case, only 2.5g P/ha gets to the
fish in the end. This reduction or loss is due to food
chain dynamics.
Figure 9 addresses the question of how much
phosphorous is added from salmon runs. The
calculations show that an estimated ~3% of P in
juveniles comes from escapement, although different
lakes have higher or lower replacement amounts.
This
means that 2.5g of P per hectare is actually getting
into the fish in the system.
Table 1. Amount of P added per lake and per fish.
Table 2. Loss of phosphorous through food web.
12
In conclusion in the Nimpkish Watershed (Woss and
Vernon Lakes) sockeye typically spawn downstream
of the lakes and the juveniles then swim into lakes.
Figure 9. Actual amount of P added to system from salmon runs.
Therefore dead fish do not contribute to increased
numbers in phosphorous. Overall, the numbers of
sockeye are lower because of over-fishing and
logging. This could be countered by either stocking
the lakes or by lake fertilising. The results of our
study show that fertilisation generated successful
augmentation/manipulation. This process will
continue for two more years. If there is ever a buildup in the sockeye population then the process can be
stopped.
Discussion
Participants discussed what would happen if
fertilisation is stopped, with respect to sockeye
population losses. It was noted that if over-fishing
continues, then nothing may be done to prevent stock
loss. In response to a question about the catchment
area and if it was similar for both Woss and Vernon
Lakes, Don McQueen noted that Vernon Lake is twothirds the size of Woss Lake, but that they have similar
sized catchment areas. The importance of monitoring
to ensure that the desired algae are present in the lake
was also noted.
ECOSYSTEM CONSIDERATIONS IN THE FORMULATION OF
BIOLOGICAL REFERENCE POINTS FOR MANAGEMENT OF
SALMON IN CANADA’S PACIFIC REGION
Kim D. Hyatt, Research Scientist, Fisheries and
Oceans Canada
There are a series of issues related to the over 9,600
salmon stocks present within British Columbia.
Figure 1 describes the status of salmon stocks on the
west coast of Canada indicating the total number of
stocks and the degree of risk for each species. Recent
concerns for the health of salmon stocks have lead to
a broader conservation focus within fisheries
managment. Although the definition of this broad
focus changes over time, the main driver never
changes; that is, to manage salmon for economic
returns.
The question is how does ecosystem-based
management fit with salmon management? Salmon
management and conservation objectives have
evolved rapidly over the past 20 years, from
managing for harvest of maximum sustainable yield
to managing for a better balance between harvest,
stock conservation and maintenance of regional
biodiversity (Figure 2).
13
In June 2000, Fisheries and Oceans Canada adopted
an ecosystem-based management regime for regional
biodiversity, which views salmon as a keystone
species, and focuses on the interactions between
salmon and bears, eagles, trees, etc. For instance,
bears eat approximately 16-36% of salmon returns
and if management increases bear habitat then there
will also be an increase in salmon habitat. As shown
Figure 1. Status of salmon stocks on Canada’s West Coast.
Figure 2. Salmon management evolution over the past 20 years.
14
from Figure 3, salmon returns are key to maintaining a
high level of biodiversity within the entire system.
This new type of management would now ask: If
salmon return to rivers with decreased bear
populations, how does this affect the natural
deposition and cycling of the nutrients? Managing an
ecosystem in BC is difficult because of the variability
in the environment and the strength of the salmon
stocks. With the heterogeneous geology and
declining salmon stocks, nutrient depletion is
occurring and is a detriment to the future health of
salmon stocks. As mentioned in the previous
presentations, the carcasses of adult salmon are of
immense importance to juvenile salmon for they
replenish valuable nutrients, such as phosphorous,
throughout the habitat. Figure 4, for example,
Figure 3. Salmon are keystones to regional biodiversity.
Figure 4. Evidence for nutrient limited production in freshwater ecosystems of the eastern Pacific Rim.
15
provides evidence of a positive relationship between
total phosphorous and fish biomass of freshwater
ecosystems. This nutrient-rich habitat thus ensures
that there is enough primary production for the
zooplankton on which the juveniles feed. As shown in
Figure 5, salmon are keystone species that exert
control as predators, prey and nutrient sources in
communities of aquatic invertebrates, fish, terrestrial
mammals and birds.
Years of experimental nutrient additions to Great
Central Lake, B.C. indicate that the vulnerability of
the zooplankton forage base to cropping by juvenile
sockeye salmon varies with lake trophic status (Figure
6). With an increase in zooplankton there is an
increase in the biomass of sockeye, and also an
In the state of Washington, there is a need for up to
four times more salmon than are presently returning if
we wish to have a natural influx of nutrients to these
systems. This means that there can be no exploitation
of the stocks, and consequently this adds to
management difficulties and the question of “how
much fish are allowed to be harvested?”
As a manager how do you deal with this scenario?
Solutions such as additions of local carcasses or
nutrient loading are costly. Could dealing with direct
consumption along scavenger pathways be a better
approach? At present there is no intergenerational
connection, and we do not know how strong the
Figure 5. Relevance of salmon to biodiversity.
increase in the number of sockeye per hectare. This is
important because in areas that have bears and salmon
present, there is an increase in nutrient cycling
through riparian deposition. However, there is a point
where the number of carcasses available for nitrogen
enrichment reaches saturation. Presently many
watersheds in BC are well below this saturation point
as shown in Figure 7.
connection is. The bottom line is that we need to
know more before we start adding carcasses.
There is also the question that if there are intense
harvest levels, over time, and economic production
decreases, how much does it decrease? In the draft
Wild Salmon Policy for Canada, minimum
escapement to secure the future of salmon populations
is required. To accomplish this, there needs to be a
16
Figure 6. Effect of experimentally induced nutrient variations on the Carrying Capacity of
Great Central Lake, BC for Juvenile Sockeye salmon.
Figure 7. Approximate 15N saturation level of various watersheds in the 1960s.
definition of ecosystem reference point, which will be
higher than those used for stock recruitment functions.
Future management will demand that the role of
salmon be recognized in ecosystem maintenance,
productivity and biodiversity. Unfortunately, at the
present time the development of the ‘policy’ is far
beyond the supporting science in these areas. While
there is broad policy and community support for
ecosystem-based management, no one is yet able to
17
execute ecosystem-based management. This
discontinuity could be due to the lack of science and/
or information tools for policy implementation.
There is also a need for defining new terms and
ecosystem-based objectives and indicators in order to
be able to move forward.
Discussion
There was discussion regarding the return (i.e.
financial/number of salmon) as a result of fertilisation
costs. For example, if a certain amount of fertiliser is
added to give a certain number of fish, how can this
number be guaranteed for years later? According to
ecosystem management, the numbers can be
increased, but in reality there are too many
complications (eg., ocean survival) to make this
possible. It is also important to consider situations
such as in the Fraser River where fertilisation is not
utilised because coho are low in numbers and are
sensitive to habitat changes.
RIVERS AND SMITH INLETS: POSSIBLE INFLUENCE OF
LAKE CONDITIONS
Rick Routledge, Professor, Statistics and Actuarial
Science, Simon Fraser University
Rivers Inlet has not been fished for several years, so
the cause of the declines in sockeye salmon
populations is in question (Figure 1). Glacial retreat,
El Niño/Southern Oscillation (ENSO), global
warming, decreased food levels (nutrients), along
with destruction and pollution from logging
A question was posed: ultimately is fertilisation just
too complex for use? The discussion concluded with
the explanation that fertilisation plans (and ecosystem
management) are not meant for industrial production
but rather as recovery tools. An increase in nutrients is Figure 1. Rivers Inlet Sockeye run-size estimates (no escapement
needed for the movement towards recovery to historic estimates prior to 1948).
patterns, such as for the recently listed (COSEWIC) as
throughout the Inlet, are all plausible causes. There
“species at risk” sockeye populations in Cultus and
were a few zooplankton distribution patterns noted
Sakinaw Lakes. If used as a prescription for industry
rather than mitigation, then fertilisation will be have to from preliminary data from Year 1 of a continuing
study, one of which was that there is an increase in
be used in a different way. The focus has to be on the
zooplankton as one moves down the Inlet (see Figure
ecosystem, and on management for a better balance
between consumption and biodiversity. A compromise 2 for a map of Rivers Inlet). One idea for this
distribution is that the spring freshet may be affecting
has to be found with respect to the ability “to fish or
where the zooplankton are found in the Inlet. The
not to fish”.
spring freshet is occurring earlier than it did in the
1960s, thus affecting when the silts are carried into
the Inlet (Figure 3). The suspicion is that glacial silts
are causing the populations to decline because the
spring freshet causes the system to shut down.
Estimates of total returns compared to the spring
timing (lagged by 4 years) has an R2 = 0.47 indicating
a relatively strong correlation as shown by Figure 4.
Early spring freshet will cloud the lake which could
lead to an immediate decline in phytoplankton and a
long-term effect on salmon numbers.
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Figure 2. Map of Rivers Inlet and surrounding area.
If the spring freshet is occurring earlier, then there
may be less phytoplankton due to clouding of the lake,
and this in turn will have long-term effects on juvenile
survival rates, including marine survival. One
interesting aside that was noticed while doing the field
work was that Wyclees Lagoon sockeye (see Figure 2)
do not follow typical migration timing when leaving
for the open ocean, and for some reason remain in
Smith Inlet longer than do other populations. Sockeye
normally migrate out in April to early July after
spending a year in freshwater. Based on the size of
the smolts found in Wyclees Lagoon it appears that
they may spend at least their first summer in the
lagoon, with the sockeye reported to be present in the
lagoon as late as August. This suggests that they may
be spending their next winter in the lagoon as well.
The alternate explanation is that they delay their
migration and leave after August, but this is
considered less likely. It was also noted that sockeye
were caught near the head of the Wyclees Lagoon but
not on the west side of the lagoon until later in the
season. Since there has been extensive logging in the
Figure 3. Timing of spring freshet in three regional rivers.
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Figure 4. Return vs. spring timing 4 years before.
past along Wyclees Lagoon and Long Lake, it is
possible that the log booms are affecting salmon
utilisation of the areas. If this is the case then
restrictions on human activities may be required in the
area.
A sediment-coring project has been implemented in
Wyclees Lagoon and Rivers Inlet to look at past
marine nitrogen levels as a means to indicate past
collapses and potential problems from nutrient
depletion in the freshwater sheet as well as past
ecological conditions as gauged by microfossils,
primarily Cladocerans. The analysis is presently
underway and many Cladocerans have been found in
the core from Long Lake, while very few have been
found in the core from Owikeno Lake, indicating a
decrease in zooplankton abundance. This type of
study provides insights that can be useful in a number
of ways, such as predicting adult returns based on
food availability in Barkley Sound. The priorities for
future research in this study are to look at data on a 510 yr. basis, and to complete more extensive coring.
Discussion
Dr. Routledge asked participants and fellow presenters
to comment on these initial findings from Rivers Inlet,
and offer direction for future research. Suggestions
were made to continue research into smolt rate
change, change in smolt weight over time, glacial
sediment analysis, glacial flow estimates, and algal
production in Long Lake. Rick stated that the focus
for now is on the Inlet, and taking samples for
physical chlorophyll abundance and zooplankton as
well as the fish, in order to obtain a picture of the
whole trophic chain, as well as to look at
morphological changes in Cladocera with respect to
time. He is interested in obtaining more information
on the nutrients in the Inlet, and mortality in the sea
during the early life stages.
For more information about other Speaking for the
Salmon programs or publications please visit our
website at
http://www.sfu.ca/cstudies/science/salmon.htm
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