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Title: The Fisheries Response to Climate Change

NCAR Summer Colloquium August 4, 2009
The Response of Marine Food Webs to Climate
Variability and Change
Ken Drinkwater Institute of Marine
Research and Bjerknes Center for Climate
Research, Bergen, Norway
Marine food webs exist within a variable
environment and we know from past observations
that this variability has a strong impact on
marine biota.
We also know that the liklihood of increasing
changes in the future is high. Politicians, ocean
resource managers and the general public have
been demanding what will happen to marine
ecosystems under climate change.
Although it is impossible to predict what changes
will occur with certainty, as scientists it is
paramount that we address these issues as best we
Simplified Food Web
Biomass Changes
Stock Biomass
Mortality (including Fishing)
dB/dt G R - M - F
Hypotheses to Explain Biomass Variability
dB/dt G R - M - F
  • 1. Intra-specific - density dependent effects
  • G(B), R(B), and/or M(B) gtgt F
  • 2. Inter-specific dependence on other species
  • G(Bi), R(Bi), and/or M(Bi) gtgt F
  • 3. Fishing - fishing mortality dominates
  • F gtgt G, R, M
  • 4. Climate - environmental effects
  • G(E), R(E) and less likely M(E)

5. Complexity - combinations of 1 to 4
Climate affects
Growth and Recruitment
Direct Mortality in some cases.
  • Also affects
  • distribution, migration, availability and
    catchability, which are important to the fishery
  • reproduction and age at maturity

How Does Climate Affect Fish?
  • Physiological Effects
  • (T, S, O2)
  • Metabolic processes

Biotic Responses to Oceanographic Variability
Zooplankton Production
Tittensor et al., 2003
Calanus finmarchicus
  • Change as change in production
  • Increased temperatures lead to faster turnover

Zooplankton Distribution
Cold Period
Warm Period
There is a limit to northward movement however
due to light limitations.
Subtropic Species
Beaugrand et al. 2002. Science
Warm temperate slope species
Subarctic Species
Cod recruitment in North Sea appears to be
related to the plankton anomalies (dominated by
Calanus finmarchicus)
Beaugrand et al. 2003, Nature
Energy flow (pelagic vs. benthic pathways)-
Bering Sea
Hunt et al., 2002
Energy flow (pelagic vs. benthic pathways)
Bering Sea 2
Bloom in warm water
Bloom in cold water (ice-associated)
F. Mueter, pers. com.
Phenology - Shrimp
Egg development duration for Pandulus borealis in
North Atlantic
Purple represents day at 50 hatching and green
the peak in phytoplankton.
Koeller et al., 2009
Abundance Salmon
N. Pacific Regime Shift
(warm) Phase
- (cold) Phase
Mantua et al., 1997
Distribution - Bering Sea
  • Cold pool defines boundary between Arctic and
    subarctic biota
  • Retreat of cold pool has resulted in northward
    shift in fish distribution

Temperature ( C)
Mueter and Litzow, 2008
Northward shift, center of distribution 45
species, 1982-2006
South-North shift (km / 25 yrs)
Mean shift 31 km
Mean 31 Km
Poacher, sculpins, sandlance
Rate similar to North Sea (Perry et al. 2005) 2-3
times faster than terrestrial mean (Parmesan and
Yohe 2003)
Mueter and Litzow, 2008
Vertical Distribution
Redfish in the Irminger Sea
Pedchenko, 2005 ICES JMS
Atlantic Cod
The relative size of a 4-year old as a function
of mean bottom temperature.
Drinkwater, 2000
Changes in Growth Rates
Growth rates of Northern cod (blue line), as
measured by weight change between ages 3-5
declined drastically through the 1970s and 1980s.

This paralleled the changes in the NAO index (red
Drinkwater, 2003
Effects of Poor Growth
When in poor condition the fish use most of its
energy just to survive and have less energy to
put into reproduction and healthy eggs.
Effect on Polar Bears
Early 20th Century Warming
Why examine this event?
  • Large climate changes with noticeable ecosystem
  • North Atlantic wide with important economic
  • Less impact of fishing then later events
  • Led to the first meeting on Climate Change
    sponsored by ICES in 1948.

Climate Changes
During the 1920s and 1930s there was rapid
warming of the atmosphere and oceans primarily
north of 60ºN that produced temperatures as warm
or warmer than the present.
Johannessen et al. 2004. Tellus
Warming in the North Atlantic
SST Change (1930-60 vs 1961-90)
AMO Sutton and Hodson, 2005
Not only was there increased heat from the
atmosphere but there was documented increased
transport of warm water into the Barents Sea,
north along Svalbard, along northern Iceland and
into the Labrador Sea.
West Greenland
Iceland Connection
In the 1920s conditions were right for the drift
of larvae from Iceland to West Greenland and
there was good survival once there.
Under certain conditions cod larvae drift from
Iceland to West Greenland
This continued through to the 1960s with
increased abundances and the development of a cod
fishery that dominated the Greenland economy.
Atlantic cod moved northward by 1500 km in
response to warming.
Hansen 1940
Not only cod were effected
Other warm water species also spread northward
Atlantic Herring
Atlantic Halibut
Cold-water species such as capelin did not
migrate as far south and their abundance in
southwestern Greenland decreased while they
spread north as far as Thule.
Migration patterns of other species changed, e.g.
Beluga Whales
e.g. earlier arrival and later departure
Prior to the 1920s cod spawning was largely
confined to the south coast.
After the 1920s warming began, cod spread
northward to spawn along the north coast, thereby
surrounding Iceland.
Interestingly, the condition of the cod in the
south deteriorated during the warm period while
those off northern Iceland were in good
condition. Why?
Prior to the 1920s capelin, the main food for
cod, migrated from the Iceland Sea south to spawn
along the to the south coast of Iceland.
After the 1920s warming with the influx of
Atlantic water along the north coast of Iceland,
capelin did not have to migrate to the south
coast and they spawned along the north coast. In
the abscence of thier main prey, the condition of
the cod that remained along the south coast
deteriorated while those along the north coast
did well.
Invasive Species
Basking Shark
Atlantic Mackerel
Several warm water species such as basking
sharks, tunny, mackerel, saury pike and sunfish
appeared occasionally and some frequently in
Icelandic waters whereas previously they were
rare or absent altogether.
Norwegian Sea
Atlantic Herring
The population of Norwegian spring spawning
herring rose dramatically in parallel with the
temperatures as recorded in the Kola Section.
Vilhjalmsson, 1997
Toresen and Østvedt, 2000
Atlantic Herring
Juvenile herring spend 1-3 yrs in the Barents Sea
before returning to the Norwegian Sea. During
the 1930s a herring fishery developed along the
Murman coast where previously this species was
almost unknown.
Barents Sea
Cod spread northward from the southwestern
Barents Sea appearing in large quanties on Bear
Island Bank and west of Svalbard. This lead to
the re-establishment of a cod fishery there after
an absence of almost 40 years.
Cod (and haddock) also penetrated farther
eastward to Novaya Zemlya.
Drinkwater, PiO, 2006
NE Arctic Cod Stock
Total and spawning stock biomasses and CPUE
maximum for NE Arctic cod stock during early 20th
century warm period due to .
  • Improved recruitment
  • Higher weight at age.

The mean weights of cod in the Lofoten region
increased by 50 during the warm period. (from
Godø, 2003)
Drinkwater, PiO, 2006
Barents Sea cod spawning districts along the
Norwegian coast
Spawning in East Finnmark since 2004
Sundby and Nakken, 2008, ICES JMS
Arctic species retreated and the number of boreal
species increased along the Murman coast such
that the relative amount of boreal species
Nesis, 1960
Off West Svalbard, comparison of benthos prior to
the 1930s with those of the 1950s indicated that
Atlantic species spread northward by
approximately 500 km.
Benthic Species
Blacker, 1957
Bottom-Up Response
  • Available phytoplankton and zooplankton
    information during the later part of the warm
    period and the following cool period suggests
    that the increased fish production may have been
    due to increased phytoplankton and zooplankton
  • Increased phytoplankton production was due to a
    combination of less sea ice, northward spread of
    Atlantic waters with higher nutrients and faster
    turnover rates.
  • Increased zooplankton production is thought to
    be due to a combination of higher primary
    production and faster turnover rates.

Drinkwater 2006
Climate vs Fishing Impacts
Climate vs Fishing Effects
It is often stated that we need to separate the
effects of climate from fishing. However, for
many stocks this can not be achieved as the two
interact in a non-linear way.
  • This can lead to changes in the ecosystem
    structure and function. Different size
    individuals and different species respond to
    climate in different ways.

Fishing increases sensitive to climate
The age structure of Barents Sea cod has changed
due to fishing. Old spawners have been removed.
Correlations between temperature and recruitment
increased and was interpreted as a result of the
changing age structure, i.e. an effect of fishing.
Running Correlation Coefficient
Ottersen et al., 2006
Interactions between fishing and growth changes
For the Northern Cod off Labrador and
Newfoundland, condition and size declined during
the 1980s and early 1990s, due largely to poor
environmental conditions. Fishermen dumped small
fish in favour of larger fish for which they
could obtain a better price (highgrading)
Dumping peaked in the mid- to late 1980s. This
contributed to the collapse of this stock.
Kulka, 1997
Predicting Future Changes
Prediction is difficult,
especially if it involves the future. Neils
Prediction is easy, getting it right is the
difficult part!
IPCC, 2007
Possible effect of global warming and shut down
of the Atlantic thermohaline circulation
Low probability high impact

Wood et al., 2006
What do the models suggest?
  • Large uncertainty
  • Most climate models produce 20-30 reduction in
    the strength of the AMOC
  • The associated reduction in the poleward
    transport of heat is less than the atmospheric

Predicting Future Ecological Changes
Future zooplankton production
-Barents Sea
Use Biophysical Models
Production decreases in Arctic Waters
Production increases in Atlantic Waters
Ellingsen et al. (2008)
Shifts in Fish Distribution
Highly likely to be a general northward movement
in response to climate changes (ACIA, 2005).
They are already occurring!
Year 1
Year 10
Bioclimate Envelope Models
Polar cod
Year 20
Year 30
Cheung et al., 2008, UBC Report
Capelin Spawning in Response to Climate Change
Present Spawning
Future Spawning
Direction of distributional shift of adult
feeding migration
Huse and Ellingsen, 2008
Cod Recruitment and Temperature
Warm Temperatures decreases Recruitment
Warm Temperatures increases Recruitment
ln Recruits
Mean Annual Bottom Temperature
Planque and Fredou (1999)
Drinkwater, 2005
If BT lt 5 and T warms stock recruitment
generally increase If BT between 5 and 8.5C
little change in recruitment If BT gt8.5C
recruitment generally decreases
If BT 12C we do not see any cod stocks
Drinkwater, 2005
Cod Abundance Projections
Drinkwater, 2005
Ice-Dependent Marine Mammals
- Highly likely polar bear abundances will
decrease and may disappear
- Walrus abundance and distribution will depend
upon finding appropriate suitable benthic feeding
grounds with appropriate resting grounds.
Polar Bear
Changes in ecosystem function (Barents)
Food web in Atlantic water
Food web in Arctic water
The food web changes may be far more dramatic for
the higher compared to the lower trophic levels
Falk-Petersen et al. 2007
Changes in Seabirds (Barents)
Little Auks
Climate Change in the Barents is likely to result
in a decrease of plankton feeding birds such as
Little Auks and increase of fish-eating birds
such as Guillimots.
Falk-Petersen et al. 2007
There is the possibility that boreal species from
the Arctic and Pacific will move into the Arctic
and may start to mix.
Neodenticula seminae, Reid et al., 2007
What do we need to Improve Projections of Future
Ecological Changes?
What do we need?
  • More emphasis on quantitative estimates
    (mechanistic modelling)
  • Better understanding of the processes
  • Improved parameterization of the models
  • Regional models
  • Measure of uncertainty

What kind of Models do we need?
What kind of Models do we need?
  • What is the role of observationalists?
  • Observationalists and Modellers need to work
    closer together
  • Modellers to help determine what, where and how
    often observationalists should measure.
  • Observationalists should provide more feedback on
    model results (requires available model results,
    positive criticisms)
  • All motherhood statements but not generally done

Need Comparative Model Studies
1. Ecosystems are complex helps determine what
is a fundamental process and what is unique.
2. Provides insights that one cannot obtain by
looking at a single ecosystem
3. Single model applied to several ecosystems,
different models applied to single ecosystem
4. Sharing modelling approaches
Need to include Fishing Effects
Models need to be used to determine interaction
between climate and fishing and explore effects
of management strategies on stocks under climate
change scenarios.
Fishing and Climate
Response to climate change will depend on fishing
Multivariate autoregressive models of Baltic cod
under increasing salinities.
Martin Lindegren, Ph.D. Student, DTU Aqua,
Developing Regional Impacts of Global Change
  • Need Regional Models
  • IPCC provides Climate Change scenarios from GCMs
    from 1950s or 1960s to present and future up to
    2100. Multi-Model Dataset (ensemble runs) of
    climate scenarios (
  • Use IPCC senarios for downscaling GCMs output
    by regional models for hydrodynamics (and biota)
    in regional seas

Some Present IPCC GCMs Limitations
  • ?Small to large (1-3?) scales mixing and
    turbulence, friction, waves, clouds, marine
  • ?Arctic sea ice conditions not well represented
  • ?Tides, tidal variability has the potential to
    impact significantly on climate e.g. (W.Munk et
    al., 2001)
  • ?No variability considered (temporal, spatial) in
    tidal forcing (IPCC, 2007)
  • ?Generally poor representation of ENSO, NAO, etc.


IPCC GCMs Limitations
?No initialisation to the present state
(particular problematic for the ocean)
  • Dr. Kevin Trenberth stated
  • None of the models used by IPCC are initialized
    to the observed state and none of the climate
    states in the models correspond even remotely to
    the current observed climate. In particular, the
    starting state of the oceans, sea ice, and soil
    moisture has no relationship to the observed
    state at any recent time in any of the IPCC

I postulate that regional climate change is
impossible to deal with properly unless the
(global climate) models are initialized (to the
current state).
Surface Temperature error IPCC model ensemble
Chapter 8, IPCC, 2007
Solomon et al., 2007
ST error o C Mod-Obs
Validation of global climate models
Drift problems? Sea-ice problems?
Solomon et al., 2007
IPCC, 2007
Regional Climate Models
One main conclusion ?RegCM are critically
affected by the driving large-scale fields from
GCM and are very similar to GCM results
Regional downscaling IPCC Chapter 11
  • Only very few coupled ocean-atmosphere models on
    the regional scale
  • Fewer models do ensemble runs using different
    global models
  • Regional models that are available mostly use
    previous IPCC global model assessments
  • Few full dynamics ocean model? none reported in
    the last IPCC
  • Few coupled ecosystem models? none reported in
    the last IPCC report

Recently Improved global decadal predictions by
improving initialisation
  • Doug Smith et al., 2007, Science
  • Noel Keenlyside et al., 2008, Nature

Related publications indicated the importance of
AMO for the NA region - Knight et al. (2005)
Keenlyside et al., 2008
Next IPCC Runs
  • Going to Earth System Models
  • Initialization to present day conditions
  • Many of the models will be total new with
    increased number of paramaterizations
  • Will this lead to increased spread in model

Conclusions on Future Projections 1
  • Uncertainty due to global, regional and biolgical
    models is (much?) larger than the signal to study
  • Need to develop uncertainty estimates of future
  • Improved understanding of processes and better
    paramaterization of the models
  • Develop models that include fish and fisheries

Conclusions on Future Projections 2
  • IPCC scenario model predictions (and consequently
    the RCMs based on these) are only of limited use
    at present for regional climate change assessment
  • Presently might be able to learn as much
    performing controled sensitivity tests with
    validated regional models
  • Decadal-scale predictions from GCMs might provide
    improved forcing data, but lose performance after
    approx. 1 decade (??)
  • Inspite of difficulties need toget on with it.

  • In the past climate variability has led to
    significant changes in higher trophic levels
    (recruitment, growth, distribution, phenology,
    etc.) . Responses are species dependent.
  • Fishing interactions with climate to produce
    observed responses.
  • We are in early stages of end-to-end models that
    include fish and higher trophic levels
  • For responses to future climate change need
    improved regional models but have a ways to go.
  • Lots of opportunities for graduate students!

Thank You!
Any Questions?
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