ruth joy university of british columbia marine mammal … · 2011-04-06 · ruth joy university of...
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Decline of the Steller sea lion :
Challenges to addressing a dramatic signal
in the dynamics of a marine ecosystem.
Ruth JoyUniversity of British ColumbiaMarine Mammal Research Unit
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Kelowna
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Kelowna
1960 1970 1980 1990 2000Year
0
20
40
60
80
100
1950
Per
cen
t o
f M
axim
um
Fur Seals
Sea LionsHarbour Seals
DeMaster et al. 2006
Dramatic Signal
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Section 7 of the ESA –states that federal agencies must
ensure that“any action authorized, funded, orcarried out does not jeopardize the
continued existence of anyendangered species”.
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MISSING
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1955 1960 1965 1970 1975 1980 1985 1990 1995 2000
0
25
50
75
100
125
150
Biom
ass
caug
ht (m
etri
c to
nnes
)
Year
Pollock Fisheries Data, Aleutian Islands
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Start ofdecline
1976 2000
0
150
75
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Ecosystem
Shift?
Harvest?
Emigration?
Entanglement?
Toxins?
Whaling?
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A change in food availability?
Fisheries reduced stock size so that SSL did not have enough to eat.
Environment change increased stock size so that sea lions eat a less nutritious diet (Junk food Hypothesis)
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Available Data and Approaches
Captive animal studies
Computer and animal models
Field studies
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2004
1977
1955
WEST EAST 10
ALASKABering Sea
Aleutian IslandsGulf of Alaska
Counts
Year
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ALASKABering Sea
Aleutian IslandsGulf of Alaska
2004
1977
1955
WEST EAST 11
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Nutritional Stress: A problem of proof
• What evidence there is – reduced body size in 1980’s over 1970’s in the 1 area in which we have data (Calkins and Goodwin 1988).
• No change in blubber depth
• No change in skull size
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Limitations of the field data
• No pre decline data
• No consistency of collection methods
• Opportunistically collected
• Biology is such that you never know what exactly you are collecting
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We try to make a link between the captive animals in a controlled environment and the wild population
Captive animal experiments : Physiology
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NUTRITIONAL STRESS
Two aspects to nutritional stress:
There is the restriction in QUANTITY of food, but there is also the restriction in QUALITY of that diet.
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Metabolism
Thermoregulation
ForagingLocomotion
Growth/condition
Digestion
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Captive Results
• We have shown that young animals cannot buffer the effects of low quality diet. For example, feeding young animals as much as they can eat, they still lose mass on a low energy diet due to restrictions of stomach capacity and digestion efficiency.
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Week 4
Pro
po
rtio
n o
f b
od
y m
ass
lost
as
bo
dy
fat
or
as le
an m
ass
(%)
-120-100-80-60-40-20
020
Week 4
-120-100-80-60-40-20
020
Restriction Jeanniard du Dot et al. in review
Summer Winter
Herring Herring
Pollock Pollock
Week 4 Week 4
Lipid massProtein mass
Body composition response to nutritional stress
18Recall pollock = “junk food”
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An adult male would require 30 kg of herring per day (C.I.: 22.3, 37.7),
but would require 41 kg of pollock per day (C.I.: 31.3, 50.7)
a 37% increase in prey biomass
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“Real World” Implications
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Limitations on Captive Experiments
Although we have a “huge” number of marine mammals by captive standards, it’s only 12 animals, and they differ by gender, age, and captive environment.
At the end of the day, the inference for the results is for a captive environment, and the link to the wild is not always obvious.
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1955 1960 1965 1970 1975 1980 1985 1990 1995 20000
25
50
75
100
125
150
Biomass caught (m
etric tonnes)
Year
Standardized counts of SSL begin 1973
Pollock Fisheries Data, Aleutian Islands
Broad scale diet data begins 1990
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Start of decline
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Was it fisheries?
• Classical statistics GEE’s attempt to link biomass fished to rates of population change (Dillingham et al. 2006).
• Ecosystem modeling (Guenette et al. 2006)
• Population Dynamic Modeling (Matthiopoulos et al. 2008, Wolf et al. 2006?)
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Modeling limitations
Dependent on assumptions about things we don’t know, and modeling this complex system is only as good as our understanding of the system.
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Challenges
There’s no reliable PRE DECLINE data
Heterogeneity of the environment and the complexity of sea lion biology make it difficult to separate cause and effect.
No ecosystem level experiments to directly test the question
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$ 190 million question
Do fisheries jeopardize the survival and recovery of the Steller sea lion?
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Closing comments
As a statistician, it is a challengeto work on such a high profile
problem and yet have suchlimited data.
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Thank you
• www.marinemammal.org