Comparative Analysis of Salmon and Cod: the role of population dynamics in environmental forcing
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Comparative Analysis of Salmon and Cod: the role of
population dynamics in environmental forcing
Loo Botsford, UCD
Lee Worden, UCB
Francis Juanes, U Mass
Alan Hastings, UCD
Mike Fogarty, NMFS, WH
Matt Holland, UCD
Steve Teo, UCD
Hui-Yu Wang, U Mass
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US GLOBEC, 1990s-present
The effects of environmental change on global ocean ecosystems
A mechanistic approach
But typical scenario:
time time
physics Fish population
Correlated -> causal influence
Modeling: physics, NPZ….
What’s missing? Population dynamics of higher trophic levels
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Coho salmon collapse coastwide mid-1970s
Same time as change in new index = PDO
Example: CCS salmon
Chinook salmon does not
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CCS coho salmon
PDO Change in zooplankton composition
Coho abundance
But how (point of action)?
1. Coho growth rate
2. Coho survival year 1
3. Coho survival year 2
Also, why didn’t chinook salmon respond in the same way?
Different physics? Different population dynamics?
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semelparous (die after spawning)
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Recent findings in population dynamics
1. Point of action (e.g., survival at age 3, juvenile growth rate) makes a difference in response
2. Age distribution of reproduction and mortality also determine response.
3. Fishing changes that response
Worden, et al. 2009 - coho and chinook salmon
Myers, et al. (1998) - sockeye salmon
Bjornstadt, et al. (2004) - Atlantic cod
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Several dominant modes of response:
1. Geometric decay
2. A cycle with period = dominant age of reproduction
Varying survival rate geometric decay mode
Varying maturation/age schedule cyclic mode.
N
time
N
0 2 4 6time
Nequil
Nequil
Effects of environment?
From Worden, et al.
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Example: CCS coho salmon
Variable survival rate Variable growth rate
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Fraser River sockeye salmon spawning runs, major streams (Myers, et al. 1998)
Example: cyclic salmon populations
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View of response depends on method of observation:
1. Recruitment
2. Spawners
3. Catch (constant fishing)
Less variability on short time scales
Example: CCS chinook salmon, variable growth rate
Recruitment Catch
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Results of fishing or long-term decline in survival:
1. Increase in resonance
2. Decline, then collapse
Example: CCS coho salmon
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CCS coho salmon
Variable growth rate
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Relevance to climate change
1. Sensitivities to slow change
2. Sensitivity to change in time scales of variability, e.g., ENSO.
ENSO
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Our plans:
Synthesis of what is known re: Pacific and Atlantic salmon, Pacific and Atlantic cod response to environmental variability
How much of the differences in response are due to differences in life histories vs. differences in physical forcing?
Determine population response to variability on these different time scales from data and modeling results.
Interact with physicists regarding current and likely future time scales of environmental variability