Trophodynamics and LargeScale Forcing

1
Trophodynamics and Large-Scale Forcing
Trophic basis of production Calculating primary
production supporting fish stocks What limits
fish productivity? Scales of ocean and
population variability Meso-Scale Frontal
Systems ENSO Decadal Anthropogenic
2
Trophodynamic Approach
Term is taken from Ray Lindemans classic
paper Refers to the idea that you can look at
inter-relations between animals with respect to
energy transfer Today, we often call these
energetic food webs
3
Primary Production Supporting Fish Populations
Assume a 10 transfer Efficiency
Total Production 0.1 g C / m2 / yr
Blue Shark
Requires 1 g C / m2 / yr
Flying Squid
Euphausiids
Requires 10 g C / m2 / yr
Small Zooplankton
Requires 100 g C / m2 / yr
Requires 1,000 g C / m2 / yr
Phytoplankton
4
Primary Production Supporting Fish Populations
Total Production 0.1 g C / m2 / yr
Assume a 10 transfer Efficiency
Blue Shark
Flying Squid
25
75
Euphausiids
20
80
Small Zooplankton
Phytoplankton
5
Blue Shark Total Production 0.1 g C / m2 / yr
Blue Shark
2152 x 10 21,520 units PP
0.25 x 615 x 10 1537 units PP
25
Flying Squid
Flying Squid
0.75 x 82 x 10 615 units PP
1 unit squid 2152 units PP
75
Euphausiids
Euphausiids
0.2 x 10 2 units PP
80
0.8 x 10 x 10 80 units PP
20
1 unit Euphausiid 82 units PP
Small Zooplankton
1 unit SZ 10 units PP
Phytoplankton
0.1 g C / m2 / yr x 21,520 2,152 g C m2 yr
6
Applications of the Tropho-Dynamic Approach

• Were there really 10 x more apex predators in the
  oceans before industrial fishing?
• We can ask how much primary production is needed
  to support that biomass?

7
Upper Food Web of the Central Pacific
5
Sperm Whales
Lamnids
Blue Marlin
Other Billfish
Swordfish
Carcharhinids
Blue Shark
4
Yellowfin
Albacore
Bigeye
Mahi mahi
Skipjack
Large Squid
Small scombrids
Baleen Whales
Trophic Level
3
Small Squid
Mesopelagic Fish
Epipelagic Fish
2
8
Changes in Apex Predator Guild After 50 Years of
Commercial Whaling and Fisheries
Essington, 2006
9
Primary Production Required to support food web
under three food web configurations
Mean primary production 700 g / m2 /yr
10
Iverson, 1990

• Approach the problem from the other direction
• How much fish production is expected based on
  some observed primary production?
• Fish Production PP x 10(Trophic Level-1)
• Beware of the fallacy of the mean!
• X f(Y)
• E(X) rarely equals f(E(Y))
• Keep in mind that in the last example, mean
  trophic level of blue sharks was 5.13.

11
Alternatives to Trophodynamic approach

• Basic approaches presume that fish production is
  limited by energy
• Perhaps they are limited by other nutrients?
• P, N
• At least in freshwater fishes, there is no
  evidence for P or N limitation (C is nearly
  always limiting)

12
Essential Fatty Acid Hypothesis

• Just like there are essential amino acids, there
  are also essential fatty acids
• Key components to cell membranes, some of which
  cannot be synthesized by animals
• This means that the type of primary producer
  could be crucial
• Could shifts in species composition be due to
  changes in primary producers?

13
Litzow et al. 2006

• Examine several examples of fish community
  shifts
• Pelagic (usually clupeids) replaced by demersal
  (usually gadoids, flatfishes)
• Clupeids typically have a higher lipid content
• Relate population dynamics to lipid content
• Relate lipid content to required levels of
  essential fatty acids

14
Scales of Ocean Variability
15
Impacts on Marine Fishes

• Typically two issues
• Changes in species abundance / community
  composition
• Changes in spatial distribution

16
Mesoscale Eddies

• Typically 20 50 km in diameter (some may be
  larger)
• Persist for several months
• May be cyclonic (counter-clockwise in N.
  Hemisphere) or anticyclonic (clockwise in N.
  Hemisphere)

cyclonic
anticyclonic
17
Possible Roles of Eddies Sardines in the
California Current
Temp
Potential Larval Growth Rate
Copepod
Larval Biomass /km2
Larval Biomass (mt)
Production index (MT /day)
Logerwell et al. 2001. Progress in Oceanography.
49 391-406
18
Frontal Movement

• Example N. Pacific Transition Zone
• Region where the subtropical gyre meets the
  subarctic Gyre

19
Cross section through front
Temp
Salinity
Chlorophyll
Nitrate Nitrite
Polovina et al. 2001. Progress in Oceanography.
49 469-483
20
Seasonal Front Movement
Band of high chlorophyll forms at the
intersection of these two currents
Polovina et al. 2001. Progress in Oceanography.
49 469-483
21
Albacore Tuna Troll CPUE
Polovina et al. 2001. Progress in Oceanography.
49 469-483
22
Scales of Ocean Variability
23
El Niño
La Niña
Slide courtesy N. Mantua
24
El Niño 1997-98
La Niña 1999-00
Slide courtesy N. Mantua
25
Equatorial Ocean Temperature deviations from the
long-term average 1982-2006
82/83
97/98
91/92
86/87/88
02/03
94/95
93
EN
LN
95/96
05/06
84/85/86
99/00/01
88/89
Slide courtesy N. Mantua
26
ENSO in Upwelling Ecosystems California Current
La Niña Cool water, weak stratification high
nutrients, a productive subarctic food-chain
with abundant forage fish and few warm water
predators
El Niño Warm stratified ocean, few nutrients,
low productivity subtropical food web, a lack
of forage fish and abundant predators
Slide courtesy N. Mantua
27
Shifts in Skipjack Tuna Movement with El Niño
event
Tag displacement pre mid El Niño
Pre- El Niño Tuna Catches
Tag displacement mid late El Niño
Tag displacement late - post El Niño
El Niño Tuna Catches
Lehodey et al. 1997. El Niño Southern Oscillation
and tuna in the western Pacific. Nature. 389
715-718
28
Lehodey et al.

• Review impacts of ENSO on fish populations
• Peruvian Anchoveta crash of 1983
• Distant impacts of ENSO events
• Sardine / Anchovy species shifts

29
Scales of Ocean Variability
30
Pacific Decadal Oscillation (PDO)
Warm (Positive) Phase
Cool Phase
Sea Pressure
Intensified Aleutian Low Warmer SST along
coast cool offshore Upwelling is enhanced
Weakened Aleutian Low Cooler SST along
coast Warmer offshore Upwelling is diminished
31
PDO Impacts in E. Pacific
Coincides with shifts in anchovy (cool) and
sardine (warm) dominance
Chavez et al. 2003. Science. 299217-221
32
Wanna know more?
Chavez et al. 2003. Science. 299217-221
33
PDO and marine communities in the N. Pacific
1960s
1970s
1980s
From Anderson and Piatt (1999) Mar. Ecol. Prog.
Ser 189 117-123.
34
Theres a North Atlantic Oscillation Too!

• Phases of the NAO correspond with the Gadoid
  outburst

35
Even Longer-Scale Cycles
Reconstructed sockeye salmon abundance in Alagnak
River, AK Determined salmon abundance from 15N
ratios in lake sediment Cycles with periodicity
of 100 years!
Schindler et al. 2006. CJFAS. 63 1439-1444
36
Issues to Ponder

• How to disentangle decadal climate signals from
  anthropogenic climate signals
• From pattern recognition to mechanistic
  understanding