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Introduction Methods
Acknowledgements: Thanks to Keith Cox, John Moran, Fletcher Sewall, John Hudson, Robert Bradshaw, PWS Science Center, ADF&G Cordova, Dave Csepp, to the Captains and crews of the M/V Steller, R/V Medeia, R/V Solstice, R/V John N. Cobb, F/V Montague, M/V Auklet, F/V Kyle David, Sitka Sound Science Center, ADF&G Sitka, Sitka Tribe, Jan Straley, Matt Dietrick, Cedar Stark, Andrew Eller, Lawrence Schaufler, Ebett Siddon, Ed Neal, Suzie Teerlink, Doris Alcorn. This Project was funded by the EVOSTC.
PWS
LC
SS 50 km
50 km
JUVENILE HERRING COLLECTIONS
• Before & after winter (Dec-Feb & Mar – May)
• 3 winters (‘06/’07, ‘07/’08, ‘08/’09)
• 3 herring stocks: PWS, SS, LC
• Measured length, mass, stomach contents (ID & mass), age
Results
• The dominant fish predator on juvenile herring in PWS was Pacific cod
•Juvenile herring incur size-selective mortality
•73% of the herring in fish stomachs were age 0
• Modal size of herring consumed was 75mm
Juvenile herring adhere to the CRITICAL SIZE HYPOTHESIS, where need to forage outweighs the risk of predation until a critical size of 75 mm is attained
Energetic tradeoffs between foraging and predation risk in the winter
for juvenile Pacific herring in the Gulf of Alaska
JJ Vollenweider1*, Ron Heintz1, Mary Anne Bishop2, and Jordan T. Watson2 1 Alaska Fisheries Science Center, NMFS, 17109 Point Lena Loop Road, Juneau, AK 99801 2 Prince William Sound Science Center, PO Box 705, Cordova, AK 99574 * Email: [email protected]
The recommendations and general content presented in this poster do not necessarily represent the views or official position of the Department of Commerce, the National Oceanic and Atmospheric Administration, or the National Marine Fisheries Service.
Juvenile Pacific herring (Clupea pallasii)
WHOLE BODY ENERGY CONTENT:
• Bomb calorimetry (n=40)
• Proximate composition (fat, protein, water) (n=156)
Calculated total energy using energy equivalents (36.43 kJ*g-1 for lipid and 20.10 kJ*g-1 for protein)
• Bioelectrical Impedance Analysis (n=1215)
Best models (AIC) calibrating energy content to Reactance in parallel (Rp):
Winter Total Energy = -18.8 + 9.19 8 Rp + 6.90 * Mass, R2 = 0.98
Spring Total Energy = -16.4 + 4.48 * Rp + 5.65 * Mass, R2 = 0.94
PREDATOR COLLECTIONS:
• Before & after winter (Nov & Mar)
• 2 winters (‘09/’10 and ‘10/’11)
• 1 herring stock: PWS
• Measured length, mass, stomach contents (ID, length of prey)
Pacific cod (Gadus macrocephalus)
Alaska
PROBLEM: Several populations of herring in the Gulf of Alaska have been depressed for decades despite cessation of fishing. Large recruitments are needed to bump them out of these low abundance states.
Sampled two depressed herring populations, Prince William Sound (PWS) and Lynn Canal (LC), and one robust herring population, Sitka Sound (SS).
How do starvation and predation influence winter survival of juvenile herring in the Gulf of Alaska?
BACKGROUND: • In the winter, energy is limited for juvenile fish
• Energetic trade-off: Store energy to prevent starvation? vs Use energy for growth to reduce predation risk?
• Large fish can store more energy & seek refuge from predators
• Small fish lack energy to meet winter demands & must forage, exposing themselves to predators Size Selective Mortality
Critical Size Hypothesis Juvenile fish at high latitudes much reach a critical
size to ensure overwinter survival
WINTER ENERGY LOSS OF JUVENILE HERRING PISCINE PREDATORS MECHANISM FOR CRITICAL PERIOD
Frequency (#) of herring in predator stomachs
Winter energy cost (% of total energy)
Predation Pressure vs. Winter Energy Cost
Herring fork length (mm)
Age-0 Age-1 Age-2
Highest predation risk, Gaining energy by foraging
Decreasing predation, Foraging less & relying a bit on energy stores
Little predation, Becoming more free to forage
Minimal predation, Energetic costs increasing due to maturation
energetically neutral
Greater energy cost with size (cost of maturation at age 3)
Less energy cost with size
Age-0 Age-1
Age-2
winter
spring energetically neutral
Winter energetic strategies of juvenile herring vary by age
