A Model for Early Life History Survival for Pacific Herring in Prince William Sound Brenda Norcross, Seanbob Kelly, Peter-John Hulson, Terry Quinn School of Fisheries and Ocean Sciences University of Alaska Fairbanks

Herring – An Important Species Forage fish  Commercial fishery

Prince William Sound

Recent History of Herring Fishery closed in March 1989 following the Exxon Valdez oil spill Stock collapsed 1993 due to (VHSV) Species has not recovered to pre-oil spill abundance

Spawning and Larvae Herring spawn onshore in April   Larvae herring are advected counter- clockwise through open water

Years 1 and 2 June-August metamorphosis Nursery habitats at heads of bays In nursery bays for 2 winters Leave bays and join adult schools

Early Life History to Age-1 4 stages - eggs, larvae, fall juveniles, winter juveniles Know mortality changes as life stage changes Determine which life stage is most influential

Early Life History Model Life-stage specific survival to age-1 Builds on an earlier range-based study (Norcross & Brown 2001) Statistical distributions of survival to account for uncertainty Data input from published estimates

Standard Year-Class Model ( Quinn and Deriso 1999) Cumulative mortality - z for each stage multiplied by number of days per stage Total mortality - combines mortalities of sequential life stages to age-1,

Delta Method (Seber 1982) Converts standard error of survival to that of mortality Assumed normal distribution Allows determination of 95% confidence intervals.

Egg Stage - first 21 days (Haegele 1993) Subsurface oophagy - crabs, sea anemones, and snails (Rooper et al. 1999) Duration of air exposure - exposure abiotic forces, and avian predation

Larval Stage - next 92 days (McGurk et al. 1993) Larval mortality caused by advection, predation, and inability to feed Data from Auke Bay, Southeast Alaska Comparable to estimates from British Columbia

next 92 days Fall Juvenile Stage - next 92 days (Stokesbury et al. 2002) Greatest mortality due to predation Averaged over four bays and two years

next 135 days Winter Juvenile Stage - next 135 days (Patrick 2000) Energy reserves (WBEC) and water temperature affect survival Age-0 winter mortality due to starvation Averaged over 12 bays

>Age-3 spawn first 21 days mortality 0.07 d -1 next 92 days mortality 0.07 d -1 next 92 days mortality 0.01 d -1 Egg Stage Larval Stage Fall Juvenile Stage Winter Juvenile Stage next 135 days mortality d -1 Age-1 hatch drift nursery bay

Results Total survival through age herring out of 1 million eggs Compare to range-based – 1-6,500 Consistent with the results of age- structured assessment (ASA)

Average ELH mortality is lower than ASA mortality ASA incorporates mortality ages-0 through -3 Greater uncertainty in the distribution of ELH mortality Total Mortality (Z) Frequency ASA (age-3)ELH (age-1) ELH ASA Distribution of total mortality Total mortality

Single-Stage Sensitivity Analysis Altered mortality of each life stage by 10% Total survival was most affected by the larval stage Length of stage (92 days) and mortality level (* 0.07 d -1 ) is cause Other life stages had an order of magnitude less effect

Conclusions Life stages did not contribute equally to mortality and survival Larval stage has the largest influence on total survival This model shows that there is high uncertainty in the early life history

Acknowledgments Exxon Valdez Oil Spill Trustee Council Jeep Rice Mark Carls

Daily Survival and Daily Mortality.

Results of single-stage sensitivity analysis. Both of the textured series are the results from increasing (left) or decreasing (right) daily mortality (z i ) while the black series is the total survival estimated from the base early life history (ELH) model

Interaction Sensitivity Analysis Determined all possible paired combinations of life stages Altered each pair of mortality estimates by 10% Larval stage combined with any other life stage contributed the most to total survival Total survival maximized by decreasing mortality for larval and egg stages