Is recruitment synchrony due to shared susceptibility to environmental variables?

Is recruitment synchrony due to shared susceptibility to environmental variables?!Megan Stachura1*, Tim Essington1, Nate Mantua1, Trevor Branch1, Anne Hollowed2, Paul Spencer2, and Melissa Haltuch3!

1University of Washington, School of Aquatic and Fishery Sciences, 2NOAA Alaska Fisheries Science Center, 3NOAA Northwest Fisheries Science Center, *Email: mstachur@uw.edu!

Background!Synchrony of extreme recruitment events!Results:  Eastern  Bering  Sea/Aleu3an  Islands  

Data!

Funding was provided by the NOAA Fisheries and the Environment program and the H. Mason Keeler Endowment for Excellence. !

Results: Gulf of Alaska

•  Recruitment!o  Recruitment and spawning stock biomass estimates for 14 Gulf of

Alaska (GOA) and 14 Eastern Bering Sea/Aleutian Islands (BSAI) stocks from stock assessments!

o  Used residuals from the best of three stock-recruitment relationships (Ricker, Beverton-Holt, and Mean) in analysis!

•  Life history!o  Compiled information including spawning time, spawning mode,

pelagic duration, and juvenile habitat!•  Environmental variables!

o  GOA: upwelling, sea surface temperature, freshwater discharge, and sea surface height!

o  BSAI: ice, wind, sea surface temperature, freshwater discharge, and sea surface height!

o  Used principal component analysis (PCA) to summarize the major patterns in the environmental data in a smaller number of principal components (PCs)!

Question: Is recruitment synchrony for groups of marine fish stocks due to shared susceptibility to environmental variables?!!

•  Synchrony of extreme fish recruitment events has been observed in Alaska's marine ecosystems!

•  We hypothesize that synchrony in recruitment is due to shared life history traits that yield shared sensitivities to regional scale environmental events!

•  Bayesian hierarchical models can estimate group level effects of predictors, so this is a good method for estimating environmental effects for groups of fish stocks!

Synchrony of extreme recruitment events!

Acknowledgements!

•  Less synchrony in recruitment than expected!•  Less correlation within groups than expected in the response

of recruitment to the regional environmental variables tested!•  Positive coastal GOA SSH anomalies, associated with onshore

transport, coastal downwelling, and accelerated Alaska Coastal Current (ACC), is associated with high recruitment for the GOA cross-shelf transport group. This may reflect enhanced onshore transport of larvae and nutrients, and/or precursors to enhanced mesoscale eddy activity in the ACC one year later. !

•  Offshore upwelling conditions associated with SSH PC2 are associated with higher recruitment for the GOA cross-shelf transport group and flathead sole. This may indicate an important role for enhanced nutrient supplies from offshore upwelling and onshore advection. !

•  Future research!o  Test additional environmental variables!o  Nonlinear effects!o  More early life history information to improve grouping!

Parameter distributions. The stocks in the cross-shelf transport group tended to have a positive relationship with SSH PC1 and PC2.!

Sea surface height principal component loadings. Higher recruitment for the cross-shelf transport group occurred during years of positive coastal GOA SSH anomalies and negative offshore GOA SSH anomalies. !

Parameter distributions. There was little correspondence within groups in the relationship of recruitment with the predictors.!

Modeling Results: There were 3 groups in the BSAI model: cross-shelf transport, retention, and parental investment. The model with the first 5 PCs across all environmental variables was the best model tested. !

Analysis!•  Recruitment synchrony!

o  Identified the 25% strongest, 25% weakest, and 50% near average year classes!

o  Chi-square test to identify years of synchrony in year classes!!

!!!!!!!•  Bayesian hierarchical modeling !o  Grouped stocks based on the processes thought to be important

to recruitment!o  Fit linear models with environmental variable PCs as predictors!o  Tested models with 2 PCs from the individual environmental

variable types and 2-5 PCs across all environmental variables!o  Model selection to identify best model!

Recruitment synchrony. Some stocks, like GOA arrowtooth flounder and Dover sole, showed recruitment synchrony, while others, like GOA rex sole and sablefish, showed very little.!

Modeling Results: There were 4 groups in the GOA model: cross-shelf transport, retention, coastal, and parental investment.!The model with the first two sea surface height (SSH) principal components (PCs) as predictors was chosen as the best model. !

Conclusions!

1985 1990 1995 2000 2005

-0.5

0.0

0.5

1.0

GOA Arrowtooth flounderGOA Dover sole

Sto

ck-r

ecru

itmen

t res

idua

ls

1985 1990 1995 2000 2005

-3-2

-10

12

GOA Rex soleGOA Sablefish

Year

1950 1960 1970 1980 1990 2000 2010Year

Rougheye & blackspotted rockfishPacific ocean perchNorthern rockfishDusky rockfishSitka Sound Pacific herringSeymour Canal Pacific herringWalleye pollockPacific codFlathead soleSablefishRex solePacific halibutDover soleArrowtooth flounder

Highest 25% Lowest 25% Middle 50% High 1998-2000!

1950 1960 1970 1980 1990 2000 2010Year

Rougheye & blackspotted rockfishPacific ocean perchNorthern rockfishAtka mackerelEBS walleye pollockAI walleye pollockTogiak Pacific herringPacific codNorthern rock soleFlathead soleYellowfin soleGreenland turbotArrowtooth flounderAlaska plaice

Highest 25% Lowest 25% Middle 50% Low 1982!High 1977! Low 1994!

Index

Cross−shelf transportRetentionParental investment

! Group−level median 95% credible interval

−0.6 0.0

Index

0

PC1!

!

!

−0.2 0.0 0.2

Index

0

PC2!

!

!

−0.1 0.1

Index

0

PC3!

!

!

−0.2 0.0

Index

0

PC4!

!

!

−0.1 0.1 0.3

Index

0

PC5!

!

!

Parameter

Index

Cross−shelf transport

Retention

Coastal

Parental investment

Arrowtooth flounderDover solePacific halibutRex soleSablefish

Flathead solePacific codWalleye pollock

Seymour Canal herringSitka Sound herring

Dusky rockfishNorthern rockfishPacific ocean perchRougheye & blacksp. rockfish

! !Stock−level median Group−level median 95% credible interval

−0.2 0.0 0.2 0.4 0.6

Index

0

PC1!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

−0.4 0.0 0.2 0.4 0.6

Index

0

PC2!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

Parameter

30

35

40

45

50

55

60PC1

170 160 150 140 130 120

30

35

40

45

50

55

60PC2

Loadings

Longitude (°W)

Latit

ude

(°N

)

−0.04

−0.02

0.00

0.02

0.04