What kinds of models are there?

Which models are best for management decisions? (Conclusions!)

Food webs and fisheries--two examples

• Preface: What is a "forage fish"?

• Alaska pollock: ecological research with a food web model
  "How does ecosystem structure affect dynamics?"

  • Distinguishing climate, fishing, and food web interactions
  • Dealing with uncertainty

• Atlantic herring: fishery management strategy evaluation
  "Which harvest control rules best consider herring's role as forage?"

  • Balancing fishing benefits and ecological services
  • Diverse stakeholder interests
  • Needed timely answers!

What is a forage fish?

How does ecosystem structure affect dynamics?

Alaska pollock: a tale of two ecosystems

Alaska pollock: a tale of two ecosystems

Alaska pollock: a tale of two ecosystems

Alaska pollock: a tale of two ecosystems

Ecosystem models and uncertainty

Model ensemble https://xkcd.com/1885/

What is a food web model?

$$B_i\Big(\frac{P}{B}\Big)_i*EE_i+IM_i+BA_i=\sum_{j}\Big[ B_j\Big (\frac{Q}{B}\Big)_j*DC_{ij}\Big ]+EM_i+C_i$$

Ecosystem models and uncertainty: grading inputs

Ecosystem models and uncertainty: run a scenario

Ecosystem models and uncertainty: run a scenario

Ecosystem models and uncertainty: run a scenario

Ecosystem models and uncertainty: run a scenario in an ensemble

Ecosystem models and uncertainty: run a scenario in an ensemble

Ecosystem models and uncertainty: run a scenario in an ensemble

Ecosystem models and uncertainty: run a scenario in an ensemble

Defining ecosystem structure in the EBS and GOA: expectations

Ecosystem reaction to pollock if pollock is a "wasp waist":

Pollock reaction to other groups if control is bottom up or top down:

Perturbation results: ecosystem reaction to 10% pollock increase

Perturbation results: pollock reaction to 10% increase in others

Perturbation results: ecosystem reaction to 10% phytoplankton increase

Simulated increased pollock fishing (significant changes only)

Insights for fishery management

• Differences in food web structure between two adjacent ecosystems with similar biological communities and fishery management

  • Which species respond to the same perturbation
  • Level of uncertainty / predictability in response

• EBS: Influential group at mid trophic levels

  • Wasp waist transmits signal to other groups (neither AK system)
  • Self regulating dominant group (beer belly) absorbs signals
  • Beer belly systems are more predictable, stable as long as the beer belly maintains itself?

• GOA: Influential groups at high trophic levels

  • Magnifies bottom up signals and top down?
  • A less predictable system?
  • Subject to more radical change?

• Structure of a food web may determine how predictable a system is under perturbation, and how changes in primary production propagate through systems

Are any Atlantic herring harvest control rules good for both fisheries and predators?

What is Management Strategy Evaluation?

The Dream and The Reality

Design: link models matching stakeholder-identified objectives

Design: multiple (herring) operating models spanning uncertainty

Harvest control rules: Fishing mortality (F) based on:

• Biomass (SSB) (1, 3, and 5 year blocks of catch)
• Biomass with a 15% restriction on interannual change
• Constant Catch (proportion of MSY)
• Conditional Constant Catch (not to exceed max F)

Economics: Min-Yang Lee's talk last week

• Some modeling, limited by project timeline
• The dream: predator response links to ecosystem services, human well being
• Fishery complexity rivals or exceeds that of food webs!

Predators

Seabirds: data collected here! (and throughout Gulf of Maine)

• Colony adult and fledgling count data used to develop population model
• Chick diet observations examined in relation to fledgling success

Terns and herring--developing a modeled relationship

Although there were no clear significant relationships of common tern productivity and the proportion of herring in diets across all colonies, there were some correlations between herring total biomass and tern productivity.

Hence, the relationship on the right was developed to relate herring biomass to common tern productivity.

Testing the model--does it work?

Predator results summary

Three control rule types--Constant catch, conditional constant catch, and 15% restriction on change--were rejected at the second stakeholder meeting for poor fishery and predator performance.

Food web modeling; supplemental results

Tradeoffs between forage groups apparent

Compare 10% change with more extreme "herring" biomass

More uncertainty with increased herring biomass?

Tradeoffs in Remaining Control Rules

What control rules give us 90% of everything we want?

• Tern productivity at 1.0 or above more than 90% of the time
• Herring biomass more than 90% of SSBmsy
• Fishery yield more than 90% of MSY  
   
• AND fishery closures (F=0) less than 1% of the time (second plot).

What have we learned? Modeling allows us to test options

• Tern/Tuna/Groundfish/Mammal productivity is also affected by predators, weather, and other factors not modeled here
• Even relatively weak relationships still showed which herring control rules were poor
• Managers did select a harvest control rule considering a wide range of factors!

External Resources

• Wasp Waist or Beer Belly?

• New England Atlantic herring management

• New England herring MSE stakeholder process paper

• New England herring MSE modeling paper

• Rpath codebase

• Slides available at https://noaa-edab.github.io/presentations

Questions?

Thank you!