Ecopath and Ecosim in the Eastern Bering Sea An evaluation focusing on Steller Sea Lion Issues Kerim Y. Aydin 1 Collaborators Nancy Friday 2 Patricia Livingston 3 1 School of Aquatic and Fishery Sciences, University of Washington 2 Alaska Fisheries Science Center (NMML) 3 Alaska Fisheries Science Center (REFM)

Ecopath methods Just a population-scale quantitative food web. Mass-balance (not necessarily equilibrium) quantifies known and unknown flows for each box.

Base Estimates Biomass Production Mortality Diet Composition (at a given reference point, not necessarily equilibrium) Dynamic Rates B/B ref. Instantaneous production and mortality as functions of B/B ref. Functional responses External forcing Modeling Framework Model Scale Time and place to suit hypotheses THIS IS AN EXPLORATORY TOOL (emphasize issues and explorations not results) ScaleWeb Dynamics

Scale No scale is universal scale of model => scale of hypothesis => scale of action Spatial scaleSpatial scale Community scaleCommunity scale Temporal scaleTemporal scale

Scale Current model –EBS trawl survey area –Stellers on Edge –Jellyfish ‘unimportant’ –Missing Sea otters Atka mackerel Nearshore infauna, kelp... ‘Whole EBS’ scale results‘Whole EBS’ scale results

Scale Community scale –Species emphasize groundfish Extremely good diet and assessment data Data quality –Key interactions present –Specific weaknesses (forage fish) –(Sensitivity later) Temporal reference points?Temporal reference points? GoodMed.Poor

Scale Time scale –Average annual production and annual anomalies-no seasons –“Present” –(but no reference points for S.S.L.s)

Unexplained (could be balance or loss) metabolism Mass balance (not an equilibrium) Biomass Consumption Predation Fishing Ecotrophic (or Modeling!) Efficiency (EE): Quantified at a single (temporal) reference point.

Unexplained (could be balance or loss) metabolism Mass balance (not an equilibrium) Biomass Consumption Predation Fishing OK for fish. For Steller Sea Lions: WHEN???

Reference points For each species of interest Need a time snapshot when most sources of production and mortality are quantified. (or assume equilibrium- Not for S.S.L.s). 55% of mortality “unexplained”. (Loughlin and York 2001) All data (especially predation) poor.

Reason for past decline A modeling tautology: –Anything you want, according to Ecosim

Projected percent in diet

Some key components are missing… Direct link to large zooplankton (euphausiids) Forage fish and cephalopods

Dynamic Structure (Ecosim) Biomass based »ok - exploratory Food web based » ok - isolate these effects Equilibrium »ok - use sensitivity analyses (or start in decline) »Expect unmodeled invasions functional responses, bioenergetics, populations »Keep results exploratory, qualitative »Sensitivity »1 Ph.D. Unit of work

But since answers are required… Time constraint for management –What do best current models say? –How should we use the results? –Improvement - how and when?

Assume Unknown mortality is “black box” Unmitigatable or proportional. Problem is not local This model is the correct scale. Worthwhile questionsWorthwhile questions Likelihood of past patterns given hypothesesLikelihood of past patterns given hypotheses Time scale of responseTime scale of response Unexpected responsesUnexpected responses

Indirect effects Unexpected indirect effects of fishery manipulation Preponderance of the evidence explaining multiple trends (regimes)

Direct top-down interactions can’t be confirmed Tautology again –Food web is the only interaction. –But largest changes may occur here. (general agreement with life-table analysis). A single trajectory for a single species is non-explanatory.A single trajectory for a single species is non-explanatory.

Bottom up? ‘Physical forcing’ with anomalies ‘Wiggle and test’ data exploration Historical fishing incl.

Primary production forcing Preponderance of the evidence?Preponderance of the evidence? Frequency response.Frequency response.

Additional data: anomalies in consumption –Systematic anomalies in consumption rates? Food habits Predator size Prey size abundant year classes Age class models –Evidence of alternate stable states?

Result of Global S.S.L. prey manipulation (fishing) Elimination of pollock from the EBS through fishing Harms birds, many fish spp. Harms S.S.L., although some compensation Exact amount depends on (uncertain) forage fish. Biomass /B start

Result of Global S.S.L. prey manipulation (fishing) Restoration of pollock in the EBS through fishing closure Exact amount depends on (uncertain) S.S.L. bioenergetics. Helps S.S.L., but only a tiny amount - most food goes to other fish. (similar to MSVPA results: fast-growing eaters of younger pollock win). Biomass /B start

Result of Global S.S.L. prey manipulation (fishing) Exact amount depends on (uncertain) invasion potential. Reduce pollock and cod fishing to 10-50% of current levels Remove all fish predators of pollock Increase of 5- 15% in S.S.L.s after 20 years MSVPA results: eaters of younger pollock win. Biomass /B start

Result of Global S.S.L. prey manipulation (fishing) Exact amount depends on (uncertain) invasion potential. Reduce pollock and cod fishing to 10-50% of current levels Remove all fish predators of pollock Increase of 5-15% in S.S.L.s after 20 years Management does not equal Control !!

These results are sensitive to: S.S.L. diet assumptions »Energy vs. biomass. »Other forage fish dynamics. Bioenergetics »Some key parameters are 2 trophic levels down. »Fish and zooplankton as well as S.S.L.’s. »Pup death and other amplifiers. Regimes and invasive species »Dogfish? Skates?? But what about locally?

Spatial resolution Community-level central place foraging creates local conflicts with fishery.Community-level central place foraging creates local conflicts with fishery. These conflicts are probably more important than global interactions.These conflicts are probably more important than global interactions.

Methods of concentric circles Red : 50 nautical miles radius Green : 100 nautical miles radius Yellow: 150 nautical miles radius the boundary that accommodates energetics demands Energetics-based ecosystem boundary: the boundary that accommodates energetics demands of species within the system = foraging range of C.P. Foragers How does fishing change this boundary? Ciannelli et al. submitted

Consumption: TL> NM Ciannelli et al. submitted Time period:

Model Output: increase of area Ciannelli et al. submitted Migration only way to support seals at 50 nm

Vectors showing 119 foraging trips made by 97 fur seal females Median distance km What do fur seals do? Robson et al. submitted Also looks at fisheries edge effects

Result of EBS scale pred/prey manipulation Climate regime work ongoing. Global (EBS) pred./prey manipulation: –Predation has large direct effect if such data is input into the model. –Increasing Pollock fishing generally harms S.S.Ls. –Decreasing global fishing can help S.S.L.s, IF there is also complete elimination of fish predators, and IF... –no dogfish/jellyfish/etc. show up. Local effects (fishing reductions) may be more relevant.Local effects (fishing reductions) may be more relevant.

Proposed/planned steps –Bering Sea regime/sensitivity work in progress. –Bioenergetics, bioenergetics, bioenergetics (1 Ph.D.) –Fish and plankton as well, forage fish especially. –Local Ecosim/Ecospace? (1 Ph.D.) –Still parameter sensitive. –Best available ref. points are not strong. –Seasonal and migratory modeling poor (so is data). –Successive (nested) Ecopath models (1 Masters) –SE vs. Pribs. vs. Aleutian islands –Protected areas –Collaboration with other scales of models