Importance of Habitat in salmon declines and recovery

Ray HilbornSchool of Aquatic and Fishery Sciences

UW

What is wrong with salmon?The 4-H’s

• Harvest– We take too many

• Habitat– We degrade their streams

• Hydroelectric– We block passage, turn rivers into lakes

• Hatcheries– We try to “mitigate” for habitat loss by artificial

production

Structure of talk

• Trends in abundance– How bad is the problem

• Ocean conditions – the BIG driver

• Hydroelectric

• Harvest

• Hatcheries

• Habitat

Myth IWe are running out of wild

salmonThe “truth”: there are nearly as many wild salmon in western North America now as any time since Europeans arrived

But: this due primarily to Alaska, and in the Lower 48 many stocks are extinct and most are well below historical levels

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Myth IIThe ocean is big, unlimited and salmon abundance is driven by

freshwater and habitat

The “truth”: most large scale variation in salmon abundance is driven by ocean changes

But: this only means it is harder to detect anthropogenic impacts

Lake Nerka, SW Alaska

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referencelakes

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Historical sockeye population dynamics

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Schindler and Leavitt (2001)

Lake Nerka, SW Alaska

Historical sockeye population dynamics

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Effects of sockeye population on phytoplankton production

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Survival rate by Realm

Arctic

SE Alaska

Coastal BC

Georgia Strait

Puget Sound

Coastal Washington

Columbia Basin

Coastal Oregon

California

CohoFall

chinookSpringchinook

Avg survival rate

Coho survival rate by Domain

Release year

Survivalrate

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Alaska and YukonBC and Puget SoundCoastal WaOrCaColumbia basin

Fall chinook survival rate by Domain

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Columbia basin

Spring chinook survival rate by Domain

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BC and Puget Sound

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Columbia basin

Coho survival~SST regression

Coho survival~SST regression (incl. resid)

Gulf of Alaska – Small set of structuring variables operating at different speeds - Whammo!

Myth IIIThe decline of NW salmon is due

to damsThe “truth”: systems without dams have had similar trends

But: clearly dams are not good for salmon and are part of the problem

Chinook survival by river segment

Fall chinook Spring chinook Fall chinook

Columbia Columbia Fraser

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B: Columbia below damsW: Willamette RiverA: Columbia above damsS: Snake River

L: Lower FraserT: Thompson RiverU: Upper Fraser

Chinook survival in Columbia BasinFall chinook Spring chinook

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Upstream (miles)

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Chinook survival in Fraser Basin

Fall chinookS

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Upstream (miles)

Myth IVHatcheries are necessary to

mitigate for lost of habitat and over-harvest

The “truth”: hatcheries have strong negative impacts on wild salmon

But: if we eliminate hatcheries we might have no salmon left in some places

Hatcheries

• The basic assumptions– Freshwater habitat is limiting– Egg to smolt survival in the wild is about 5%– Hatcheries can usually obtain 80% egg to smolt

survival– Release smolts ready to go to sea – they don’t

need any freshwater habitat

Why hatcheries were built

• To compensate for over-harvesting

• To compensate for habitat destruction

• To mitigate for dam impacts

• To buffer natural variation

• To provide extra fish for harvest

• To conserve threatened stocks

Total Releases of Chinook - West Coast

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Total Releases of Coho - West Coast

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Total Releases of Pink Salmon - West Coast

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Total Releases of Sockeye - West Coast

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Total Releases of Steelhead - West Coast

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Numbers, by ten-year periods, when existing West Coast hatcheries began operations

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Ten-Year Periods

Did Hatcheries Work

• We have over 300 hatcheries in the Pacific Northwest

• “If hatcheries were the solution, we wouldn’t have a problem!”

• Much disagreement, what would have happened without hatcheries

OPI Coho Salmon

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Concerns about hatcheries

• Generate over-harvesting on wild fish in mixed stock fisheries

• Compete with wild fish in freshwater and ocean

• Introduce and exacerbate diseases• Genetically degrade wild fish by

domestication and hybridization• Provide an excuse to allow habitat loss

Pink salmon hatcheries in Prince William Sound

• Largest hatchery program in North America

• 600 million fish stocked each year

• Competing hypotheses re marine fish stocking– stocking augments wild production– stocking replaces wild production

• We have BACI !!!!!!

Prince William Sound salmon production

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Guess

Correct

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Total return

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Wild fish production

Prince William Sound

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Hatchery

Myth VThe collapse of salmon in the late

80s and 90s is due to habitat changes

The “truth”: habitat has not changed that much

But: habitat is definitely declining

Few (if any) attempts to integrate all factors in combined analysis

• We have detailed harvest models

• We have no hatchery impact models in use

• Changes in ocean conditions are being better understood but not used in evaluating recovery plans

• A number of habitat models, EDT the most used

Framework for impact of habitat

• Multi-stage life history model from Moussalli and Hilborn 1986– each life history stage as a Beverton-Holt curve

with a productivity (initial slope or survival) and a capacity

• Key question is how to relate habitat to productivity and capacity

Sharma coho carrying capacity

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Key Model ComponentsSHIRAZ

• Spatially explicit – reaches or estuarine areas

• Life stages as many as you want• Stocks may be life histories, wild/hatchery etc• Capacity and productivity – any life history• Habitat characteristics by reach• Stochastic factors (flows, ocean survival etc)• Functional relationships between habitat

characteristics and stochastic factors and productivity and capacity

Reach Characteristics• Passage• Square meters spawning gravel• Distance• Square meters rearing habitat• Percent fines in gravel• Watershed area by reach• Percent impervious by reach• Temperature, DO etc.

Functional relationships

• Spawning gravel and egg capacity• % fines in gravel and egg to fry survival• Up the the user to define what you want to

use• Will ultimately build a “library” of

functional relationships much like EDT …– But the user will decide which ones to use from

the library

General model framework

• Read in the data – reach-specific habitat– hatchery input– Functional relationships– Hatchery practice– Harvest and ocean conditions specification– habitat interventions

• Loop over time

– Calculate the change in habitat

– Calculate the change in population size

• End the loop

Habitat Changes

• Annual habitat change: habitat degradation

• Habitat change due to a 1-time event: habitat restoration

Hatchery Influence

• Affect wild fish through competition

• Interbreeding can cause domestication of wild fish, and reduced survival

Functional RelationshipsMark I version

• Spawner capacity depends on gravel area

• Egg survival as a function of fines

• Fry survival as a function of percent

impervious and rearing area

Spawners to Egg• capacity depends on gravel area

• productivity depends on age specific fecundity and age distribution of spawners

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Eggs to Fry

• capacity is unlimited• productivity depends upon % fines

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• capacity determined by rearing area• productivity determined by % impervious

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Other outstanding issuesBeyond current efforts

• Allow for parameter uncertainty

• Formalize reality checks

• Potentially imbed the above in formal Bayesian framework

Current status

• Muckelshoot tribe using to meet TRT requirements for a rebuilding plan – Green River chinook well developed, White and Lake Washington just beginning

• Joint work with NMFS and Mark Sheuerell to interface SHIRAZ with PRISM dynamic hydrology models

Essential Fish Habitat:SHIRAZ provides a format

• To calculate the sensitivity of population size to each habitat indicator in each area

• This allows a quantitative ranking of the importance of different habitat characteristics and sites

• This ranking can be used to define “essential”, much like NMFS defines “overfishing”

Summary I

• Current work in evaluating natural and anthropogenic impacts on salmon suffer from lack of unified modelling framework

• SHIRAZ can serve as an initial general model structure for cost benefit analysis, policy evaluation, and parameter estimation

Summary II

• The Ocean, and the four H’s are all important

• We need to identify where time, effort and money will be best spent in salmon restoration

• This will require a new generation of models, data collection and analysis