Evaluating the proposed MPA designs under California MLPA using fully age

and spatially structured models

Ray HilbornUniversity of Washington

Talk layout

•Brief outline of the model

•A bit of “reality” about overfishing in general and the California current ecosystem

•Results of the model

Key elements of model

• Model coast as an array of 200 1 nm strips

• Track numbers at age by area

• Use usual age structured model including age specific maturity, fecundity, vulnerability and weight

• Assume annual dispersal that is normally distributed, one s.d. for larvae, another sd for all other ages

• Post dispersal density dependence

• Assume total exploitation rate on entire stock and catches taken outside the MPAs

• Assume fleet distributes itself in relation to catch rates

Limits to the model

•Runs are deterministic

•First cut assumed uniform habitat

•No economics of harvesting – all biology

Summary of model

•Basically the same model as in Hilborn, Micheli and de Leo except instead of biomass dynamics, each area has full age structure and larvae have different dispersal distances.

Is overfishing the big problem

Orange roughy in New Zealand

European Cod

W. Baltic

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The ecosystem

History of catch

From Little et al

Revenue (constant $)

from Little et al

Overfishing is not costing much decrease in potential yield

Maximum biomass of key species in the ecosystem

Pacific whiting

7,272,000

Dover sole

596,000

Pacific sardine

4,015,000

Shortbelly rockfish

295,000

Jack mackerel

1,905,000

Widow rockfish

265,000

Northern anchovy

1,598,000

Shortspine thornyhead

230,000

Pacific mackerel

1,394,000

Longspine thornyhead

228,000

Sablefish

723,000

Yellowtail rockfish

138,000

None of these stocks are overfished – no

lost yield

•These stocks constitute 97% of the biomass!

•All of the overfished stocks are low abundance stocks, they constitute 1.3% of the unfished stock biomass

Maximum biomass of less abundant species

Canary rockfish

93,000 Dark blotched

28,000

Pacific Ocean Perch

83,000 Petrale sole

26,000

Lingcod 76,000 Vermilion rockfish

21,000

English sole

63,000 Blackgill rockfish

21,000

Chilipepper rockfish

58,000 Black rockfish

20,000

Bocaccio 46,000 Bank rockfish

14,000

Pacif ic w hiting

Pacif ic sardine

Jack mackerel

Northern anchovy

Pacif ic mackerel

Sablefish

Dover sole

Shortbelly rockfish

Widow rockfish

Shortspine thornyhead

Longspine thornyhead

Yellow tail rockfish

Canary rockfish

Pacif ic Ocean Perch

Lingcod

English sole

Chilipepper rockfish

Bocaccio

Darkblotched

Petrale sole

The overfished

stocks

State of the Pacific fisheries

•What is the problem?

• It depends on the question –what is the objective

What is the problem?

• If the objective is yield – the problem is not overfishing, but discarding and regulations imposed to try to keep all stocks above the overfishing threshold – loss of yield from overfishing is very little

What is the problem?

• If the objective is intact ecosystems – the problem is fishing and the desire to produce yield and jobs – less fishing, less yield, and fewer jobs would provide for more intact ecosystems

What is the problem?

• If the objective is jobs – the problem is discarding due to the trip limit system and regulations to protect overfished stocks, and the economic inefficiency of a large fleet – the same catch could be caught by a much smaller fleet

What is the problem?

• If the objective is profit – the problem is the trip-limit system, the regulations to prevent overfishing – the lack of a rational economic management system

•From a taxpayer perspective the problem is public subsidies

Results

•From Walters, Hilborn, Parrish … submitted to CJFAS

Simple model parameters Abalone Widow

rockfish

Lingcod Bocaccio

rockfish

Cabezon

Base recruitment (Ro) 1 1 1 1 1

Annual "adult" mortality (M) 0.1 0.125 0.25 0.15 0.3

fishing mortality rate (F) 0.08 0.06 0.25 0.056 0.2

Adult emigration rate (~mi-yr) 0.01 1 6 6 1.5

Larvae per adult (k) 100 100 100 100 100

Goodyear compensation ratio (K) 3 20 10 4 10

Larval transport distance

parameter (S)

0.3 40 15 45 1.5

Model parameters

Abalone Successful management

(low F) outside MPAs Overfishing outside MPAs

Abalone

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Package 1, N=714.6 No MPAs, N=580.6Package 3R, N=739.0 No Fishing, N=2000.0Package 2, N=810.2

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Package 1, N=441.3 No MPAs, N=.1Package 3R, N=497.5 No Fishing, N=2000.0Package 2, N=654.5

Bocaccio

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Package 1, N=242.6 No MPAs, N=208.9Package 3R, N=234.3 No Fishing, N=792.4Package 2, N=248.9

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Package 1, N=88.3 No MPAs, N=27.6Package 3R, N=65.4 No Fishing, N=792.4Package 2, N=94.9

Conclusions

•The outcome depends primarily on he fisheries management outside of reserves, ignoring management is ignoring the most important factors

•Generally these reserves are much too small to allow buildup of abundance inside the reserves except for totally sedentary species

Conclusions re MLPA

• Science process did not use models – seemed to rely on intuition of biologists. This can easily be improved in subsequent applications since models are available and easy to use.

• Entire process seems to be predicated on the mis-conception that the “ecosystem” suffers from overfishing

• The concept of “connectivity” is ill thought out and irrelevant unless there is “scorched earth” management outside of reserves

Conclusions re flow fish

•We have models that can be used to answer very important social questions

The End