Marine fish stock assessment - introduction

1. M Srinath

2. 2
Stock assessmentStock assessment
 What is stock assessment ?
– Quantitative evaluation of status of the exploited
stock
– Functional relationship of stock size or yield with the
factors that affect the dynamics of the stock
 Stock assessment and management
– Evaluation of the fishery under different management
regimes
– Development of management reference points
– Socio-economic objectives

3. 3
A typical stock assessment processA typical stock assessment process
Ecosystem based

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Dynamics of the stockDynamics of the stock

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ApproachApproach
 Macro level assessment
– Catch & effort analysis
 Micro level assessment
– Stock characterstics
 Growth, mortality,recruitment, age structure,
length structure
– Fishery characteristics
 Gear selectivity, age/length at capture

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Biomass
F = q.f

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• Macro approach
 Catch, effort,
survey based
data
MSY, fMSY, Biomass
Biomass,SSB,MSY, Fmsy,
tc,lc, mortalities,growth
Parameters etc
•Micro approach
Age frequency,
length frequency,
capture-recapture
APPROACHES & OUTPUTS

8. 8
It’s a complex worldIt’s a complex world
Multi-species
Multi-species & multi-fleet
Time-series analysis
Ecopath analysis
– Ecosystem Based Fisheries Management
– Everybody talks about it
– Nobody knows what it is!
Bayesian approaches
– Risk assessment & uncertainity
– Participatory approach

9. 9
Stock assessment involves understanding and making predictions
about the response of fishery systems to alternative management
actions.
Must help managers make choices about dynamic fishery systems
in the face of uncertainity
The output of a stock assessment should not be recommended
quotas or fishing effort – it should be biological consequences of
different actions.
The people doing stock assessment are not likely to be the right
people to weigh the risks of alternative management actions.
……. Ray Hilborn & Carl Walters
…………… thus spake wise

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THE END
…. not yet