data preparation, catch history correction, and catch rate ...€¦ · data use procedures have...
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Data Preparation, Catch History
Correction, and CPUE Standardization
for Stock Assessments for Pelagic Fishes
William A. Walsh
University of Hawai`i
Joint Institute for Marine and Atmospheric Research
Pacific Islands Fisheries Science Center
Stock Assessment Program
2013 External Scientific Review
June 2013
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Background: SAP Data Use for Assessments
The SAP uses “corrected” catch data for stock assessments
Corrected catch = Observed catch + Accepted logbook catch + Logbook catch corrections + Logbook releases corrections
Bycatch species (e.g., sharks)
Logbook catch corrections: statistical model estimates
Logbook releases corrections: PIROP observers’ rates
Incidentally caught species (e.g., istiophorid billfishes):
Logbook catch errors: identified by statistical model
Logbook catch corrections: verified with sales records
Logbook releases corrections: PIROP observers’ rates
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Major Problem with Catch Data:
Under-Reporting Shark Catches in Logbooks
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Major Problem with Catch Data:
Misidentifications of Istiophorid Billfishes
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Blue marlin: mean catch per set in 1°squares,
September-December 1995
Mean=0.6
SD=1.7
Mean=1.1
SD=3.3
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Catch History Correction:
Integrated use of multiple data sets
Observer catch data (response) &
Observer operational & environmental data (predictors)
Statistical model
fitting
Model coefficients
applied to logbook
data (same predictors)
Possible outliers
evaluated using
regression techniques
Correction or
replacement of errors
CPUE standardized
with most accurate data
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CPUE Standardization:
Analytical Complexities
Discontinuous time series in the shallow-set sector
Catchabilities on longline gear may differ between
targets and bycatch or incidentally caught species,
making identification of explanatory variables difficult.
Zero inflation often typical of catch data for bycatch or
incidentally caught species.
The geographic expanse of the fishery, typical
operational procedures, and regulatory regime have
changed during the last decade.
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CPUE Standardization:
Excess Zeros as Analytical Complexities
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CPUE Standardization:
Excess Zeros as Analytical Complexities
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CPUE Standardizations:
Strengths of these Analyses
Multiple standardization models (e.g., delta-
lognormal, delta-Gamma, Poisson, negative
binomial, zero-inflated Poisson, zero-inflated
negative binomial) developed and compared for fit
using objective method (Akaike weights).
Comparable results (i.e., high correlations and small
angular deviations among CPUE trajectories) with
several models indicate that findings are robust.
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Species of Interest:
Completed Work with Sharks
Blue shark Oceanic whitetip shark
(Prionace glauca) (Carcharhinus longimanus)
ISC stock assessment CPUE standardizations
in progress; expected completed; zero-inflated
completion July 2013 negative binomial model
selected by objective method
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Analytical Complexities:
Blue Shark Bycatch in a Changing Fishery
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Analytical Complexities:
Blue Shark Bycatch in a Changing Fishery
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Species of Interest:
Several CPUE Standardization Models Yield
Consistent Trends with OWT Shark
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Species of Interest:
Ongoing or Completed Work with Marlins Blue marlin
(Makaira nigricans)
Striped Marlin
(Kajikia audax)
ISC stock assessment
completed in July 2012.
CPUE standardization
favorably reviewed in
December 2012.
Comparative evaluation of
zero-inflated and other
CPUE standardization
models is in progress. ISC
stock assessment completed
in May 2013.
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Species of Interest:
Stock Assessment Work Scheduled for 2014
Shortfin mako
(Isurus oxyrinchus)
Swordfish
(Xiphias gladius)
The ISC BILLWG will
conduct a swordfish stock
assessment in 2014.
The ISC SHARKWG
will conduct a shortfin
mako stock assessment
in 2014.
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Conclusions
Data use procedures have proven useful for the stock
assessments:
Working papers submitted to the ISC SHARKWG
and BILLWG included detailed data preparation
procedures, analyses of deviance, model selection
procedures, residuals plots, and other diagnostics.
Documents exemplified “Best Available Science”
standards.
CPUE standardizations favorably reviewed.