Scroll down or click below to get to one of the following sections on this page:
Assessment of the Pacific halibut stock at the end of 2007 (.pdf) The full account of the assessment.
Summary of the 2007 Pacific halibut assessment (.pdf) A non-technical summary of assessment results.
Comaprison of setline and trawl survey catch rates in different areas (.pdf) An attempt to check for differences in survey catchability among areas by examining the ratio of setline to trawl catch rates. The analysis is inconclusive because of the large variance of the trawl survey catch rates.
Effect of migration on the achievement of proportional harvest under a system of survey apportionment of total catch (.pdf) Analysis of whether a survey apportionment of yield will really result in proportional harvest.
Effect of station depth distribution on survey CPUE (.pdf) Analysis of the representativeness of IPHC survey stations relative to bottom depth distribution in each regulatory area.
Effect of hook competition on survey CPUE (.pdf) Analysis of differences among areas in the competition by other species for baited hooks.
External review of the 2006 stock assessment. In 2007 the Commission contracted the Center for Independent Experts (CIE) to recruit two independent reviewers to go over the assessment in detail. Here are their reports and the staff's response:
Review by Chris Francis Review by Paul Medley Staff response
Assessment of the Pacific halibut stock at the end of 2006 (.pdf) The complete (technical) account of the 2006 assessment.
Summary of the 2006 stock assessment (.pdf) A somewhat less technical account of the 2006 assessment.
Motivation and plan for a coastwide assessment (.pdf) Sets out the reasons for undertaking a coastwide assessment in addition to or in place of the customary closed-area assessments; also investigates the feasiblity of assembling a useful coastwide data set.
IPHC Scientific Report 83. Assessment and management of Pacific halibut: data, methods, and policy (.pdf) A lengthy and detailed account of the stock assessment data and model; also a summary of our analysis of stock dynamics and the IPHC harvest policy. To appear in 2006 as IPHC Scientific Report 83.
External reviews of IPHC Scientific Report 83 and authors' responses.
Further investigations of low PIT tag recovery rates (.pdf) Another couple of hypotheses are erected and destroyed.
Summary of the 2005 stock assessment (.pdf) Reports the main results of the 2005 assessment.
Assessment of the Pacific halibut stock at the end of 2005 (.pdf) The full account of the 2005 assessment.
Analysis of PIT tag recoveries through 2005 (.pdf) Reports estimates of fishing mortality and migration rates from recoveries in 2004 and 2005 of tags released in 2003 and 2004.
Effects of gear type, hook spacing, and hook size on commercial selectivity and catchability (.pdf) Compares catch rates on fixed/snap gear, the full range of hook spacings, and the major hook sizes in the commercial fishery. This analysis of commercial data complements the experimental work on gear effects being done by the Commission.
Research options for estimating winter distribution (.pdf) Discussion paper on various ways of determining the extent of winter spawning migrations, prepared for the Conference Board's Migration Research Committee in 2005.
Possible reasons for low PIT tag recovery rates in 2004 (.pdf) This paper investigates some possible reasons, like a mismatch between tag release distribution and commercial fishing effort distribution. Not much turned up.
Assessment of the Pacific halibut stock at the end of 2004 (.pdf) The 2004 assessment, little changed from 2003.
Preliminary estimates based on 2004 PIT tag recoveries (.pdf) Estimates of 2004 migration and harvest rates based on recoveries in 2004 of some 29,000 releases of legal-sized fish in 2003.
Estimates of length-specific commercial selectivity from historical marking experiments (.pdf) PIT tag recoveries in 2004 showed selectivity at length in the commercial setline fishery to be different the asymptotic schedule assumed in the assessment, but the number of returns was small. To shed more light on the question, the Myers-Hoenig separable model of recovery rates was fitted to the very large number of external tag releases from the 1960s, 1970s, and 1980s. They confirmed the 2004 results.
Simulation studies of mark-recapture estimates (.pdf) In 2003 IPHC released some 29,000 legal-sized fish with PIT tags in its coastwide survey with the intention of estimating harvest and migration rates from recoveries in 2004. The precision and variance of the estimates was studied by building a simulation model that had much greater detail than the standard estimation model. Fitting the esimation model to the simulated data provided a measure of the effect of heterogeneous migration and recpature rates on the estimates.
Assessment of the Pacific halibut stock at the end of 2003 (.pdf) Full account of the 2003 assessment, which uses an age- and sex-structured model, length-specific selectivity, and smeared age compositions.
Nonparametric estimates of age misclassification from paired readings (.pdf) Reports a method of estimating age misclasification probabilities by fitting the observable distribution of differences between paired readings.
Statistical distribution of IPHC age readings (.pdf) Provides a functional description of the bias and variance of surface age readings, and of the variance of break-and-burn readings. The formulas in this paper were used to smear the ages in the 2003 assessment.
A method of estimating the sex composition of commercial landings (.pdf) In IPHC setline survey catches, the proportion female as a function of length within age is always well described by a logistic function. The age-specific length distributions of commercial landings can therefore be keyed out to sex using a large number of logistics estimated from survey data. This is how the sex composition of commercial landings was estimated for the 2003 assessment.
Sources of uncertainty in annual CEY estimates (.pdf) The chief area of uncertainty in the halibut assessment (and others) is not statistical variability but model specification.
A conditional constant catch policy for managing the Pacific halibut fishery (.pdf) Paper that describes a more stable alternative to the present constant harvest rate policy. Published in NAJFM. (Clark, W.G., and S.R. Hare. 2004. NAJFM 24:106-113.)
A model for the world: 80 years of model development and application at the International Pacific Halibut Commission (.pdf) A short history of IPHC modeling work, from Thompson and Bell through the present. Published in Natural Resource Modeling and posted here with permission. You can also view the manuscript version containing grainy photos of the principal characters that were unsuitable for publication in the journal.
Assessment of the Pacific halibut stock at the end of 2002 (.pdf) Full account of the assessment, including a few alternative fits.
Summary of the 2001 stock assessment (.pdf) Summary of data and results.
Assessment of the Pacific halibut stock at the end of 2001 (.pdf) Full account of the assessment, including details on methods and historical estimates.
F35% revisited ten years later (.pdf) Reconsiders the F35%/F40% strategy in light of recent declines of rockfish stocks in the Pacific Council area. Published in 2002 in NAJFM 22:251-257.
Effects of climate, stock size, and region on recruitment and growth of Pacific halibut (.pdf) Analysis indicating that recruitment is mostly determined by environmental conditions (over the range of observed spawning biomass) while growth is density dependent. A northward shift in the distribution of recruitment during the 20th century may be a result of global warming. A condensed version of the paper appeared in 2002 in NAJFM 22:852-862.
Results of the 2000 stock assessment (.pdf) Summary of data and results of the 2000 assessment.
Assessment of the Pacific halibut stock in 2000 (.pdf) The full account, including a discussion of model issues, goodness of fit, and retrospective behavior.
Assessment of the Pacific halibut stock in 1999 (.pdf)
Assessment of the Pacific halibut stock in 1998 (.pdf)
Effects of an erroneous natural mortality rate on a simple age-structured stock assessment (.pdf) This paper, published in condensed form in the Canadian Journal of Fisheries and Aquatic Sciences (1999. 56:1721-1731), was the basis for lowering the working value of natural mortality used in the assessment from 0.20 to 0.15.
Accounting for bycatch in management of the Pacific halibut fishery. Explains how the bycatch of sublegal and legal-sized halibut in other groundfish fisheries is treated in the development of catch limit recommendations. Published in 1998 in NAJFM (18:809-821).
Report of an external peer review of the IPHC stock assessment. Report of an expert panel convened in 1997.
The effect of recruitment variablility on the choice of a target level of spawning biomass per recruit (.pdf) Follow-up to the 1991 paper on the F35% strategy; considered stochastic rather than deterministic models and concluded that F40% was better. The citation is: Clark, W. G. 1993. The effect etc. Pages 233-246 in G. Kruse, R. J. Marasco, C. Pautzke, and T. J. Quinn II, editors. Proceedings of the international symposium on management of exploited fish populations. University of Alaska, Alaska Sea Grant College Program Report 93-02, Fairbanks.
Groundfish exploitation rates based on life history parameters (.pdf) Grainy copy of the the 1991 paper that developed the F35% harvest strategy. It also reported the B40% strategy as a better alternative, but that part of the paper was largely overlooked at the time.
Assessment data for recent years can be generated directly from the computer databases. For some of the early years the data are not in the databases, or the data series are incomplete. For those years the assessment uses legacy data series that have been compiled and completed in various ways.
Commercial landings of Pacific halibut, 1929-1990.
Age and size composition of commercial landings, 1935-1990. Includes commercial catch at age.
Commercial catch per effort, 1974-1982.
The actual stock assessment data are not posted at present because of the large bias and variance of IPHC age readings in data through 2001, requiring the use of an age misclassificiation matrix in the assessment