NOAA Technical Memorandum NMFS-NWFSC-43
Richard D. Methot
Northwest Fisheries Science Center
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Marine Fisheries Service
The Northwest Fisheries Science Center of the National Marine Fisheries Service, NOAA, uses the NOAA Technical Memorandum NMFS series to issue informal scientific and technical publications when complete formal review and editorial processing are not appropriate or feasible due to time constraints. Documents published in this series may be referenced in the scientific and technical literature.
The NMFS-NWFSC Technical Memorandum series of the Northwest Fisheries Science Center continues the NMFS-F/NWC series established in 1970 by the Northwest & Alaska Fisheries Science Center, which has since been split into the Northwest Fisheries Science Center and the Alaska Fisheries Science Center. The NMFS-AFSC Technical Memorandum series is now being used by the Alaska Fisheries Science Center.
Reference throughout this document to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA.
This document should be cited as follows:
Methot, R.D. 2000. Technical description of the stock
synthesis assessment program. U.S. Dept. Commer.,
NOAA Tech. Memo. NMFS-NWFSC-43, 46 p.
Most NOAA Technical Memorandums NMFS-NWFSC are
available on-line at the Northwest Fisheries Science Center
web site (https://www.nwfsc.noaa.gov)
Copies are also available from:
National Technical Information Service
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5285 Port Royal Road
Springfield, VA 22161
This HTML file represents the Introduction only; the rest of the document is available only in PDF format.
Synthesis is an age-structured population assessment tool. It includes a population simulation model to calculate the abundance and mortality of a harvested population, an observation model to relate this population model to observable data from the population, and a statistical model to adjust parameters of the population model and observation model to achieve the best fit to all the data. Synthesis has both an age-structured and a size/age-structured version. Both are capable of simultaneously examining data from several fisheries and several surveys, each with its own pattern of selectivity. Synthesis calculates selectivity with modified logistic functions. Parameters of these functions can take on time-specific values, thus allowing flexibility to track changes in fishery selectivity. The goodness of fit is quantified in terms of a log-likelihood function composed of independent terms for each kind of observation from each type of fishery or survey. Synthesis estimates the best parameter values through numerical calculation of parameter derivatives and application of a modified Newton method. This provides estimates of parameter variances and covariances, and provides for calculation of the variance of spawning biomass through application of the delta method. Both versions of synthesis allow inclusion and estimation of spawner-recruitment functions. When detailed age composition data are lacking, the estimated spawner-recruitment curve can be used to generate the entire time series of recruitments, thus turning synthesis into a simple production model. At the other extreme, inclusion of the spawner-recruitment curve in data-rich models allows estimation of this curve while taking into account all available information. Although most population modeling is done within unit stocks, age synthesis provides the capability to model up to three geographic areas and to estimate the degree of migration between areas. Size synthesis adds a body size dimension to the population. This allows fuller use of size-based data, and allows estimation of growth curves while taking into account size-selectivity of the sampler and taking into account the effect of variability in the age determination process.
The rest of the document is available in PDF format.