Title: The assessment of the witch (Glyptochephalus cynoglossus) in Icelandic waters. Comparison of the different assessment models and assumptions

Final project
Year of publication:
Place of publication:
Number of pages:


The report presents a comparison of different assessment methods on the witch stock (Glyptocephalus cynoglossus) in Icelandic waters. Three alternative assessment methods are used: age-based ADAPT, length-based ADAPT and Age-disaggregated Dynamic Production Model.
Most of the data used in this study are unpublished and were made available to the author in form of unpublished preliminary reports or as tables extracted by the staff of the Marine Research Institutes (MRI) from the MRI-database.
Age-disaggregated observations are used as input data for the age-based ADAPT method and age-disaggregated dynamic production model. For the length-based ADAPT method, the length frequency data are used as input source and converted into age using the least squares corresponding to a simplified version of maximum likelihood method (Macdonald and Pitcher, 1979) and then used as input data for an ADAPT analysis.
The different models give similar trend in fishing mortality rates over the period used (1987-1999) and about the same F in the final year (0.18-0.22). The stock biomass declined from approximately 18000 tons in 1987 to around 10000 tons in early 2000. The predicted yield for the year 2000 is about 1200-1400 tons.

Documents and links