Title: An assessment on Plaice (Pleuronectes platessa) in Icelandic waters. Comparison of the different assessment models and assumptions

Author(s): Li Jiuqi
Type:
Final project
Year of publication:
2005
Publisher:
UNU-FTP
Place of publication:
Reykjavík
Number of pages:
64

Abstract

The report presents a comparison of different assessment methods and the state of the plaice stock (Pleuronectes platessa) in Icelandic waters. Four alternative assessment methods are used: age-based ADAPT, length-based ADAPT, age-disaggregated dynamic and the surplus production model. Most of the data used in this study are from the Marine Research Institutes (MRI). 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 the input source and converted into age using the slice method and then used as input data for the length-based ADAPT model and catch by year, biomass indices and CPUE for the surplus production model. The reference points model with R-S relationship (B-H) is used to estimate the stock state. The different models give similar trends in fishing mortality rates over the period studied (1987-2004) and similar F in the final year (0.16-0.25). The stock biomass declined from approximately 50,000 t in 1987 to around 22,000 t in 2004. Mean recruitment from 1987-2004 is around 30 million and declining. The long term predicted yield for the next 15 years is about 7,000-9,000 t and the short term predicted yield for the next three years is about 4,000-5,000 t. Results from the surplus production model show that the stock biomass declined from approximately 80,000-90,000 t in 1905 to around 14,000 t in 2000 and then increased to about 23,000 t in 2004. The estimates of reference points show that the current fishing mortality has declined to historically low levels. The recruitment between 1987 and 2004 was variable and included a few high values. Since 2000, recruitment has decreased and has been less than average. The SSB estimated in 2004 of 22,000 t is above the Bpa of 15,389 t. Short term predictions suggest that SSB will increase to around 26,000 t by 2007 at current levels of fishing mortality. The recommended fishing mortality from long term predictions is less than 0.26 for the period 2005-2015 to increase the stock and catch to around 40,000 t and 8,000 t.

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