Title: Stock assessment of Lemon sole (Microstomus kitt) in Icelandic waters using a gadget model.

The Gadget modelling framework was used to build a stock assessment model to analyze lemon sole population dynamics in Icelandic waters and establish its trends in recruitment and fishing mortality. Both age and length estimation by the model fit well with the observed data. Most fish caught were between age 5 to 10, and of length between 25 cm to 40 cm. The highest proportion of the catch was between age 6 and 7. The estimation of the length-age growth curve fit well with the observed commercial data for most of the years. However, the fit was not as good for the survey data, especially for the older fish. The simulated abundance trends showed that the amount of smaller fish has been stable recent years, while the amount of bigger fish (35 cm and larger) has increased in last five years. The simulated trends of the abundance of younger fish did not fit well at the highest abundance values while the fit is better for older fish. The abundances indices of fish between 10-35 cm length were relatively stable, while larger fish (between 35-60 cm) increased noticeably between 2010 to 2018. Estimated fishing mortality had fluctuated between 1990 to 2005 while it has been relatively stable for the last five years around 0.25-0.3. The biomass of mature lemon sole increased from 2,500 tonnes in 1990 to 11,000 tonnes in 2018. Since 1997, recruitment has been variable between 10 to 17 million fish per year.