Distribution and timing of spawning Faroe Plateau cod in relation to warming spring temperatures

Abstract

Abstract The Faroe Plateau cod stock has been in a poor state since 2005, while temperatures in the region have been increasing. However, the importance of distributional changes in contribution to the poor stock size and the mechanisms that drive the distribution of spawning Faroe Plateau cod are still not clear. Density dependent processes and temperature limitations imposed due to the narrow thermal niche for cod during spawning are two potential drivers for the geographical distribution of spawning cod. We analyse the changes in the geographical location, spawning area, timing of spawning and realised temperature niche in relation to abundance and temperature. Distributions were modelled using generalized additive models (GAM) based on CPUE and bottom temperature data from Spring Bottom trawl survey. We can clearly separate the two main spawning areas of the Faroe Plateau cod and show that there are no indications of density dependence effects on the distribution within these spawning areas. However, we found both a geographical shift in the north-eastern direction and a shift in the timing of spawning in the northern area, while no changes in distribution or timing of spawning were found within the western spawning area. Both shifts were significantly correlated with temperature, leading us to conclude that temperature plays a key role in the spatial and temporal dynamics of the Faroe Plateau cod. However, due to the limited data of this study, future studies should re-examine the mechanisms controlling the distribution of spawning cod when a longer timeseries is available.