Spawning of Kattegat cod (Gadus morhua)—Mapping spatial distribution by egg surveys

•Multiple egg surveys were done in Kattegat during cod spawning seasons 2004–2006.•Distribution of cod eggs was examined by spatial modelling.•The estimated daily egg production ranged from 0 to 20 eggs m−2 d−1.•Distribution was broadly consistent with two previously recognized spawning areas.

The Kattegat cod has been heavily depleted and is classified as exhibiting reduced reproductive capacity. There is therefore a need for updated information on cod spawning activity and specific locations of spawning grounds in the area. To address this, data from dedicated egg surveys in the Kattegat between 2004 and 2006 were analysed. Positively identified cod eggs confirmed that cod were spawning in the area during the period. The estimated daily egg production was highest in the southeastern part of the surveyed area (∼20 eggs m−2 d−1) close to the entrance of the Sound and off the Swedish coast. North of latitude 56°45′ N the daily egg production was low (0–5 eggs m−2 d−1). The predicted distribution of daily egg production was broadly consistent with the two major spawning areas proposed by Vitale et al. (2008), although shifted southwards emphasizing the importance of the southernmost spawning area closer to the Sound. These results provide a baseline for future studies of spawning and life history characteristics of Kattegat cod, and also in studies designed to disentangle the stock complex in the Kattegat-Sound-Belt area.