In 2016, a fishery for whelks (Buccinum undatum) was initiated in the Danish part of Kattegat and the Belt Sea. Until then the whelk had been a pristine resource in Danish fisheries. The inner Danish waters are not covered by EU regulations and very little is known about the whelk population characteristics in the area. Thus, the Danish whelk fishery is at present carried out without any administrative regulations or specific biological knowledge. This work gives novel information about the Danish whelk populations in the Southern Kattegat and Belt Sea. The stock size (shell length 40 mm) in Kattegat was estimated to be in the range of 230,250–921,000 tons. The overall meat percentage in the three studied fishing zones ranged from 58.2–65.6 %. The size at maturity (sexes pooled) ranged from 62.9–70.3 mm corresponding to 4–4.5 years of age. The average shell length of the studied populations ranged from 64.1–73.2 mm and the asymptotic shell length was estimated to be 77.6–83.1 mm. Test fishery showed the CPUE quickly to decrease in a southern direction in the Belt Sea due to the prevailing salinity gradient. Commercial fishermen achieved an average CPUE of 1.3 kg pot-1 in the Southern Kattegat (January 2017–November 2018). Although the three zones studied are adjacent, significant differences were found in several of the measured parameters. This underlines the need of local monitoring of population characteristics in order to advice authorities on possible regulation of whelk fishery. The ongoing whelk fishery in the Southern Kattegat has at present an intensity not believed to cause recruitment overfishing. However, the Danish fishing authority is encouraged to implement a minimum conservation reference sizes (MCRS) based on locally determined size of maturity (SOM).