The more sheltered, the better-Coastal bays and lagoons are important reproduction habitats for pike in the northern Baltic Sea

The Quark Archipelago, in the northernmost part of the Baltic Sea, provides valuable reproduction areas for coastal fish such as pike (Esox lucius L.). Here, pike stocks are still in good condition compared to the southern Baltic Sea, where pike stocks have declined. Hence, this area offers a unique opportunity to study the underlying causes of successful pike reproduction and to identify a productive pike reproduction habitat. This study suggests that the key factor defining suitable reproduction habitats for pike in the Quark Archipelago was the level of shelter. The more sheltered a habitat, in terms of morphology and level of isolation of the site and the site's exposure to wave action and shoreline density, the better the reproduction habitat was for pike. Gloes, which are the most isolated successional stages of coastal lagoons, represented the most sheltered habitat type and showed the highest pike larvae abundance. Additionally, sheltered bays and flads, less isolated successional stages of coastal lagoons compared to gloes, were also used as reproduction habitats by pike but with a lower abundance of larvae compared to the gloes. Gradually increasing salinity and the occurrence of sticklebacks (Gasterosteidae) reflected the morphology of the site. Pike larvae were observed in locations without sticklebacks and with low salinity. Pike larvae were found mostly amongst fallen reed (Phragmites australis) and in areas with moss (Fon-tinalis sp.) growth, which supports earlier findings. This study provides valuable new knowledge on larval pike habitats and highlights the significance of sheltered bays and gloes in the northern Baltic Sea. The information can be utilised for planning conservation and the restoration of pike reproduction habitats to protect and restore pike populations on both a regional and larger scale.