Long-term variations in the diet composition of Atlantic wolffish, Anarhichas lupus marisalbi (Zoarcoidei: Anarhichadidae), in Kandalaksha Bay, White Sea

Understanding the diet variability of the White Sea wolffish, Anarhichas lupus marisalbi Barsukov, 1956, is essential for explaining its population dynamics and variations in its life cycle. This study examined the food spectrum of wolffish from the coastal waters of Chupa Inlet (Kandalaksha Bay, White Sea) and analyzed interannual and seasonal changes in the species composition of its diet. During the summer period, wolffish feeds on a variety of macrobenthic organisms in its feeding grounds, particularly molluscs, echinoderms, crustaceans, and ascidians. The diet was predominantly composed of bivalves and gastropods, with Buccinum undatum Linnaeus, 1758 and Serripes groenlandicus (Mohr, 1786) being the most important prey species. Statistical analysis of multi-year diet data from 2001 to 2023 revealed interannual variations in the frequency of occurrence of key food organisms in wolffish stomachs. The results showed that in the early 2000s, the role of epibenthic crustaceans Hyas araneus (Linnaeus, 1758) and Pagurus pubescens Krøyer, 1838 in the wolffish diet was significantly greater compared to other years of the study. The dietary importance of the bivalve S. groenlandicus increased gradually and statistically significantly during the observation period, while Buccinum undatum dominated the wolffish diet throughout the entire study period. Overall, three species (B. undatum, S. groenlandicus, and Mytilus edulis Linnaeus, 1758) accounted for a significant portion of the wolffish diet during 2001–2023. In some years, other mollusc species, as well as crustaceans and the ascidian Styela rustica Linnaeus, 1767, were also included in the group of important prey items. The feeding intensity of wolffish in Chupa Inlet showed interannual variability. Throughout the observation period, certain years were identified as having the greatest frequency of fish with empty stomachs. Female wolffish showed a seasonal pattern in the frequency of occurrence of individuals with empty stomachs: the highest occurrence of such fish was observed during the spawning period of wolffish, in late July to early August. No significant seasonal changes in the frequency of occurrence of individuals with empty stomachs were found in males.