Habitat Preference and Activity Pattern of Wels Catfish (Silurus glanis) at its Northernmost Distribution Area.

Knowledge of Wels Catfish (Silurus glanis) at its northernmost distribution area is limited on even basic behavioral characteristics, such as habitat preferences and activity patterns. It has thus proven difficult to aid the species in any predictable way. In a telemetry study on Wels Catfish, I examined habitat preferences, activity patters and site fidelity of ten adult individualsat their most northern range. Fish were surgically equipped with acoustic transmitters, frequently recording the position of each individual in a small Swedish lake. Wels Catfishpreferred deeper areas than randomly expected during the entire year, except for late spring and early summer. This indicates that spawning took place at shallow, vegetated areas in May-June 2019. Fish were highly active during summer, utilizing the entire lake. Behavior shifted during winter as fish became bottom dwelling with minimal activity, small home ranges and likelyminimal feeding. Wels Catfish had a nocturnal activity pattern during the entire year, but especially during summer. Fish preferred shallower areas during night than during day, indicating that deeper areas were used for resting and shallower areas for foraging. Lastly, home ranges were much larger than expected during summer, implying that S. glanis might be less territorial in small lakes than previously believed. In summary, conservation efforts should focus on protecting and restoring shallow areas with lots of vegetation and food items, adjacent to deep areas with underwater structures. These areas are important for the survival of S. glanisas they fulfill requirements for feeding, reproduction, resting, and hibernation