Behaviors of Grey Seals (Halichoerus Grypus) Addressed Towards Human Swimmers During Experimental Open Water Encounters Off Heligoland (German Bight, North Sea)

Risks arising for humans during swim encounters with seals are poorly understood. This study was initiated to examine behaviors of unhabituated grey seals addressed towards humans during experimental, noncommercial seal-swim activities off Heligoland. In total, 26 in-water encounters were conducted. Behavioral classes and the number of seals simultaneously approaching swimmers were time sampled. A set of risky and nonrisky interactive behaviors was continuously sampled. Seals spent approximately the same amount of time interacting with swimmers (53%) as they did ignoring them (47%). Seals displayed higher rates of nonrisky behaviors than risky ones, but risky behaviors occurred during 73% of all seal-swims. Seals remained ≤20 m near swimmers for 51% and ≤1 m for 13% of the time. A mean number of 0.65 and 0.18 seals approached swimmers per minute within a range of ≤20 m and ≤1 m, respectively. Behavioral classes, interactive behaviors, and the number of seals approaching ≤20 m did not vary significantly throughout seal-swims but the number of seals approaching ≤1 m moderately decreased. Due to high rates of risky behaviors, it is recommended to promote public awareness on site and to regulate seal-swims before commercial operations emerge.