Reactions of Steller Sea Lions (Eumetopias jubatus) to Vessels at a Haulout in Glacier Bay - PROGRESS REPORT

Mathews, Elizabeth

Private and commercial vessels visiting Glacier Bay National Park commonly approach South Marble Island to observe Steller sea lions. To minimize disturbance of wildlife, National Park Service (NPS) regulations require that boaters remain more than 100 yds from haulouts. This study was designed to determine if the distance limit prevents disturbance and if visitors comply with the regulation. On 23 days we recorded resting and non-resting behavioral states and the number of animals in the water at 2 or 3 min intervals throughout the day and we measured vessel distances. Ninety cases involving paired control (before approach) and experimental' (during approach) observations were analyzed. Nineteen (21%) vessels approached closer than 100 yds; 2 of these were commercial tourboats, others were private motorized vessels or kayaks. Sixteen (18%) vessel operators caused disturbance of sea lions, defined as a >20% increase in activity or >10% increase in the number of sea lions in the water. Compared to tourboats and private boats, kayaks were significantly more likely to approach the haulout closer than 100 yds and more likely to cause disturbances. Disturbances occurred at distances of 42 345 yds (mean = 152 yds; SD = 84; n = 15). Disturbances of sea lions by vessels could be reduced by increasing the 100 yd distance and improving compliance with regulations through visitor education and increased enforcement, but it is likely that other factors in addition to distance affect sea lion behavior.