Assessing the efficacy of ecological reserves: killer whale beach rubbing behaviour and vessel disturbance

ABSTRACT: Area-based protection is an important tool for safeguarding key habitat. Reserves that focus on mitigation of specific threats are particularly effective and are more likely to support a measurable outcome. In the marine environment, reserves that limit vessel presence have the potential to reduce disturbance to marine mammals. However, assessing the efficacy of reserves has been an ongoing challenge. Physical and acoustic disturbance from vessels is recognized as a primary threat to recovery for the northern resident killer whale (NRKW) population in Canadian Pacific waters. The Robson Bight Michael Bigg Ecological Reserve (RBMBER) was developed to support the behaviour of beach rubbing, a culturally distinct and traditionally important activity. Beach rubbing provides a rare opportunity to quantify vessel disturbance of a behaviour associated with a fixed geographic location, identifiable by visual cues, and verifiable acoustically. Observations on vessel presence, NRKW rubbing frequency, and duration were collected from a beach inside the reserve and compared to a beach in proximity to, but outside of, the RBMBER. In 2019-2022, vessel counts near the RBMBER beach were significantly lower than near the unprotected beach, and overall, rubbing occurred more frequently inside the reserve (78% of visits) than outside (35%). However, outside the reserve, concurrent vessel presence did not predict the occurrence of rubbing activity, indicating that vessel presence may negatively affect beach rubbing through long-term learned avoidance of frequently impacted areas.