June 13, 2024

Responses of Steller Sea Lions (Eumetopias jubatus) to In-Air Blast Noise from Military Explosions


Mike W. Demarchi, Meike Holst, Dave Robichaud, Mike Waters, and Alexander O. MacGillivray


Abstract: The Steller sea lion (Eumetopias jubatus) is a species of conservation concern and is protected from anthropogenic disturbances by federal legislation in Canada and the United States. Although the breeding population has tripled since intensive culling ended ~40 y ago, conservation concerns persist due in part to the species’ vulnerability to anthropogenic factors, including noise. Published data on the nature and consequences of Steller sea lion responses to loud, impulsive noises such as explosions are sparse, yet useful where important haulouts are adjacent to such events. Herein, we document the short-term behavioural responses of Steller sea lions on a winter haulout complex to military explosions on southern Vancouver Island, Canada, over a period spanning 1997 to 2010. Blasting activities have been ongoing for over 70 y, involving ordnance disposal and on-land demolition training with high explosives—both of which disturb pinnipeds at nearby Race Rocks Ecological Reserve (RRER). Acoustic measurements confirmed that in-air noise reached levels capable of causing pinniped disturbance (i.e., > 109 dBF peak) but not injuries such as a permanent threshold shift in hearing (i.e., < 149 dBF peak). Sea lions showed a significant increase in activity following blasting and were commonly displaced from haulouts. Within minutes of the disturbance, however, activity levels dropped sharply, and displaced animals usually began returning to haulouts. Activity levels on the day after blasting were similar to levels on days prior to blasting. General linear models showed no evidence (2 models) or no conclusive evidence (1 model) of an effect of blasting on sea lion abundance. Repeated exposure to in-air blast noise has short-term effects on Steller sea lions at RRER. We speculate that long-term effects on sea lions using RRER are unlikely—especially considering the increase in the peak numbers of Steller sea lions at RRER in recent decades while blasting has been ongoing.

Key Words: Steller sea lion, Eumetopias jubatus, C4, disturbance, explosion, harassment, military, noise, ordnance, Race Rocks, Salish Sea, eastern stock

Document Type: Research article

DOI: 10.1578/AM.38.3.2012.279

Page Numbers: 279-289

Info SKU: Vol__38__Iss__3__Demarchi Category: