A Place for Orcas to Call Home

Drackett, Logan, and Suzana Dragićević. “Suitability analysis of acoustic refugia for endangered killer whales (Orcinus orca) using the GIS-based logic scoring of preference method.” Environmental Management 68.2 (2021): 262-278.

In recent years, increased shipping traffic has impacted orca behavior. Since orcas use sound to communicate and echolocation for navigation, high levels of marine noise pollution can disrupt feeding, social and other behaviors, and in turn, impact their chances of survival.

A pod of orcas in Alaska. Photo by Ashley Mickens (2017).

While orcas face pressure from marine noise pollution, they are also at risk from other human activities, such as overfishing and habitat degradation. In response to these threats, some scientists and policy makers have proposed the idea of creating an “acoustic refugia” where orcas and other marine mammals are protected from disruptive anthropogenic activities. But where is the best place to set up this refuge? The authors of this paper propose using an innovative mapping technique in order to find some prime locations.

In this paper, the researchers perform a habitat suitability analysis using geographic information systems (GIS), which is a type of mapping software, and data collected from both the US and Canadian governments. For the study area, the team chose the Salish Sea, which boasts a resident pod of orcas. By analyzing three sets of factors, they were able to generate a score indicating suitable locations for the refuge at several areas on the map. The factors included:

  1. Anthropogenic Activities – proximity to fisheries, treatment plants or marine protected areas
  2. Environmental suitability – presence or absence of food (salmon) and kelp beds
  3. Noise pollution – concentration of maritime noises at the same frequencies that orcas use to communicate/navigate
Figure 1. The Salish Sea is home to a pod of resident orcas. Image from Google Maps.

After setting the appropriate parameters for each set of factors, the team ran a detailed programing script within the GIS interface to get suitability scores for each possible location. As an added measure, they also created three scenarios (based on previous shipping data) in which a low, medium and high number of vessels transited through each location.

The final output was a map showing the level of suitability for the entire Salish Sea, with the green areas being the most suitable habitat for the orca population. Many other locations are moderately suitable, but very few areas of high suitability were identified. The researchers highlight the Haro Strait, between Vancouver Island and the San Juan Islands, as one of the critical habitats for the resident orcas in the area. While there has been previous work suggesting that the Haro Strait may be prime orca habitat, two other locations, the Sechelt Inlet and Lasqueti Island, were also identified as critical habitats.

Figure 2. Map showing Lasqueti Island and the Sechelt Inlet, two of the primary areas of interest for an acoustic refugia. Image from Google Maps.

The results show that it is extremely important to protect these locations for the orcas and the team recommends that their map be used as a starting point for decision making and policy rationale. While their map identified highly probable locations for suitable orca habitat, the team hasn’t yet conducted field surveys and don’t know if orcas actually use these locations for foraging and socializing. Regardless, the researchers were excited about the results, because the model shows that simply reducing marine noise pollution can increase the suitability scores of many other locations in the Salish Sea. While the authors recommend multiple approaches to protecting the orcas, they are hopeful that these tools will help resources and efforts be allocated more efficiently.

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