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Surface-Based Observations Can Be Used to Assess Behavior and Fine-Scale Habitat Use by an Endangered Killer Whale (Orcinus orca) Population
Abstract: Behavioral observations can provide insight into the ecology and habitat use of marine species. Studies have shown that movement patterns are influenced by prey availability and that the presence of vessels can reduce foraging, resting, and/or social behaviors in delphinids, including killer whales (Orcinus orca). Southern resident killer whales are listed as “Endangered” in both the United States and Canada. Reduced prey availability and vessel disturbance are risk factors for this population. Surface observations were conducted to understand southern resident killer whale behavior and habitat use in their Endangered Species Act-designated core summer critical habitat. The activity budget comprised 70.4% travel, 21.0% forage, 6.8% rest, and 1.8% social behavior. Dive duration, surface duration, and swim speed varied significantly among activity states and validated the activity state classifications. For example, traveling killer whales swam the fastest and had the lowest surface to dive duration ratios, which presumably minimizes energetic costs while maximizing distance traveled. Movement patterns, spatial arrangements, and configurations of killer whales also varied significantly among activity states and, to some extent, varied by geographic location. We found that killer whale spatial arrangement and configuration patterns were strikingly different in two adjacent areas, indicating that these may change abruptly. This may be informative for vessel operators who are required to maintain a 182.9-m distance from killer whales. Killer whales engaged in most activity states throughout the area, but foraging and resting predominantly occurred in some localized regions. Activity budgets reported in the present and other contemporary studies differ from those reported 20 to 30 y ago. The proportion of forage in the activity budget has decreased in recent years, yet the main foraging area has persisted for several decades. These findings are important for understanding key risk factors for southern resident killer whales and may aid in formulating mitigation measures to protect them from vessel traffic and other human activities.
Key Words: activity state, behavior, forage, killer whale, Orcinus orca, MPA, rest, vessel impact
Document Type: Research Article
Page Numbers: 168-183