Finding the window of energetic opportunity traveling North Atlantic right whales use dive depths that avoid surface drag

Meeting Abstract

P2.165  Tuesday, Jan. 5  Finding the window of energetic opportunity: traveling North Atlantic right whales use dive depths that avoid surface drag MCGREGOR, Anna E.*; FISH, Frank E.; NOWACEK, Douglas P.; Duke Univ. Marine Laboratory, Beaufort, NC; West Chester Univ., PA; Duke Univ. Marine Laboratory, Beaufort, NC

Swimming immediately under the water’s surface incurs the maximum amount of drag for a body, which can be up to 5 times greater than in free stream conditions. Cetaceans must swim at the water’s surface to breathe or use energy to dive away from the surface, which then requires overcoming drag and buoyancy forces. We investigated whether traveling North Atlantic right whales (Eubalaena glacialis) dive to depths based on the amount of surface drag experienced. Suction-cupped archival tags (Dtags) were attached to free-ranging whales in their northern summer foraging habitat, the Bay of Fundy, Canada (BoF), and in their southern winter calving habitat, the South Atlantic Bight, US (SAB), over five years, recording a total of 439 surface dives, those less than 50 m in maximum depth, from 25 individual whales. Surface dives averaged 8.2 m in depth in the BoF and 10.3 m in the SAB. Body depth of an adult right whale is estimated to be approximately 3 m, which would cause them to experience surface drag effects when submerged to depths less than 9 m. In addition, the majority of dives made in the SAB waters were from one pregnant individual, and its dives were to significantly deeper depths than those of nonpregnant animals in the BoF, although they were still close to the calculated depth of minimal drag. During pregnancy, right whales undergo abdominal distension, which likely increases body depth and could influence the depth at which surface resistance becomes negligible. This initial analysis suggests that right whales may dive to depths that minimize both surface drag and travel time to the surface, thereby decreasing their energetic expenditure during horizontal travel.

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