New Insights into Blue, Fin, and Humpback Whale Feeding, Movements, and Impacts of Human Activities from Medium-duration Archival Tags

Advances in tag technology have dramatically improved the ability to measure and evaluate whale behavior. Previous tag deployments on large whales have primarily consisted of either longer duration (several month) satellite tags that provide data of limited metrics and resolution (due to transmission bandwidth), often with high uncertainty, or archival tags that can record high-resolution data but for periods of hours. We report on the development and deployment of two tag designs attached with short darts that provide high-resolution position, kinematic, and acoustic data for periods of days to weeks. More than 50 archival tag deployments (>20h each) on three large baleen whale species (blue, fin, and humpback) were conducted off the U.S. West Coast from 2013 to 2019, providing more than 5,000 hours of data. Individual tag attachment periods ranged up to 770 h and tended to be longest in blue whales and shortest in humpback whales. These data provided new insights into different aspects of whale behavior in a human-impacted ecosystem, including: 1) even though dive behavior and movements varied among species, all three spent higher proportions of time closer to the surface at night where they would be more vulnerable to ship strikes, 2) diurnal variations in whale location reveal that daytime positions may not accurately represent the distribution of whales in relation to areas of high ship traffic, 3) accurate feeding rates of whales could be quantified for the first time avoiding the bias from past short-term deployments that sampled primarily during daylight hours on animals already engaged in feeding near prey concentrations, 4) better estimates of calling rates could be assessed, again avoiding bias related to the behavior at the time of tagging; several deployments recorded thousands of calls, indicating high variance in calling across individuals, 5) there were substantially greater opportunities to document interactions with ships and incidental exposure to ship noise, military sonar, and other human disturbances were facilitated with longer attachments. While these tags provided new insights into whale behavior, they also present new challenges, including increased chance of damage from whale-to-whale contact and long-distance movements during deployments requiring considerable recovery effort.