Widespread passive acoustic monitoring reveals spatio-temporal patterns of blue and fin whale song vocalizations in the Northeast Pacific Ocean

Abstract

The NOAA-NPS Ocean Noise Reference Station Network (NRS) is a passive acoustic monitoring effort to record the low-frequency (<2 kHz) sound field throughout the U.S. Exclusive Economic Zone. Data collection began in 2014 and spans 12 acoustic recording locations. To date, NRS datasets have been analyzed to understand spatial variation of large-scale sound levels, however, assessment of specific sound sources is an area where these datasets can provide additional insights. To understand seasonal patterns of blue whale, Balaenoptera musculus, and fin whale, B. physalus, sound production in the eastern North Pacific Ocean, this study explored data recorded between 2014 and 2020 from four NRS recording sites. A call index (CI) was used to quantify the intensity of blue whale B calls and fin whale 20 Hz pulses. Diel and seasonal patterns were then determined in the context of their migratory patterns. Most sites shared similar patterns in blue whale CI: persistent acoustic presence for 4–5 months starting by August and ending by February with a CI maximum in October or November. Fin whale patterns included persistent acoustic presence for 5–7 months starting by October and ending before April with a CI maximum between October and December. The diel patterning of blue whale song varied across the sites with the Gulf of Alaska, Olympic Coast, Cordell Bank, and Channel Islands (2014–2015) exhibiting a tendency towards nighttime song detection. However, this diel pattern was not observed at Channel Islands (2018–2020). Fin whale song detection was distributed evenly across day and night at most recording sites and months, however, a tendency toward nighttime song detection was observed in Cordell Bank during fall, and Gulf of Alaska and Olympic Coast during spring. Understanding call and migration patterns for blue and fin whales is essential for conservation efforts. By using passive acoustic monitoring and efficient detection methods, such as CI, it is possible to process large amounts of bioacoustic data and better understand the migratory behaviors of endangered marine species.

Long-distance communication can enable collective migration in a dynamic seascape

“…As Northeast Pacific blue whales migrate northward in the early spring, individuals have limited personal information about contemporaneous forage conditions, leading to a reliance on spatial memory of long-term foraging hotspots (Abrahms et al 2019). Moreover, social information transfer via song is sparse during the early foraging season with individuals producing little song during the summer months (Širović et al 2015;Pearson et al 2023). As the foraging season progresses and krill prey become less abundant (Croll et al 2005;Fossette et al 2017), the relative value of longdistance social information should increase as individuals must determine if local prey depletion is representative of broader forage availability.…”

“…During the foraging months, blue whales in this population produce song primarily at night due to intensive daytime foraging effort, but transition to a more even diel song distribution following the cessation of foraging and onset of breeding migration . These diel patterns enable researchers to track population-wide behavioral transitions throughout the Northeast Pacific (Oestreich et al 2022b;Pearson et al 2023), thus prompting the question of whether blue whales themselves use longdistance information about conspecifics' behavioral state to inform their migratory decisions.…”

“…These diel patterns enable researchers to track population-wide behavioral transitions throughout the Northeast Pacific (Oestreich et al . 2022b; Pearson et al . 2023), thus prompting the question of whether blue whales themselves use long-distance information about conspecifics’ behavioral state to inform their migratory decisions.…”

Environmental DNA: The next chapter

“…Automated or passive samplers in aquatic environments have also unveiled new opportunities for long-term sampling strategies. Using remote controlled vehicles, boats or unmanned aerial vehicles allows us to sample otherwise inaccessible areas and reduce the risks of contamination (Aucone et al, 2023;Doi et al, 2017), as do pre-programmed sampling platforms (Mirimin et al, 2021;Pearson et al, 2023;Sepulveda et al, 2020;Yamahara et al, 2019).…”

“…Automated or passive samplers in aquatic environments have also unveiled new opportunities for long‐term sampling strategies. Using remote controlled vehicles, boats or unmanned aerial vehicles allows us to sample otherwise inaccessible areas and reduce the risks of contamination (Aucone et al., 2023; Doi et al., 2017), as do pre‐programmed sampling platforms (Mirimin et al., 2021; Pearson et al., 2023; Sepulveda et al., 2020; Yamahara et al., 2019). Despite ongoing developments and the need for flexibility in study design, the community should continue working on the integration of best practices and evaluation of the high standards required in the eDNA workflow.…”