Songs are distinct, patterned sounds produced by a variety of animals including baleen whales. Fin whale songs, which consist of short pulses repeated at regular interpulse intervals (IPIs), have been suggested as a tool to distinguish populations. Fin whale songs were analyzed from data collected from 2000-2012 in Southern California and from 2004-2010 in the Gulf of California using autonomous acoustic recorders. IPIs were measured for each identifiable song sequence during two random days of each month with recordings. Four distinct song types were identified: long doublet, short doublet, long triplet, and short triplet. Long and short doublets were the dominant songs in Southern California, while long and short triplets were dominant in the Gulf of California. An abrupt change in song type occurred in both areas during the monitoring period. We argue that each song type is unique to a population and these changes represent a shift in the primary population in the monitoring area. Occasional temporal and spatial song overlap indicated some exchange or visitation among populations. Fin whales appear to synchronize and gradually modify song rhythm over long time scales. A better understanding of the evolutionary and ecological importance of songs to fin whale populations is needed.

Blue whales Balaenoptera musculus and fin whales B. physalus are common inhabitants of the Southern California Bight (SCB), but little is known about the spatial and temporal variability of their use of this area. To study their distribution in the SCB, high-frequency acoustic recording packages were intermittently deployed at 16 locations across the SCB from 2006 to 2012. Presence of blue whale B calls and fin whale 20 Hz calls was determined using 2 types of automatic detection methods, i.e. spectrogram correlation and acoustic energy detection, respectively. Blue whale B calls were generally detected between June and January, with a peak in September, with an overall total of over 3 million detections. Fin whale 20 Hz calls, measured via the fin whale call index, were present year-round, with the highest values between September and December, with a peak in November. Blue whale calls were more common at coastal sites and near the northern Channel Islands, while the fin whale call index was highest in the central and southern areas of the SCB, indicating a possible difference in habitat preferences of the 2 species in this area. Across years, a peak in blue whale call detections occurred in 2008, with minima in 2006 and 2007, but there was no long-term trend. There was an increase in the fin whale call index during this period. These trends are consistent with visual survey estimates for both species in Southern California, providing evidence that passive acoustics can be a powerful tool to monitor population trends for these endangered species.

Blue whales need to time their migration from their breeding grounds to their feeding grounds to avoid missing peak prey abundances, but the cues they use for this are unknown. We examine migration timing (inferred from the local onset and cessation of blue whale calls recorded on seafloor-mounted hydrophones), environmental conditions (e.g., sea surface temperature anomalies and chlorophyll a), and prey (spring krill biomass from annual net tow surveys) during a 10 year period (2008-2017) in waters of the Southern california Region where blue whales feed in the summer. colder sea surface temperature anomalies the previous season were correlated with greater krill biomass the following year, and earlier arrival by blue whales. our results demonstrate a plastic response of blue whales to interannual variability and the importance of krill as a driving force behind migration timing. A decadalscale increase in temperature due to climate change has led to blue whales extending their overall time in Southern California. By the end of our 10-year study, whales were arriving at the feeding grounds more than one month earlier, while their departure date did not change. conservation strategies will need to account for increased anthropogenic threats resulting from longer times at the feeding grounds. Productivity in the California Current Ecosystem (CCE) is fueled by the seasonal, wind-driven coastal upwelling of nutrient-rich waters 1. Upwelling pulses are followed by phytoplankton blooms ca. one week later, and an increase in zooplankton biomass weeks to months later 2. Seasonal upwelling and the ensuing assemblage of zooplankton and forage fish create rich feeding grounds that are exploited by highly migratory predators 3,4. The timing of these physical-biological couplings is strongly influenced by environmental variability on interannual to multi-decadal scales 5. Environmental variability may create a temporal mismatch between the migration timing of a predator and fluctuations of its prey 6,7. Migration between discrete feeding and breeding grounds involves complex internal and external processes and species-specific environmental cues 8. At the feeding grounds, prey availability determines the timing and physical condition of an animal at its departure, which influences the timing of arrival and physical condition at its breeding grounds, ultimately affecting reproductive success 9. Animals migrating long distances minimize predator-prey mismatches by altering the timing of their migration 10 , while balancing time spent on foraging or reproductive-related behaviors 11. Plasticity in migration has been well studied in terrestrial birds and mammals 12,13 , but less in aquatic animals. Blue whales (Balaenoptera musculus) are a model species for investigating the relationship between environmental interannual variability and migration phenology. As a long-lived, highly migratory species, individuals experience interannual to multidecadal-scale environmental variability. Although the cues they use for the timing of mi...

Three killer whale Orcinus orca ecotypes inhabit the northeastern Pacific: residents, transients, and offshores. To investigate intraspecific differences in spatial and temporal occurrence off the outer coast of Washington State, USA, 2 long-term acoustic recorders were deployed from July 2004 to August 2013: one off the continental shelf in Quinault Canyon (QC) and the other on the shelf, off Cape Elizabeth (CE). Acoustic encounters containing pulsed calls were analyzed for call types attributable to specific ecotypes, as no calls are shared between ecotypes. Both sites showed killer whale presence year-round, although site CE had a higher number of days with encounters overall. Transients were the most common ecotype at both sites and were encountered mainly during the spring and early summer. Residents were encountered primarily at site CE and showed potential seasonal segregation between the 2 resident communities, with northern residents present mainly during summer and early fall when southern residents were not encountered. Offshore encounters were higher at site QC, with little evidence for seasonality. Spatial and temporal variability of residents and transients matches the distribution of their prey and can potentially be used for further inferences about prey preferences for different transient groups.

The Gulf of Alaska is an important habitat for a diverse array of marine mammals, many of which were severely depleted by historical whaling. To study current cetacean distributions in this region, passive acoustic monitoring was used to detect species-specific call types between 2011 and 2015 at five locations spanning the continental shelf, slope, and offshore seamounts. Spatial and temporal detection patterns were examined for nine species to compare differences in behavior and habitat use. Mysticetes showed seasonal increases in calling that indicated possible behavioral shifts between feeding and breeding in blue (Balaenoptera musculus), fin (B. physalus), and humpback (Megaptera novaeangliae) whales, and matched known migration timing of gray whales (Eschrichtius robustus). Interannual changes in blue and fin whale calling may relate to the marine heat wave that began in 2013 and lasted through the end of the monitoring period. Odontocete detections revealed unique spatial distributions, with killer whales (Orcinus orca) most common on the continental shelf and sperm whales (Physeter macrocephalus) most common on the continental slope, where detections occurred year-round. Beaked whales showed both spatial and temporal separation: Baird’s beaked whale (Berardius bairdii) detections were highest at Quinn Seamount in the spring, Cuvier’s (Ziphius cavirostris) at Pratt Seamount in winter, and Stejneger’s (Mesoplodon stejnegeri) on the continental slope in the fall. The year-round presence of many species highlights the ecological importance of the Gulf of Alaska and the spatiotemporal information reported here should inform future conservation efforts.

Blue whales need to time their migration from their breeding grounds to their feeding grounds to avoid missing peak prey abundances, but the cues they use for this are unknown. We examine migration timing (inferred from the local onset and cessation of blue whale calls recorded on seafloor-mounted hydrophones), environmental conditions (e.g., sea surface temperature anomalies and chlorophyll a), and prey (spring krill biomass from annual net tow surveys) during a 10 year period (2008-2017) in waters of the Southern california Region where blue whales feed in the summer. colder sea surface temperature anomalies the previous season were correlated with greater krill biomass the following year, and earlier arrival by blue whales. our results demonstrate a plastic response of blue whales to interannual variability and the importance of krill as a driving force behind migration timing. A decadalscale increase in temperature due to climate change has led to blue whales extending their overall time in Southern California. By the end of our 10-year study, whales were arriving at the feeding grounds more than one month earlier, while their departure date did not change. conservation strategies will need to account for increased anthropogenic threats resulting from longer times at the feeding grounds. Productivity in the California Current Ecosystem (CCE) is fueled by the seasonal, wind-driven coastal upwelling of nutrient-rich waters 1. Upwelling pulses are followed by phytoplankton blooms ca. one week later, and an increase in zooplankton biomass weeks to months later 2. Seasonal upwelling and the ensuing assemblage of zooplankton and forage fish create rich feeding grounds that are exploited by highly migratory predators 3,4. The timing of these physical-biological couplings is strongly influenced by environmental variability on interannual to multi-decadal scales 5. Environmental variability may create a temporal mismatch between the migration timing of a predator and fluctuations of its prey 6,7. Migration between discrete feeding and breeding grounds involves complex internal and external processes and species-specific environmental cues 8. At the feeding grounds, prey availability determines the timing and physical condition of an animal at its departure, which influences the timing of arrival and physical condition at its breeding grounds, ultimately affecting reproductive success 9. Animals migrating long distances minimize predator-prey mismatches by altering the timing of their migration 10 , while balancing time spent on foraging or reproductive-related behaviors 11. Plasticity in migration has been well studied in terrestrial birds and mammals 12,13 , but less in aquatic animals. Blue whales (Balaenoptera musculus) are a model species for investigating the relationship between environmental interannual variability and migration phenology. As a long-lived, highly migratory species, individuals experience interannual to multidecadal-scale environmental variability. Although the cues they use for the timing of mi...

A variety of cetacean species inhabit the productive waters offshore of Washington State, USA. Although the general presence of many of these species has been documented in this region, our understanding of fine-scale habitat use is limited. Here, passive acoustic monitoring was used to investigate the spatial and temporal distributions of ten cetacean species at three locations offshore of Washington. Between 2004 and 2013, a total of 2845 days of recordings were collected from sites on the continental shelf and slope, and in a submarine canyon. Acoustic presence was higher for all species at sites farther offshore. Detections were highest during the fall and winter for blue (Balaenoptera musculus), fin (B. physalus), and humpback whales (Megaptera novaeangliae), likely related to reproductive behavior, while minke whales (B. acutorostrata) were only detected on two days. Odontocetes showed temporal separation, with sperm whale (Physeter macrocephalus) detections highest in spring, Risso’s (Grampus griseus) and Pacific white-sided dolphins (Lagenorhynchus obliquidens) highest in summer, and Stejneger’s beaked whales (Mesoplodon stejnegeri), Cuvier’s beaked whales (Ziphius cavirostris), and the BW37V signal type highest in winter or spring. There was interannual variation in detections for most mysticete species, which may be linked to oceanographic conditions: blue and fin whale detections increased during 2007 and 2008, and fin and humpback whale detections increased in 2011. These results inform our understanding of cetacean behavior and habitat use in this region and may aid in the development of conservation strategies suited to the dynamic conditions that drive cetacean distribution.

Worldwide, the frequency (pitch) of blue whale (Balaenoptera musculus) calls has been decreasing since first recorded in the 1960s. This frequency decline occurs over annual and inter-annual timescales and has recently been documented in other baleen whale species, yet it remains unexplained. In the Northeast Pacific, blue whales produce two calls, or units, that, when regularly repeated, are referred to as song: A and B calls. In this population, frequency decline has thus far only been examined in B calls. In this work, passive acoustic data collected in the Southern California Bight from 2006 to 2019 were examined to determine if A calls are also declining in frequency and whether the call pulse rate was similarly impacted. Additionally, frequency measurements were made for B calls to determine whether the rate of frequency decline is the same as was calculated when this phenomenon was first reported in 2009. We found that A calls decreased at a rate of 0.32 Hz yr-1 during this period and that B calls were still decreasing, albeit at a slower rate (0.27 Hz yr-1) than reported previously. The A call pulse rate also declined over the course of the study, at a rate of 0.006 pulses/s yr-1. With this updated information, we consider the various theories that have been proposed to explain frequency decline in blue whales. We conclude that no current theory adequately accounts for all aspects of this phenomenon and consider the role that individual perception of song frequency may play. To understand the cause behind call frequency decline, future studies might want to explore the function of these songs and the mechanism for their synchronization. The ubiquitous nature of the frequency shift phenomenon may indicate a consistent level of vocal plasticity and fine auditory processing abilities across baleen whale species.