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A diverse group of toothed whale species inhabits the pelagic habitats of the western North Atlantic, competing for overlapping prey resources. Historical data deficits have limited fundamental research into many of these species, such as establishing baselines of distribution and abundance, so their occurrence and habitat use patterns are not well characterized. Periodic cycles in activity have been reported at a range of temporal scales for odontocetes in other regions, such as seasonal movements, foraging activity modulated by lunar cycles, and diel activity patterns. A variety of spatial, temporal, and behavioral separation strategies have also been observed among predator guilds in both marine and terrestrial systems, and these may also contribute to observed spatiotemporal patterns in activity. Recently, passive acoustic data has been applied to monitor odontocete species continuously, with improved detection and species discrimination for some cryptic species. We used a long-term passive acoustic data set collected at sites spanning the western North Atlantic shelf-break region to quantify presence and characterize seasonal, lunar, and diel activity patterns for 10 species. Our results demonstrated strong regional preferences and clear patterns of spatiotemporal separation between species with similar foraging ecology. Latitudinal shifts in seasonal presence peaks may suggest meridional seasonal migrations for some dolphin species. We also observed strong diel activity patterns that were modulated by both seasonal and lunar cycles. This study reveals complex behavioral patterns arising in response to natural cycles playing out over multiple temporal scales and provides new insights into habitat partitioning among toothed whale species.

The California Current System (CCS) is a highly productive eastern boundary upwelling system. Cross-shore transport is driven by horizontal stirring from mesoscale (and submesoscale) eddies, fronts, and filaments, which shift surface productivity away from the narrow upwelling zone inshore. Using an unprecedented 25-year daily record of finite size Lyapunov exponents (FSLEs), we characterize the spatial and temporal patterns of mesoscale stirring in the entire CCS and quantify correlations of FSLEs with satellite-measured chlorophyll a and climate indices. The annual cycle of mesoscale stirring is highly correlated with seasonal upwelling in the CCS, with bands of intense FSLE propagating to the west during the upwelling season. Annual cycles and interannual variability in FSLE intensity were most prominent to the north and inshore of the CCS, and weaker to the south and offshore. Interannual fluctuations in mesoscale stirring showed 3–12 month lagged responses to climate indices, with the CCS oscillating out of phase with waters west and north. Chlorophyll a is positively correlated with FSLE intensity in a meridional band 200–600 km offshore, consistent with the hypothesis that increased horizontal stirring increases the export of chlorophyll a to offshore waters. When mesoscale stirring intensifies during negative phases of the Pacific Decadal Oscillation and Ocean Niño index, we predict greater offshore transport of organic carbon. Our analyses underscore the predictability of annual and interannual cycles of mesoscale stirring and chlorophyll a fluxes in the CCS and their links with climate indices.

In the Southern California Bight, the common dolphin Delphinus delphis is the most abundant dolphin species and preys upon small pelagic fish, mesopelagic fish, and cephalopods. Mesopelagic fish and many cephalopods are available throughout the year, and they form deep scattering layers, some of which characteristically undergo strong diel vertical migrations. The extent of vertical migration depends on the degree of sea surface solar and lunar illumination. At their daytime depth, mesopelagic prey are beyond the range of shallow-diving dolphins. Autonomous acoustic recorders were used tomonitor dolphin echolocation at 2 offshore recording locations from 2009 to 2014. Manual and automated classification techniques were used to identify periods of high echolocation activity, indicative of common dolphin foraging. Clear lunar patterns existed in cool months, when echolocation activity was highest during the darkest periods of the night and lunar month, indicating times when dolphins were foraging, possibly on mesopelagic prey. Echolocation was more abundant during warmmonths, but diel and lunar patterns in echolocation were weaker. Generalized additive mixed models show that the observed patterns in echolocation activity are correlated with lunar day and position of the moon in the night sky. Seasonal patterns may represent geographic shifts in common dolphin populations, shoaling scattering layers, or prey switching behavior during the warmmonths, whereby dolphins target small pelagic fish not associated with the deep scattering layers. Overall, dolphin foraging activity declined from 2009 to 2014 during warm months, which may be related to a declining abundance of small pelagic fish.