LONG-TERM PASSIVE ACOUSTICS AS A NOVEL APPROACH TO ASSESS SPATIAL AND TEMPORAL PATTERNS OF ATLANTIC COMMON BOTTLENOSE DOLPHINS (<i>Tursiops truncatus</i>) IN THE MAY RIVER ESTUARY, SOUTH CAROLINA
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Marian, Alyssa Drew
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Abstract
In this study, passive acoustics and visual surveys were combined to identify spatial and temporal patterns of dolphin vocalizations in a typical tidal river estuary and to investigate how acoustic detections correlated with visual sightings. Results showed vocalizations were influenced by location, year, month, day/night cycle, and tide. Vocalizations were highest near the mouth of the May River estuary, where salinity and dissolved oxygen was higher and less variable (<i>i.e.</i>, more conducive for prey) than locations near the headwaters. At the mouth, vocalizations were greatest in the late fall and winter. One hypothesis was that this pattern was driven by changes in abundance, distribution, or residency of dolphins. Another hypothesis was that perhaps in the winter when less food was available, dolphins echolocated more frequently in search of prey. Visual survey data were used to determine whether abundance and distribution correlated with vocalizations. This approach was successful in identifying distinct spatial patterns, where dolphin abundance was greatest at the mouth and paralleled the observed acoustic patterns. Through year-round photo identification efforts, site fidelity indicated that the May River was composed of a large population of non-residents and a smaller population of year-round residents that had varying degrees of overlap throughout the year. Non-residents were observed during late summer and fall. Residents dolphins shifted their distribution towards the mouth in the fall and winter. A combination of non-resident arrivals in the fall, shifting distribution of residents, and less prey may explain the increase in vocalizations observed at the mouth of the May River in the fall and winter.