Date of Award
Level of Access Assigned by Author
Master of Science (MS)
Second Committee Member
Third Committee Member
Les E. Watling
Emergence-trap sampling has shown that several species living primarily on or in the sediment emerge nightly into the water column. This behavior was investigated using acoustic and traditional sampling methods. A TRACOR acoustic profiler, TAPS, was mounted on the sea bottom, looking upwards in approximately 10 m of water in the Damariscotta River estuary, Walpole, Maine. TAPS emits high-frequency (265-3000 kHz) sonar pulses and each minute measures backscatter from 12.5-cm range bins in the water column. TAPS data showed a distinct increase in backscatter in the water column most evenings, beginning around or after dusk and terminating before dawn. The duration, intensity and initiation time of this emergence pattern varied. Emergence-trap samples suggest that the acoustic signal was dominated by Neomysis Americana and Crangon septemspinosa. In addition, there appeared to be more than one emergence event per night. A higher-density emergence event occurred shortly after the highest tidal speeds, as the tidal currents were decelerating. High-density emergence events were observed at a fixed stage (approximately 3.5 - 4 hours after local slack tide) of both incoming and outgoing tides. Although "emergence" of hyperbenthic organisms has only been documented as occurring at night, a similar increase in backscatter was observed during the day at the same stage of the tide as nocturnal emergence events. The backscatter increase measured during the day, however, was significantly less than at night. Our acoustic results suggest that emergence is tidally modulated. They also suggest that emergence in an environment with strong tidal velocities may be more temporally complex than previous studies by non-acoustic means have been able to resolve.
Taylor, Leslie E., "Tidal Modulation of Nocturnal Vertical Migration from the Benthos: A High-resolution Acoustic Analysis" (2003). Electronic Theses and Dissertations. 171.