Broadband simulated dolphin echolocation signals were used to measure the ex situ backscatter properties of mesopelagic boundary community MBC in order to gain a better understanding of the echolocation process of spinner dolphins foraging on the MBC. Subjects were captured by trawling with a 2-m-opening Isaacs-Kidd Midwater Trawl. Backscatter measurements...
Acoustic backscattering strength is often used as an index of biomass; however, the relationship between these variables has not been directly validated. Relationships were investigated between acoustic cross section at 200 kHz, measured as part of a previous study, and measured values of length, biovolume, dry weight, ash-free dry weight,...
Groups of spinner dolphins have been shown to cooperatively herd small prey. It was hypothesized that the strong group coordination is maintained by acoustic communication, specifically by frequency-modulated whistles. Observations of groups of spinner dolphins foraging at night within a sound-scattering layer were made with a multibeam echosounder while the...
A broadband sonar system and digital camera with strobe lights were mounted on a vertically profiling frame with a depth sensor. The echo strengths and densities of animals within individual mesopelagic boundary community patches were investigated as a function of depth. Time and distance from shore were also investigated. Simultaneous...
Sonar techniques were used to quantitatively observe foraging predators and their prey simultaneously in three dimensions. Spinner dolphins foraged at night in highly coordinated groups of 16–28 individuals using strict four-dimensional patterns to increase prey density by up to 200 times. Herding exploited the prey’s own avoidance behavior to achieve...
The characteristics of acoustic echoes from six species of deep-dwelling (up to 400 m) Hawaiian Lujanid snappers were determined by backscatter measurements at the surface. A broadband linear frequency-modulated signal and a short dolphinlike sonar signal were used as the incident signals. The fish were anesthetized and attached to a...
A 200-kHz echosounder modified to digitize the envelope of the received echoes directly into a computer was used to measure the ex situ target strength (TS) of live animals from the Hawaiian mesopelagic boundary community as a function of animal size, tilt and roll angle, and biological classification. Dorsal aspect...
The roles of nocturnal light and lunar phase in the diel migration of micronekton from a nearshore scattering layer were examined. Migration patterns were measured over six complete lunar cycles using moored upwardlooking echosounders while nocturnal surface irradiance was recorded. We hypothesized that animals would remain at a constant isolume...
The target strength as a function of aspect angle were measured for four species of fish using dolphin-like and porpoise-like echolocation signals. The polar diagram of target strength values measured from an energy flux density perspective showed considerably less fluctuation with azimuth than would a pure tone pulse. Using detection...
The hypothesis that sounds produced by odontocetes can debilitate fish was examined. The effects of simulated odontocete pulsed signals on three species of fish commonly preyed on by odontocetes were examined, exposing three individuals of each species as well as groups of four fish to a high-frequency click of a...