Showing papers by "Andone C. Lavery published in 2019"

An advanced sensor platform for acoustic quantification of the ocean twilight zone

Abstract: The ocean twilight zone (OTZ) is the vast, globe-spanning, layer of water between 200 and 1000 m depth—home to diverse communities of small fishes, cephalopods, crustaceans, and gelatinous organisms. Yet, little is known about the biology, abundance, biomass, and distribution of these organisms. The OTZ is difficult to sample due to a combination of organism patchiness and avoidance, and difficulties capturing fragile species. Recent evidence suggests that the global OTZ biomass may be sufficient to commercially harvest. Furthermore, much of this biomass performs daily vertical migration (DVM) and may play a potentially critical role in regulating Earth’s climate through the export of carbon to the deep ocean. Deep-See, an advanced senor platform, was developed to fill the technological void for characterizing the OTZ. This towed vehicle integrates wide-band, split-beam acoustics (1–500 kHz) with optical, environmental, and eDNA sensors that can address many of the challenges associated with sampling in the OTZ. Data from the inaugural cruise in August 2018 highlight that (i) a surprisingly high abundance of organisms can be found outside the dense sound scattering layers and (ii) the target strength of many organisms that perform DVM changes with the depth, which is critical to estimate biomass.

Broadband acoustic quantification of mesopelagic zooplankton

Abstract: In addition to its critical role in biogeochemical cycling, the mesopelagic zone has the potential to become an important global fisheries resource. A growing number of studies have focused on estimating the global biomass of mesopelagic fishes, but that of mesopelagic zooplankton is far more uncertain. Yet, quantification of zooplankton biomass and distribution is crucial to both understanding the ecology of the mesopelagic zone and informing policy makers on sustainable exploitation. Shipboard, narrowband, volume backscattering measurements—typically performed at 18 and/or 38 kHz—are likely dominated by gas-bearing organisms, hindering accurate assessment of zooplankton biomass. A towed vehicle, Deep-See, was developed and equipped with broadband acoustics from 1–450 kHz, optical sensors, and environmental sensors to address the challenges associated with systematically acquiring holistic, quantitative data to infer mesopelagic biomass. Broadband backscattering spectra (50–160 kHz) collected by Deep-See in Summer 2018 and 2019 off the New England shelf break are used to classify scattering layers into fluid-like zooplankton (e.g., jellies, copepods, krill) or gas-bearing organisms (e.g., fishes, siphonophores), then physics-based scattering models are used to estimate abundance and biomass. Consistent with the acoustic measurements, digital holographic images collected by Deep-See reveal multiple deep scattering layers, some consisting mainly of weakly scattering krill.