Wave Glider fisheries acoustics: Environmental drivers of North Sea zooplankton patchiness

Bristow, Martina (2023) Wave Glider fisheries acoustics: Environmental drivers of North Sea zooplankton patchiness. Doctoral thesis, University of East Anglia.

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Abstract

Zooplankton are a key component of marine ecosystems across the world’s oceans, playing an important role in the biological carbon pump and serving as a trophic link between primary production and higher predators. Monitoring zooplankton is difficult as they form patchy aggregations of varying scales. Understanding how variability in the pelagic environment influences patchiness of zooplankton distributions is crucial to improve monitoring and predict how environmental change might affect their role in the ecosystem.

Advances in autonomous technologies have opened up new possibilities for ocean observations. Autonomous surface vehicles (ASVs) have shown promise as mobile sensor platforms capable of conducting acoustic surveys of fish and zooplankton at small spatio-temporal resolutions. We deployed an echosounder-equipped Wave Glider ASV in the North Sea to collect in-situ measurements of the environment and acoustic measurements of pelagic animal distributions. By combining and analysing these measurements, I investigate environmental drivers of zooplankton patchiness at sub-mesoscale and sub-seasonal scales.

In this thesis, I reveal diel vertical migration behaviour of physonect siphonophores and the critical importance of bathymetry in structuring spatial distributions of zooplankton and schooling fish. I evaluate the Wave Glider’s capacity as an acoustic platform, finding that, as with other surface vessels, data quality is affected by the wind. At wind speeds above 10ms-1 attenuation and transient noise resulted in significant data loss, however below this speed acoustic data of high quality were obtained. Poor integration of the echosounder onto the Wave Glider also resulted in significant data loss; means to optimise integration are discussed. Further, I present a novel technique to semi-quantitively assess acoustic data quality and efficacy of data cleaning, which I call the ‘two-layer comparison technique’. Overall, I conclude that an acoustically-equipped Wave Glider has the potential to make a significant contribution to our understanding of the environmental drivers of zooplankton patchiness.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Environmental Sciences
Depositing User:	Chris White
Date Deposited:	10 Apr 2024 13:44
Last Modified:	10 Apr 2024 13:44
URI:	https://ueaeprints.uea.ac.uk/id/eprint/94887
DOI:

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