The mesopelagic zone is the part of the open ocean between 200 and 1,000 m depth, often referred to as the ‘twilight zone’. A distinguishing feature of this zone is the Deep Scattering Layer (DSL), so-called because of the mass of organisms that aggregate at around 500 m which scatter sound from SONAR devices. In and around this layer are mesopelagic fish, which include myctophids and bristlemouthes. These fish may have a total global biomass of 1 billion tonnes, and so could be the last and largest untapped source of wild protein on the planet. Before these fish are targeted commercially, we need to get ‘ahead of the game’ to understand the ecosystem services that the fish in this ecosystem provide – including carbon drawdown via the biological carbon pump – and hence what might be at risk from harvesting. A key part of that understanding is a robust estimate of biomass, which is also necessary for any future sustainable exploitation. At present, our knowledge is clouded by biases in the common methods of estimating fish biomass. Net avoidance casts significant doubt on estimates from trawl surveys, and acoustic surveys are hampered by the uncertainty around the source of echoes in the deep scattering layers in which these fish reside: much of the apparent ‘fish’ echo energy could arise from gas vesicles in siphonophores. The project will deliver improved understanding of species diversity in the mesopelagic (fish, zooplankton, cephalopods) and hence enable better interpretation of acoustic survey data, leading to improved biomass estimation and – ultimately – improved fisheries management and a better understanding of the DSL’s role in carbon drawdown.
This project will combine underway fishery-acoustic sampling (scientific echosounding, including with new-generation broadband echosounders) at sea (we have several planned sea-going opportunities, and applications under review for more), trawl sampling, in situ acoustic sampling (using a lowered echosounder), stereo photographic and holographic sampling (using lowered cameras acquired recently with a NERC equipment grant ), and acoustic Target Strength modelling (TS is a measure of the proportion of sound reflected by a target such as a fish or siphonophore). The supervisor team is proficient in all of these data-collection and analysis techniques, and has all of the necessary hardware/apparatus in their research groups. A key component of the research will be pairing images of individual fish/siphonophores with echoes from them. The student will thus receive training in a wide spectrum of modern deep-sea sampling techniques.
Contact for informal enquiries: Prof Andrew Brierley ([Email Address Removed]), Dr Roland Proud ([Email Address Removed]), and Prof Paul Fernandes ([Email Address Removed]).
How To Apply
Please make a formal application to the School of Biology through our Online Application Portal.
We require the following documents; CV, personal statement, 2 references, academic qualifications, English language qualification (if applicable).
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