Project StockDNA; Combining marine eDNA and hydroacoustics to improve the accuracy of pelagic fish monitoring surveys.

• Main Author: Brodie, C
• Other Authors: Mariani, S
• Format: Thesis
• Language: English
• Published: 2023
• Subjects: QH301 Biology; QL Zoology; North East Atlantic
• Online Access: http://researchonline.ljmu.ac.uk/id/eprint/18789/; https://researchonline.ljmu.ac.uk/id/eprint/18789/1/2023christopherbrodiephd.pdf; https://doi.org/10.24377/LJMU.t.00018789

The vast and dynamic swathes of pelagic ecosystems in the North-East Atlantic house multiple ecologically and economically important fish species. To ensure that humans do not over exploit these fish, and their habitats, multiple routine monitoring surveys take place. These surveys typically involve the use of hydroacoustic echosounders with trawling methods and collect information on the age, sex, size and weight of species that is used in dynamic models to predict changes in the mortality rate and stock size of cohorts of species. Although this method can be used to target pelagic fish, it has difficulty separating fish schools by species, typically requiring trawling validation methods to confirm the identity of the fish. However, trawling does not guarantee a representative catch of the fish schools which can skew the partitioning of hydroacoustic data, resulting in non-valid estimations of pelagic fish populations. Environmental DNA (eDNA) is a tool that has been utilised to detect pelagic fish species and is not impacted by the same bias as trawling. To investigate the use of eDNA to become a “net with no holes”, validating fish schools detected by hydroacoustics, this thesis first aimed to refine the eDNA sampling strategy for marine pelagic fish. By collecting eDNA during routine pelagic hydroacoustic surveys this thesis first demonstrates that the sampling depth and hydrological conditions of the water do not significantly impact the number of pelagic fish species, communities, or the number of eDNA reads. Using these inferences on the eDNA sampling strategy for pelagic fish facilitated further investigations into the temporal utilisation of eDNA sampling for the highly migratory Atlantic bluefin tuna (ABT). Whereby surface water eDNA samples were collected from smaller, more cost effective, research vessels from summer to winter. I found that using this method ABT was detected across seasons while also revealing the presence of important potential prey species and marine predators providing useful ...