Fish tracking PhD

Phd student, Emily Winter explains how fish tracking is informing science, and revealing what happens below the water line.

Acoutsitc tag

In consultation with anglers and the Environment Agency, the project funded a PhD with Bournemouth University to track bream and pike within the River Bure, River Ant, River Thurne system. The overall purpose of this research was to understand how the isolation and biomanipulation of Hoveton Great Broad from the River Bure affects the movements, spawning and recruitment of common bream and pike.

Working with the Environment Agency and Fishtrack Ltd., a total of 181 bream were tagged from the Upper Bure & Lower Bure, Thurne, and Ant for the PhD between November 2017 and September 2018.  They were monitored between November 2017 and February 2020 using a network of 56 acoustic receivers deployed across the Rivers Bure, Thurne, and Ant.  The PhD has provided fascinating and new insights into how bream use Hoveton Great Broad, Hudson’s Bay, and the wider system.

Understanding how the project will affect the movements, spawning and recruitment of bream using Hoveton Great Broad was one of the main objectives of the PhD. This is reflected in the study design, with a focus on the Upper Bure both in terms of tagging and receiver density. Generalisation of what the data tells us, beyond the conclusions of the PhD, should be avoided as tagging was not randomised throughout the system – 49% of the total bream tagged were from the Upper Bure, 28% from the Lower Bure, 9% from the Thurne, and 14% from the Ant. Furthermore, varying survival rates between these groups further complicates the picture.

Nevertheless, the fish tracking data revealed that Hoveton Great Broad and Hudson’s Bay are a favoured spawning site for sub-populations (groups) of bream within the Upper Bure, Lower Bure, and Thurne. Only a small proportion of bream tagged on the Ant used Hoveton Great Broad or Hudson’s Bay during spawning season, suggesting they used alternative spawning sites. Bream not visiting the Upper Bure during the spawning season were recorded visiting Ranworth/Malthouse Broad and Barton Broad.

Different sub-populations of bream appear to adopt different movement behaviours. Some groups remained largely resident in the Upper Bure, while others were more migratory, where some made repeated ~25km migrations during the spawning season. Such diversification of behaviours probably plays an important role in maintaining resilience within the population, such as in helping to protect against localised threats to the fish survival (e.g. reduced food availability).

Bream
Pike

Individual movement was highly consistent between years, suggesting high levels of site fidelity. It is likely that different sub-populations of bream were mixing during spawning. This suggests that the groups of bream, despite their different movement behaviours, represent a single large population that converge at particular off-channel sites to reproduce on an annual basis.

The project is committed to undertaking further fish tracking with Bournemouth University following the installation of fish barriers at Hoveton Great Broad. This tracking will allow us to monitor changes in bream movement behaviours as a result of the project, and therefore better understand any potential impacts. A fishery advisory group, including anglers, is being set up to share results from this tracking and to discuss any implications for the fish communities of the Broads.

Further elements of the PhD study included the practical consideration of tracking fish, such as tag retention and variability in tag detection. The PhD study also undertook stable isotope analysis (analysis of particular chemical element variants) of fish tissues as a way to mapping fish movements. The published academic papers associated with these elements of research have enhanced understanding of these techniques and will no doubt contribute to improvements in these areas of fish monitoring.

For further information you can view Dr Emily R. Winter’s PhD thesis via Bournemouth University’s online library.