Fish Surveys

For a project like this one it's not just the physical environment that needs monitoring. Surveying the fish populations not only allows us to see how our project is affecting the living organisms that use Hoveton Great Broad but also gives us insight into how they use not only our Broad but the connecting water bodies as well.


Sonar cameras use sound to create a picture instead of light. Sound waves aren't affected by turbidity and can create a very similar picture to light; bouncing off obstructions such as fish and casting shadows. These sorts of cameras are also used offshore to provide information on the sea bed and finding shipwrecks. We use this technology to find out how large the fish populations are and where they are at different times of the day.


Bream, pike and perch are all found in the Broad, though the most common is bream. It takes experience to be able to identify the different shapes and shadows in the picture, but it can provide us with a lot of important information such as size and behaviour. Useful for our project we've been able to highlight how the fish use the water ways. For example in the neighbouring Hoveton Little Broad - or Black Horse Broad - we found bream sleeping there during the day and leaving to feed in the river during the night. This highlights that the different areas are important for the fish for different reasons and the health of each one can affect whole populations.


Usefully for our project these surveys also found a 'fish motorway' at one of the openings to Hoveton Great Broad where there were two lanes of traffic; the large and the small fish either leaving or entering the Broad and different times of day. This information can be used for the bio-manipulation part of the project as we can wait until all the large fish leave; placing a barrier to prevent them from re-entering while allowing the small fish to pass through. Then when the small fish have left we can place the second barrier which keeps all fish species out. Other methods of fish removal will also be used to make sure they've all been removed, but this way we can make sure the majority are out of the Broad without having to catch them ourselves.


Furthermore this survey should highlight alternative water habitats for the fish to use instead of Hoveton Great Broad and make sure that the bio-manipulation, while important for the daphnia populations, doesn't impact the fish too severely.


These surveys are very extensive and take about two weeks. Other methods are used other than the sonar cameras such as electro fishing but I wasn't able to see those myself. The main reason for our visit on that day was to get the boat the surveying team lives in for two weeks, refilled with fresh water and have the toilets pumped. Living on a boat may sound glamorous but when that time is spent working - getting wet and muddy - it can be exhausting. Then it can be the little things that help a lot, such as having your groceries delivered to you by a helpful member of the team, or having someone else restock your boat with water so you don't have to take time out of your day to do it, extending the survey even longer.


It was another pleasant day out, not only did I get to see the sonar cameras in action but I got a tour of the section of the river alongside Horning and, yet again, I had lovely weather for it. Not to mention we also saw the wildlife that lives on the Hoveton Little Broad; mainly geese and swans - which I had never seen fly until that day - but also grebe who honoured us with a view of their courtship dance.