How do we know what fish are doing under the sea?
This requires some investigation!
To find out about the behaviour of sunfish when they are deep below the sea surface, we can use electronic bio-logging equipment. In this case we will be using accelerometers, which will tell us precisely what the sunfish is doing. This method will provide us with data describing the acceleration of the fish in all three axes (surge, heave and sway, as seen in this photo).
The accelerometer and the axes it records movement in
The sunfish will carry the accelerometer on a stretchy, custom-made rubber harness designed by Dr Jonathan Houghton (one of my supervisors) which is non-intrusive and will self-release from the fish at a pre-determined time (after a few days). This provides the least-stressful method to attach essential bio-logging equipment to large fish, requiring a single capture event to put the harness on the fish, and no pain to the animal at all! (See the photo of a sunfish happily wearing it’s harness below.) We will be working to refine this design in wave tanks on a model fish to quantify and reduce drag and ensure that the harness does not significantly effect the fish or add to its energy budget. We hope by designing such a non-invasive method to study the fish, to significantly improve animal welfare (no piercing darts or under skin tags needed!) and create a system that will be useful for many fish species!
Harness trials to observe fish response to ensure best welfare practise
Once the accelerometers automatically release from the fish, we can re-collect them and use the data to reconstruct the sunfish’s entire behavioural repertoire and proxies for energy use, even though it could have been diving up to 600 meters deep!
So, why does any of this matter? Well to begin with I mentioned in my previous blog post how sunfish populations are subject to a lot of pressure from human impacts from accidental bycatch to unregulated fisheries. A central aim of this project is to consider how the mass removal of ocean sunfish may affect the local ecosystem: If we know what sunfish are eating (from the dietary studies mentioned in previous posts) and combine this with their behaviour (i.e. feeding events at the seabed) and an understanding of their energy budget, we can assess the relative importance of the role of the sunfish in the local area! We can even assess if sunfish energy requirements change as they age, leading to diet alterations which may show that sunfish of different ages play different roles within the ecosystem… watch this space!!
As always, if you fancy a fishy chat or have spotted a sunfish please get in touch!